Hello! I got -88 Trans Am with 350tpi engine. Stock bottom end, slightly modified heads, Flowtech short headers and bad exhaust, 24lbs injectors, comp cam grind. CS XR269HR-12 and P1SC with 12 psi pulley. Cr is about 9,5:1. Megasquirt controls fuel and spark. Tranny is th700. Without supercharger the engine produced 260hp*4600rpm/340lbs*3200rpm With supercharger 420hp*4900rpm/480lbs*4400rpm Accidentally the engine had more than 6Krpm and caused a blown head gasket. I'm going to open and check the whole engine. Do you think that stock bottom end can handle 600hp and 12 psi and 6-6,5Krpm without blowing up? I'm going to get forged pistons but should the stock rods and crank also be changed to forged? Okay another question: How I can get 600hp at crank? I think stealth ram intake with right cam would help. What else? I want it to be as fast as it can be on strip and still maintain exellent streetability. Edit: 600hp is the minimium target but more is not bad at all.

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-Rob

The easyest way is to change the 9 to a S and the 8 to a 1. You are a half there after you do that.

those numbers at the wheels i'm assuming? 420 seems low for a L98 on that much boost

What i'd do is go forged everything while you can. Although loads of power have been done before on stock bottom ends, its NOT recommended at all.

If you can afford a complete bottom end, go for it. I'd run around 9 to 1 compression, with good aluminum heads, keep the cam, up the boost to 15lbs, change rods/rod bolts and crank while your at it. 600hp crank is 500 ish whp. I think the stock crank with good rods/bolts with proper pistons canhold that power but why make it a handicap? Go all forged for security/reliability

forged internals are a must IMO. I have melted pistons for proof. Although having a SAFM system will help the motor out alot. Precise tuning = easy on internals. do it right, not twice. go forged or you will be throwing the dice.

No way will the bottom end handle that you will need forged crank & rod rated for at least 600 hp. 700 + Rating would be better. Also the block will need splayed 4 bolt main caps & may be even more goodies. You'll all so need some top notch heads, a mini ram & a big votec blower, a good turbo system ( like gale banks stuff) or multi stage trick gas system. to me the turbos or a well tuned nos system would make it more street able. you could also try one of those monster smallblock 427ci, 454ci we see in the car mags. imo

420hp is from crank. Maybe 300rwhp?

What is SAFM system?


Okay I will get forged pistons, rods and crank. How about full 355 stroker kit (or should it be 383) from Eagle? How much power I can get with stock TPI? TPI would be a huge torque monster with right cam an great steet ability. What E/T can I get with TPI?

I had a stock l98 longblock. Had a good tune and ran 12 psi on pump gas for over a year and about 10,000 miles car went 124mph in the 1/4 with a 6-speed and 3:08 gears. Only mod to the engine was a holley stealth ram. Car never blew and when I pulled it looked fine inside. I did have a good tune with my fast ecm and was running twin turbos. The tune is the ticket, save some dough and be shocked at what can be made to live! I think I was making 600 flywheel with that MPH and a heavy street car.

What was your redline? With stock pistons? Sounds like a stock l98 can handle a lot of power.

5500 tops
the entire longblock was stock.

SAFM - Stand alone fuel management. FAST, ACCELL, Megasquirt etc. Like superirocz said the tune is the ticket. And he is right about that, but i still say better safe than sorry.

Why would he need a 427 or 454 to make 600hp with a blower? Those motors can make that much on nuts alone.

blower - 355ci is not comonly a "stroker", just a .030 over-bore. The stock stuff will handle more than most people think, but there is MUCH less room for error.

How would you prep the stock block to handle as much power as it can?
Forged pistons, cr ~ 9:1, rev limiter to 5500rpm, new bearings and what else?

Says 'modified heads'. Probably iron L98 castings.. Flowtech headers = 1.5" primaries, 2.5" collectors. He's lucky he's making that much power.


