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Downdraft V's Sidedraught V's Carb Intakes

39K views 151 replies 23 participants last post by  JoeP 
#1 ·
According to the HD website the "side draft throttle body and ham can cleaner" cant be that bad, as the Nightster is chucking out 79 ft/lb at 4000 rpm and the XR is only 73.9 ft/lb at 4000 rpm, and its lighter by 23 lbs !!!

Even the 2007 was putting out 79.1 ft/lb at 4000 rpm so the side draft throttle body seems to perform as well if not better than the downdraft, and you would get better airflow from the filter surface on the side draught throttle body with it being a larger filter surface area so you get a better CFM rate. The filter surface is a very small area on the XR and no matter how much bigger the airbox was made (not that you can get it much bigger) the surface area of the filter is very limited, and restricts air flow.
This, in my mind is why the XR is down on power from the XL's. Not the airbox but the filter surface size.

Matt was talking about the ram effect on these things, to my mind that has no effect on the XR as it has a ram style airbox and is down on power.

And the 2006 carburated XL1200's were putting out 79 ft/lb at 3500 rpm, which again is higher than the XR. Which also gave the same MPG figures as the XR 45/52 MPG, so much for EFI :rolleyes:

Now, why is it EFI runs much hotter with the same MPG as a carb...!!

And that is why i am not a great lover of the EFI on these bikes, just a lot of electronic witchcraft with no benefits as far as i can see.
It costs you an arm and a leg to buy something that gives you access to play with it.
You have around 10 electronic parts you could throw in the trash if you had a carb on the bike, which is then easily tunned.

Maybe if the airbox was bigger it might perform a little better but i dont think a bigger airbox is gonna give you much more than 6 or 7 ft/lb's anyhow, and even then you would have to raise the filter surface area, which would put it right in the same figures as the XL1200.

Maybe the top end HP would be ever so slightly better, but torque is where its at with these things, anyone that was buying an XR or any Harley for that matter, for the HP is playing with the wrong bike.



As much as i love the XR, it is a bit of a pig in a bag if you look into it properly, its the heaviest and has less torque than the rest of the 1200 range...Go figure.

I can see when folks start tunning the XR for performance that air box and downdraft manifold is gonna go completely, to restrictive and impractical to do anything with.
Most people in my opinion loose sight of the fact that this is a pushrod motor and i honestly dont think the downdraft intake makes the slightest difference, Harley's own figures pretty much tell you that.

The only thing that makes the XR feel quick is the 883 gearing, without that it would feel exactly the same as an XL in the motor department

My recipe for more power out of the XR is...

11/1 Compression
Stage two or three headwork (which is a bit of a grey area as yet)
A good performance two into one exhaust system comprising of Remus headers and Supertrapp tunable muffler.
Free flowing larger surface air cleaner, which in my eyes will mean stretching the filter surface area around the side of the airbox.
And cams (again a grey area as yet)

Nearly forgot...A 40/42mm Mikuni carb to make tunning much easier :D (another plus side to a carb is you could dump the oil cooler)

Whatcha think??__________________
 
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#2 ·
hmmmmmm

I'm gonna mull that over for a while.....
 
#3 ·
The reason why the XR is down on torque over the other models is nothing to do with the downdraft throttle vs side draft. In fact if you fitted the side draft throttle body/filter assembly the XR would probably have less power and torque than it has now.

The XR has a lighter crank, different pistons, different heads and all sorts of other differences from the Nightster and other XL 1200 models, so a direct comparison is a lot more complicated than just looking at torque figures and all up weight.

The XR trades torque for horsepower at higher revs, so a direct comparison with the other XL1200 models isn't really correct. In a straight race the XR would blow the Nightster away in a straight line and round corners. Any torque advantage the XL has would be negated after about 20 yards.

My local farmer's tractor has way more torque than my car, but he wouldn't win any races in it, and you wouldn't want to be driving it all day.

Simply measuring the surface area of the filter is not an indication of air flow. The filter may be bigger on the 'ham can' style filters, but the actual size of the air inlet is tiny (just the small gap around the edge of the filter). The XR has a more direct and larger air inlet than the older design, and I guarantee you that it will flow better.

