mn_vette

I'm going to be lowering my compression and I'm not sure if I should go with new pistons(custom of course) or get some better flowing heads with bigger chambers. The engine will be a 383ci.

My current heads flow around 250, stock ported. But my big concern is that I'm going to be running a t-76 and I'm thinking that I could almost bump up to a bigger turbo now and if I get the bigger heads I don't know if the turbo will be able to handle the airflow at low boosts 7-15psi.

I have some pistons with a -24cc dish from my 393ci that I could reuse if I get bigger heads and that would give me an extra 10ci plus the extra flow from the heads.

Let me hear some suggestions. Thanks for the help.


I wonder if I could do something dumb like put a smaller throttle body on the intake to create more boost at the turbo charger to cause it to run in it's efficiency range more to flow more #/min. hmmmm

Baldturbofreak

nope just go to a bigger turbine housing. but if I were you Id go Tv85 or t-88

mn_vette

I'm confused how going with a bigger turbine housing will help the compressor supply more air.... please explain.

tjwong

You can get a set of Dart Pro1 CNC heads and have them converted for use on a LT1 engine. They come with 64cc chambers. There is a guy thats converting them for about $400.

mn_vette

Tj

I've been running the numbers and I need a 74cc chamber to get down to the 8.5:1 that I want to shoot for. The heads that I'm looking at are AFR 227's so I'm looking at about a 20% increase in cfm. Perhaps with that much extra flow I wouldn't need to run the extra boost and wouldn't need that low of a compression. But even then I'll need a 68cc chamber to get me to 9.0:1


I am interested in seeing how they do their conversion though, do you have any links or anything?

ztrips

What is involved in the conversion process??

tjwong

Damn I can't find the phone number to the guy. But if you go to:

www.eportworks.com

Give Lloyd a call and ask him about getting them converted. He knows a guy that does it commercially, I think his name was Trevor. I don't know what the process is but I am currently having a set done by this guy through Lloyd.

If you need the 74cc heads you should be able to find a set of 23 degree heads in a 76cc chamber and have it milled to 74 which should take about .012 off the deck. Then have them converted to LT1 specs, Brodix, Dart or someone has to have a head with a 76cc chamber.

Baldturbofreak

Im sorry, your going into choke, and I was thinking surge. you could always reduce the r's your gonna turn. Shift it like a big block. But I would go up to a 88mm wheel and housing.

mn_vette

Going to an 88mm wheel would be ideal, but I'm REALLY going to be streaching the budget,then I'm thinking of buying heads which will run me about $1k more than pistons, the compressor wheel would have to wait. Do you think I could just get a replacement compressor and housing, not a whole new turbo? But running a p-trim I may want to anyways. I wonder how soon I'd have to shift.....let me play with the numbers.

I think I may call that company and see if they can get me some large chamber heads and convert them. Getting a set of SBC heads may be a bunch cheaper.

Baldturbofreak

as far as I can tell, the only difference between lt1 and sbc heads is the extra hole in the front and the deletion of the coolant passages up top. Am I wrong? Because if thats the case you could probably do it yourself.

mn_vette

I just called the guy that Tom sent me to and he said that he could have it done for $350. Now I just need to find me some good flowing heads with some big **** chambers.


BTF, there's one other thing, you need to drill and tap some holes for the intake manifold to bolt down to. The bolt pattern is different with the LT1 than the old school carb stuff.

ztrips

Hmmm... So this could be done to any SBC head??? I'd love to have a nice set of Brodix heads....

Would the fact that regular SBC heads have the extra coolant passages effect flow at all? What about the "steam" vents out the back of the LT1 heads?

mn_vette

Well, I'm not sure the old school heads are such a good idea anymore. I called some companies and here's what they recommended.

Dart
Dart Pro 1 72cc chamber
215 intake runner flows 245 @ .500
next size up were 230's

Brodix
IK200 72 cc chamber
200 Intake runner flows 265 @ .500
or
215 track one head 285 @ 500 but $2300 for the heads

Trickflow
215 intake R-series 67cc chamber
273 @ .500

Edelbrock
Victor Jr 70cc chamber
215 runner 265 @ .500



I'd want atleast a 20cfm difference at my max lift if I'm going to bother getting new heads. Trickflow has the only one that will do that and not by much. I might have to go to a large intake runner like a 230cc.

SloRvette

Looking around for a PT 88 in the future wouldn't be a bad idea. You should be able to fit it onto the headers that you're putting together. That 76 p trim is old school, and odd ball now. I ran a 76 q trim on a 274 cu in motor, and had exellent manners with it. That p trim wheel with the extra cu in's is going to want to start spinning the minute you fire that motor. Maybe not quite but you get the picture. Think alot of wastegate action/flow to try to control that.

Personally, I'd rather get volume in a piston dish than combustion chamber size. If you can work with a piston manufacturer to get a shaped dish that matches up with your combustion chamber you can still get good quench action. That's for when you really want to start splitting hairs. That'll also burn a budget. That's also when you start thinking shorter connecting rods. On a 3.75" stroke standard deck SBC, serious turbo builders recommended a 5.7" rod.

It sounds like you originally started off with a deal on a turbo, and now you're getting ready to spend money on a project, and you're still working around that deal turbo.

Right now, if I was in your shoes, I'd be thinking about building around that turbo's frame size with your performance goals in mind, and a new turbo on your wish list.

Cylinder head flow is key to making power in anything, but realisticly with a turbo, it becomes much less important. Making 3 flywheel hp per cu. in. with heads that flow in the 260's isn't real tough. Think low to mid 20's psi with a turbo that'll flow enough air and a proper tune up. Cam in the mid to upper 230's. 7000 rpm.

On a SBC when you really start pushing, the issue becomes the siamesed center exhaust ports and keeping head gaskets in place. That's where the Fords and BBC's have the advantage. If you want to get wild think about the spread exhaust port SBC stuff.

I'm just rambling. One of these days I'll get the money together to build what I want. Maybe I'll forget about the 3 stages of dry N2O for the 12:1 SBC 396 and just put on the GT42 I've got lying around and run 30 psi on methanol

mn_vette

Acutally, I started out with a t-76 because I didn't have room for a large frame turbo, it was a pain in the **** just to make that one fit. I did take a deal on only getting a p-trim, but I'll save the extra $500 for a down payment on the next turbo if I can get all this to work worth a darn.

My problem is that I blew up my stroker motor this summer and now have to rebuild it. I also just found out that the piston skirts are hosed on my current pistons too so those are getting replaced. Looks like my question is answered then, new pistons it is.

Baldturbofreak

coatings coating coatings! my friend, they can save your ****! especially on piston skirts and rod bearings. Stick with your heads, get deep reverse dome pistons and coat the crap out of everthing that sees fire (or load). you should spend the rest of your dough on a t4 frame gt88 q-trim

ztrips

Where do you get your coatings done?

I'm planning on piston tops & combustion chambers with thermal barrier, and piston skirts with dry lubricant. What to use on rod bearings?

Baldturbofreak

I use swain tec coatings. Partially 'cause they were among the first, partially cause they are just 10 miles from my house. they have every coating you will need. They have a website, google them.