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Discussion Starter #1
I have recently fitted my GT30 kit and custom fuel rail with 720cc injectors,but here in the UK a guy has just rolled 400rwhp and mentioned they were on their limit?
Does anyone know any different?
 

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If you want to keep the duty cycles sensible, on a UK dyno around 450 at the wheels would be the limit. Andy's car was being kept at a very safe limit, he wants to run another 6-7psi of boost over what Thor dyno'd up to, so they left it at 410 rwhp until he rectified other issues he had :)

Note : It'll partly depend on what base fuel pressure you go for
 

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Discussion Starter #3
Hmm,
I dont really want to limit myself too much as i know the turboi can provide enough for 500hp.
I cant rememer what the duties or boost levels were on andy's TBH.
I Still have to run it in etc so i may stick with them until the engine can be fully opened up.
Anyone?
 

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I'd presonally go with 850's - the phoenix power car up in Scotland made 613 at the fly (blowing exhaust manifold) on them and its been dyno'd to just over 700 at the fly. Which is pretty much their limit.

I'm going with 83lb/hr (850cc approx) injectors and I've not even got a built engine
 

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Discussion Starter #5
So if 350rwhp are rthe limits for 550cc' surely we could squeeze more than [email protected] flywheel out of 720's?
WHat kind of fuel pressure was Andy running do you know steve-o?
 

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720s for 400rwhp should be a piece of cake.

One of our cars.. is running 680ccs @ 50psi base pressure.. its currently sitting at 330rwhp with 30% duty remaining and tuned quite rich... if thats a help.

-Tristan
 

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Over the weekend, I street tuned my car out to 23 psi (unbelievably fun!). My datalogs (DFI Gen7) show my Siemens 83lb injectors are at 99% duty cycle at peak torque. I'm going to inrease the fuel pressure a bit and see if I can get out to 26 psi (hoping to dyno it at 26 psi in a couple of weeks).
 

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jose rosario said:
you should be able to make 450whp safe on those injectors.
I woudn't say "safe", but you could do it. I think at 450whp you should think about moving up to a larger injector. At least a 880cc (like the ones I'm running). You're going to have to run a lot of fuel pressure and high duty cycles-which I personally wouldn't want to do. Most of the experts feel that you should keep the duty cycles around 85%. I know people who run 100% without problems-for now-but I'd rather be safe than sorry.
 

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flupstar said:
720s for 400rwhp should be a piece of cake.

One of our cars.. is running 680ccs @ 50psi base pressure.. its currently sitting at 330rwhp with 30% duty remaining and tuned quite rich... if thats a help.

-Tristan
The car in question was running stock fuel pressure and they only dyno'd at 410rwhp to 1.6 bar. He's had a HG issue, so they didnt go further. The plan is to tune to 2 bar, so this is why he's changing from the 720's to larger injectors. This is on pump with a A/F of usually around 11.5
 

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LandJet said:
I woudn't say "safe", but you could do it. I think at 450whp you should think about moving up to a larger injector. At least a 880cc (like the ones I'm running). You're going to have to run a lot of fuel pressure and high duty cycles-which I personally wouldn't want to do. Most of the experts feel that you should keep the duty cycles around 85%. I know people who run 100% without problems-for now-but I'd rather be safe than sorry.
Here is the formula:
injectors size X # of injectors / 5.8 = RWHP-10% = rwhp safe

720cc X 4/5.8 = 496.5rwhp-10% = 446.8rwhp safe!

stock injectors would come up to
440cc X 4/5.8 = 303.4rwhp-10% = 273.1rwhp safe!
 

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jose rosario said:
Here is the formula:
injectors size X # of injectors / 5.8 = RWHP-10% = rwhp safe

720cc X 4/5.8 = 496.5rwhp-10% = 446.8rwhp safe!

stock injectors would come up to
440cc X 4/5.8 = 303.4rwhp-10% = 273.1rwhp safe!

Injectors cannot be given such HP ratings. so many other factors contribute to power losses or gains.

Extremely general guide for entirely average engines only
 

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...and you think just because it says so on a website, its true? :) Most people on here realise that 50% of what you read on the net is in some way incorrect... and most of the rest of it is still based on opinion..

I respect Ricky's knowledge but its not gospel, I dont agree with it.. and everyone's idea of "safe" and "ideal" AFRs varies..

tell me, if you have a motor pushing 275rwhp on stock 440ccs.. on their "safe limit"... what happens when you rebuild it with lighter internals, larger tollerences.. with a bigger turbo pushing cooler air through a larger intercooler and a bigger turbine side creating less backpressure against the piston... and a revised intake manifold flowing more evenly with less restriction...

and if you adjust boost to create the same AFRs at the same duty cycle as before...the horsepower will rise.. you're making the engine more efficient with less losses..

But it doesnt have to be that complicated. Shove in some 9:1 compression pistons and you will make more power with the same amount of fuel. Throw in some 8:1s and the reverse will happen.

And all of those factors cannot be put into a formula with two variables.

Like I said.. its alright as a very general guide for average engines. It is nowhere near being a be-all-end-all answer. Ricky's primer is a fantastic article.. dont get me wrong..! But its not the last word on the subject.

Its about as accurate as those 1/4 mile calculators which ask you for two things. a) power and b) weight. Not factoring track conditions, power/torque curve, tyres used, driver, wind, gear ratios, aerodynamic drag, altitude, and so on forver..

Sure, it'll get you in the ballpark..

-Tristan
 

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When I made 460 rwhp on 850's I was at 78% duty cycle. Man I would think 720's around 400 tops. Don't push that 100% duty cycle for long.
 

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jose rosario said:
Here is the formula:
injectors size X # of injectors / 5.8 = RWHP-10% = rwhp safe

720cc X 4/5.8 = 496.5rwhp-10% = 446.8rwhp safe!

stock injectors would come up to
440cc X 4/5.8 = 303.4rwhp-10% = 273.1rwhp safe!
I didn't say it couldn't be done. Jus because you have some little math formula doen't mean it's "safe." Look at your datalogs and determine from there. That is, if you're even making 446whp...
 

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LOL .... just a little side note update. One of the fellas I mentioned in the UK above has a gen 3 car he imported from japan, spec to his knowledge was as follows

- HKS GT3037s Turbo
- HKS Racing External Wastegate 50mm
- Skyline R32 GT-R Boot mounted IC
- 850 Injectors
- Upgraded Fuel Pump (unkown origin)
- Trust Oil Cooler (Boot mounted)
- HKS Air Filter
- HKS F-CON Pro V-Spec Gold
- HKS EVC IV EBC
- Exhaust Manifold (Custom made)
- Down Pipe (3 inch Bore)
- Screamer Exit pipe from EXT WG
- Y Exit Exhaust pipes (3 inch Bore)
- Intake pipe (4 inch Bore)
- IC piping from Turbo through to throttle Body (2.5/3 inch bore)
- OS GIKEN type D Twin Plate clutch
- Lightened and Balanced Fly Wheel
- TRD Diff


He's been running around on 28-30psi of boost on 94 octane for about 3-4 months. LOL ... he's just found out the internals are stock gen 3 :D Just goes to show how strong they are :headbang:
 
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