My 67 has a 77 350 in it. It has pretty good power. 300/300 at rear wheels. I bought vortec heads. Originals were 76 cc
New will be 64.

Wondering how much I would gain switching to true flat top pistons. This doesn’t seem like much dish to me.

Very low mileage engine. No ridge, and bearings were perfect when I dropped pan last year.

Not going racing, just looking for a little more power as I go through the gears.

Thanks!Tim

 

I guess you got a vortec intake to go with it. doesn't those engines have reverse cooling. how does that effect a 77 block?

 

You would probably be approaching 10:1 comp with yur numbers.
I think you would like the combination. Add a 151 cam from GM or a similar roller and you would like it more. May require 93 unleaded but that’s a small price to pay for a good boost in HP 👍👍

Others will jump in soon with recommendations

 

I checked Sealed Powers ratings based on your information. The 77 engine would have had 76cc heads and is rated at 8.62:1 compression at .030 oversize. Just changing heads to 64cc heads bumps the compression to 9.72:1
So moving compression by a point would give a little more power but not major I am thinking 5% but moving to the Vortec design which does offer better flow numbers will add some power also.
Where did your engine make 300/300? At what RPM did it see 300 HP? The Vortec heads are a big advantage up to 5,000 RPM but pretty much done by 5,500 on a 350. If that matches the cam you are running you might feel a nice seat of the pants upgrade but if your cam was making power well past 6,000 RPM before I would guess someone had worked on the heads you have already and opened them up for better than stock flow.
Something does not add up though because a 77 350 was a pretty wimpy engine not a 300/300 at the rear tire which would be more like 350/350 at the crankshaft. That engine can't be stock.

You might take a compression check prior to removing your heads. If it is 150 to 160 your heads are probably stock. If it is 175 or better the chambers are not 76cc or maybe your pistons are not flat tops but are domed.
As mentioned, your existing engine is much stronger than expected so something is modified to give you 350 HP at the crankshaft.
A friend built a couple 383 engines for his boat a while back, used Vortec heads on them. He called and was concerned because it had 200 PSI compression with flat top pistons, he was afraid it was going to have detonation issues but ended up running really well for him. His cam was the bone stock GM Marine cam so it had high compression.

Reverse Cooling was only used on the LT1 engines from the 95-99 dates, after the Gen 1 small block and before the LS engines came along.

 

My 92 LT1 (first year) had the reverse flow cooling.

 

I knew it was the 90’s version LT1 not the 1970 LT1 but the years escaped my memory. They also had the optispark ignition which worked great until they caused engine damage on 😣. Good runners though great power and torque. I only rebuilt one and it was for my sons Z28.

 

Thanks for the input guys. I had it chassis dynoed this summer because I was trying to find a vibration at about 3000 rpm. It helped me identify binding at the half shafts,from camber adjustment being way off.

Both hp and torque were strong by 3000 and I wouldn’t let him rev it over five. Both had peaked by then.

I don’t know how the numbers were so high with a stock replacement 350. When I pulled the heads it had mildly dished pistons with 76 cc heads.

When I made the initial post I had decided on the vortec heads, based on a couple articles I read. I was undecided on changing pistons too
to get full 10:1.

I decided this is my chance so I ordered pistons and pulled the engine. There is no ridge, or any sign of wear, and pistons are standard,so I continue to believe this is a very low mileage engine.

Will let you know in a month or so how it turns out.

 

No offense but why would you keep pouring money into a run of the mill 350. At this point building a 383 or 400 sb would yield way better results

 

lol. I was debating whether or not to add that tidbit when I saw your post…. My first Corvette was a ‘92 C4 in Dark Red Metallic. LT1 first yr of reverse coolant flow
Maybe I was just lucky but never had troubles with PotiSpark

 

Your 92 and mine were pretty much the same. Mine was a convertible, same exterior color as yours, black top and interior. It was a good car but I did replace the “Optional Spark” with an aftermarket MSD billet distributor.
Who was the GM genius that decided to place the distributor under the water pump and the ECM computer under the battery?

 

Mine was a coupe with both body color and transparent tops and of course the black interior.
Sharp color combo but ran out of garage after getting a C6 and growing list of drivers in the family. Good problems to have 😃

 

Why spend money on this engine?
It has just a few thousand miles since new.
For less than 1000 I can have about 400 hp which is more than I need. It should have even more bottom end, which was pretty good before.

For that money I couldn’t even get the machine work done.

 

A good running 350 with 400 HP is a very fun engine to drive. No doubt a 383 or 400 has more torque and HP but a 350 is durable, proven and cheap. I can see Vetteguy's point.

 

I would double check the specs for your compression ratio on a good calculator like Wallace racing has. no reason to try and push 10:1 on an iron head motor with today's crap gas! my 97 vortec 350 truck motor even rattles under load and it has a knock sensor!
You can get a decent 400 HP 350 with a decent top end better flowing heads and a bigger cam. intake selection a little tricky for best performance vs hood clearance on C2. if you have a good short block that is a reasonable way to go. But as you try and bump HP up the idle quality will go down with the cam selection

Vortec heads do flow better than most previous GM iron heads even the Bowties. head flow IS the big deal for making power.

Vortec 350s in trucks did have a reverse direction water pump due to the serpentine belt set up but not reverse coolant flow.