|10-20-2012 03:01 PM|
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.
|10-20-2012 12:24 PM|
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++
|10-18-2012 06:40 PM|
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.
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.
|10-18-2012 05:53 PM|
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.
|10-18-2012 04:53 PM|
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.
|10-18-2012 04:21 PM|
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.
|10-18-2012 03:28 PM|
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.
|10-17-2012 10:09 PM|
|hcompton||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.|
|10-17-2012 09:05 PM|
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.
|10-17-2012 06:11 PM|
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!
|10-17-2012 05:07 PM|
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.
|10-17-2012 02:57 PM|
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.
|10-17-2012 01:59 PM|
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.
|10-17-2012 01:23 PM|
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.