L98 heads and dome pistons
 

Hello Rod Buddies. Well, here is my first post. I want to see if this is possible on hot motor build sbc 4" bore. Plan on running 480 lift solid cam and 110 petro and 3600-4200 stahl. Would like to use L98 aluminum heads (10088113) on my sbc with Wiseco dome pistons. .035 mls gasket and 3" stroke. Setting the head on I see the dome pushes against the structual rib that's by the spark plug hole inside. Can I grind the rib down for clearance and not worry about structural damage to the head. I have cast heads also, 375 F.I. and also 882's that will probably fit fine. I think I know I'll have high compression motor but don't know exactly how high. I've never used an aluminum head and would like to try this set-up if it's possible. Any help would be greatly appreciated.
Thanks...T.J. ;)

Ya you can remove that bump by the spark plug. It is a foundry locating point.
You still have to verify piston dome to chamber clearance at TDC. Should be .050" minimum.
Minor grinding on the chamber wall and or piston dome is fine to get clearance as required.
Check with play doe.

4" bore x 3.00" stroke builds a 302CID. the 113 heads are 58cc (nominal cc)
CC yours. What is the piston dome volume and assembled piston deck clearance @TDC?
You need this to calc the compression ratio.

The 113 aluminum L98 head head has moderate/modest port flow in stock form but flows very good once fully ported. Best with 2.00" x 1.56" "LT-4 style valves and generous porting.
They will make very good power. 450++HP capable on a capable motor.

If you want to build a good high compression ratio engine you want to get the net quench clearance right .038" ish is good.

L98 heads and dome pistons
 

Use a marker to shade the area on the piston that's hitting. Using the gasket that you will assemble the motor with, set the head in place with 3 to 4 bolts. Roll the motor over until piston contacts head. Pull the head off to see where it is hitting. You will have to feather back (grind) the dome in this area. If you do not feel comfortable doing this take it to a machine shop. If there is too much dome preventing you from bolting the head you probably will have to buy new pistons. The L98 heads were probably designed for use with flattop and dished pistons. They are 58cc chambered heads. You need to know piston volume (+12.8cc or +8.00cc) which with these heads will give you a compression ratio 12 - 14+:1. The rotating assembly will have to be balanced after grinding pistons.

Yeah i agree with the other posters. L98 heads are good but they run flat tops. Zero deck is fine but your pop ups are not the right kind. You need the ones that only pop up on the valve side. Regular domes wont work. Sounds like your pistons are standard dome for large chamber heads. They are made to give 11:1 not 14:1.

Since the squish band will be screwed it will knock like crazy even if you retard the timing and put in good gas. 110 will not fix it.

You need pop up pistons made for 58cc heads they are completly different shape. They can give you the same cc's without grinding anything. If you cut the heads you will trash the heads and still have to replace the pistons.

Buy cast iron 76 cc heads. Some stock ones flow very good and are very cheap because everyone wants to run flat tops or dish for large cams and lets face it. It is hard to check piston to valve clearence so nobody does it. Cause if you run flat tops and smalller lift cam it works fine.

If you want to make the 302 scream it will need compression and High lift cam. Without the correct pistons the valves will hit long before the cam is big enough to hit the 6k rpm power peak you need.

11:1 and a 250@.050 or bigger with high lift and tight lobe like a 106 or 108 12:1 would be even better and will work with 110 octane fuel.

And yes if your going for super high compression you can usally cut 1/4 inch out of most of the head area. Use a stiff wire to check the water jackets and try to measure up how thick they are. You can take a little more out of the head flat surface area across from the vavles but be easy around the spark plug area its pretty thin.

Proform i think makes aluminum heads dirt cheap in all port and chamber sizes. They are not the best but flow good and at about 700 a set complete its hard to beat. 76cc chambers and 210cc intake port should be real nice since they are all about the same price.

Sorry for the long post hope this helps.

These are a pretty small chamber head like 58 cc's the factory used a.053 inch thick gasket with them. You need to find out just how high this compression is. I gather this a 302 4 inch bore 3 inch stroke. Actaully getting to the compression ratio starts with the cam and running calculations that drive out a Dynamic Compression Ratio in the range of 8 to 9:1 which drives out the higher Static Compression Ratio (SCR) once you have the dimensions that make this happen you can select the parts that make the needed ratio.

When you say the dome contacts the structural rib by the spark plug, the only thing I could see being called a rib by the spark plug on this L98 head is the spark plug boss itself. This is an essential part of the combustion chamber design that is intended to catch the wet fuel flow entering on the long side of the port and remix it with the air entering the cylinder so there is a homogenoius and burnable mixture of fuel and air.

I'd like to know more about the cam from the specs on the timing card. .480 inch lift doesn't strike me as all that much so I'm wondering about the super high stall converter and whether the cam really warrants that much stall. Although I have to admitt to thinking that on a 302 that cam will react as if it's bigger than it would on a 350 or 383, so maybe!

Bogie

Horse-
powerLifterIntake LiftExhaust LiftIntake DurationExhaust DurationRocker RatioPart NumberCasting


290 M .485 .485 346 346 1.50 3849346 3849347
CAM SPECS EXACT AS FACTORY, NOT 480 LIFT SORRY

THE CC ON 67-69 Z28 HEADS WERE 63-64, SO HOW WERE THEY INSTALLED FOR CLEARANCE ISSUES WITH FACTORY DOME PISTONS. THEY REFERRING TO THE FACTORY ALUMINUM HEADS FOR THAT TIME TOO? ANYONE KNOW THE EXACT STORY ON 69 302 MOTOR? I'M REALLY INTO THIS...THANKS T.J.

