project-boosteD

My set up:
straight line specialties top mount kit with sc61 s cover
built type r head
gsr block, darton sleeved 81.5. cp 9:1's
cometic .027 MLS head gasket
RC 750 saturated
aem high volume fuel rail and FPR
walbro 255 high pressure
Fuel pressure set to 50psi at idle

the tune went alright, not what i hoped but all is well.... we hit the tuning at 15psi and the duty cyle started to hit 81% with the fuel pressure dropping back to 55 after 7k/rpm
we pushed forward and got up to about 18.3 psi with it dropping down towards 17.5 with a 91% duty cycle

i just ordered some peak and hold 1200's to fix this problem... but is there anything else i need to factor in to this issue?... are those 750's bad? fuel rail/regulator? my final tune was 450whp at 11.6a/f throughout and ignition timing at 18degrees... is the sc61 with the s cover just flowing to much air for the 750's?
Any input would be greatly appreciated.

0mtber

iTrader: (2)

What engine management are you using to calculate injector duty cycle?
Your fuel pressure shouldn't be dropping as you stated it was.

You really should have used a set of Injector Dynamics or FIC injectors instead of low impedance 1200cc injectors. It is a night and day difference.

I wouldn't trust most duty cycle calculators.

GsrRussell

Where did you get it tuned at? Local?

You can pm me if you don't want to put their name out there.

project-boosteD

i'm using hondata s300


but that was what i couldn't figure out... the only thing i could think of is the cap at the end of the fuel rail, it being stock and restricting flow into the fuel rail. is there a way to change out the feed lines from the fuel filter to the fuel rail to avoid that cap? if so where i can find it and how well does it work?

project-boosteD

i'm also spitting coolant into my resevoir under load and overheating... its like my cap can't hold that pressure.. i ordered a new 1.3 cap (1.1 was my old one)... but could it be something else? headgasket? oil is not milky that i can see from the dipstick or under the oil cap

hybrdthry911

not sure what your question is. 750s max out around 450whp so of course your duty cycle is going to get up there.

jjspec

Sounds like the headgasket may be compromised. It wont necessarily mix with the oil. You have head studs?

0Deatschwerks

I'm with hybrid, you are getting close to maxing these injectors out a their tested flow rate (43.5 psi).

Are you using a 1:1 FPR? If so, that should be giving you a little room as boost is applied. Do you have a fuel pressure gauge you can monitor while doing the pulls? Is the fuel pressure staying where it should thoughout? (I'm guessing it is, since your saying your AFRs are staying constant at 11.6) Also, with you running a little on the rich side, that is going to require a little more fuel.

The step up in size was good move, especially if 450whp isn't where you plan on stopping.

project-boosteD

Hybrid, thank you sir... that is one of the answers i was looking for!

jjspec, yes i have arp head studs... a mistake i made was to only torque them down to 65lbs.. after driving the car for the day (no boost) i realized the peice of paper in the box that said to torque down to 80lbs... could driving it on the 65lbs have messed it up?

Deat: I have your run of the mill AEM feul pressure regulator, the gauge i have sits on the fuel rail so i just stand by the car during the pulls to keep an eye on it

hybrdthry911

deat the rise in fuel pressure as boost is applied doesnt actually deliver an increased amount of fuel. the added pressure is just to overcome the resistance of the air pressure against the injector so it can deliver the same amount of fuel as it would at 43.5psi with no pressure. so 100 percent duty cycle at 43psi no boost = 100 percent duty cycle at 63psi for fuel, with 23psi of boost.

honestly ive seen people have a lot of issues with cometic head gaskets it might be the problem, an oem gasket would have been an excellent choice for you. i would definately do some troubleshooting before you pull the head off.

project-boosteD

i will def. trouble shoot and look into it before i rip the head off, but if it comes down to it, how would i get around using an OEM headgasket with a 81.5mm bore on my motor? or is that not much of a bore to make a difference at all?

0Deatschwerks

Yes sir, you are correct. ...my direction of thought is that he is starting with a base pressure of 50psi instead of 43.5 psi, then the injectors will be a little "bigger".

project-boosteD

also what are some other options other than cometic and oem that work really well under high hp and high PSI pulls