.030 over pistons for 302: specs/supplier?

[vabeach56wagon]

We are rebuilding the engine in our '69 Z....We have a .010 overbore block which is correct for the car...but the clean up bore will be .030 over. Can someone advise on the best pistons I should buy? Want to stay at 11-1, floating pins, 4.030 bore, 3" stroke

Rings ductile iron? .062 top and bottom; .124 oil?

Thanks

paul

[ZLP955]

Paul,
I'm interested to follow this. Not yet ready to buy, but did the research several years ago. Things seem to change quickly, so there may be more, or better, choices now. But the 2 options I had narrowed it down to were:
SRP 202890
Wiseco PT042H3
Both used 1/16", 1/16", 3/16" rings.
Dome volume on the Wiseco was slightly greater, giving higher compression of around 11.0:1 with stock 186 heads. Was considering possibly milling the domes down a little to reduce compression, but figured I would hold off until choosing head gasket compressed thickness, and seeing what that did to quench distance.

EDIT: just had another look for those Wiseco pistons, seems they may have been discontinued; one source recommends ICON IC802KTD-30 as an alternative, but evidently I need to do more research!

[x66 714]

I saw the ICON pistons in a Keith Black catalog yesterday...Joe

[Stingr69]

Paul,
I'm interested to follow this. Not yet ready to buy, but did the research several years ago. Things seem to change quickly, so there may be more, or better, choices now. But the 2 options I had narrowed it down to were:
SRP 202890
Wiseco PT042H3
Both used 1/16", 1/16", 3/16" rings.
Dome volume on the Wiseco was slightly greater, giving higher compression of around 11.0:1 with stock 186 heads. Was considering possibly milling the domes down a little to reduce compression, but figured I would hold off until choosing head gasket compressed thickness, and seeing what that did to quench distance.

EDIT: just had another look for those Wiseco pistons, seems they may have been discontinued; one source recommends ICON IC802KTD-30 as an alternative, but evidently I need to do more research!

Do not cut the dome.  You need every bit of that compression for the 302 to do its job.  Depends a lot on the cam I know but the RPMs dictate the C/R requirement.

[vabeach56wagon]

While I'm at it, we are looking at the LT1 cam rather than the '69 30-30....I've always tightened the LSA for SBC's unless there was a critical need for vacuum. I see an LSA of 116 on the current "repro" cams.  First, gotta find the pistons, then gotta find the cam or have it ground...was thinking no more than 110 LSA. I built a 383 with a hydraulic roller in it at 112 which gave me good vacuum for the brakes once the revs came up to 1100...This car will not be driven on a daily basis but we want it to have the crispness of high compression and quick-response cam timing when we do pull it out of the garage or cruise into a show.

paul

[ZLP955]

Do not cut the dome.  You need every bit of that compression for the 302 to do its job.

That was an option to consider, once all other engine build parts had been determined and the CR reviewed. I only mentioned that here because the dome size of the 2 pistons I suggested differ in volume.
A friend rebuilt his 302 using Speed Pro pistons, that were said to be a direct replacement for the original TRW slugs. It suffered badly from detonation. When he tore it down and re-measured everything, including head chamber volume, it gave a CR closer to 12.0:1 rather than the theoretical 11.0:1

[Stingr69]

Crane F-278-2 has similar open and close points as the LT-1 at .050" but  it has more lift.  It has faster ramps.  I run that and have used it several times in other engines. Needs upgraded valve springs to go over 7000 RPM but the PAC tool steel circle track springs work with the stock spring pockets. I break the cam in on some old GM brown stripe springs first then swap to the PACs.

[firstgenaddict]

an overbore will increase  the compression ratio all other factors kept same.

FWIW
The solid roller Dave Crower designed for a basically set of stock 186's was incredible, it made 15" of vacuum at 1000 rpm, made 350 ft# of torque by 3000RPM and revved to the moon.

636 gross valve lift
277 intake
281 exhaust duration
112 lobe sep

Designed it to be VERY EASY on the valve seats. GRANTED you have to run screw in studs and guide plates.

Dave Crower explained everything about the cam to me when I had him design it...
Runner volume in the 186 is fairly small so in order to flow you need to open the valves UP and keep them there... you don't want to bounce the valves off the seats hammering them so he lets them down QUICK but not to the seat they rest onto the seat at a very low rate.


