350 engines to avoid for a rebuild

Z-Life

Nasty Member
Oct 3, 2016
199
Florida
Whenever you get a new or rebuilt engine, Treat the freshly bored block and new internals with PTFE resins (Slick50, teflon) I have a rebuilt 406 cubic inch small block I treated and it has 230,000 miles on the rebuild and still going strong. PTFE wont work on any engine that has been ran, the pores in the metal need to be clean to absorb the teflon, its incredible stuff that really works when done right.
 

procharged81

Veteran Member
Nov 16, 2011
134
NE PA
I've got an LT1 in my Firehawk and it runs great as it's still low miles but I'm waiting on the Optispark to give me issues. Like it from the factory but never considered it for a transplant.

I went to by the Vortec today and it looks like I'm a day late. It was $500 for a complete motor with front accessories.

Glad the lifters I have will be of use. Bought them as a kit for my 468 and never could get them to work and had to go linked style. I was kinda of stuck with them and it wasn't worth the hassle to fight over the kit not working.

I'm looking forward to the computer part of fuel injection and the 4l60e swap. I've got Fitech on the 468 and it controls the timing too. Timing adjustments are a breeze with the computer and a little more flexibility. It did take some time to learn how to tune it but now that I am pretty comfortable with the system, it should be a breeze the second time around. I get 12-14 mpg around town if I baby it and 10.5 to 11 if I have fun with it. The old cam could get 22-24 on the highway with the AC on but I haven't had a chance to test it yet with the new cam. I'm expecting the same as the around town mileage is up with the roller cam.

I scored a 4l60e tranny tonight and am picking it up tomorrow. Part of the puzzle down. Planning on using the FITECH controller and the FITECH injection and it looks like the two play nice together.

Caden and I haven't decided which we will swap first, but we are doing one and then the other as I don't want two sets of variables. Get one system dialed in and then the other. I'm leaning towards the trans first so he can learn to tune it on the old motor.

Thanks again for all of the help.
I have the 1200HP PA system and it was the best decision I ever made. No issues at all. Customer service has a little to be desired, but once past that, all has been good. Can’t beat the drivability and tuning of FI.
 

need-for-speed

Veteran Member
Feb 7, 2003
1,275
Conroe, TX
I've got an LT1 in my Firehawk and it runs great as it's still low miles but I'm waiting on the Optispark to give me issues. Like it from the factory but never considered it for a transplant.

I went to by the Vortec today and it looks like I'm a day late. It was $500 for a complete motor with front accessories.

Glad the lifters I have will be of use. Bought them as a kit for my 468 and never could get them to work and had to go linked style. I was kinda of stuck with them and it wasn't worth the hassle to fight over the kit not working.

I'm looking forward to the computer part of fuel injection and the 4l60e swap. I've got Fitech on the 468 and it controls the timing too. Timing adjustments are a breeze with the computer and a little more flexibility. It did take some time to learn how to tune it but now that I am pretty comfortable with the system, it should be a breeze the second time around. I get 12-14 mpg around town if I baby it and 10.5 to 11 if I have fun with it. The old cam could get 22-24 on the highway with the AC on but I haven't had a chance to test it yet with the new cam. I'm expecting the same as the around town mileage is up with the roller cam.

I scored a 4l60e tranny tonight and am picking it up tomorrow. Part of the puzzle down. Planning on using the FITECH controller and the FITECH injection and it looks like the two play nice together.

Caden and I haven't decided which we will swap first, but we are doing one and then the other as I don't want two sets of variables. Get one system dialed in and then the other. I'm leaning towards the trans first so he can learn to tune it on the old motor.

Thanks again for all of the help.
Regarding the tranny crossmember: I swapped in a 700R4, and kept the original (turbo 350) cross member. I slid it back to where the front 2 holes in the cross member were bolted to the back 2 holes in the subframe. I drilled 2 more holes in the subframe for the back 2 holes in the cross crossmemeber. I spent about $60 having the driveshaft shortened and rebalanced. Everything bolted up just fine.
 

JeremyM

Veteran Member
Aug 12, 2005
107
Rolla, MO
After reading everything here and across the internet, I have a few more questions.

