I have a 350 that I want to replace the current 993 heads on it. The 993 heads are of a 75-76 cc chamber range.

I've been told this engine has a .030 bore but I don't know anything about how stout the bottom end is built or what kind of pistons it has or anything like that. The block doesn't appear to be decked.

I can't decide if I want a 64 cc chamber head or a 70 cc chamber head. I want the most power I can get and I want to keep the c.r. at or just below 10.0:1 but I don't want to blow out the bottom end or have the valves crash into the pistons.

Would it be safe to go with 64 cc chambers or would it be better to go with 70 cc chambers?

What cam is in the engine?

Comp cam Xtreme Energy 274 cam

I would think the XE274 would like the 64cc heads, that's what I'd run.

The only thing is I don't know what kind of pistons I have inside since I didn't build the engine or have ever had the head off. The current heads are 993 with 75 cc chambers.

I can run 87 octane without a single ping all day long if that says anything.

What I don't want is a head that will destroy my engine if the pistons and the valve make contact. Thats why I'm wonderong.

Also (and I'm kinda new to this) but is it possible that the cam will have so much lift it will actually push the valve into the piston?

There is very little danger of V/P contact. The main issue is CR. With flat tops (6cc), .040" quench, and the 64cc heads SCR is about 10.2. The DCR with the 274 is about 8.25. This should work just fine with pump gas. The 70cc heads are a bit big for the cam. More than likely, the pistons are flat. Popups are not too common any more. If they are dishes, the 64cc heads are even more desirable.

Pop ups...you mean dome pistons right? I thought those were used primarly in diesels?

Yeah I had a few people telling me I needed to check first to make sure the piston doesn't come too far up to kiss the valves. This engine has the standard 3.48 stroke and doesn't appear to be decked.

Popups = domes.

The valves are in the same position with 64cc heads as with stock heads unless you go exotic. Larger valves can sometimes be a problem with a stock type piston. The valve pockets are sometimes not wide enough. With the cam you have, if you're OK now you should be OK with the new heads. However, it is always a very good idea to check it. The pistons will not come up any farther with the new heads than with the old heads.

To maximize compression and optimize quench with an undecked block, you can use a .015" shim gasket. This will give you a .040" quench distance (provided the pistons have the correct pin height) that will cause the mixture to burn better and be more resistant to detonation.

Well actually the cam I mentioned will be the cam I use with the engine. Right now it has a Crane cam but I don't know the specs on it.

If the engine has dished pistons would the valve sizing still be a problem?

Probably not.

Of course I see that for the Edelbrock Performer RPM heads they also make a cam for it....looks like it has a .488 intake/.510 exaust lift with 234 intake/244 exaust duration with a 112 degree lobr seperation as compared to the XE274 cam that has .487 intake/.490 exaust lift with a 230 intake/236 exaust duration with a 110 degree lobe seperation. Any real difference between these two cams?

You think I could get away with using the valve springs that come with the Edelbrock heads?

Yes, there is a good amount of difference between the two cams.

The RPM cam has a lot more advertised duration then the CC cam. This, to me tells me that it really needs more CR. to run it's best vs the CC cam.

But there are guy's running it in lower CR. motors and doing OK for them so I suspect it's a judgement call??

AND when I mean higher CR., I am talking about 10 to 1 and PREFERRABLY 11 to 1 for the RPM cam unless it's advertised duration numbers have been shortened up and I am not aware of it..

As always, jmho..

pdq67

PS., here are the spec's between the two so you can compare then directly.

RPM = 300/234/310/244, 112/107, .488"/.510".

XE274 = 274/230/286/236, 110/106, .490"/.490".

I thought the RPM cam was 308/318. I'd advise not using the RPM cam. I ran one for over a year. While it sounds great, it doesn't make much power until 3000 rpm. As PDQ said, and Edelbrock told me this too, it wants 11:1+ CR. It is an old design with very lazy ramps. I'd go with the 274 cam and the 64cc chambers.

Pat,

It might be b/c I got the spec's from my old Wolverine Blue Racer cat.

It's still plenty big, imho...

Put the old sucker in a 11.5 to 1, 327 along with 3.73's or maybe 4.10's and hold on!!

pdq67

I think you'll be fine as far as piston to valve contact goes, I've got a 385 stroker (hence the name), it is decked, flat-top pistons, comp xtreme energy 284 hydraulic cam installed straight up, 1.6:1 rockers, 2.02/1.60 valves. Plenty of clearance. Checked it using clay on the piston top, installed the head, spun the motor over 2 complete revolutions. Hardly touched the clay.

Thanx, now I just gotta pray if my pistons are flat tops the valve reliefs are big enuff for those 2.02/1.60 valves

Junkyard,
Here is my experience. I built a budget 350 and got a lot of power for cheap. Use 64 cc heads. combustion works better with a flat top piston than a dome piston. to get close to 10:1 with 76 cc heads, you need dome pistons. I bought the sportsman II heads and assembled them myself for a total of under $700. I really looked around for places to buy the heads, valves, etc. Ran stock cast crank, stock rods, and it was an awesome reliable engine. I rev'd it up to 6500 all the time. I had 9.73:1 C.R. and could run 87 octane. I never experienced pinging. what kind of heads were you thinking about using?

Well I had two in mind....Dart Iron Eagles or Edelbrock Performer RPM. I wanted to go with a 64 cc chamber. I wanted to keep it pump gas friendly.

Right now my biggest problems are 1. Finding out if the valve to piston clearance with the new heads will work and 2. Finding a cam to work with the heads, then finding out if the valve springs already on the heads (buying assembled heads) would work with the cam.....basicly scratching my head in frustration and going thru what porbably alot of hot rodders go thru.


But...I did see that Trick Flow also makes a top end kit for sbc's....comes with aluminum heads, cam, lifters, timing chain, rockers, gaskets, etc.

Originally posted by Pat Kelley:
There is very little danger of V/P contact. The main issue is CR. With flat tops (6cc), .040" quench, and the 64cc heads SCR is about 10.2. The DCR with the 274 is about 8.25. This should work just fine with pump gas.Hey Pat, with thisa combo what octane fuel would I need to run?

Thanx!

91 for sure.