Alright,
I have a question about my combonation. The car is a sunny day driver that I want to take to the track on occasion. The motor is a small block 350, with stock pistons and crank. The cam is the 270 series extreme energy from comp cams, the heads that are going on it are the proline iron heads in 72cc configuration. The rockers are comp 1.5 ratio and the intake is a stealth intake. Lastly the carb is an edelbrock 600cfm with vac. secondaries and electric choke. The exhaust is single three inch off of dynomax ceramic coated headers. Finaly my question is are the rockes ok or should I go with 1.6? Also do you think the carb is holding back the combo? Its a five speed car with 3.73 rear gears. I really appreciate the input. The motor is in pieces right now awaiting the heads, and new bearings. Thanks agian, Jered

 

I am not an expert, but I would say go with a 750 carb if you are staying vac secondary. I dont know exactly what size but with a manual people tend to recomend double pumpers instead of the vac secondary but usually it seems that they recommend smaller double pumpers than they would if it was a vac secondary. Are the rockers stock or are they roller. If they are roller I dont think they would be a big difference being as you already have a decent sized cam but if they are stock and you need to replace them I would say it would depend on how much lift your heads can handle.

Ben

 

Your carb is killing you.

Your heads will benefit from additional valve lift, they have enough flow that the rocker ratio will make a significant difference. Make sure your springs are adequate, or just buy the recommended springs and hardware when you get the rockers.

There's no such thing as a "305 HO" Berlinetta. You should become factually accurate so that people don't laugh at you.

 

It all depends what the 350 came out of, and thus what "stock" compression ratio it had.

It could be a 10:1 or as low as 8:1 compression ratio.


This is important, because if you use the 72cc heads, depending on what cc the original head had, you could be raising or lowering compression ratio. Not to mention, you might be changing the quench ratio.......too much can still cause spark knock / detonation, even with LOW compression ratios.

What's the motor out of?

 

Actually, stock it was probably no more than 9.3-9.5:1 no matter what it was and it probably had no larger than 72 cc chamber heads. That means it would be no more than 9.5:1 in all likely hood and probably 8.?:1. This is really bad for that cam you have. You should probably be running as close to 10:1 as possible in my opinion. Has the block been decked by any chance? Have you already ordered the heads?

Ben

 

your guess is as good as mine as to what it came out of, I dont think it has been decked. The pistons appear to be the same old cast slugs you see in every stock small block. I havent ordered the heads yet. Also I have never heard of quench ratio? whats that? THanks for the input.

 

Okay... look at the engine.

Passenger side, front. On the BLOCK, right under where the cylinder head mounts to the block. Normally right behind the alternator on a V-Belt car. There will be a set of letters / numbers there. It might take some cleaning to be able to clearly read them. Post those numbers here, and I can look 'em up and narrow down what the engine came out of originally, and more than likely we can get some specs for it.

IF the numbers aren't there, it means the block has been decked. So this would mean the engine has been rebuilt, and decking brings other things into the equation.

The piston quench area is pretty simple. It's the thickness of the head gasket ( compressed thickness ) + the distance that the piston sits down inside the bore at it's highest point.

.040" is the number I've used for years, as recommended by more than a few guys who make their living building engines.

This will help power, as well as keeping the engine from getting "hot spots" and getting detonation.

HTH

Chris

 

ona 350 small block if a flat top piston does not come all the way to the top then 72cc heads will result in a too low compression ratio for the cam you have (for best results)
If you have dished pistons it's really! going to be low.

This is probabily more critical right now than wether you have a 600cfm carb or 1.5 rockers.

Identify your pistons ( dished, flat top) and measure your deck height first before ordering heads.
A 64cc or smaller head will probabily be better.
This is worth the bother to get it right.

You can download a good compression ratio calc utility from
www.download.com

Search for "engine cr" (ver 1)

 

Ok, first off I really appreciate all comments and info. I looked at the block and didnt see any numbers, so I guess its been rebuilt. The pistons are flat top, with only relifs cut into the piston top. The more I look at this whole motor I think it would be wiser to start fresh with parts I know. I have a new oem 350 cast crank, for the block. What I want to know is what pistons should I go with that would be compatible with the heads I am looking at. The car is street driven in the summer and on sunny days so amazing gas mileage isnt a big deal, but reliablity is. This will be the first complete build up for me, I am not going at it alone I have a friend who is a current GM tech and ASE certified so thats not a concern of mine. Do I need to go with new rods as well? Any suggestions on carb type? The car is a 5-speed and if or should I say when that goes broke I still will keep it a manual trans car. So probably something w/ mechanical secondaries. I am looking at doing this right the first time and dont want to shortchange the motor. Again I appreciate the input.

 

no idea's?