It looks like the 87-95 blocks might be a good starting point assuming the heads are junk. I can find these blocks close and affordable and started looking at top end kits.

What confused me was one of the Summit Kits stated 67-86, but most of the others stated 67-2002. Is there some reason a top end kit for a SBC would not work on an 87-95 block that I am missing?
 

Lowend

Administrator. .a car, a man, a maraca.
Staff member
Lifetime Gold Member
Mar 25, 1999
16,802
San Jose, CA, USA
The early heads will fit a late block. The late heads have a slightly different bolt angle on the innermost intake manifold bolts, so they aren’t a drop on for a 1 piece rear block, but the bolt holes on the intake can be slotted with little effort.
 

FS87LT

Member
Apr 3, 2010
85
DFW, TX
I'll add another type of sbc which I avoid: Gen II '92-'97 ... heads can't interchange with other sbc, reverse flow cooling (not simply reverse rotation) and Optifart ignition. They run great; until they don't. Another of GM's better ideas. 🦃 YMMV
Nothing wrong with reverse flow cooling. Dirt trackers were modifying their engines to do this well before Chev designed those engines. As for the ignition system, with a dual plane intake, just put a normal distributor back there in the normal hole. Might need to remove/alter the existing oil pump drive to make it work. The reverse flow cooling is one reason the higher CR on those motors can work, cooling the combustion chamber first rather than otherwise. At least, looking at the GM parts books indicated that the architecture, as I mentioned, is all still there to support a normal distributor.

In Smokey Yunick's book, he talks about spark timing variations resulting from the harmonics of the distributor being driven at the back end of the camshaft, rather than the front. As poorly-executed as the OptiSpark might be, it addresses that issue, being driven off of the crankshaft nose. Plus all of the spark plug wires are "down there", for a cleaner look engine, IF that might matter. Which also allows for those "high rise" rear exit (Chrysler 440HP look-similar) exhaust manifolds to exist nicely on the engine.

With a 2.73 rear axle ratio, OD is not a good option, as many have discovered. Can't use OD until over 70mph, especially with a carburetor. EFI is more tolerant as to throttle response at higher load/low rpm cruise situations, it seems. But the 2.73 was in the GenIII F-body cars, as factory equipment and the shorter tires they came with . . . which effectively made it a lower total gear ratio. Not the same with a more-normal G70-15 tire, by comparison.

IF the humps on the bottom of the intake ports were supposed to increase throttle response, that was their "fix" to increase port velocity at lower airflow rates, I suspect. Which would be the lower rpm levels with an OD trans at 60mph cruise, for example. Not the same thing as the humps that were in some 1970s exhaust ports to promote residual EGR before EGR valves were used.

I had a '87 Chevy 1/2 ton, 5.7L TBI motor, THM700, 3.08 rear axle and P235/75R-15 tires. With easy driving, I did several 20mpg tanks, when the speed limit was 55mph. But we had to stock 3.42 rear axle ratio pickups so we could dealer-trade with other dealers. That engine was impressive, in many ways, even with the 3.08 gears.

When Chevy did the L69 305 Z/28s, there was nothing magical in that motor. Same (basically) modernized 350/300 cam, 1.84/1.50 valves, same exhaust manifolds, BUT they finally put a decent under-car exhaust system on it. So, basically, what they had was "a torque motor with an exhaust system that flows well". To me, not a drag racer, but a road driver, that approach makes sense.

In looking for cams, look for ones with a-symetrical lobe configurations. Like the original Comp 268HE used. Part of their "more area under the lift curve" is due to the fact that the valve remains at max lift for a full 10 degrees of crank rotation, rather than 1 degree on a stock or some competitors' cams. The earlier versions did sound like a mechanical cam when first installed, although they were hydraulic, but quietened down after several thousand miles. Lunati also has some cams like that, but probably not roller cams, as I recall. Of course, the roller cam lobes seem to have more dwell time at max lift than flat tappets do. BTAIM

Just some thoughts,
FS87LT
As for cyl head porting, I discovered some David Vizzard porting videos on YouTube the other day. He explains it all and it works.
 

sandlapper

Veteran Member
Oct 9, 2020
1,457
SE CSA
Nothing wrong with reverse flow cooling. Dirt trackers were modifying their engines to do this well before Chev designed those engines. As for the ignition system, with a dual plane intake, just put a normal distributor back there in the normal hole. Might need to remove/alter the existing oil pump drive to make it work. The reverse flow cooling is one reason the higher CR on those motors can work, cooling the combustion chamber first rather than otherwise. At least, looking at the GM parts books indicated that the architecture, as I mentioned, is all still there to support a normal distributor.

