Supercharged newbie needs advice

edge-540 · Jan 12, 2009

I bought a 92 GT with a ton of stuff done to it and need some direction.
Engine: 306 (fresh rebuild)
Heads: Edelbrock aluminum with 190 valves and scorpion 1.6 rockers
Cam: F303
intake: Typhoon upper and lower 75mm tb and MAF
MSD 6AL ignition
Vortech vs1 supercharger pushing 11psi. Has stock vortech bypass valve
BBK fuel pr. reg.
motorsports 42lb injectors

I'm sure there's something else I'm missing. The previous owner had it dynoed at 464 at the wheels, my concern is with the stock bottom end, should I be dialing it back? I'm running 100 octane avgas in it, where should my timing be? I'm not running an FMU, should I be? The vortech bypass valve is only rated to 375 hp, should I switch to a mondo?

Saleen8786 · Jan 12, 2009

How much boost are you running? Do you have a t-rex or other inline fuel pump??

FastDriver · Jan 12, 2009

Your concerns about your stock bottom end are justified, but if it's working for you, then let it be.

Do not take any specific timing advice from someone over the internet. The only exception to this is someone knowledgeable who is looking at your data-logs. If you don't have a data-logging ECU, then dyno and custom tune it.

You should not need an FMU. Undoubtedly, your AFPR adds 1 lb of fuel pressure for every lb of boost. FMUs are used to compensate for fuel injectors that are too small by increasing the fuel pressure:boost ratio.

I have no idea about stock vortech blow-off valves.

Chris

bentley429 · Jan 12, 2009

I wouldn't be worried. Is the bypass valve the plastic bosch one or is it the mini race bypass? I made 475 rwhp with the plastic one and it saw up to 17 psi and held it. No FMU with a dyno tune, as for the timing it should be set at base 10 degrees. If it is dyno tuned I am sure it is all worked in the chip.

edge-540 · Jan 13, 2009

I'm running 11 psi of boost, the car has been dyno tuned at a place near Philadelphia (Have a ton of info on the tuning sessions). It has a BBK 255 fuel pump on it.

edge-540 · Jan 13, 2009

Yep it's the stock plastic Bosch bypass valve, I'll keep running this one and see what happens. The bottom end only has about 500 miles on it, I'm just a little concerned that even the place that dynoed this thing said "the bottom end of this engine is rated for max. of 350 hp.. Please note that any abuse will result in catastrophic engine failure".

FastDriver · Jan 13, 2009

They're saying that to save their own ass. The stock 5.0 block is ok for what you're doing. Going over 500rwhp is pushing its limits, and over 600rwhp is on borrowed time. Just don't get even more aggressive with the tune, and leave it be. You should be fine.

Chris

90lxcoupe · Jan 14, 2009

as long as you dont over rev the motor you will be fine, if it was tuned then the A/F ratio should be good, but it wont hurt to put a wideband in the car. what kind of MSD box are you running?? When i got my car tuned with the blower it made 480 rwhp, stock block, bosch bypass valve, and no MSD box... i missed a gear at the track and learned the hard way

My tuner changed the factory revlimiter to something rediculous because the factory one is set at 6250 and cuts fuel not spark. So me not getting around to putting an MSD box in cost me a motor. I dont know if you have one, but if you dont... call summit and order one right now. Also, with that combo there shouldnt really be a need to run 100 octane. 93 octane should be plenty, what are you paying for the race gas?

millhouse · Jan 14, 2009

90lxcoupe said:
as long as you dont over rev the motor you will be fine, if it was tuned then the A/F ratio should be good, but it wont hurt to put a wideband in the car. what kind of MSD box are you running?? When i got my car tuned with the blower it made 480 rwhp, stock block, bosch bypass valve, and no MSD box... i missed a gear at the track and learned the hard way

My tuner changed the factory revlimiter to something rediculous because the factory one is set at 6250 and cuts fuel not spark. So me not getting around to putting an MSD box in cost me a motor. I dont know if you have one, but if you dont... call summit and order one right now. Also, with that combo there shouldnt really be a need to run 100 octane. 93 octane should be plenty, what are you paying for the race gas?

Over-revving certainly will decrease the lifespan of the stock block. The best you can do is to keep it under 6krpm with a decent tune and hope for the best.

As for you 90lxcoupe….that damage was not caused from the factory fuel cut….but rather floating the valves at high rpm. I’m not sure where you were going with it….but the factory fuel cut is actually far safer of a hard cut limiter than spark only, especially on boosted applications.

