350 bored .040, 58cc heads 1.84/1.50 valves, 11cc dished pistons, .025 deck clearance
with my current .040 head gaskets it puts me around 9.8:1 cr
would i still be able to run pump gas if i put thinner head gaskets maybe .015-.018 to get the quench area tighter even tho the compression will climb to nearly 10.5:1?

Yes you should be able to run on pump gas put 93 octane in it. Should be fine .JMO


Cole

 

ive been running 89 in it no problems the way it is now. i dont have easy access to 93 where i'm at nor have the budget for it. would there be much of a performance gain by the swap or just a waste of time and money?

 

350 bored .040, 58cc heads 1.84/1.50 valves, 11cc dished pistons, .025 deck clearance
with my current .040 head gaskets it puts me around 9.8:1 cr
would i still be able to run pump gas if i put thinner head gaskets maybe .015-.018 to get the quench area tighter even tho the compression will climb to nearly 10.5:1?

If the pistons have a full dish then there is no quench area. If they are D dished then you are OK.
If the bottom end is fresh but you have cast rods and crank then stay around 40 + on the quench (.025 gasket and .020 gasket-.019 etc.).045 is a safe number if you have cast parts and are at or below 6000 rpm.
The dynamic compression ratio is a little more important.The static being 10.5 to 1 is important but a dynamic over about 8.5 - 1 will have detonation on anything less than 93 + up.
You need to figure the dynamic comp ratio before you build.CC your heads to be sure and if you arent running D dish pistons you better go down a little on both compression ratios.
With your combo you will have to open the heads up a little if you tighten the quench by using a thinner head gasket Taking .020 off the head gasket thickness means you will need to add 4-5 cc s to the chamber size to keep it down around 9.8 -1

 

with a .040 gasket you will have a quench area of about .065" this is on the high side of normal, i personally have always built my engines with a quench area of .038-.045"

with a .020" gasket you are sitting at 10.26:1 compression and my guess is that you are using a set of 4416 305 HO heads. this compression will certainly be pusing the limits of what you will be able to do on pump gas, if not be just beyond it. the problem is that the heads you have picked wont rev that 350 up past 5000rpm on a good day so therefor going with a cam with enough overlap to bleed off some of the cylinder pressure is out of the question as you would need a cam that would run the engine upwards of 6000 or so rpm, and you just wont flow enough air through those heads for that. the next thing to look at is LSA because a higher LSA can help to bleed off some of the cylinder pressure, but you would need a cam with upwards of 114+LSA to bleed off enough pressure and when you go looking at cams with a LSA of 114 they dont tend to be very performance minded (more on the stock side)

i would say that your best bet would be one of these options, run the .040 gasket which will put you at 9.8:1, have more of a relief (about an additonal 6cc per piston) machined into the dish of the piston (w/.020 gasket), have the combustion chambers cleaned up for about another 6cc per chamber (w/.020 gasket), buy a new piston with more relief, or buy a better set of heads with a 64cc chamber.

i would personally recomend buying a new set of heads, as i think you will end up disapointed with heads you have if you are trying to build a mild performance motor. the cheapest option would be to use the .040 gasket but you will still be at about 9.8:1 compression and you still might not be able to use a cam with enough overlap to bleed off the cylinder pressure you will need in order to run pump gas.

 

ive been running 89 in it no problems the way it is now. i dont have easy access to 93 where i'm at nor have the budget for it. would there be much of a performance gain by the swap or just a waste of time and money?

waste of money, you might gain 10-12hp, you'll barely be able to feel that while driving if you can at all

 

using a cam to bleed off dynamic compression to run pump gas is going to give you a doggie low end. You will hate it.
unless you are bracket racing or roundy roundin the 5000 rpm breathing limit on those heads wont kill you on the street. Any good street engine will have to through the entire operating rpm to perform well on the street.The fact that flow curtails at and above 5000 rpm isnt that crucial in my opinion. Having no low rpm horse power and torque is an issue.