Add that to the less efficient side draft throttle body and poor, old fashioned design of the ham can and it is no contest. Why do you think that Buell moved away from the ham can in 1996 in an attempt to get more volume into the airbox?

As for ram air. It has been proved beyond doubt by numerous manufacturers/engineers that any amount of ram air effect is beneficial to air intake volume . We have had two customers who have dyno'd their XR before and after fitting the larger air scoop and Pipercross filter, and both showed a 3bhp increase, so it works.

The only thing that makes the XR feel quick is the 883 gearing, without that it would feel exactly the same as an XL in the motor department
No it wouldn't. It is a more powerful engine than the rest of the XL range, so would still be more powerful and quicker if you changed the gearing. That is without taking into account the better chassis and handling than the other XL's.

My recipe for more power out of the XR is...

11/1 Compression
Stage two or three headwork (which is a bit of a grey area as yet)
A good performance two into one exhaust system comprising of Remus headers and Supertrapp tunable muffler.
Free flowing larger surface air cleaner, which in my eyes will mean stretching the filter surface area around the side of the airbox.
And cams (again a grey area as yet)

Nearly forgot...A 40/42mm Mikuni carb to make tunning much easier :D (another plus side to a carb is you could dump the oil cooler)
I agree that a compression increase would be good. However, you have to be very careful doing head work on both this and the Buell XB models, because the head design is extremely good to start with. It is extremely easy to make it worse rather than better. For instance, I know a race team in Germany that had great results fitting smaller exhaust valves than stock and welding in a 'step' into the inlet tract to their XB12 racer rather than the traditional route of bigger valves and larger ports.

Why do you think that the Supertrapp muffler would be better than the Remus or other modern 'Acoustic wrap' designs? The Supertrapp muffler is old school and not that great compared to more modern pipes (how many racers outside Xr7850 flat trackers do you see using supertrapp 'tuneable pipes').

Stock cams are about as wild as you can go without having to do more head and valve train work, and are good for around 130bhp before you need to change them.

Stretching the air filter around the side of the filter will NOT increase airflow. The throttle body can only flow a certain amount of air at atmospheric pressure. Making the opening larger at the side or removing the airbox altogether will not make it flow any more. The only way to do this is to increase the pressure in the airbox, and that means intelligent airbox design incorporating some form of ram air.

Even if you could fit a carb, the Mikuni HSR40 would be too small. You would need a 45 or 48 to make performance on par with the stock EFi system. Doing that would increase fuel consumption without necessarily increasing power. I know plenty of people who have gone off on long and fruitless carb fitting journeys for their Buell XB, and I have yet to find anyone who has actually improved performance or rideability over the stock system. Modern fuel injection is so much better in every respect than carbs, that I really don't think it would be a viable option for performance tuning. EFi does run hot due to emissions regulations, but that can be altered very easily without throwing the whole system away.

If you want a living example of what your mods would end up with, take a look at the old 2003/4 XL1200S models.

Most of the mods that you mention yet still 20+bhp down on the XR1200.
 
#5 ·
raising compression

Matt-Thanks for the information. Would raising the compression to 10.5 to 1 cause the engine to run hotter and decrease engine lifespan? Especially for those of us who live in warm climates and get stuck in slow traffic? Just going .3 higher from 9.7(stock XL) to to 10.0 to 1(stock XR) resulted in Harley adding the oil cooler and oil cooled heads. Is that enough cooling to safely cover and .5 increase? Mort
 
#6 ·
Matt-Thanks for the information. Would raising the compression to 10.5 to 1 cause the engine to run hotter and decrease engine lifespan? Especially for those of us who live in warm climates and get stuck in slow traffic? Just going .3 higher from 9.7(stock XL) to to 10.0 to 1(stock XR) resulted in Harley adding the oil cooler and oil cooled heads. Is that enough cooling to safely cover and .5 increase? Mort
An increase in compression ratio doesn't necessarily mean a big increase in engine heat or a necessity for an oil cooler. The XR needs the oil cooler simply because it revs much higher than the normal Sportster, where cooling is not so crucial. Higher revs mean more firing strokes per minute and of course more heat. What used to happen with the early Buells was that the rear cylinder would overheat badly and seize. This was before they started fitting an oil cooler as standard, and were using basically the same motor as the XL but with a lighter crank and Thunderstorm heads. Fitting the oil cooler on the later XB models and providing oil jets to the underside of the pistons has now made this a thing of the past thankfully. The XR motor should really be viewed in very much the same way as the Buell rather than as a XL engine, as that is the only other H-D air cooled motor revving to around 7000.

