Raptor Forum banner

1 - 19 of 19 Posts

·
Registered
Joined
·
55 Posts
Discussion Starter · #1 ·
Hey everyone; just curious has anyone felt the need to go to a larger fuel injector. I'm new to fuel injection but it seems like there is only so much fuel you can get through a stock injector. I've seen them on GEisick website. Just wondering if anyone has tried one and had luck. I'm currently running my pcIII as rich as it will go on top end and i think it still needs more fuel.
 

·
Premium Member
Joined
·
5,119 Posts
I have been doing some re search into this as there has been a lot of debate about injector size needed for a givin HP level.

The stock injector is 425 cc min @ 45 psi at 80% duty cycle

For an example if you had 73 RWHP and a brake specific fuel consumtiom of 0.45 (most 780's & 804's are at 0.45 to.050) and your max duty cycle you would want injector to see is 80% (rule of thumb)
then you would need a 424 cc min injector.

There is some fudge room as I know of a few 80 RWHP 700R's running the stock injector, but to do it by the book, anyone planning on exceeding 70 RWHP should consider a 550cc min @ 45 psi performance injector like what Geisick is selling.
Those will take you to 94 HP safely, again based on my research.

Hope this helps some of you make an informed decsion on if you need to upgrade your injector or not.




on edit, I should add that the AF ratio of the fuel map will have an effect on how close you are to your 80% duty cycle IE: if your at 59 or 60 RWHP and have a fat map, your hitting duty cycle sooner than a higher HP Machine and leaving power on the table IMHO.

Randy
 

·
Registered
Joined
·
511 Posts
RaptorRandy27 said:
I have been doing some re search into this as there has been a lot of debate about injector size needed for a givin HP level.

The stock injector is 425 cc min @ 45 psi at 80% duty cycle

For an example if you had 73 RWHP and a brake specific fuel consumtiom of 0.45 (most 780's & 804's are at 0.45 to.050) and your max duty cycle you would want injector to see is 80% (rule of thumb)
then you would need a 424 cc min injector.

There is some fudge room as I know of a few 80 RWHP 700R's running the stock injector, but to do it by the book, anyone planning on exceeding 70 RWHP should consider a 550cc min @ 45 psi performance injector like what Geisick is selling.
Those will take you to 94 HP safely, again based on my research.

Hope this helps some of you make an informed decsion on if you need to upgrade your injector or not.




on edit, I should add that the AF ratio of the fuel map will have an effect on how close you are to your 80% duty cycle IE: if your at 59 or 60 RWHP and have a fat map, your hitting duty cycle sooner than a higher HP Machine and leaving power on the table IMHO.

Randy

Randy u have way to much time on ur hands lol :thumbsup: nice research ;)
 

·
Registered
Joined
·
204 Posts
RaptorRandy27 is pretty much dead on with his post.

When I calculate it I usually use a .5 BSFC to error on the safe side. Also it seems like you are doing the math correctly, but I believe that your hp numbers are based off crank hp. This also needs to be taken into account, as the crank hp numbers and wheel hp numbers are much different.

For example: with a stock injector at 80% duty cycle, 45 psi at the rail and a BSFC of .5 you will be at about 66 crank hp. However if you change it to a BSFC of .45 and all the other factors are the same the hp the stock injector can support is about 73.

With that being said this is crank hp, and not rwhp. I'm not sure what the drive train percentage loss is on a atv (as I have never dynoed an atv at the crank), but typically on a manual transmission the loss is anywhere from 15%-20%.

This means that with a 15% loss (which is more likely with motorcycles) and based on the numbers from above a stock injector with BSFC of .5 should handle about 56 rwhp, and a BSFC of .45 with stock injector is about 62 rwhp.

Now don't take these numbers as "if I hit 56 rwhp then my injector is maxed out." Because there are many factors involved, and elevation is the biggest. Just because the dyno shows you have 60 hp at the wheels, doesn't mean you are really making that at your elevation. Dyno's put in correction factors for humidity, elevation, temperature etc....

