phildo

iTrader: (7)

We have established that I have a backpressure issue but I am thinking I may have another problem as well. I have a 402 with a Turbonetics 76mm with a .96ar. There is no real power. I would guesstimate 380-400rwhp @ 10psi of boost. Could this all be the turbo being too small? Seems like alot of loss. Should I be looking somewhere else also? I have seen that Ninetres made 700rwhp with his 76 and a 364. I realize I am further out of the compressor map but that is a huge difference from mine. I was hoping to make it through the summer w/ the 76( low cash and car will be down for some time while the t-4 to t-6 swap) but will switch to a t-6 88 if the turbo it the whole problem. If not I want to find the other problem and make it through the summer with the 76.

I am running a ls2 block with -28cc pistons, stage 2 l-92 heads, and a l-76 intake. If I figured compression right it is 8.5 to 1. Also running a 4l80e and a 273 rear.

Thanks guys for any poss suggestions!

ss_girl

iTrader: (9)

Something sounds very wrong. You should be making that much power on your motor alone. Have you checked your tune? Is the car running smooth? I would agree that the turbo is too small but it should still be making way more power.

phildo

iTrader: (7)

It is running a air /fuel of 11.0 and about 16* timing. I am spraying straight meth. It runs o.k. at light throttle and 3-4 psi but anything more and it sounds funny and gets flat. If I hit it hard it will break the tires loose at first (1-5psi) then once it boosts past 4-5psi loose all power and torque (6-15psi) and get flat.The tires even stop spinning once the initial 1-4psi are surpassed.There is no knock retard.But the exhaust sounds funny when it looses power. Plugs are tr6's gapped at .035 so I don't think the spark is being blown out. I am at a loss!

ss_girl

iTrader: (9)

Did this just start happening or is this a new install?

phildo

iTrader: (7)

Engine and trans are a new install. The kit was on my stock motor and moved out good for only 6psi. Much quicker than this motor on 10psi.

phildo

iTrader: (7)

Anyone else out there this late?

2000TurboVert

iTrader: (17)

I would go take it to the dyno and see what they can come up with... They need to scan this soon to be monster and see whats going on... Somethings DEF not right... You should be making upper 500's into the 600's on 5-7 psi with that motor......

JAvenger007

iTrader: (9)

What A/R are you running?

Do backpressure test and see how its doing. Does the car overheat during 10psi runs? Locally, I've only seen 364ci guys running T76s, so I'm sure yours is out of range on that 408.

phildo

iTrader: (7)

.96 ar

No it does not overheat at 10psi. and IAT's do not climb but I have a massive intercooler and spray meth on top of that. My Iat's only get a couple degrees above ambient.

The only problem w/checking the pressure is there are only 2 02 bungs on my crossover pipe, so I would have to pull a o2 to do it. Would run pig fat on that bank but I guess I could try it. Who carries the gauge to measure pressure?

DaveSchott

iTrader: (5)

Have you tried scaling back the meth (is it progressive)? You might want to use hi octane gas and try it w/o the meth, get the tune right, (full insturmented dyno runs)then begin to substitue meth and 93.

RW99

Dave beat me to it; it sounds like you may be spraying too much methanol too quickly. Ditto the above advice; turn off the methanol and get a base tune on higher octane fuel... and of course when you're back to normal fuel and methanol you'll probably need to pull some fuel out when the methanol is maxed out.

Even with a progressive (Alkycontrol) system, you can spoil your own party by adding too much too early as the car responds to WOT. That's why the little ramp adjustment **** on that controller is there. My system is set to ramp pretty slowly.

alwaysinboost

what kind of wastegate are you running and are you using a boost controller or just running of the WG spring pressure?

another thing you might want to try is a pressure test to see if you have any leaks in your charge piping.

red beast

when I was starting my build, I was going to do meth and was told not to use it....they were saying at high horsepower levels you do not want to rely on a pump going out/running out, etc. and your combo is going to be a beast....I was told to tune on race gas and then if I wanted to run pump gas just turn the boost down. right now I have mine tuned on 93 pump gas, 12 psi and 14 degrees timing with no spark knock...once I go SD I'm going to tune it with 110 octane and about 20 degrees timing and 20-30 psi.....

cablebandit

iTrader: (37)

my incons were too small for the 408....

346= 820/823
408=740/920 same boost

you should have more power than you do

ddnspider

iTrader: (26)

with that timing and A/F u shouldnt even need meth @ 10psi try not spraying meth AT ALL and see what happens.theres no way your backpressure is that high causing this problem.

Pro Stock John

iTrader: (34)

Can you change the AR to a bigger one? If not, turn it down and leave it alone until you can fit a bigger turbo. Why not do a T4 88, T6 is a bigazz turbo, mine is almost 12x12x12 inches.

wannasupra

how do you have your meth set up? also, how does the car sound flat? vid? datalog? graph?

cablebandit

iTrader: (37)

lol..i JUST got it...ripped it from importatlanta......."whats NUKES?" "Tojo has left the game" rotfl

phildo

iTrader: (7)

It is like a car with a clogged cat converter. Has power till a certain load Than the exaust sounds flat or mono tone. Not crisp and aggressive.
A video will do nothing. Sound quality would be too poor.

phildo

iTrader: (7)

I have turned the meth off and it ran the same. There was no knock retard either. I have tuned numerous turbo cars on the street w/a wideband and get them pretty close before I take them to the dyno for the final tweaking. It is not in the tune. There is something mechanically wrong. I am wondering if it is blowing the spark out.

I was just hoping someone had a similar situation and could shed some light on the situation. I am sure once I figure it out it is going to be something stupid but I will try anything to get to the bottom of this.