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Discussion Starter #1
Looking for some real world advice.
I have a 61 chevy belair with a 383 (3.9 bore) LS1
stock 241 heads
8.5:1 cr
Off the shelf comp cam 285 LSR turbo [email protected] [email protected] 115lsa
Edelbrock pro flo intake with edelbrock t/body
60lb injectors
No intercooler, just progressive meth injection 80/20 mix (3 nozzles)
Borgwarner S475 turbo (T4, 83mm turbine) std cover
Log style manifolds with single 3.5 inch exhaust
Powerglide auto 9 inch diff (2.75 gears)
Link to build thread
http://performanceforums.com/forums/showthread.php?67258026-61-chev-LS1-turbo
I had this tuned and came up with a best of 450rwhp at 15psi boost. I found the converter has some mammoth slip and have purchased a converter to suit from the guys at PTC. I have also bought some 3.25 gears to go in the 9 inch. The old converter has ballooned and damaged my thrust bearings. This means I will have to pull the motor/trans/diff out, whilst it is out I was thinking of fitting a race cover to the turbo and possibly an 82mm comp wheel and reviewing the camshaft? I have done backpressure testing pre turbine and it peaked at 20psi while intake was 15psi. This is mainly a street car with occasional track time and do not intend to spin it hard.
Is the camshaft I have got completely wrong? Or should I just change the compressor side? As running no intercooler I was thinking that the cover and comp wheel will lower intake temps at same boost pressure? Willing to buy a cam if someone can spec me one?
 

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I personally don't see anything wrong with your cam selection. That cam will have zero to very little overlap at .050" lift, which should work nicely with a turbo.
Your 8.5:1 compression ratio is leaving some power on the table. You could bump that up a point and still work well with pump gas. How much ignition timing are you running?
 

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i beleive your backpressure is little high.People say 1to1 ratio.The higher boost level will make the BP higher.You can go to a bigger a/r and you will gain on the big end.
Tony
 

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1.3:1 is a little high ?

If I had to guess its a 1.32/96mm T6 on it already .



OP , have you priced that turbo upgrade ? And If so , who have you contacted ?

I talked to Bullseye and they dont do it . They dont even sell their cover seperate anymore .
 

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Drag Week Survivor
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Borgwarner S475 turbo (T4, 83mm turbine) std cover
At 383ci I would think the exhaust side of the turbo is going to hurt you the most. What AR is it?

It's probably fun as hell on the street, but it's killing 1/4 potential on your combo.
 

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It's not the compressor side killing power, it's the hotside but there's probably not much you can do about that if your space limited. The compressor side will support 700+hp on that motor as it is with the right backside.
 

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It's not the compressor side killing power, it's the hotside but there's probably not much you can do about that if your space limited. The compressor side will support 700+hp on that motor as it is with the right backside.
You can upgrade to the 87 or even the 92mm turbine all in the same turbine housing.
 

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The camshaft and turbo are matched pretty well together. 20 psi of backpressure for 15 psi on a hotside setup like that is pretty nice. I bet that thing is a hoot to drive. That 4 inch stroke really generates some piston speed for that ci of engine. I love undersquare turbo motors for street cars. The camshaft is a tad small imo considering the heads are bone stock.

If you were to do Joses 92 mm turbine upgrade coupled with a camshaft that adjusts the EVO accordingly would be best case scenario for you without going to the trouble of redoing your kit for a T6 flange. Your thought process about the bigger compressor having lower IAT's at the same boost level is dead on. Itd be a much happier combo with the 80 or 82 mm wheel.
 

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Discussion Starter #11
Cheers for all the replies. It is fun to drive at the moment but is just lacking. Timing wise it doesn't want any more than 17- 18 degrees. DrTurbo, what is the pricing for the rear turbine upgrade in parts (im in Aus). LilJohn, I was thinking about the compressor upgrade as my tuner was worried about the intake temps getting high. Although not alot of people in my area have had much to do with meth inj and no other intercooler. If intake temps are my main concern should i still focus on turbine upgrade and camshaft modified accordingly? Or do the intake? I don't intend to run bigger boost levels or spin it hard. If money was no concern I would just do both. Cheers again
 

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I would probably just upgrade the whole turbo to be honest. Its more money but probably.less headache.

Id do the 80 mm compressor with the race cover. Put that in front of the 92mm turbine wheel and youd have an optimal unit imo.

I can see the timing sensitivity... The 75 with a standard cover hase been know to put out 300+ degree IAT's.

Couple the bigger compressor with the bigger turbine, then redo the cam with a more aggressive EVO to drive that turbine.... And you shouldnt lose any spool. An added benefit is the added aggressiveness in the exhaust lobe will help get some heat out of the cylinder which may take away some of the timing sensitivity you are experiencing now.
 

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That exact turbo (t4 83mm turbine) goes 145mph at 3300# and 16psi in my car on a 364ci engine so the turbo isn't your problem. Some people run tc76 and tc78 turbos on 6 liter engines with decent results and that turbine is tiny compared to the 83mm turbine on the BW on your turbo.
 

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Chupa Cabra
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That exact turbo (t4 83mm turbine) goes 145mph at 3300# and 16psi in my car on a 364ci engine so the turbo isn't your problem. Some people run tc76 and tc78 turbos on 6 liter engines with decent results and that turbine is tiny compared to the 83mm turbine on the BW on your turbo.
Just because it goes 145 doesn't mean a properly sized exhaust housing can't go much much faster than what you're doing now.

I wouldn't call ANY of the TC 76 or 78 units along with the T4 83mm turbine being optimal or properly sized on a 364 c.i. motor with any kind of aggressive camshaft. It would have to be a pretty small exhaust lobe to not back all that up in the turbine housing.
 

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Just because it goes 145 doesn't mean a properly sized exhaust housing can't go much much faster than what you're doing now.

I wouldn't call ANY of the TC 76 or 78 units along with the T4 83mm turbine being optimal or properly sized on a 364 c.i. motor with any kind of aggressive camshaft. It would have to be a pretty small exhaust lobe to not back all that up in the turbine housing.
That has nothing to do with the point I was making, that turbo will make ALOT more than 450whp than the original poster is making, the turbo is NOT the reason he is making 450whp. Im sure I could put a PT106 on a stock LQ4 and set the two step to 5000rpm and sit and burn the transmission down spooling it up and get one 160mph pass but whats the point on a street car.

The turbo is NOT what is limiting this setup to 450whp, has nothing to do with it, there is a problem somewhere else. That turbo will make an easy 800 crank hp on a 383 without crazy back pressure.
 

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Chupa Cabra
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You are correct there. Not sure about not having crazy back pressure on the 383 at 800, but it isn't the reason he is down on power you are right.
 

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Discussion Starter #17
At 15psi I was expecting about 550-600rwhp on my setup. Could the bad converter be the reason for the low power reading? As it made the same sort of power at about 7psi of boost. I would have thought the T4 turbine would have had more backpresuure than it had? I will see if DrTurbo can give me a price on the bigger turbine etc? Or does everyone else use Reed? I don't think the turbo is the whole problem, but when i bought the turbo it was only going to be 346ci. Now I think it is a bit undersized.
 

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Same power reading on the dyno from 7 psi of boost to 15.....

Bring this up again if you still arent happy after the new converter. Until then you need to leave things alone on the engine and work on the rest of the driveline. No need in even talking about spending money with me or anyone else till thats done.
 

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Get that gear put in and some bigger injectors too.

I have a set of hi imp 80's but i honestly would like to see 96's minimum in your motor.
 
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