I would say that increasing compression ratio to around 10.5:1 would certainly be safe with the stock oil cooler arrangement and oil cooled heads. It would probably be safe at higher CR as well, but then you run into problems getting fuel of high enough octane to run big compression.
 
#7 ·
Matt, i disagree with a lot of what you say and its pretty pointless throwing things around on here.
I intend to do work on this motor so we will see what happens, I've been tunning HD's for around 23 years but this is my first sporty.
I am pretty sure i can squeeze a fair bit more out of the XR its just a matter of working through some stuff and seeing where i end up.
As i said before i am more interested in the torque than the HP, the smaller 42 Mikuni is gonna give me what i am looking for as far as torque is concerned going to 45 or 48 would just make it to flat in the torque department, that of course is if i decide to go with the carb. I managed to get 110 HP and 115 ft/lb out of a 95" BT with a stock size 42mm carb, jetted and tuned to suit the mods done on the bike.

Like i said the heads and cams are a bit of a grey area as yet, so i cant really comment on that side of things for now.
We are gonna have to agree to disagree on the intake side of things for now, i am not convinced that the downdraft makes a substantial difference on the XR.
As far as the scoop and the Pipercross filter making 3 HP, how much of that is the scoop and how much is the filter?
And as i have said before the ram effect wont show on a dyno run as the bike is stationary when dynoed, and if the airbox makes a difference by letting the motor take in less turbulent air, as i have read someone say, then the ram effect just cant be doing any good as this would fly in the face of what the airbox is there for.
i certainly dont see a problem with 11/1 compression on this bike.

Supertrapp 2-1 pipes have proved their worth over and over again, they can be altered to suit any mods you make on your motor unlike any other after market pipe you can buy, i have seen on several occasions over the years engines that have been tunned and not worked well with the pipes that were on their even though they were a performance exhaust but when a Supertrapp 2-1 system was fitted opened the motor right up, matter of fact if Boz that has just joined the forum is the guy i think he is he will back me up on that.
A good example of the exhaust side of things is Python AR11 pipes worked really well on engines up to 88" but if you went over that they would fall flat, this is the same for any unadjustable exhaust, it is tunned for so much and then it looses the plot when you go out of the manufacturers tune peramiters, the Supertrapp can be altered to suit work you have done, and can be tunned for torque or HP depending on what you are looking for from your motor. I've had far more success with Supertrapp than any other pipes, Python 11, Hooker, Khrome Werks AR100, Samson D&D Screaming Eagle and others, though believe it or not Screaming Eagle are one of the best. Companies like Remus and the like have not even made a dent in the BT market, why i ask myself, because their are hundreds of thousands of them on the roads worldwide, so they have a massive market to aim at.

As far as EFI goes, i have yet to see a tunned HD EFI motor making more power than a carburated one with the same engine work.

I also dont agree that the XR has an oil cooler because it revs to 7000, as far as I'm concerned the sportster has the oil cooler for no other reason than the EFI making the bike run hot, you must also remember that carburated BT dyna motors can rev safely to 7000, (31789-04A) without oil cooling. Screeming Eagle do a 7500 ignition unit for evo sportsters (32969-98A) and one for 04-06 Sportsters that revs to 7000, (31758-04A)
Its purely an EFI heat issue.

Like i said Matt, i aint new to this and have no axe to grind with anyone, but i aint behind the door with this stuff.