FastDriver · Jan 14, 2009

millhouse said:
As for you 90lxcoupe….that damage was not caused from the factory fuel cut….but rather floating the valves at high rpm. I’m not sure where you were going with it….but the factory fuel cut is actually far safer of a hard cut limiter than spark only, especially on boosted applications.

Really? That's counterintuitive. Cutting spark to a boosted engine still leaves a proper AFR in the cylinder. Cutting fuel could result in a lean condition if it cuts the injection in the middle of a duty cycle.

millhouse · Jan 14, 2009

FastDriver said:
Really? That's counterintuitive. Cutting spark to a boosted engine still leaves a proper AFR in the cylinder. Cutting fuel could result in a lean condition if it cuts the injection in the middle of a duty cycle.

Most OEM turbo vehicles use a fuel cut as their hard rev limiter. It's simple, safe and effective. The fuel is cut to alternating cylinders instantaneously which immediately reduces rpm to safe levels (it is never done in the middle of a injector event, but immediately afterwards).

FastDriver · Jan 14, 2009

Thanks Millhouse. It makes sense to me...

Why would cutting the spark to achieve the same ends be detrimental? Or would it be detrimental at all?

millhouse · Jan 14, 2009

FastDriver said:
Thanks Millhouse. It makes sense to me...

Why would cutting the spark to achieve the same ends be detrimental? Or would it be detrimental at all?

While cutting spark alone works, it has some negatives to it. First off, it has a tendency to wash the cylinder walls down with fuel. Now, many use it without issues, imagine 1000 hp worth of fuel at WOT hitting a spark cut rev limiter. There is the possibility of a ton of fuel being dumped at an extremely high rpm.

Again, many people use the MSD cut feature that pulls spark to alternating cylinders....and it seems to work just fine. I don't believe however it will hold the rpm down forever....and in the end, the OEM's way of a hard cut (fuel cut) is the safest surefire method.

FastDriver · Jan 14, 2009

millhouse said:
While cutting spark alone works, it has some negatives to it. First off, it has a tendency to wash the cylinder walls down with fuel. Now, many use it without issues, imagine 1000 hp worth of fuel at WOT hitting a spark cut rev limiter. There is the possibility of a ton of fuel being dumped at an extremely high rpm.

Again, many people use the MSD cut feature that pulls spark to alternating cylinders....and it seems to work just fine. I don't believe however it will hold the rpm down forever....and in the end, the OEM's way of a hard cut (fuel cut) is the safest surefire method.

Thanks man. I learn something new almost every day. When I get a chance, and I finally get my car over to him, I'm going to ask Steve Petty for his opinion on this. I'd imagine that the BS3 can do a hard fuel cut too.

Chris

millhouse · Jan 15, 2009

FastDriver said:
Thanks man. I learn something new almost every day. When I get a chance, and I finally get my car over to him, I'm going to ask Steve Petty for his opinion on this. I'd imagine that the BS3 can do a hard fuel cut too.

Chris

No problem....and I imagine it should. You should be able to have a soft rev limiter (spark only) followed by a hard fuel cut for when it can't hold any more.

90lxcoupe · Jan 15, 2009

millhouse said:
As for you 90lxcoupe….that damage was not caused from the factory fuel cut….but rather floating the valves at high rpm. I’m not sure where you were going with it….but the factory fuel cut is actually far safer of a hard cut limiter than spark only, especially on boosted applications.

I guess i wasnt clear... My tuner programs the factory rev limiter to like 8000 rpms when he burns a custom chip, he assumed that i had an MSD box, and i didnt, so when i missed the gear the motor revved to the moon, and that was the result. I didnt mean to say that a fuel cut caused that damage. but it still isnt a good idea to cut fuel at those kind of RPM's with boost, cutting spark is the ideal choice

millhouse · Jan 15, 2009

90lxcoupe said:
I guess i wasnt clear... My tuner programs the factory rev limiter to like 8000 rpms when he burns a custom chip, he assumed that i had an MSD box, and i didnt, so when i missed the gear the motor revved to the moon, and that was the result. I didnt mean to say that a fuel cut caused that damage. but it still isnt a good idea to cut fuel at those kind of RPM's with boost, cutting spark is the ideal choice

Ahhh, I got ya.

Well have to agree to disagree on the fuel cut, even at those RPM's. It's the method used by almost all OEM's (including turbo'd vehicles) specificially because of it's saftey. Now keep in mind, were not talking about bouncing off the rev limiter rpm limiter here....but throttle body stuck open type of limiter. The soft limiter is typically still held by spark only....and wont typically hold those type of situations.

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