Okay, I'm doing a TT305. I'm making a Frankensteinian header/log for the exhaust. The goal is to make 500-600 HP under 6000rpm. I was considering using two T3 (.60/.48) turbos. I threw out a question to the guys at JGS Precision Turbo and here was the reply:

"For 500-600HP, you will need a 8-8.5:1 compression engine and around 15-20 psi of boost (depending on head flow, the better the head flows the less boost you will need). Those units would be fine for a 305, a little small for the 350."

Okay, so on a 305, I would use stock short block, and swap to L98 aluminum (vette) heads. That should drop the CR to around 8.5:1. Can these heads be ported, or will I run into valve clearance issues?

Secondly (and more importantly): I will eventually upgrade to a 350/355. Now if the above T3s are too small for the 350, what is a suitable turbo size (bigger T3, T3/4) that would work well on a 305, but be "big enough" for a 350?

Lastly, the setup won't be intercooled right away. How will that affect power levels and boost levels?

Sorry, I don't have the whole mapping concept down yet. Maybe I can begin to figure it out once my books arrive. If it matters to anyone, the 'charged air will be thrown into a SD HSR setup.

Thanks for any help guys,

MILT

 

Intercooling will dramatically increase hp levels, it makes the boost more colder/denser and alows you to run higher boost without causes exseive detonator. Water alchol injection also does this but water is subadised for fuel and not as huge power gains. But it is expensive that is alot of air huge intercooler needed.

 

"Intercooling will dramatically increase hp levels, it makes the boost more colder/denser and alows you to run higher boost without causes exseive detonator. Water alchol injection also does this but water is subadised for fuel and not as huge power gains. But it is expensive that is alot of air huge intercooler needed."
When your done with that hit pass the J my way I think we need a spell/grammer/intoxication checker for this board! hahahaha J/K You may want to proof read your posts a little more carefully I had a hard time trying to decipher what you were saying. No offence, I'm guilty of it too

 

First....what size are the combustion chambers in the stock 305 heads? i know in the 350s its i belive 64cc and the vette heads are 55cc aren't they? So if the 305 heads have big chambers like the 350 heads, you'll be increasing compression not decreasing it by swapping.

second....i thought there were only a limited amount of heads that will work on the 305 because of the small bore?

 

305 heads are universally 58cc heads.
A 64cc head (like the l98) will put you to around 8.6:1 compression (if you started with 9.3:1)
I would not recommend doing tts on a stock short block unless you hate it and WANT to blow it up. ; )

 

just thought of something - you could get some 76cc heads and have 'em milled to what ever you want/ need.

 

Oh I don't hate the 305, I'm just starting with what I have--a stock short block. After it blows up, then I'd be happy to build a proper 350 for the setup!

So the L98 heads would be decent. A 72cc head milled (for 8:1 CR) would be better. Also, would I run into problems w/ valves?

Thanks again guys.

 

you shouldn't have valve problems.

 

not to mention 76cc heads are everywhere - as long as you don't have an adversion to porting. 882 casting heads are every where but the will need to be ported massivly.

 

Okay; I won't do the portin personally, so what type of port job should I get done (and what type of cost?)? Also, what size valves would be best on a 305?

Thanks

MILT

 

valves - the biggest that will fit (i am pretty sure 2.02 / 1.6 will fit)

if you get 882 heads they will have to be ported ALOT. There is plenty of metal there but most shops won't do that much porting if they will port heads at all. you might be able to get some one to do it for you though.

If you aren't adverse to spendin money just about every aftermarket head can be had with 72cc chambers and they will work on a 305.

 

The aluminum L98 heads flow terrible for the price. You would be better off with something else.

 

MMMkay. I think I'll start off w/2 .60/.48 T3s. I'll skip the heads for now. Once I get the "bugs" out of the setup or frag the motor (whichever comes 1st), then I'll upgrade to a 350 built for 8-1 compression. I can then upgrade to .63 housings to help feed the 350.

Or would it be worthwhile just to pull a set of 76cc smoggers from the JY for the timebeing? Would they flow better than a TPI 305 head?

Thanks

 

The aluminum L98 heads have 58cc chambers, the same as stock 305 heads. They will keep your compression stock, in the 9.3 range.

 

I sirously doubt the 882s will flow better than tpi heads with out alot of port work. Just stick with the stock heads and keep the boost low.

 

Stock 882’s will outflow stock L98 vette heads by about 20-25cfm. With the smaller 305 bore you have to stay with 1.94/1.50” valves, for that matter, even at those sizes you start running into valve shrouding problems with the small bore. 76cc heads with the .015” felpro gaskets should put you right around 8:1 (with better quench). Not sure why you’d want to port them for the combination that you’re talking about anyway, stock they’ll flow more then the 305 will use up to about 6500-7000rpm (good luck in getting it to rev that high).

The only problem with using 882’s are that they are crack prone, and a turbocharged application will only make that worse, though they will work. Iron L98 heads (64cc chambers) will put your compression at about 8.7:1 with stock style head gaskets, but they don’t flow even as well as the early smog heads, though they should still be OK up to about 5500 rpm. If you’re willing to deal with figuring out intake manifold problems, I’d seriously look at a set of vortec heads. They’ll flow more then you’ll ever use on that 305, relatively cheap and have a killer chamber/port design. Otherwise I’d be on the lookout for some 64 or 76cc pre lightweight casting heads or stick with the stock heads and intercool it or run race gas when you push it hard.

 

I dont know where you get that. 882's are some of the least crack prone heads GM ever produced. It is such a sure head that some remanufacturers often chose not to leak test and crack test them. they are that sure. In the universe of stock heads, 882's are the "Rock of Gibraltar" among heads. I dislike them myself as far as the chambers are a bit too large even milled down but otheriwse they are a fine way to reduce compression ratio if quench is not a factor.

 

where do I get that? Well, I've only seen 3 cracked heads in person, and they all happened to be 882's. For that matter I just flipped through Lingenfelter's On Modifying Small Block Chevy Engines, p74 “The 882 heads… they are prone to cracks usually in the combustion chamber area.” And he even has a picture of cracked chambers in 882’s…