You are asking yourself, well how do I know when the stock injector is maxed out? Well while you’re on the dyno if you hit 80% duty cycle this is about as much as you want to push an injector. Sure you can go way beyond 80% duty cycle (many people have), but this is bad for a number of reasons. The biggest being inconsistent fuel delivery, as the injectors needle begins to bounce. Also it is stressing the injector beyond the point it was designed to operate at. The biggest give away when an injector is maxed out is told while you are dyno tuning it.

As you push the duty cycle higher and higher you will hit a point where the injector acts "goofy." It will not increase fuel as much as it was before (say 5% increase on the fuel map does not yield an actual 5% delivery of fuel), or it will add a big burst of fuel suddenly. This means the injector is probably past the max duty cycle it can handle and as a result you see the inconsistencies.

There is your fuel injector lesson of the day! :eek:
 

·
Registered
Joined
·
55 Posts
Discussion Starter · #5 ·
well guys I'm an idiot. Would I benefit frm a larger injector or is it gonna be a waste of money?
 

·
Registered
Joined
·
511 Posts
burlyrider142 said:
well guys I'm an idiot. Would I benefit frm a larger injector or is it gonna be a waste of money?
Read above^^^ if you plan on doing major internal mods then yes depending on mods..

Capt.
 

·
Premium Member
Joined
·
5,119 Posts
burlyrider142 said:
well guys I'm an idiot. Would I benefit frm a larger injector or is it gonna be a waste of money?

Have you had it on a dyno? If so what RWHP are you at now?
 

·
Registered
Joined
·
767 Posts
I'd also be interested to see what kind of loss between Flywheel and RWHP we see. :thumbsup:
 

·
Premium Member
Joined
·
5,119 Posts
Yamaha rates the HP at the crank, I believe, but don't quote me on it, that they rated the 700R at 46 HP at the crank. Mine was 38 at the wheels stock.
I always figure 8 to 10 HP loss from the crank to the wheels on a modern chain driven ATV, but that's just my guesstimate, there are other factors that come into play.
 

·
Registered
Joined
·
669 Posts
randy do you feel that it whould help to have the larger inectors for the mods i have done? ken whanted to put in a larger throtel body.or is this the same?
 

·
Registered
Joined
·
661 Posts
ill be geting the bigger throttle body and injector on mine cuz ill be spayin on it and dont want the inconsistant fuel flow out of the stocker.
 

·
Registered
Joined
·
669 Posts
Chicagoland atv thanks for all the help. I thought the forum was to help you learn about this stuff :mad:
 

·
Registered
Joined
·
815 Posts
any of you guys that are wanting the 550cc Geisick injector.... send me a PM.... I have one BRAND NEW still in box.... that i was planning on installing.... but i have decided not to.... so if any of you are going to buy an injector, PM me first.... i will sell it a few dollars cheaper than a new one...

Plattner
(LTE's and stage II cam in forsale section)
 

·
Registered
Joined
·
357 Posts
Jdog said:
Chicagoland atv thanks for all the help. I thought the forum was to help you learn about this stuff :mad:
Yeah, I guess next time I won't post a link that has very technical information from the company that makes the injectors, telling you how to exactly calculate proper injector size for your application. ::)

:stupid:
 

·
Registered
Joined
·
180 Posts
Anyone know if the Geisick injector's atomize the fuel better than stock?
 

·
Registered
Joined
·
511 Posts
Im sure if you call him he can answere that for ya. :thumbsup:
 

·
Registered
Joined
·
262 Posts
We'll find out tomorrow. One thing the injector doesn't protrude down into the intake like the stocker so it could help not haveing any obstructions in the intake runner. :3question:
 

·
Premium Member
Joined
·
5,119 Posts
Jdog said:
randy do you feel that it whould help to have the larger inectors for the mods i have done? ken whanted to put in a larger throtel body.or is this the same?

If Ken puts the 54mm throttle body on I think they put a 550 CC injector in it. Give him a call and see what he thinks. I'm getting by fine on mine right now but I opted to stick with the stock throttle body for now.

Randy
 
1 - 19 of 19 Posts
Top