Two years ago I had so much trouble with wiring in my 1996 Camaro that I decided to change it for an air aspirated 8 cylinder. At the time I didn’t care what so I met a motor builder that would make the swap. Basically a rebuild of used block, 193 heads, crank, with new: Edelbrock 600 4-barrel carb, MSD ignition, Edelbrock performer intake, Comp cams 268 flat tappet cam, 1 5/8” headers, 1.5 roller rockers, Spector cold air intake, alternator, motor starter, hoses, belt, oil pump, all new.
after 2 months running water was entering the cylinders. Opened the heads and a piece of metal was left in the cylinder. The shop took it out to repair it, in the process I bought .060 over flattop eyebrow pistons, a 4-bolt main block and the machine work was done all over again and the motor assembled. The car does cool burn outs but really isn’t that fast. Probably due to the 193 heads (?) Also probably never got quit tuned in, 2500rpm timing set at 36. Then more problems.
Now I’ve got a rod knocking and plan to rebuild the entire lower end using a 383 kit with all new parts at a much higher quality shop. My question is do I spend the money and change the cam and heads or just re-do the lower end and be happy with the top end the way it is? Will the 383 bottom work ok with the flat tappet and 193 top end? About how much HP will it be with the 383 lower end, flat tappet cam, and 193 heads -vs- spending the $ to change the heads and go to a roller cam? This is a street car that maybe I’ll take to the strip just to see what it can do.

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"Opened the heads and a piece of metal was left in the cylinder."

Seriously? Who assembled that thing? I've never heard of an engine even starting without being shut down immediately with "a piece metal in a cylinder". But then I've never seen anyone assemble an engine and do that.

Glad to hear your switching shops.

Never run those heads however don't hear anything about them being a performance head.

 

Thanks for your reply! Seriously metal in the cylinder! I had no idea what I was getting into, unfortunately I´ve learned more about Chevy small blocks than I ever expected. I´d tell anyone that wants to pull out a 6 and put in an 8 Don´t do it!! hahaha buy a car with an 8 in it and save some $!. But its done and doesn´t look half bad. The 193 are not a performance head, they burn the tires off the rims with the low end torque but run out of air at 4500rpm. I´m on a budget so I may port them myself.
-My concern is will the 268 flat tappet hold up with the 383 bottom end, that is, will it run for a while or will it wear out right away?
-What kind of horse power would this combo deliver: 600cfm carb on a performer cold air intake, 268 flat tappet cam, 383 bottom end, .060 over flat top pistons, 193 heads through 1 5/8" headers with catback x exhaust?

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Stock compression then? 8.5 or 9:1?

 

Stock, then. But now I put in flat top pistons. I have pictures posted in an album you can look at. I´m still wondering if the 268 flat tappet cam will hold up with the 383 bottom end? Haven´t got any responses from the group yet.

 

Okay your heart is in the right place.

I'm 65 and have built and assembled 100s of engines since I was 17. My tech school and first 20 years were as an engine machinist.

We need to start at square one. Building a new short block 383 with new flat tops is a great idea!

I will quote the great David Vizzard a GM small block guru I very much respect and agree with.
"The camshaft doesn't select the engine. The engine selects the camshaft" so lets put aside the 268 cam for now.
" The real power is in the cylinder heads" said David Vizzard and everyone else that knows how to hot rod anything.

Your short block (crank, rods, pistons assembled in a block ready to go, no heads) will be about 9.5:1 compression IF the decks are stock. IF the decks have been machined you need to know by how much. Ideally .025" a side will net you both a 10.2 : 1 ratio AND a tighter quench! We'll get to the heads and the chamber size which is also very important.

Find out if the decks get done on your project/purchase and how and how much.

THE CAM
This may seem complicated however its really not and there are a few websites that you can plug the numbers into and get a really good answer.

Static Compression/Dynamic Compression Get this wrong and you will not be happy.

The most important byte of cam data is intake valve closing point ABDC as expressed by the duration at .050.
The intake valve closes while the piston is "compressing" on the compression stroke. IF you close the valve too early you compress too much and will end up buying Octane Boosters or worse buying fuel!
IF you close the intake valve too late you bleed off power and will have a mutt on your hands.

A computation leaving your engine with a DYNAMIC compression of 8.0/8.3:1 is ideal.
You can end up with a Static 10.2:1 engine that has a dynamic compression of 8.3:1 and runs like a champ on pump premium.

Your Comp Cam 268 shows Duration @ 0.006": 268° / 280° Duration @ 0.050": 224° / 230° (love Comps Data!) it could work out well IF you know everything else. The good news is it can be advanced or retarded 4 degrees either way easily.

BTW your 268 cam can't hurt the bottom end. No cam can do that although when using a cam over .490" lifts a good engine builder clay strips the pistons on assembly and checks the rod big end to be sure they don't come too close to the cam lobes.

HEADS
Sorry however the 193 head from everything I've seen and read are good to 4000 rpms on a smaller displacement engine and simply won't pull any after that. Just not a suitable head at all and the 383 cubes and cam won't help a bit.
All the compression math I thumbnailed is based on a 64cc chamber which is very common for performance heads. You could hunt down some Vortecs? 2nd hand World Sportsman 2s? just keep in mind a smog headed 76cc chamber is another bad idea. There are cost effective inexpensive heads out there. It is an SBC after all;-)

 

Thanks for the input. They open the motor tomorrow, I´m curious to see what they find. I´ll look for some other heads and find out about the Decks. Thanks again!

 

I found some Flotech Heads, part# FLK-1200HRSB505S aluminum, 200cc runners, 64cc combustion chambers, 2.02" intake valves and 1.6" exhaust valves, for a flat tappet or roller cam depending on the rod length, max valve lift .54, single springs, rocker studs included, with center or perimeter valve cover bolts; more than I want to spend, but the cheapest I could find, $450 each. Thinking about getting them, I don´t know if my pushrods, lifters, etc. I have will work or not, I´m going to ask the shop taking out the motor what they think before getting them, but was curious if I´m headed in the right direction by putting these heads on top of the 383 bottom end kit?

 

I know where your coming from on being budget minded.

I've always taken the stand that I should have a cash fund on the go. I don't like building a hobby car using credit.

I checked them out on line and they will be a definite upgrade for you. With springs and valves its a pretty good deal. I ran 200cc World Heads on a 406 and it was a torque monster although that had a lot to do with some other parameters too. On a 383 those heads should perform really well. I wouldn't go any bigger on the intake cc volume though. 200 is the high end to still make torque.

Remember the old drag strip adage..."Horsepower sells cars, torque wins races". You're trying to get a 3000-3500 lb car going from a stand still!

Regards pushrods that's almost the last thing when assembling. With a cam, a still to be determined deck height there can be slight changes in length. I have an adjustable pushrod "length checker" to correctly size them. I'd be surprised if your engine builder isn't aware of this as well.

 

Thanks!!
I´m sure they do. I´m pretty surprised, they pulled the motor out of the car yesterday, took apart the motor and diagnosed the problem today. Monday they said they will quote some options, from fixing like it sits, to the heads and 383 kit