 
I would run a short compression height piston with a 6" rod, IF I were building a 302 and buying new pistons.

[ban617]

Hi , with the Crower cam did you run roller rockers & a stud girdle or possibly a rev kit ?
Thanks

[cook_dw]

I just got my rotating assembly back from the machine shop.  Im using a custom piston.  0.043", 0.0625" & 0.1875" ring setup.  Should be a touch over 11 to 1.   

5.7 rod, 1178 crank, custom solid roller, shaft mounted rockers and 8500 shift points.  It will go on the engine dyno once finished but hoping for strong numbers.  We shall see.  Too many irons in the fire right now but its coming..   Sooooon..

[firstgenaddict]

Hi , with the Crower cam did you run roller rockers & a stud girdle or possibly a rev kit ?
Thanks

Needle bearing roller rockers with a 636 lift will fit under stock -non dripper covers if you use a felpro thick and felpro thin cork gasket glued together.

As far as rings... I ALWAYS run ZERO GAP rings if I spec the parts- my opinon is it's free HP.
And my theory on the pistons is if you are buying expensive pistons why not use a LONGER better aftermarket rod?  6" eagles are pretty inexpensive while also allowing the piston to dwell at TDC longer to build pressure while longer = less side loading.

[cook_dw]

I agree a 6” rod is the way to go but for me already having said components it is what drove me to my selection.

[vabeach56wagon]

After much discussion with my local gurus, we ordered a set of .030 over JE forged Pistons PN#202890 described as a 302 SBC 10.4-1 Dome, for Rings we ordered the J103F8-4030-5 which are 1/16 - 1/16 - 3/16 .

I know these are not 11-1 but the consensus is that at 10.4 we can, carefully, run pump 93 and not jeopardize the motor...will have to experiment with the advance curve and if we need to continue to run some of the 110 race fuel as we're doing now, so be it. I don't know yet how deep in the hole these JEs will be. Don't want to end up with anything more than 11-1.

Over the weekend we scored an Eagle forged 3" stroke large journal standard, 2 piece seal, crank at an extremely good price. It's at the shop now for fluxing and miking to see if it needs to be turned.

Still no decision on the cam configuration: how tight the LSA can be without a vacuum deficiency at the booster is the question. Can anybody chime in?

paul

[firstgenaddict]

ok -
I looked at my notes from Dave Crower, originally he suggested a 114 lobe separation... I said I was thinking more along 112 and he said that not a bad idea, it will give you a little bit more low end torque.
Here are the contents of the entire cam card.

Corwer part # F -3823
engine: 302 CHEVROLET
grind number: SPECIAL ROLLER
Advertised specs
Intake dur: 277 lift: .636 clearance hot: .016
Exhaust dur: 281 lift: .636 clearance hot: .018
For degreeing:
intake open 13.0 BTDC
intake closes 49.0 ABDC
exhaust opens 59.0 BBDC
exhaust closes 7.0 ATDC
Lobe Sep 112 deg

The duration at .050 is
242 int
246 exh
lobe lift .424 each -

Using lobe center method of degreeing cam installed on intake center line of 108 deg

NOTES:
 B 1694 INT .  B 1695 EXH. 
With the solid roller DO NOT WORRY ABOUT VACUUM you will have more than you need.
The engine made 15" at 1000rpm idle.

[SMS]

After much discussion with my local gurus, we ordered a set of .030 over JE forged Pistons PN#202890 described as a 302 SBC 10.4-1 Dome, for Rings we ordered the J103F8-4030-5 which are 1/16 - 1/16 - 3/16 .

I know these are not 11-1 but the consensus is that at 10.4 we can, carefully, run pump 93 and not jeopardize the motor...will have to experiment with the advance curve and if we need to continue to run some of the 110 race fuel as we're doing now, so be it. I don't know yet how deep in the hole these JEs will be. Don't want to end up with anything more than 11-1.

Over the weekend we scored an Eagle forged 3" stroke large journal standard, 2 piece seal, crank at an extremely good price. It's at the shop now for fluxing and miking to see if it needs to be turned.

Still no decision on the cam configuration: how tight the LSA can be without a vacuum deficiency at the booster is the question. Can anybody chime in?

paul

Just put a 112 LSA in my 68 Z due to the brake vacuum needs.  Should be adequate.

Here is my cam spec.  Still on a stand however, so its just theory but based on other builds.