I dont think he can pick a cam since the heads dont fit the block. He is going to end up with diff heads or pistons before its right. At the very least he will need the compression ratio. If it super high those small cams will be more trouble than the lack of hp is worth. If you get my meaning.

I guess I've been at this too long, I start with a general idea of how much power we want and the RPM range we need that happen in. I have at that time a general idea of pistons and heads which probably comes from doing this more than once but never-the-less the cam timing is in large measure going to drive the compression ratio which will drive the combustion chamber and piston crown sizes and shapes. So once I'm settled on that choice and know where the intake valve will close in crankshaft degrees of piston position in the bore, then I compute the DCR and SCR that the cam needs to be efficient and effective. Then the heads and pistons start to get narrowed down as to port, valve and combustion chamber size, and piston crown shape, deck clearance, and gasket thickness that are needed to dial in the compression with minimal squish/quench clearance along with adequate spark plug, valve and chamber contour clearances. The head selection will drive on the piston crown shape and volumes as to flat top, dome, or dish for best fits and clearances that minimize having to mill the piston to shape as most catalog pistons don't have enough head material, nor should they, to go change the crown shape. If you're getting into that then you need to order a custom semi-finished slugs and machine the crown to suit myself. This obviously is on high buck motors; certainly that kind of effort isn't done on street or claimer engines. I realize, especially with drag engines that very wild cams end up driving you into domes alternate fuels can drive you into large open chambers which also take you to domes, but I bust my hump to avoid domes as best I can because they don’t play well with flame front travel and create a lot of surface to volume which makes the whole chamber run like it’s a giant squish/quench deck, this drags you to other compromises in fuel mixture ratios and ignition advance that drive sufficient perhaps but certainly less than optimal tuning solutions.

I'm always amazed how guys just order a bunch of parts without thinking this through. For the hobbyist and tinkerer their best strategy is to copy one of the many magazine and soft cover book builds or cruise the web for similar information, this can save the average guy a lot of money and time while letting him/her build a very nice engine they can be quite proud of.

Bogie

thinking it through...
 

Well the best reply I can stumble thru is this:
1969 Z28 302 SPECS
Z28 crank 1178
Z28 dome pistons
Z28 cam grind
Near Z28 Head specs 64cc, intake and carb.

How do you replicate a 69 Z28 302?

Best I recall, GM had a pretty solid engineering prowess
when they threw all that crap together...lol. :welcome:

Looks like they used 64cc heads on the original 302. Also those heads are common in 1.94 valve size. 2.02 will be easy job for machine shop if you want to go oem.

These might work. They are cheap at $419 a set ready to bolt on. The same guys has many casting numbers to choose from. cast and alum.
Performance 327 350 400 Chevy Cylinder Heads 434 SBC Bronze Guides 500 Springs | eBay

Looks like 64 cc heads should work with your stock style pistons. At least that is what the interent says. LOL

They have better options over the gm 30-30 cam. But it should work. i think its solid lift.

Also have you thought about a thick intake gasket. They make copper ones pretty thick these days for chevy. You can just order in the size you need to clear.

L98 heads and dome pistons
 

Check out your pistons compared to these Wiseco PT042H3 pistons. They are the correct pistons for 67-69 Chevy DZ302. The compression height is probably different. Wiseco PT042H3 - Wiseco Pro Tru Forged Piston Kits - Overview - SummitRacing.com. Expensive too! The 30-30 solid lifter cam(PN 3849346) was the cam used in the DZ302.

Here is the link for the comp updated 30-30 plus. Close to the same numbers but after valves open they go toward make lift sooner.

http://www.compperformancegroupstore...ry_Code=SMFTNP

If its got all forged internals i would go with something lot bigger. But i love giant cams and dont mind the problems. Thats just extra music.

To build a medernized version of the old Z/28 302 you'd be much better off building with a flat top piston'and mill the L98 heads to 56cc to get a 10:1 finished compression ratio. Now it will run on todays premium pump gas. (based on a 0 deck height) . You'd be much better off using a modern mechanical street roller camshaft rather than the old 30-30 cam. Use a street roller with less duration but more valve lift.
Say the Comp Magnum CS280AR-10 280-280 236 236 .550" .550" 110LSA. Comp #12-702-8
The motor will make a lot more torque and power than the 302 of 1969.

Port the L98 heads with the 2.00x1.56 valves. Use a origional GM Z/28 aluminum hi rise intake manifold
(A holley 300-36 or a Edelbrock Performer rpm is a good substitute) and a 750 cfm DP carb.
Use 1-5/8" long tube heaers.

Combine with a 4speed or 5speed trans or a th350 with a 3500stall converter. The old 302 Z/28 liked to rev and loved gears. This modern one will too. Don;t be shy with the gears. 4.10++

The valve train is bound to come up, so here's a page giving info on the valve train.

On a short stroke engine like this, the valve train stability and strength is VERY important. It's really the key top making an engine like this capable of surviving the rpm required to make any real power. The bottom end is also important, but is much easier to spec out- forged crank, good rods, light pistons and careful attention to detail along w/careful assembly will go a long way towards making the bottom end survive just fine.