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Discussion Starter · #1 ·
Its seems rather accepted that efi bikes are limited as to potential HP in the aftermarket arena. Why is this when in motorsports efi is the only way to go, for 10+ years.

Jimmyk indicated in one prior post that the size of available injectors was limited. Is this the "only" reason? Is it lack of familiarity? Or ??

Secondly, what is the percieved limitation, is it engine size , fuel flow/horsepower, or ??

Greg
 

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The fuel injectors have to be capable to deliver enough fuel for the HP. I do not know what the stock injectors are capable of, and I do not know what is available in the aftermarket. However, injector bungs are a kinda universal fit, so other vehicles may fit. The problem is the wiring, and the amount of resistance the computer is designed to handle. Those are simple issues to get around.

The next issue, which os fairly easy to get by is mapping. Mapping can best be compared to jetting for your carburator. The mapping sets up how much fuel your engine needs. If you make changes to the engine, you would need to change the jets because the engine would run lean. The same is true for EFI. The stock HD computer is esay to remap with dyno tuning. There are also aftermarket EFi systems that can be tuned with anything from a few knobs on the ECM, to a lap top computer.

Best options are to convert to a carb if you are not up to the money and time to tune the EFI, and just settle with the complications of a carb (though only minor). Or, go ahead and modify the EFI. For me, I would rather modify the EFI, that is my plans for my truck, and eventually my bike (both I plan to run an aftermarket ECM). I plan to add EFI to my VW, the ECM is on the way.
 

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Discussion Starter · #3 ·
Sidewalk, I have a Power Commander (brand new, got it because I'm computer illiterate, the HD dealer is close and thats what they said They understood). Isn't this very conceptually similar to the EFI Tuner?

I am curious to hear from Hippo, since I'm pretty sure he feels the efi is limited in the high HP arena (Hippo, not trying to put words in your mouth). Also JimmyK ans others. Iwould like to explore getting my engine up to something in the 100-110+ torgue and HP, but using efi and keeping Very reliable and ridable. I want something I can leave on a 1-2k trip w/ nomore concern than a stock 88.
 

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The EFI is not the limit, it is the tuning (dealer or yourself) ability, and the injectors. As for HP, my EFI Buell is stock 101 HP at the flywheel, so those injectors are capable. They may (I do not know) work for you.

From what I can tell, Hippo is the HD engine person in the know. His suggestions will over-ride mine.

I do not know too much about the PC, I do not trust them myself, but that is just me.
 

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Secondly, what is the percieved limitation, etc.
From where I sit it would probably be engine architecture and packaging if you consider money not to be an issue.
The injected VTwins that make good power are mostly 90 degree ones, with some older 60 degree designs hanging in there. You need a straight shot at the intake valve and airbox volume, and that isn't going to happen on a street Big Twin.
Carburetors are much more primitive, but that is their strenght when matched to a primitive layout.

100TQ with reliability is easy, the 100 HP to go with it is the problem.
I don't care how much power you put into a chassis limited bike, it may be quicker on acceleration but will become more difficult to ride and under anything other then perfect conditions probably slower over a course.

Even world class road racing teams detune their bikes to make them faster around a track over race lenght and the guys that ride them are in a world of their own.

It's real easy, you can spend a fortune trying to get a percheron into the Kentucky Derby, but it isn't going to win unless all the other horses die.
 

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Discussion Starter · #6 ·
Hippo, don't think I understood. 1) Does efi need a straight shot into the intake valve and can't get it due to the physical layout? If correct, do carbs not need this which is why you say primitive design is better?

2) you say 100hp very difficult....... I understand the reference to racing, but not the specifics. Is 100+ HP difficult with carbs as well, i.e. 100 HP baggers are a pain in the ass, period? Or, does getting that much with efi create the problem?
 

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A little of both. While a carb will also benefit from a straight shot, with EFI in addition to everything else you need a stable MAP signal unless it is a strictly mechanical racing system. When you are locked into short intake runners and no airbox volume, a engine with only two cylinders and a uneven firing order you have a very unstable MAP signal.
This is probably one of the main reasons why the Delphi bikes are so sensitive to pipes. The Marelli bikes were not that sensitive, but then again their logic was heavily TPS based while the Delphi bikes logic is preponderantly MAP based.

100HP on a bagger while maintaining smooth low end drivability is hard. The abity to make HP depends on a large extent on winding the engine up high and on these engines with their large individual cylinders and long stroke it is exceedingly expensive and the higher you wind them the more radical the components and the more you kill torque in the low range where you ride most. The more HP you go for the more you push the max TQ up in the rev band, and to do this you need more and more cam and the more overlap the more unstable the MAP signal.

A carb doesnt care about MAP signal, it's dumb, all it knows is air velocity ie pressure differential. Obviously if the thing gets way out of kilter, like with drag pipes or extremely large carb throats that drop velocity you'll start having the same issues as with EFI.

EFI is just like some people, way too smart for some jobs. Like putting a mathematician to dig a trench. Sometimes you are better off with a workhorse.
 

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This doesn't mean the MM is better then the Delphi in their existing versions. The MM was originally intended for a 80 CI engine and when used on a 88 CI it was pretty close to running out of juice.

The Delphi was designed fully knowing from the get go that they would run 95 CI and probably 103 CI.

They change stuff all the time and don't tell anyone. I was playing with a 103 FLHRSEI and noticed the injectors are a different color, typically this would mean a different flow rate.

One would need the parts books to find out and with all these more and more frequent changes it gets expensive and too time consuming to keep up just for the sport of it, too bad that those that have access to all this stuff for free have little or no interest, but there is no question in my mind it is by design in a futile attempt to hopelessly confuse everyone, monopolize the market, and allow them to sell most people anything they happen to have handy.

The old mushroom treatment, they keep us in the dark and feed us bull$hit.
 

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I would be pretty surprised if someone could get there without opening the engine, and if you do it will be expensive as you would need different heads and pistons.

On the other side the numbers don't mean that much. My riding partner just picked up his FLHRSEI on saturday and we put a couple hundred miles each on it yesterday. It's a sweet running bike.
 
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