I had a combo like that. 9:1, 15psi. H beam rods, forged crank and 4 bolt mains. Didn't make 600hp though, not even close. Alum heads take a lot of heat out of the chamber which is good and bad at the same time. My 9:1 iron headed motor (sportsman heads) with 15psi made more power..

-- Joe

Yes iron L98 casting.

Funny I thought that aluminium heads produce more power than iron heads.

And myhical beings walk the land.

Typically aluminum castings are CNC'd and have better chamber designs to promote combustion so they make more power than their iron counterparts to a degree. Aluminum also sucks more energy out of the combustion process and into the coolant. But aluminum heads weigh a lot less. But they also pull threads out and warp easier.

Say we have two identical castings, one iron and one aluminum. Identical chamber, identical flow specs, etc. The aluminum head will need roughly 1 full point more compression to make the same power as the cast iron head.

However since most aluminum heads are better than iron castings the thermal losses are not as pronounced.

-- Joe

I'll take those weight savings anyday! iron L98's are HEAVY compared to my AFR's.

So Can A Factory L98 Block Bored Out To A 355 Or 383 With All Forged Internals Handle 600 Flywheel HP With A Supercharger Or Procharger? My Goal Is 500 RWHP But Can The Stock L98 Block With Forged Internals Handle That Without The Block Cracking? I Want To Make This TPI Hit 500 RWHP So I Don't Have To Go With An LS Motor, I'd Rather Keep My Iroc-Z Original.

Well assuming you remove the TPI and replace it with a performance oriented intake.

You start off with a 2bolt block, and align bore the mains and drill for splayed caps.

Make sure both decks are straight, and parallel with the crank centerline, same height, etc.

Sure..


My love affair with stock blocks is long over. I'm at the point where my attitude is buy a dart block and be done, rather than spend $1500 cleaning and machining a 30 year old block of questionable durability.

-- Joe

Factory 3.8 turbo Buick motors are all cast, and the heads don't flow for anything, and have tiny little intake valves from the factory, yet they can push out 500+ horsepower easy with the right cam, turbo and tune. An L98 will do the same with less boost pressure, just keep detonation in check and it will live. As for the TPI, siamese the base of the intake (lower runner entry) and you will reach your goal...

summit racing also sells a machined block for 600 or so. Should be good to go with a preliminary check on block dimensions before assembly to make sure its machined correctly. Should handle 500whp from boost easily.

Ok Well I Want To Keep The Stock GM L98 Block & Bore That Out To A 355 Or 383 With All Forged Internals With A Good Cam & Probably Go With AFR Heads, Then Maybe Run A Procharger Or Supercharer. I Also Want To Keep The Factory TPI Plenum & Bore That Out Then Get Better After Market Runners. I Want My TPI With The Factory Plenum To Keep The Original Look, If I Have To Replace My Stock Plenum I'd Rather Go LS Then Put Those Ugly After Market Intakes On My Engine. My Whole Idea Is Keeping My Engine Looking Close To Stock On The Outside Besides The Runners And Having Around 500 RWHP, With A Good Supercharger Or A Procharger Can That Be Done Or Is It Not Happening? LoL

The trick to making power is in the heads/cam/intake. The trick to getting it to hold together is in the short block.

The cam you have looks good. Pull the intake as mentioned and port it heavily. Siamese the runners, increase the port volume etc. It is likely what is holding you back right now. Depending on the level of modification some porting on the heads wouldn't kill anything by any means.

What are the full specs on your exhaust? I am wondering if it's time to step up some on this. You may be hitting a choke point. 1.75 primaries and a dual 2.75 or single 3.5 wouldn't hurt anything in all probability. Little on the racey side though.

Also how are you tuning? This could also be leaving tons of power on the table especially with boost. The power (and risk) is to do with the timing and the leanness of the engine.

If I were redoing the short block on a budget (absolute minimum parts replacement) and wanted it to live I would do ARP bolts in a set of stock rods then have wider gaps in the top and second ring to keep them from butting. These 2 steps will let you rev more if need be (not like you're going to with the TPI really.) and be more boost tolerant.