In Smokey Yunick's book, he talks about spark timing variations resulting from the harmonics of the distributor being driven at the back end of the camshaft, rather than the front. As poorly-executed as the OptiSpark might be, it addresses that issue, being driven off of the crankshaft nose. Plus all of the spark plug wires are "down there", for a cleaner look engine, IF that might matter. Which also allows for those "high rise" rear exit (Chrysler 440HP look-similar) exhaust manifolds to exist nicely on the engine.

With a 2.73 rear axle ratio, OD is not a good option, as many have discovered. Can't use OD until over 70mph, especially with a carburetor. EFI is more tolerant as to throttle response at higher load/low rpm cruise situations, it seems. But the 2.73 was in the GenIII F-body cars, as factory equipment and the shorter tires they came with . . . which effectively made it a lower total gear ratio. Not the same with a more-normal G70-15 tire, by comparison.

IF the humps on the bottom of the intake ports were supposed to increase throttle response, that was their "fix" to increase port velocity at lower airflow rates, I suspect. Which would be the lower rpm levels with an OD trans at 60mph cruise, for example. Not the same thing as the humps that were in some 1970s exhaust ports to promote residual EGR before EGR valves were used.

I had a '87 Chevy 1/2 ton, 5.7L TBI motor, THM700, 3.08 rear axle and P235/75R-15 tires. With easy driving, I did several 20mpg tanks, when the speed limit was 55mph. But we had to stock 3.42 rear axle ratio pickups so we could dealer-trade with other dealers. That engine was impressive, in many ways, even with the 3.08 gears.

When Chevy did the L69 305 Z/28s, there was nothing magical in that motor. Same (basically) modernized 350/300 cam, 1.84/1.50 valves, same exhaust manifolds, BUT they finally put a decent under-car exhaust system on it. So, basically, what they had was "a torque motor with an exhaust system that flows well". To me, not a drag racer, but a road driver, that approach makes sense.

In looking for cams, look for ones with a-symetrical lobe configurations. Like the original Comp 268HE used. Part of their "more area under the lift curve" is due to the fact that the valve remains at max lift for a full 10 degrees of crank rotation, rather than 1 degree on a stock or some competitors' cams. The earlier versions did sound like a mechanical cam when first installed, although they were hydraulic, but quietened down after several thousand miles. Lunati also has some cams like that, but probably not roller cams, as I recall. Of course, the roller cam lobes seem to have more dwell time at max lift than flat tappets do. BTAIM

Just some thoughts,
FS87LT
As for cyl head porting, I discovered some David Vizzard porting videos on YouTube the other day. He explains it all and it works.
you said it ... optifart is "poorly-executed". That little bit of harmonics is, for most users, a tempest in a teapot. Otherwise, you'd see tens of thousands of GEN II in Circle Track & Drag; they're not even an afterthought.
some have fitted a carb & HEI dist on GEN II ... but the special intake for it is Stupid Expensive $$$$.
GEN II heads were great performers in their day; but nothing special in this century. Way back I've seen guys spend tons of T&E $$ welding and milling to adapt them to GEN I blocks; not today! Again, GEN II = GM's Edsel. If you like 'em; great.
 

JeremyM

Veteran Member
Aug 12, 2005
107
Rolla, MO
Looks like I found a complete vortec engine to rebuild. Headed to the junk yard to look at it tomorrow. It is out of a 99 Tahoe with an R as the 8th character in the VIN so from what I can tell it should be the Vortec. I'll check the part numbers to be sure but should be a good starting point.
 




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