Lets just see how things pan out. :D
 
#9 ·
Scotty, Scotty, Scotty, Carburetors (carburettor) are better the fuel injection? Please! Most of the automobiles on the planet use fuel injection, why? Tuning and air polution mainly. The Spitfire was a better fighter than the ME109 no question but the way to escape was to go into a power dive and the Spit could not follow, why? The ME109's had bosch fuel injection and the Spit had carburetors and would starve for fuel. Old story I know but it prooves a point.

With a carburetor you may adjust the float level, needle setting and main jet and idle jet on a Mikuni. If it is equipped with an accelerator pump also. If you need to make a change just stop and take the carb apart and make changes and try it again. If you're on a dyno with a sniffer you can make a good guess, but a guess.

With fuel injection you do a dyno run check results make changes to the exact mixture needed at the exact RPM. Doing a change takes minutes with no fuel spillage. Much better!

Most race cars use down draft induction. Why? Because it works. The fewer turns the intake charge takes the better it is for flow. In a turn the intake charge has differant speed depending on where it is. Fast on the outside and slower on the inside causes turbulence and hurts flow. Try falling up a hill sometime.

Air scoops crowd more volume into the throttle body (fuel injection talk) which can increase intake speed and flow. It is hard to measure the differance on a dyno but one run without and one with with all other conditions equal the results are the results.

I am an oldtime carb guy and a real good guesser. Raiseing the needle helps but I think the needle jet is too small. Reading the plugs is a talent many don't have. Reading the lap top is much easier. Opinions are like assholes and belly buttons every one has one.

Don't be pissed Scotty, be encouraged to maximize your fuel injection and you will com out ahead. We're your friends and will wait for you to start your bike after you flood it. :D Later,
 
#10 ·
hey,hey,hey.......

Y'all don't be gettin' my Scottish mate all cranked up! Scotty, I got 'chur back dude!

They said the Titanic was unsinkable, the Hindenburg was crashproof, that cold fusion was the powersource of the future, and Y2K computer glitches were gonna shut down the world! You know what? They were wrong.....I'm not sure what my point is but I think it's this...just because everybody knows you're wrong is no reason for you to stop being wrong! :D
 
#13 ·
Y'all don't be gettin' my Scottish mate all cranked up! Scotty, I got 'chur back dude!

They said the Titanic was unsinkable, the Hindenburg was crashproof, that cold fusion was the powersource of the future, and Y2K computer glitches were gonna shut down the world! You know what? They were wrong.....I'm not sure what my point is but I think it's this...just because everybody knows you're wrong is no reason for you to stop being wrong! :D
I agree with all of you.
:D :D

 
#12 ·
Billy, Billy, Billy, I aint got a dyno, i aint got the money to keep paying the guy with the dyno, and i aint good with a computer :)
Its a Harley pushrod motor for goodness sakes, i can understand what you are saying and I'm sure it all works fine with a high reving high performance motor, but i aint got one of those either, I've got a Harley V-twin that was designed when by a Brontosaurus.
Like i said above i aint ever seen a fuel injected HD outperform an EFI HD yet with the same mods.
I like to keep messing and uprating stuff and for me a carb is far more accessible, just the cost of Thundermax or TTS is way up on a carb conversion and then i gotta start saving all over again to pay the dyno guy every time i change anything.
i aint saying that i am gonna do the carb thing for sure, but it is an option i am considering, thats if it can be done!
Down draft may perform fine on high tuned race motors, but last time i looked, i could still see them Bronto prints on my motor :D
Look at the figures i layed out in my first post, XL side draft carb and XR downdraft injected, carb sidedraught made more power, same mpg, so the old carb aint doing to bad now is it.
If Harley had a choice in the matter their aint no way they would have injected these things.
Cars are injected, yes, they are multicylinder liquid cooled motors that run at specific temps and injection works just fine, but on air cooled V-Twins it aint that easy, engine temps are eratic, so injection is being given different signals so i cant see it working half as efficiently as it does on multi cylinder liquid cooled vehicles....Which explains the HD heat issues.

