MatthewH

Has anyone run these heads on a 305? In the fine print Racesearch.com and Jegs said that you can use these on small bore blocks as long as a cam with less than .450 lift is used. This shouldn't be a problem since I plan to run either a stock or mild cam. The fact that these heads have 2.02/1.60 valves seems like a big plus to me as far as flow. The only thing that confuses me about these heads is the 60cc chamber. My engine was bored .030 but I'm using dished pistons, and I haven't changed the deck height. I know that the formula for compression ratio is:

total cylinder vol+chamber size+gasket vol
---------------------------------------------
chamber size+gasket vol

But when I work out the formula (97 cc cylinder volume, 9 cc gasket volume, 60 cc chamber volume) I get 2 point something or other...what am I doing wrong here? Shouldn't I be getting a number like 8 point something? But then there is the question of the compression ratio itself. The stock ratio of the LB9 is 9.5:1 (I think)-how much performance am I going to lose if it drops to say 8.0:1-or is it not going to drop that much?

Thanks,

Matthew C. Hall

blak92!

Valves are too big for the small 3.75" bore of the 305. The valves will contact the bore with a cam lift of over .450 (depending on deck height, gasket thickness etc.).

------------------
Hybrid Black 5.7L 5 Speed
'95 Competition Yellow Corvette Coupe ZF6

MatthewH

That won't be a problem-I'll be using the stock cam...I'm mainly worried about compression ratio.

soulbounder

I'm not sure, but maybe I can point you in the right direction. I think NJSPEEDER has these heads on his 305 TBI with the stock cam. If I remember correctly, he said the compression didn't drop all that much from the 58cc to 60cc change. Try emailing him or posting on the TBI board.

steve8586iroc

Where are you getting the 97cc cylinder volume from? If you are ccing the cylinder with the piston at bottom dead center and adding that to the head gasket volume plus the combustion chamber volume, then you need to re cc the cylinder volume with the piston at top dead center and add the gasket and cumbustion chamber volume then devided the larger number by the smaller number and you should have the correct static compression ratio. Am I right or wrong on this one guys?
97cc's seams way to small, maybe 970cc but not 97cc.

Steve

MatthewH

Steve,

You're right-I figured out what I was doing wrong. To convert the cubic inches to cubic centimeters I was multiplying by 2.54.
Instead I should have been multiplying by 16.387 (which is 2.54 cubed) so the equation should go like this:

305 bore (.030 over) = 3.77
305 stroke = 3.48
Constant = 0.7853982
ci's to cc's = 16.387
Chamber Volume = 60 cc
Gasket Volume = 9 cc

14.2129 x 3.48 x .7853982 x 16.387 = 636 cc

636 cc + 60 cc + 9 cc = 705 cc

705 cc
-------- = 10.2:1
69 cc

I think that's it-of course this is assuming the block has been zero decked and the pistons are flat tops. I have to find some way of measuring the dish and deck gap to find the true ratio. You'd think that a physics major would've gotten this right on the first try

Later,

Matt

88IROCs

I don't think valves that size are going to be a big plus on a 305. Even if they clear the deck, you will have severe valve shrouding - especially on the exhaust side. In this case, smaller valves would probably increase flow.

If you insist on aluminum heads, find a set that use the standard 1.94/1.5" valves. This will still be an improvement over the standard 305 valve sizes. The additional benefit would be the ability to use a higher lift cam, which should also improve flow.

If you can consider cast-iron heads, the WP 305 Torquer head might be a good option. I believe the valve angles on these heads are rotated to further unshroud the valves(hopefully someone can confirm or correct me on this). Some of the money you save by going to cast-iron could be better spent to get a camshaft that more closely matches the increased compression ratio. A stock(or near stock) lift cam will not do a very good job of filling the cylinders at the compression range you are aiming at.

AJ_92RS

88IROCs is right that shrouding will kill the whole purpose of having the large valves. Not only that but it will hurt the velocity of the air flow which will hurt your low end torque. The smaller area that air goes through will increase it's velocity (speed). This will help pull air in faster at lower RPMs.
The 2.02/1.60 valves are great for higher RPMs 'cause the faster piston stroke will increase the airflow speed, and the cylinder will also get more air. But if you plan on mostly street/strip duty then it'll take 2500 to 3K RPMs to get that engine pulling. 1.94/1.50 should be good for a 305, even bored out, especially if you're gonna stick to the stock cam. It's all in the combo of the engine. The stock cam is set up for torque, so putting on high flow heads is like telling a 10 yr. old that he can use a bigger shovel to move more dirt faster. He couldn't handle it!

MatthewH

Thanks guys,

Ok, now I have a good idea of what I want to do as far as heads...The only reason I was going to stick to a stock cam before was because of the recommendation from Edelbrock about the lift restrictions. I guess I'm going to shift my attention back to the Corvette heads, but I'm not even sure about those because of compression issues with my dished pistons...Since this engine is going into a Volvo the big attracting factor for aluminum was weight over the front end. Of course I don't want to have a light car that's a total dog either

I called Jegs because I was originally going to order S/R 305 Torquers, but the parts guy told me that they only came in the pre '86 intake style. Is there a TBI intake made that will bolt to that? I know there are carb manifolds that you can bolt a TBI spacer to, but I'm worried about hood clearance in the Volvo. Of course yet another option is to buy Vortecs and shave them down-then get the GM TBI manifold.

Decisions, Desicions....

Later,

Matt