Ok here is the deal, I currently have a 468bbc with a precision 106 mm turbo on it with a 1.0 housing and a g trim wheel. the engine has 7.9-1 com ratio and cnc ported dart 320 heads on it. Mechanical roller reverse split cam with .714 lift and 274 in and 264 exhaust duration at .050 with a 115 centerline. the problem I have is that I am sick of the spool time it takes at least 5 seconds to get it against the converter on the brake. I am thinking about putting a pair of gt4788 turbo's on it with a .96 housing.

What other turbo's would you guy's recommend?


The car is a all steel camaro that weights 3500lbs with glide and a converter that goes to 3800 with 8 psi. running a 3.50 gear with a 32-16-15 tire.

I am even considering putting nos on it just to spool it.

Thank you in advance for your suggestions

 

Do you have a 3step for staging purposes? Possibly more compression would help out as well.

 

Why the reverse split? Why not go single pattern? What rpm do you spin the motor to? Twins would really help with the spool time.

 

Why not reverse split? And as far as the combo, I am confused on how a 468" motor is having trouble spooling a 1.00 ex housing. I realize its a big *** turbo, but the ex side seems rather small for HUGE lag.

 

Single patterns seem to work well, most turbo guys seem to lean toward single pattern. How is a reverse split better? I'm looking for knowledge, not being a smart a__.
I was wondering the same thing on the 5 second lag, that's a big motor.

 

I didn't say they were better. Just asked you why you recommended a single pattern. I had my set-up evaluated by Stenod/Camotion and they came up with a BIG reverse split cam.....THAT I LOVE. Very similar to yours, except reverse spit w/ lots more lift.

Also, Mr_president had a nice overall combo with a baby reverse split cam that spooled his turbo instantly.

 

I would first look at finding a way to raise compression. It may also benefit you to chat with Don Bailey about a cam...he'll get you there.

 

Before I d go swapping parts I d wonder about a few things.

1. tune, what is controlling this beast? Whats the fuel and timing like? Esspecially at 3000-3800, were in stalls. If its going 10.0 to 1 and has very little timing....that could be the entire cause, esspecially on a 7.8 to 1 motor. It should be taking a ton of timing unless your running a spool retard?

2. Was the cam degreed? If if that monster wasnt....then I d start there. I dont like reverse splits, if its not clearing the cylinder, and the exhuast housing is small, then your bp is high, virtually causing a simulated exhuast system behind the turbo, slowing it down.

3. that brings up another question....this is a open down pipe correct? Gotta ask in the world of noise regulated tracks.

I d be surprized if it couldnt be improve a lot with no parts being changed, but there is always the secret weapon......

 

I like the baby cams. I'm very close to a single pattern now.

 

Ok , I have a fast bank to bank controlling everything with a set of 160lb injectors, the timming on the engine is 42 degrees up to 100kpa the air fuel is 12.5 up to 100 kpa. When it has over 15 psi of boost the richest i like is 10.8 to 11.0. All the way up to 30 psi.
Once it is building boost I am slowly pulling timming, dropping it to 38 drgrees at 119 kpa and decreasing it as boost comes in until high rpm than I have to add some back in under high boost high rpm.
There is no 3 step on this car.
The exhaust on the car is a 5 inch downpipe to a 5 inch dynomax muffler which exits in front of the rear tire.
The reason for the cam is back when I built this car 5 years ago that is what they recommended from cam motion. The cam is actually advanced 2 degrees, they wanted the intake centerline to be installed at 110. When I just recently freshened the engine, I advanced the cam to 108. I thought it would help but it really did not.
As far as what I spin the engine to so far on the best pass it came thru the traps at 7800, but the converter was slipping 19 percent, which I have since had tightened. it ran a 8.09 at 177 mph. which is pretty slow for what is in it!

 

Also try posting this on turboforums...

 

I like the BIG cams

 

Whats your staging procedure like? Single caliper rear brakes? Usually there is alot left on the table in staging/tuning. Was the car easier to spool before the converter change?

 

My staging procedure is start bringing it up on the converter with the brakes, and roll in to the first lites and then basically i hit the transbrake and roll in the throttle more and bump it into the stage lite and deck it if the other guy is ready, or I wait for him if I can.

It actually was about the same before I tightened the converter. The only difference is before I would 2 step it at 4600, and it would hold it there, not that the converter is redone, I can get 8 psi at 3800, and that is as high as it will let it go. Before without the two step it would go as high as you would let it go, I was actually messing around with it one day and it went to 6800 on the brake.
I have thought about just putting like 100 shot of nos on it just to get it to spool and shut it off with a pressure switch when it reaches 10 psi or so. I would have to just try it and see what would work the best.

Has anyone messed around with using nos to spool a turbo on here?

 

Nitrous will give you spool, but twin power adders are only used by supras jk.

Most classes do not allow spooling with nitrous so most dont run them.

A 3step will get more heat in the exhaust which in turn will get the turbo online a bit quicker, the issue with this is usualy the single calipers cannot hold back the car when it starts to see boost, hence doing twin calipers.

3step against the converter while dragging brakes, then get into the beams and put it against the brake and 2step, then fire at will.

 

7800 @ 177? The cam isnt big enough to make power to 7800.....274/264....I d guess would fall off at around 7000-7200 with a 320 head.....Does that ad up? 3.50 gear a 32 inch tire and 7800 @177, I guess thats the 19% slip huh.

Flow numbers in the heads? Is the exhuast goodcompared to the intake or poor? For what a cam costs, I try another grind. Id try out a longer duration exhuast, typical nitrous cam. 260-274 .....114-116.

I have used nitrous to spool a large turbo on a buick. I used a pressure switch (adjustable) to shut off at a set level. I ussually shut it off at 10 psi. The turbo was laggy to 10 then would take off. I could stage on a three amber tree, go on the brake (last to stage) wait for the first amber, wot....and leave at 10 psi or higher on th ethird bulb. I used a single fogger nozzle in my intercooler tank exit (it was thick) with what would have been like a 100 shot I think.....I think it was a 42 nitrous.

 

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have to agree.. the cam is too small for power @ 7800
a 426 cube with 106mm turbo , with nearly identical cam had max power @ 7200, and still made ok power @ 8000....
chassie car went 6.3's @ 233
468 cubes will no way have max power at 7800.....

my 358 cube has high 260's and 270's dur @ .050 so i can spin it up past 8000 for max power...