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Old 10-28-2012, 08:30 AM
Clayton A's Avatar
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SBC 350 Engine Advice needed

I recently acquired a 1971 Chevelle from my dad!!!! The engine sounds real good but I think the combination of parts are hurting the engine more than they are helping. I built the engine when I was 18 (12 yrs ago) and didn't have the first clue as to what I was doing. Dad knew how to put an engine together so that is exactly what we did. Now at I look back at some parts I used and I think we made a few mistakes. The engine block is a 1980 - 1985 350sbc Casting number 14010207 bored .40 over. The heads are Vortec Heads (bought new from Summit) Casting number 12558062 (milled for a higher c/r) I am thinking about changing the valve springs and rockers....any suggestions?, The intake is a Edelbrock Performer 2116. The carb is a Edelbrock Performer 1406. The cam is a Crane Cam with a 516 lift (I think the lift is way to high for these heads, can't remember the duration). Stock 350 crank that I had checked by a machine shop. I don't remember the brand of pistons but I do remember they were flat top style and a compression ratio of like 10:1 (Not engine c/r but the pistons). Not sure what the actual C/R of the engine is. I plan to go back through this engine and try and get all the right parts that I need to produce the best HP.
Any suggestions on what to do to produce the best HP from this engine? I plan to re-use the heads and crank but would consider swapping out the rest. I believe my dad has a Performer RPM intake that I plan to use.

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Old 10-28-2012, 08:44 AM
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You need additional info when your using the cast iron heads. What is the cc of the chamber of the heads now they where cut and was the block decked when you built the engine??. That is going to get you to the SCR and what needs to be done to run on pump gas. Is this for street use?.

The answers to that will lead you to if a stroker is doable or if the SCR would be too high.

Last edited by 1Gary; 10-28-2012 at 08:50 AM.
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Old 10-28-2012, 09:26 AM
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depending on the duration the cam may or may not be a good match for your heads, the lift isn't hurting anything at all.

An RPM intake will help some but don't expect a huge difference, especially at street RPM.
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Old 10-28-2012, 09:28 AM
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what are you expecting from the engine? where does it fail now?
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Old 10-28-2012, 02:25 PM
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Quote:
Originally Posted by 1Gary View Post
You need additional info when your using the cast iron heads. What is the cc of the chamber of the heads now they where cut and was the block decked when you built the engine??. That is going to get you to the SCR and what needs to be done to run on pump gas. Is this for street use?.

The answers to that will lead you to if a stroker is doable or if the SCR would be too high.
I don't know the cc on the heads after I had them milled (It was 12 yrs ago and I can't remember that). I need to have them checked once I pull them off. I am going to drive the car around town a couple times a month and maybe to the local strip from time to time. More street than strip. Minimal highway use. I think I have a lot of information I need to get the accurate answers I am looking for.
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Old 10-28-2012, 02:27 PM
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Originally Posted by ap72 View Post
depending on the duration the cam may or may not be a good match for your heads, the lift isn't hurting anything at all.

An RPM intake will help some but don't expect a huge difference, especially at street RPM.
I can't remember the duration of the cam. I had all the info but have since lost that info.
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Old 10-28-2012, 02:28 PM
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what are you expecting from the engine? where does it fail now?
The engine is pretty stout now but I am thinking I can get more HP from it.
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Old 10-28-2012, 02:45 PM
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getting more horse power is as easy as opening your wallet.There are so many good parts available.You need to know exactly what you have before you can improve it,would look silly if you bought the same part again.
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Old 10-28-2012, 02:47 PM
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Quote:
Originally Posted by vinniekq2 View Post
You need to know exactly what you have before you can improve it,would look silly if you bought the same part again.
There's the answer.
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Old 10-31-2012, 11:02 AM
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Cam Info

