302 cid Small Blocks

[Mike Cobine]

Re: 302 cid Small Blocks

> A 67-69 302 is almost identical to a 1970 LT-1 except for the stroke

Not really. The '67 and '68 were based on the small journal block with 2 bolt mains. The '69 was on the large journal block with 4 bolt mains. That also meant different rod sizes.

For sheer revability, I'd take the '67-'68 over the '69. Lighter bottom end.

> I run a basicaly stock 302 and it is definately a lot of fun
> but they are realy pretty inefficient at low RPM. If you can
> cope with that, they are a blast.

Easy to cope with, run a 4.11 rear. I had a 4.11 with mine and I could still run 160 on top end. I felt it was much like a big motorcycle engine, with a wide range of power. It began making power about 3000 rpm and didn't quit until over 8500. That is a 5500 rpm power range, more than what some engines can even run, much less make power.

Granted mine wasn't stock, but the changes were mostly for life and not so much power, and it could shift at 9000. I couldn't, th eidea of spinning a small block that fast never set well.

But even then, and the lack of low range power, with the 4.11, getting started wasn't a problem, even using the L-88 12 lb. flywheel.

[Joe L.]

Re: 302 cid Small Blocks

Mark and Mike----

Actually, there were quite a few differences between the 302 engines used over the 67-69 period. The 1967 was the only year that used the small main journal block. 1968 and 1969 used the large journal. Chevrolet went to the large journal in 1968 for most small blocks, including the 302, although it's possible that some early 1968s used the small journal block. All of the 67-68 302's were 2 bolt main bearing blocks----only 1969 got the 4 bolt blocks

The rod lengths were the same for all 302's and these were the same center-to-center length as PRODUCTION 265s, 283s, 327s and 350s. Only PRODUCTION 400 cid small blocks (and their aftermarket derivatives using a 400 crank) use the longer rods. For small block Chevrolet, the different cid displacements are accomodated by the position of the piston pin in the piston. This makes the piston used for most displacements unique with respect to pin position. Consequently, the 302 Chevrolet used pistons unique to the 302 application, even though the bore size was the same as 327 or 350 cid engines.

The rods, themselves, were different for the 3 years. 1967 used the GM #3864881 rod. This is the same small journal rod used for most 327s from about 1965 onward. Most 1968 302s used rod GM #3923282. This is the first iteration of the "pink" rod and was also used on 69 Corvettes with L-46. This rod used a pressed-fit piston pin. Late 1968 and 1969 Z-28 applications, used rod GM #3946841. This rod is, basically, the same as the 3923282 except that it uses a floating piston pin. The evolution of the 3923282 rod, the GM #3973386 was used for most 70 Corvettes with L-46 or LT-1, 71-72 Corvettes with LT-1, 73-81 Corvettes with L-82 and 1970-74 Z-28 Camaros. It was discontinued from SERVICE in 1982 and replaced by GM #14095071 and, later, by GM #14096846.

All 302 Z-28s, with the possible exception of very late 1969, used camshaft GM #3849346. This is the so-called "30-30" camshaft also used on 1964-65 Corvettes with SHP engines. For 1970, the Camaro Z-28 as well as the Corvette LT-1 changed to the GM #3972178 camshaft. This camshaft continued to be used in Corvette LT-1 and Camaro Z-28 applications through the 1972 model year. In 1973, the Camaro Z-28 switched to the GM #3896962 camshaft, the same hydraulic cam used for Corvette L-46 and L-82 applications. The GM #3972178 became the SERVICE camshaft for 1967-69 Z-28 applications after the GM #3849346 was discontinued in December, 1971.

The cylinder head assemblies were, basically, the same for all 67-69 302's as well as 69-81 Corvette L-46, LT-1, and L-82. In 1969, the accessory bolt holes were added to the head ends and in 1970 screw in rocker studs were added for LT-1 applications. I believe that 1973-81 Corvette L-82's continued to use screw in studs as did their counterpart Z-28 Camaros.

[William C.]

Re: 302 cid Small Blocks

If you really want to add to the drivability of the "Z". tie the 4.11 to a wide ratio 4 speed.

[Joe L.]

Re: 302 cid Small Blocks

Bill-----

Absolutely! The combination of the 2.52 low gear and 4.11 rear gears would make for much better off-the-line performance. Actually, I've always thought that the wide ratio 4 speed was the best for street operation, anyway. Given a choice, it's the only one that I'd ever get.

[Bryan L.]

Re: 302 cid Small Blocks

Joe is, as usual, correct about the 302. It was the only small block that ever had a full floating wrist pin. I've had 3 69 Z/28s and they are neat cars.

BL

[Joe L.]

Re: 302 cid Small Blocks

Bryan----

Yes, the 69 302 was the only PRODUCTION small block, ever, that used floating piston pins. In fact, I think that was not only the only PRODUCTION small block so-equipped, but it was the only small block engine assembly that GM ever made, PRODUCTION or SERVICE, with floating pins.

VERY few big blocks ever got floating pins, either. 1967-69 L-88/ZL-1 were the only ones that I know of, PRODUCTION or SERVICE.

Due to warranty requirements, I think that GM was a little "uneasy" with the possibility of pin retainers becoming dislodged and ensuing "consequences".

[Clem Z.]

the new C-6 engines will have full floating

wrist pins as i watched a 260 hour durability test being run to check out the wrist pin deal.

[Clem Z.]

i ran my 1968 302 Z-28

with a #140 cam and a "vera-cam" which advanced the cam at low RPM to give better bottom end and retarded it at hi RPM to give better top end. the device worked great but the large spring the was the heart of the system kept braking. i think still have the instruction for the device if any one would like to see how it was designed.i think with better spring technology it would have lasted.

[Joe L.]

Re: the new C-6 engines will have full floating

clem-----

I'll be interested to see what they use for pin retainers if they actually go into production using the floating pins. I'll bet that it won't be anything like the old "Spirolock" retainers.

[Clem Z.]

Re: the new C-6 engines will have full floating

they will most likely use the "round wire" retainers with a beveled end on the wrist pin. this type is easy to install and the bevel on the pin pushes the "round wire" into the groove.this type is also use in very high rpm 2 stroke engines

[Clem Z.]

i used the .072 spirolocks on BBC and SBC and

never had one come out but i had bloody fingers installing them. i made my own tool to measure the width of the grooves and ground each pin to fit to get the correct end play

[Joe L.]

Re: i ran my 1968 302 Z-28

clem-----

Well, it sounds like it's "back to the future", then. Many of the new, high-tech engines that are coming out have variable valve timing (VVT, for short). I think that for 2004, the Northstar engine has it. Also, the new 3.6L "High Feature" V-6 used in the Buick Ranier and the Cadillac CTX have it, too. Many foreign engines have had it for awhile.

[Clem Z.]

V V T

the new GM inline 6 in the trail blazers also has it so i guess the new I-4 cyl and 5 cyl will also. they use the oil pressure increase as the RPM goes to change the valve timing.

[GL Anderson]

Re: 302 cid Small Blocks

Actually the 400 ci small block use a shorter rod not a longer rod due to their 3.75" stroke. Just a minor correction. GL

[Mike M.]

Re: the new C-6 engines will have full floating

clem: what's the bore and stroke on the 4.8 liter chevy pickup V-8s that are coming off the line as we speak? i guesstimate the 4.8 to be about 292 ci. bought such a pickup last spring(can't find dealer spec sheet--geezeritis?).the durn thing thinks its an early 70's 350 ci yet gets 21 mpg with 4.1:1 rear.mike