A couple of guys over here have converted their EFI TC's to carb and are loosing no performance and loosing no MPG, and both are much happier with the carb on their bikes, just saying its an option.
I've spent a lot of time reading up on folks that are using Thundermax and TTS and its quite outputting to read, now imagine a Luddite like me trying to use it :eek:

I've seen people spend $1300 on twin carbs and loose HP and torque on Harley's, you can only go so far with these things, and EFI thats set up on a dyno 100% is gonna be 80% the next time the ambient air temp and humidity changes, come on Billy its a Harley, and its got pushrods and the motor heats up and cooles down, the motor expands and shrinks, the EFI spends most of its time chasing its own arse.

Carb, thats different, it just sits their and lets the fuel go when its needed without O2 sensors, temp sensors, injectors, throttle positioning sensors, fuel pump, map sensor, air temp sensor, engine temp sensor, fast idle solinoid, the list goes on.....

People need to stop treating these things like they are Bussa eaters they aint and they never will be.

Maybe before i decide what i am gonna do some fancy EFI controller will convince me thats the way to go, but as yet the jury is still out!

Billy, i aint never been one for going with the flow, thats why I've got a 10 year old 95" BT (carburated) that will pull over 140 mph, a 103" BT EFI wont touch it.
I cant be that wrong now, can i :cool:

Each to his own Billy ;)

I aint telling anyone else to do it, I'm just throwing it out there, thats what you do on these forums!

We have a saying over here "it will all come out in the wash" lets see how we go, i might be right and i might be wrong!

Oh yea, i cant remember the last time i flooded a motor :p

And when its done...I did it http://www.youtube.com/watch?v=WIXg9KUiy00
 
#14 ·
Whew!

Man you guys are all fired up about weather a xr has more power than a xl. Well let me tell you all that the xr is faster at least. a good friend of mine has a 06 xl1200 with cams, weight reduction, and straight pipes. We lined 'em up and I won. That's good enough for me at least until the warranty is up.:cool:
 
#15 ·
ha!

Man you guys are all fired up about weather a xr has more power than a xl. Well let me tell you all that the xr is faster at least. a good friend of mine has a 06 xl1200 with cams, weight reduction, and straight pipes. We lined 'em up and I won. That's good enough for me at least until the warranty is up.:cool:

Now, there's a man who likes things in black and white! I dig it!
 
#16 ·
Some of these useless sensors(such as; Engine Temperature, Manifold Absolute Pressure, and Intake Air Temperature) address your concerns about changing air conditions. Also the O2 sensors can also make short term and long term adjustments to the tables to attain the target air/fuel ratio.
Carburetors cannot match fuel injections accuracy.
And, I would say, your buddies that were unsatisfied with their fuel injection did not have them tuned properly.

Fuel Injection = dead on accurate(properly tuned)
Carbs = close enough

Put the carb down...walk away...:)
 
#17 ·
carb v efi

I've got a lot to add to this debate, based on experience of both, but for the moment I'm working 14 hour days, 7 days a week, getting customers motors built and bikes tuned, plus my own R&D work. To do justice to it I need to sit at the computer for a while and write a proper article. When the pressures off a bit, I'll make the time and start a new thread.
 
#18 ·
Sorry Scotty, I forgot that there's a guy that comes around and lights the street lights every evening in your neighborhood. You are correct the fuel injection is always chasing it's arse but the the results are it's always correct based on engine conditions. The Harley motors are an old design forsure but why not make it better. We all love the V-Twin Bussa beater or not. All the single cylinder motocross bikes are going fuel injection. Why? It works! Harley motors do get hot, no question, fuel injection adjusts for that and yes we can change it to make it better. Sorry for the move to the modern technology. You gonna go back to kick start? :D Later,
 
#19 ·

Like i said above i aint ever seen a fuel injected HD outperform an EFI HD yet with the same mods.
:D

Its OK harping on about how good this "Fool Injection" is but i just cant see any evidence of it being better :D


The figures that i posted in my first post sorta say it all, if you go from the last carb XL1200 to the first EFI XL 1200 their is no difference in either power or fuel consumption,both putting out 79 ft/lb at 4000 rpm and both giving 45/52 MPG and both with the same gains with a stage one, I'm sorry but you just cant argue that EFI is either more efficient or more economical


That said i cant see a way of converting the XR for a couple of reasons, one being the fuel pump, if it were a BT you could just go ahead and change the tank to a pre EFI one, so its looking like its gotta stay injected for now.