The cam that I have is a Crane Cam with 238 int / 244 exh @ 050 in lift with 0.502 int / .0516 exh lift lobe separation of 106 degrees. Now that I have the specifics on the cam lets say that the heads are just out of the box Vortec 12558062 heads with 1.94/1.50 valves with 64cc chambers. Would this be too much cam for these heads?
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Old 10-31-2012, 11:30 AM
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a lot of vortecs need to be modified for lift over 450. vortecs also need exhaust port work
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Old 10-31-2012, 11:44 AM
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a lot of vortecs need to be modified for lift over 450. vortecs also need exhaust port work
What type of modifications? What do I need to do? I don't know a whole a lot about this subject so could you give me the specifics?
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Old 10-31-2012, 12:50 PM
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Here's your cam.....
Saturday Night Special, Part #110691, operating range 3,200 to 6,800 rpm's.
Flat tappet hydraulic, Performance usage, good mid and upper RPM torque
and HP, bracket racing; Street, Heavy, ProET, SuperET,
etc., autotrans w/3500+ converter, oval track; Street
Stock, Enduro, Hobby, etc., 1/4-3/8mile circle track, 10.5:1 to 12.0:1 static
compression ratio advised.
Advertised duration: 294/300
Duration @0.050" tappet lift 238/244
Lobe separation angle 106 degrees

Valve timing @0.050" tappet lift:
Intake opens 17 degrees BTDC
Intake closes 41 degrees ABDC
Exhaust opens 52 degrees BBDC
Exhaust closes 12 degrees ATDC

Intake valve lift with 1.5:1 ratio rocker arms, 0.480"
Exhaust valve lift with 1.5:1 ratio rocker arms, 0.495"

So, to answer your question, would this be too much cam for these heads? The answer is yes. The heads will stall and sign off way before the cam is done pulling. You fellows have to realize that the L31 heads were designed by GM to make the proper hp and torque to haul grandma and the kids to Disneyland, not to do things like bracket racing (description of the cam above). They're great street heads and will flow better than any other PRODUCTION Chevy cast iron head, but they are not miracle heads. Stock valve lift was less than 0.420" with these heads and I'm really surprised that some cam grinder hasn't stepped up with an off-the-shelf hydraulic roller that will work with the stock springs and rail rockers that come on these heads. Like, you could build the motor 9.5:1 SCR and use a cam that closes the intake valve at around 35 degrees ABDC with a very short lift, like around 0.400" and make excellent power on crap gasoline. All you guys seem to think that you need valve lift to the moon, but that's not true on a daily driver. Pull your head out of your kazoo and put down the hot rod magazines.

Last edited by techinspector1; 10-31-2012 at 01:07 PM.
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Old 10-31-2012, 01:05 PM
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Quote:
Originally Posted by techinspector1 View Post
Here's your cam.....
Saturday Night Special, Part #110691, operating range 3,200 to 6,800 rpm's.
Flat tappet hydraulic, Performance usage, good mid and upper RPM torque
and HP, bracket racing; Street, Heavy, ProET, SuperET,
etc., autotrans w/3500+ converter, oval track; Street
Stock, Enduro, Hobby, etc., 1/4-3/8mile circle track, 10.5:1 to 12.0:1 static
compression ratio advised.
Advertised duration: 294/300
Duration @0.050" tappet lift 238/244
Lobe separation angle 106 degrees

Valve timing @0.050" tappet lift:
Intake opens 17 degrees BTDC
Intake closes 41 degrees ABDC
Exhaust opens 52 degrees BBDC
Exhaust closes 12 degrees ATDC

Intake valve lift with 1.5:1 ratio rocker arms, 0.480"
Exhaust valve lift with 1.5:1 ratio rocker arms, 0.495"

So, to answer your question, would this be too much cam for these heads? The answer is yes. The heads will stall and sign off way before the cam is done pulling. You fellows have to realize that the L31 heads were designed by GM to make the proper hp and torque to haul grandma and the kids to Disneyland, not to do things like bracket racing (description of the cam above). They're great street heads and will flow better than any other PRODUCTION Chevy cast iron head, but they are not miracle heads.
When I built this engine I didn't have a clue of what I was doing and was just throwing parts together. I still don't know what I am am doing but at least now I am smart enough to ask people that do! lol What type of cam do you recommend for the heads?
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Old 10-31-2012, 01:16 PM
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What I recommend is that you figure out your static compression ratio and then call up your favorite cam grinder and ask for a recommendation.
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