Does anybody out there make a 1969 Z/28 302 piston that is a lower compression than the stock 11:1 pistons, or if this subject has already been discussed lead me to that posted discussion. If not, can the stock 11:1’s be milled down to a 9.5:1 or 10:1. If a lower compression piston is not available what octane rating would an 11:1, 302 with the 1969 Z/28 302 camshaft and 186 heads require? Thanks.

Doug

I spoke with Shane at JE he said they have 1 set for that 3" stroke and a 5.7 rod its the SRE series forged piston. Its .030 only and is 9.7 to 1 with a 70cc head. Part#202890
Actually KB makes this forged piston KB802 it has a .250 dome but with a .041 gasket and possibly they might work. With a 70cc head your at the 10 to 1 Not sure what heads you have.

[QUOTE=dh302]Does anybody out there make a 1969 Z/28 302 piston that is a lower compression than the stock 11:1 pistons, or if this subject has already been discussed lead me to that posted discussion. If not, can the stock 11:1’s be milled down to a 9.5:1 or 10:1. If a lower compression piston is not available what octane rating would an 11:1, 302 with the 1969 Z/28 302 camshaft and 186 heads require? Thanks.

We've just finished one unit (1969 302" DZ), have one more going on now. We use Eagle H-Beam (6.250") connecting rods and a set Ross pistons and end up with 9.6:1/9.7:1 C.R. using the same 186's that belong on the DZ's. They run excellent on 93 with no issues. We end up with a bobweight around 1885 grams. We've put some kits (rods, pistons, and rings), into inventory due to the popularity of restoring these Camaros. Due to these units be high "revvers", don't use any cast (Hypereutectic) pistons under any circumstances. Thanks, Gary in N.Y.
P.S. The "long-rod" units work great. The original pistons were very heavy, had the pins too far down (1.805 C.H.), and put excess loads on the bores. The Ross's we use have a much higher pin location (1.250+ C.H.) and make the rod/stroke ratio come in at 2.080 instead of 1.900. The higher the number the lower the side loading and increased piston "dwell" time.

I used the Wiseco 11:1 out of the box, Crane blueprint 30-30 cam and GM .028" head gaskets ( basically stock rebuild). No problem on pump gas. Get the ignition bluprinted by Jerry MacNeish and you will be good to go. 302's will not run on less compression with the 30-30 cam. Email Jerry (or John Z for that matter) or call Jerry and discuss this with him. He will talk to you and set you straight. No need for any trickery here. Do not put hardened seats in the heads and butcher them. Just get a competant machinest for boring, honing checking etc. to work with you. Make sure the heads are rebuilt properly with sleeved guides and such. You will be fine. Just what I have experienced so far.

I ran my junk301 as a daily driver for several years with the -097 Duntov cam and cheap W/JCW cast 1/8" over 283, 1/8" tall, half round dome cast pistons above 7,000 rpm many times!

I figure she was about 10.5 to 1 CR. and putting out like 325hp is all so wasn't running 8,000 rpm and 400 hp!!

Drop back to something like the little old, el-cheapo solid cam that PAW is selling that spec's 264/246, (I figure it's really 280/246!!), 108/108, .498"/.498" gross lift and needs .030" lash on both valves to bring the little motor back into the real world running pump gas below 11 to 1 CR. to help up it's terrible lowend torque....

This cam is about like a Z-25 Isky so should really go in the little motor!!

And I have the cheap PAW cam in my clothes closet now for when I build another junk301!!!!

pdq67

Another interesting post, been a good week.
Note that "tex" is using larger than stock chambers to drop the compression.
Gosfast is re-engineering the whole motor, using super long rods and a short deck height "stroker style" piston (probably a fairly expensive custom slug)
And of course, Gary L is right too, the 30/30 cam is so long that the dcr will be low enough even at 11:1 static to run pump gas as long as the ignition and carb are right-on.
Three great solutions to the same problem.

He, He!!

And I'm old-school all the way! There wasn't a 302 part in my old junk301!!

All 265, 283 and 350 stuff....

He, He!!

pdq67

hehe, right you are, Paul. After all, the only "special part" in the original 67 Z was the pistons, the rest was same like your "junk 301"!

Had my TRW pistons shaved from 12:1 to 11:1 TRW's were easy to get in the 90's but at that time 12:1 were all I could get in a 302 full floater slug .030 over. Running pump gas and tuned right on the money it runs great. I Can't put any more that 11 degrees at idle or pinging starts. And of course if you keep it above 3000 rpm it's fun to drive. Mapping the curve to be all in at 2700-2800 rpm sure makes it run good.

Nothing but smiles when I drive!

Todd

Correct me if I am wrong, but if the 283 was a 3" stroke motor, and the rods were 5.7" then the pistons were the same (other than bore size) as the 302.


The bottom line is that Doug was worried about static cr. There is no need to be worried about that if this are done correctly.

not positive, but I don't think that would add up, the piston deck height would have to be 1/4" taller than a 327, and a full half inch taller than a 350.
with a 327's 3.25" stroke & 5.7 rod, the piston deck ht is a 1/4" taller than a 350 with the same rod and a 3.48" stroke. 302 should follow, take a 1/4" stroke out (as compared to a 327) you have to put it back in the piston. A 283 slug would have the right deck ht, but of course it is much smaller as the 283 doesn't have a 4" bore.

Fwiw, I figure most later round bottomed 283 blocks will bore to .155" over like a stock 302 and 327 will.

pdq67

Gosfast is re-engineering the whole motor, using super long rods and a short deck height "stroker style" piston (probably a fairly expensive custom slug)

With a 6.25" rod and a 3" stroke you can use an off-the-shelf piston made for a 350 with 6" rods. We use a 6.125" rod and a similar off-the-shelf piston in our 331" road racing motors.

sounds like a sweet combo, too. it must take 150 grams off the end of each piston/rod assy. Bet that sucker will rev to the moon!

Now this is interesting b/c I wanted to use the 5.94" long rods as well as off the shelf pistons.

And the only reason I wanted to use 1/8" over 283 jobbers b/c they used to be common as dirt.

pdq67