So lets get back to the downdraft V's sidedraft thing
I aint even slightly convinced that works on a Harley motor in any beneficial way whatsoever!


Which takes me to the option of a sidedraft XL intake conversion to give me more options as far as air intake goes....

Billy stop harping on about the carb/EFI part of this thread (Downdraft V's Sidedraft) and give me some shit over the intake ;)
 
#20 ·
Serenity Now!

Serenity Now, Insanity Later!:)
 
G
#23 ·
Holy...

I didn't read all of the posts but after I read the word CARBURETOR I had to reply...

I cannot see a single reason why a carb would be better?
Better tuning?? Why?? You cannot adjust it over the whole RPM-band like an injection...

I'm a master car technician (diagnostician-something in english) and a (non direct)fuel injection is so much more simple layout than a carb...even to find some errors...
It basically needs very few parameters to run fine and better than a carb!

and I totally have to second what darkside wrote a few replies before...a carburetor is just inaccurate!

Scotty...scrap the carb idea :)
 
#24 ·
Benny, I'm a mechanic and I've got 30 years of expierience.

I was invited to the Norton plant in the late 1980's because i found a design flaw in the rotary motor. that all their techs missed!



"The figures that i posted in my first post sorta say it all, if you go from the last carb XL1200 to the first EFI XL 1200 their is no difference in either power or fuel consumption,both putting out 79 ft/lb at 4000 rpm and both giving 45/52 MPG and both with the same gains with a stage one, I'm sorry but you just cant argue that EFI is either more efficient or more economical"


Its all well and good what you say, but read this above again and give me an answer, everyone is cracking on how well EFI works but no one has answered the question...

Why are the figures the same, both performance and fuel efficiency if EFI is so good ;) ??????
 
G
#25 ·
Benny, I'm a mechanic and I've got 30 years of expierience.

I was invited to the Norton plant in the late 1980's because i found a design flaw in the rotary motor. that all their techs missed!



"The figures that i posted in my first post sorta say it all, if you go from the last carb XL1200 to the first EFI XL 1200 their is no difference in either power or fuel consumption,both putting out 79 ft/lb at 4000 rpm and both giving 45/52 MPG and both with the same gains with a stage one, I'm sorry but you just cant argue that EFI is either more efficient or more economical"

Its all well and good what you say, but read this above again and give me an answer, everyone is cracking on how well EFI works but no one has answered the question...

Why are the figures the same, both performance and fuel efficiency if EFI is so good ;) ??????
I don't argue about your technical skills I just wanted to point out that I'm technically trained. :)

The Fuel efficiency argument does not count on these engines as they are an outdated design with no variable cams and stuff..
A carburator would not really work on modern engines. It just cannot react to different conditions...

scotty it's not always or only about power and fuel consumption!
I got 12l/100km (do the math) with my 6.6l buick estate wagon weighting 2 tons with a carb...

Exhaust gases!
Regulated cats are impossible with a carb....there were a few attempts on cars with carbs and O2 sensors...those were a horrible design never really worked well.

Stick an exhaust gas meter into a properly running carb engine and then into an injected one...even with no cat the injected engine is WAY cleaner!

Noone (or at least me) ever said you cannot make the same power with a carb...carbs do work well on old engine designs and are good for a lot of power. I add the XR to this too.

The injection is helping this outdated pushrod aircooled engine to better exhaust gases and better behaviour (cold starts and stuff)...but it just cannot show all it's potential on such an engine! I think that's my conclusion...

I hope you got my point because it's hard for me to write it down in english like it's up in my head in german :)
 
#27 ·
As far as the emissions side of things goes, again i go back to a statement i already made.
Harley have only gone EFI because they had to and not because their is any benefit, its simply to pass modern emissions as you point out, again exactly what i was saying.
If you look at Harley's past with EFI it has caused the Moco no end of problems, i think this is the third different system they have used in the past 10 years.
Other manufacturers have stuck with the same one.
The reason Harley have had so much trouble with EFI is because its an air cooled motor, this has been the problem from day one and it will continue to be so. Just go and ask any tuner with a dyno what he thinks of trying to tune a Harley EFI compared to a Jap liquid cooled bike.