 

ive had the motor built for awhile and runs fine idle to roughly 5k (performer intake and 4x4 cam rated to 5600) i heard if you run a tighter quench u can increase compression and timing without worrying about detonation. btw the pistons are full dish with 4 valve reliefs

 

then I would leave it alone .If you plan on tearing it down use D dish pistons and Get the quench correct. Be it with a zero deck ( .005 is recommended) and a .040 gasket or .025 deck and a .020 gsket etc.
I have to agree with the 305 heads being a low flow job but decreasing the dynamic compression to run pump fuel is going to result in an engine that has nothing off the line(when the light turns green)
They will keep(or tend to) airflow velocity higher at low rpm which should give a better low end response. Still there are better heads for use on the street.

 

anyone ever use the cheapo procomp aluminum heads or should you be wary of using them?

 

you should make that question a new post for better results. Ericnova would be the guy with the plan or F bird. Those 2 guys are insanley smart about racing/ performance

 

i was only implying that it would be waste to run a cam with enough overlap to run the pump gas.

and i love how people say if you run a cam that will run up to 6000rpm+ that you wont have any bottem end. i have a street/strip 385 running a solid 242/250-282/292 cam .560/.560" 10.3:1 with worked DART iron heads, worked dual plane with 1" spacer and 750 DP, when i had it dyno tested and tuned at MPC it made 518hp/491tq, and it is making 400tq at 2500rpm and over 400hp at 3000rpm but yet can easily spin up to 6400rpm. this is more than enough street hp/tq down low to be fun trust me. this car has no dog down low (oh did i mention it can run off of 93 octane)

i do completly understand that more duration and overlap means higher rpm and less bottem end but at the same time you can build a motor that has decent top end and decent bottem end but yet a great middle band and it can still be fun.

 

i was only implying that it would be waste to run a cam with enough overlap to run the pump gas.

I agreed with you.

quote[ and i love how people say if you run a cam that will run up to 6000rpm+ that you wont have any bottem end.[ quote]

I did not say that.

i have a street/strip 385 running a solid 242/250-282/292 cam .560/.560" 10.3:1 with worked DART iron heads, worked dual plane with 1" spacer and 750 DP, when i had it dyno tested and tuned at MPC it made 518hp/491tq, and it is making 400tq at 2500rpm and over 400hp at 3000rpm but yet can easily spin up to 6400rpm. this is more than enough street hp/tq down low to be fun trust me. this car has no dog down low

Sounds like a good combination, but it is a far cry from the Op combination which is what were were talking about.
I merely said that bleeding off compression with the use of a wider LSA would decrease the low end performance.
I think we were saying the same thing, just the verbage was different.

 

Sounds like a good combination, but it is a far cry from the Op combination which is what were were talking about.
I merely said that bleeding off compression with the use of a wider LSA would decrease the low end performance.
I think we were saying the same thing, just the verbage was different.

i agree :thumbup:

 

I do also agree with your suggestions on better heads. I dont know wich ones would help, I am into pontiacs. maybe you have a good suggestion for him.

 

thanx for all the advice!! this site rocks! ...but one more quick question should go ahead and pull the motor so i can do pistons and heads or just throwing different heads on it help enough. the motor only has maybe 10k on it so it really isnt in need of an overhaul

 

I would leave it as is. If you want to build it different, scrounge up another sbc 350 and start from there. Might as well not throw away a perfectly good running bunch of engine parts. If you start a build with another motor it will cost the price of the core and the parts you were going to buy anyhow. the only difference is you will have 2 motors for the price of one and a core.
I have 3 engines for my lemans.
1 runs fine thats in it now, one is at the machine shop (389) and another is on the porch just hanging around for whenever.

 

as far as heads go i think you would be better off to leave this motor alone and find a 87' and up roller block and build it from there. as for a decent set of heads for a mild 350 that wont see over 5500rpm i love the RHS pro torker heads, they are basically a 906/062 vortec head made stronger and made to flow better, for applications under 400hp they are very much the way to go.

 

anyone ever use the cheapo procomp aluminum heads or should you be wary of using them?

You get more than you pay for IMO. The new gen3 pro comp heads are much nicer than the ones you will read horror stories about. They flow close to 270cfm @ .600" lift. Casting quality has also improved. For the price they are hard to beat. DR.J's has a CNC version flowing 308cfm @ .600" which shows their potential.

I would recommend getting them bare with the combustion chamber CNC for about $450 shipped. Then put in your own valve train. I have these with a bowl clean up and port match on a 383 pushing mid 500's.

They are made in china though.

If you can swing a grand look at profilers. Very nice USA heads.