how much boost?

[Terrible Buddhist]

hey guys...I am running a 468 with forged pistons...but most everything else is pretty stock...it is a 4 bolt main. I have a pfm intercooler, and a boost reference 900 holley. I ususally run between 92 & 100 octane.
I am running about 6-8 lbs of boost, but am looking at turning up the pressure a bit...how much can the engine handle with out self destructing?

[Unchained]

I feel that most engines can handle a lot more boost than people put to it but then the window of proper tuning becomes narrower. You need to be sure to read your plugs more often and turn your ign. timing to about 34 degrees max. If someone just changes the pulley and goes out and thrashes without checking things they often run into problems. I have seen guys where the engine is popping and backfiring and they just keep their foot in it like its going to clean out or something. Those are the guys who burn a hole in the piston and blame the blower or the carbs when it is the fault of their lack of tuning knowledge.
Does your engine have a forged crank ?
If you have a forged crank you should be able to handle 10 to 12 lbs. if its in proper tune.

[schiada96]

I run a locked out dist at 30 degrees total
16lbs of boost with a forged bottom end and J&E turbo pistons , no problems so far. TB crank up those T04.s and get it!! Don't skimp on the gas at high boost levels your asking for trouble
[This message has been edited by schiada96 (edited December 19, 2001).]

[HeavyHitter]

TB, It will depend on how good you chamber containment is. Pistons should be -.005 to +.005 off the deck depending on piston material. With 8:1 intercooled and good containment 7 psi is a good number for 92 octane. 100 octane should get you to around 15 psi. 114 in the mid 20's and 118 mid 30's. Drop the compression a point and the boost can go up by 4-6 psi. At around 18 psi composite head gaskets fail. You need to o-ring the heads and receiver grove the block to help the rest of the copper gasket seal (oil/water). Make sure your plugs are cold. NGK 9 heat range. Gap should be around .025. Your engine should make around 25 hp/lb additional boost.

[ponponracing]

If you do as those people say, your motor's life will be very short. 4-6 of boost doesn't need a lot of tuning, if I can say so. I mean it is pretty easy to tune so it last a decent time. If you want more boost, you better know what you are doing. Forged crank and o-ring head gaskets are also compulsory with boost, whatever the number. There are books written about how to tune blower motors, and they sometimes disagree, so don't imagine that by putting a little better gas (92 or 100? And where can you find 100 octane a sunny Sunday morning just before to ramp off) with a better crank you will be able to run 15pds of boost. However you may dream about it.
Blown head gaskets and melted or hammered pistons are what destroy blown motors, at the beginning. Backfires under boost are also destructive. They hit all parts all of a sudden. Why don't you go at a good shop if you want more boost, or if it works good as it is, why don't you stick with that winning combination?
My advice.

[schiada96]

TB I feel that blower boost and turbo boost are two different things the boost comes on softer on a turbo. Plus you don't have the added harmonics of the blower drive on the crank. The setup that Banks concieved has lived thru a lot of motors with 16lbs of boost.
Lots of ski race boats live for hunderds of race miles with the same setups as we have. Mine has approximatley 180 hours of service so far. I run only race gas c-110 or c-116. Its expensive but it is needed to control combustion. Oil temprature has got to be controlled also.
We have to know that a 1000 hp big block won't live forever but can be reliable.
You can talk to Ken Duttwiler he gave me alot of advise as well as Rick Head, Rick was the head of production at Turbonetics now he has his own turbo shop. Good inconel valves and good pistons were what both of them recomended for my application.
They don't live forever but what the hell, plug up the drilled holes and crank up the boost, back off the timing to 30 degrees put some good gas to it and go. You can allways pull the plugs out and bring the boost back down.
Turbos are alot easier on parts than most people think--- so I've been told !!!

[Terrible Buddhist]

I don't have a forged crank...and that doe worry me. I would like to kick it up to about 10lbs...this is my 'last me until I build my 580 twin turbo' motor...so I want to have fun...but not kill it. I took too much timing out last time I played with it and got a nice backfire...I think it just blew out the powervalve though.
is there a perfect recipe for degrees of timing and how much to take out per pound of boost?

[schiada96]

If you don't have a good crank I would not push your luck.

[BradP]

Ponpon,
Do you have any info on a good tuning book for Blower motors, like title and source.. The only book I've ben able to find is " Street Supercharging" and it is very limited in scope.
Thanks and a MERRY CHRISTMAS too all!

[sgdiv7]

I use a knock sensor on my blower motor to tune it and for safty. 8 lbs of boost with 7.5 to 1 compression on 91 octane and I run it just a little on the rich side, no chiller (30 over 454)and no problems for the last year now.
Bore scopes are nice to see whats going on in the conbustion chamber.
10 lbs of boost with good gas, no problem. I know someone that runns 14 lbs of boost in a 18' jet boat and he runns the piss out of it for a year now (every weekend) never had any problems and he runns av gas. With the chiller you don't have even worry just keep the oil cool.
Bill