I have a tunned carbed softail that gives me over 110 HP and over 115 ft/lb, i have come acros many tunned 96" and 103" motors that are injected and not one will even touch my bike. One has exactly the same work as mine (96" motor) and he has spent around £500 on dyno time and its still around 6HP and 8 ft/lb down on my bike, even the dyno tuner has told him to give up because he cant get anymore out of it.
 
#28 ·
I've figured it out! Englishmen are air cooled. That explains why they're ok with differant results with the same throttle setting. So long as it doesn't go OOOOOOOH BAH POP. Pop means it's lean. Lean means hotter but it's a Harley so so it's hot anyway. Carbs rule and so does the infamous water closet. Pull the chain and you'll be ok. :D Later,
 
#29 ·
Thats Englishmen covered, what about Scotsmen!

Still waiting Billy, put me out of my misery show me something that makes some sense and shows EFI works better than a carb on an air cooled Harley, ya cant can ya :D :D

I'll even hold my hands up and admit their is a Harley it works better on, a V-Rod, oops, i forgot they're liquid cooled :rolleyes: :)

But here we have another example of what i am saying.

Both 2003 Fatboys, and both 88" only difference is one is that new fangled "Fool Injection" and the other aint. Still no advantage with EFI there, huh.
Torque pulls for a further 500rpm with the carb though, surprise surprise!! :D





http://www.bikez.com/motorcycles/harley-davidson_flstf_fat_boy_2003.php

http://www.bikez.com/motorcycles/harley-davidson_flstfi_fat_boy_2003.php
 
#30 ·
Scotsman? A race of men that rely on advertizing to proove a point. They can also show the world that they are not able to understand or use technology. Any Harley's still have carbs? Just wondering. Scotty you will always be Field Marshall Mikuni and I will always be Dr. Delphi. We may never agree but we bring the forum truth and then of course there's always your side. Good thing our bikes still use gasoline my brother. :D Later,
 
#31 ·
Wow....
This is painful.

So ok, a carb is better than fuel injection.
Alright, well, maybe you can help us understand why this is. Like what specifically.
How does the carb make more horsepower(both being tuned properly) than a fuel injected bike.
And, lets say, they were making similar numbers at wot, I'd much rather have the drivability that you get from FI. You know, for the few occasions that your not at 100% throttle.:)

Also, what is the theory behind side draft out performing down draft. Hell, I like it just because my legs not on a freakin air cleaner!
I was under the impression that free flowing heads and manifolds made hp(with some torque losses), while more restrictive setups can help yield better power down low, at the expense of running out of steam up top.
If this were your goal, this may change your camshaft requirements and make the lightweight flywheel unneccesary.

But, I know that both rods connecting at the same point definitely make for interesting intake manifold conditions.

I'd like to check out some articles on manifold(and head) theory specific to these motors, if you know of any. I come from connecting rods being properly:p being hooked up to the crankshaft and the nice even pulses in the intake manifold you get with that. I would love to know more specifics about the air behaves in the intake manifold of these radial engines.

I'm not trying to be an arse or anything, just trying to understand where your coming from.:D

FI FTW!!!
 
#33 ·
Firstly i aint seen any evidence of this so called lighter crank, as i have just pulled the primary drive of the bike to change my gearing and the crank shaft is actually biger than the XL, so if thay have lightened it up in the flywheel department that have certainly put more weight on it in the shaft department.
I was also under the impression the crank had been beefed up rather than lightened.
Both the XR and the XL have the same stroke and bore, with a 2cc difference in displacement, so nothing there to make more power.


Where have you seen anything about the crank being lighter???



As far as i can figure the main difference with the XR over the XL's is the crank has been beefed up and the top end (heads) have been reworked and oil cooled, as far as the higher HP than the XL's i am thinking that is just down to the high lift cams as you can tell just by the rattling coming from the cam chest :)
And it is slightly up on compression, other than that no big differences!

The different cams will account for the slightly higher HP and also the lack of torque compared to the XL's
XR torque 74 ft/lb @ 4000 rpm
XL torque 79 ft/lb @ 4000rpm
Loose it on the torque and gain it in HP, simple as that.

The XL motor is also capable of revving to 7000 as Harley would not market a screaming eagle ignition unit otherwise that revs to 7000.

As far as downdraft goes, yes i will agree it will make a difference on high revving performance motors but not on Harley's, just think about the intake, the air comes in at the front then drops at a right angle into the intake then has to split two ways of at different angles again, now that is hardly a smooth downdraft air intake now is it. The XL intake air has a smoother flow into the manifold at the point of separation into each cylinder.
Do you honestly think that downdraft (if you want to call it that) manifold is on this bike for any other reason than looks, so they could clean the lines of the XR up and get rid of that old air filter cover, come on please, this thing is an agricultural engine compared to the competition, lets stop trying to make a silk purse out of a hog's ear!
If this was a performance getter on a pushrod engine dont you think it would have been done before and if it has and i missed it it didn't make a mark. The closest thing i can think of is a BMW boxer motor and they aint exactly renound for big power in the performance stakes now are they :rolleyes:
For downdraft to make any difference in my mind it has to be a straight downward flow straight into a cylinder, this HD intake is very far from that....
So it aint really what you would call downdraft is it!

As far as drivability is concerned, again, my softail has a far smoother power delivery than the XR, one thing a lot of people have mentioned about the XR is the hesitation around 3000 rpm.

As far as free flowing heads go, the whole point of any head work is to get the mixture in, burn it efficiently and get the gases out fast. You can than use this power however you see fit, neither heads, cams or compression will work alone, you have to set up to suit what you want from them, you can tune the motor for lowdown torque or high end horsepower, or an even spread of both, but as I've said before if you want big horsepower you are messing with the wrong engine, Harley's aint good at horsepower.
 
#36 ·
Carb/EFI

Just a quick one before you all get carried away.
The EFI Twin Cam 88s had different cams than the carb models. Exhaust lobes were the same, as were the intake profiles, but on the EFI the intakes were advanced 4 degrees, which lowers the point at which the torque starts, and loses a bit at the top end. (Anyone remember the 3 keyway timing gears on the old Bonnevilles?)
 
G
#48 ·
Just a quick one before you all get carried away.
The EFI Twin Cam 88s had different cams than the carb models. Exhaust lobes were the same, as were the intake profiles, but on the EFI the intakes were advanced 4 degrees, which lowers the point at which the torque starts, and loses a bit at the top end. (Anyone remember the 3 keyway timing gears on the old Bonnevilles?)

One nice thing about the '03 FLSTF/FLSTFI comparison is that by '03, carb'ed and EFI Softails (88B's) used the same cam. At least on this side of the pond...
 
G
#37 ·
OK...

conclusion:
EFI Harleys won't outperfom Carbed ones as far as max torque and max hp goes. Both work well.
But show us Torque and Hp curves..there might be some differences...

Noone can argue that EFI harleys are easier to start and do pass emission regulations. In my opinion these are the two main reasons to go EFI. Hey it's freakin 2009 and I just don't want to pull a stupid lever to cold start my bike.

I had the last Carburetor Harley before...'06 883R...to pass emissions it was awfully lean..it did not perform well and coughed a lot...yet even stalled on red lights when playing with gas..(dynojet kit solved it)...you can't say the XR has those issues in stock form..it runs very smoothly...and clean!

And stop comparing XL hp numbers to XR...if a regular 1200XL would rev to 7000rpm it had almost the same HP output..
don't forget...hp is just torque multiplied by rpm!!

(that's why all the jap bikes have lots of HP..they rev much higher!)
 
G
#41 ·
scotty that pic freaks me out everytime I see it LOL!!!!


and I don't dislike the stupid choke lever! I just don't want it on a new motorcycle like the XR is!
I love all the classic stuff! I had lots of classic cars from the 60ties and seventies! It's not my age! :)
 
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