My Big problem..need your help (long)

[Jcentsr6]

Let me try to keep this story short. I will thank everyone in advance for reading and giving feedback on this subject. I love this site...and without everyone here, I would not own this truck. You are the experts.

I bought my truck (1970 CST-10 402 BB) last summer. It never had any power when driving it. (not even enough to spin wheels) I thought it was just tuned wrong or something. It drove fine other than the power issue.

I ordered and installed many parts for the truck to get it where I wanted...including air bags, wheels, disc brakes...and many engine parts too....Headers, cam and lifters, roller rockers, Intake manifold and new carb.
Still no power. Long story short...I checked compression...its at 125 on all cylinders. I performed a pressure leak down on each cylinder....Its great, no leak down. After thinking about it......it has to have the wrong pistons in it to lower compression. No other explanation.

Either this truck had a blower on it before I bought it (blower pistons will lower compression) which I doubt it had a blower due to everything being stock on truck.

OR

The guy who owned it prior...had the motor rebuilt with the wrong pistons, could never get it to make power...and Sold it because or that.
(I cant get ahold of the prior owner)

Question is (finally : Do I pull the motor and rebuild with proper pistons???
OR do I install a blower onto this motor??
I just want to complete, drive, and enjoy my vehicle. I wish I would have check compression and everything prior to spending $9,000+ on everything....but I didnt. So what would you do now?

[neonlarry]

It would be much more likely that someone replaced the heads with larger c.c. combustion chamber ones than to have changed to lower compression pistons. Pull the valve covers and check to see what casting numbers they are and than look them up to see combustion chamber size.

[Jcentsr6]

Originally Posted by neonlarry

It would be much more likely that someone replaced the heads with larger c.c. combustion chamber ones than to have changed to lower compression pistons. Pull the valve covers and check to see what casting numbers they are and than look them up to see combustion chamber size.

\

What benifit does bigger cc heads do? Is the only fix to replace the heads...or adding something else to the mix. My techs and I were talking about bigger heads...but I dont know alot about why you would use bigger head and their benifit. Thanks for the info...I will be sure to check for casting #s. Will they be easy to find.

[straitnate14]

blower baby, once your blown you never go back

[neonlarry]

No benefit to bigger heads. They might have needed replacing (valve job etc.) and these were available cheap. A bigger combustion chamber will do the same thing as lower compression pistons, lower the compression ratio. Its just more likely the heads were changed and there are a variety of different c.c. heads that GM made and some people are not to careful in using correct replacements, especially when its cheap.

[69halfton]

have to agree with neon larry,

with the truck being tottally stock, i seriously doubt there was an engine rebuild, where they would select to put any interanls in that weren't stock. I doubt there was an engine rebuild at all.

that being said, if you just dropped a blower on, I'd give it about a week before you drive over the crank.

If its all original internals, they wont last long under boost. but i might be wrong, guys have run 150 shot of nitrous on tottally stock motors and had them last before, but its rare.

[straitnate14]

As long as you keep the boost low and you dont let it detonate you will be fine with a blower, I have 6PSI on a gm crate motor and have had no troubles and it's like somone kicks you in the ass and then puts a one inch hole in your gas tank every time you get on the gas but it's totaly worth it

[whatnow123]

Go for the blower if you got the cash!

[straitnate14]

[Jcentsr6]

Where do I find the casting #s?

How does everyone think I should find the exact answer?? Will the head castings #s tell all?

Does all that mean that I may just need new heads?

[ed2552]

Yes, if they are not stock. If you want power, and they are the wrong heads, look at the Brodix Race Rite Oval ports, i've heard they are awesome for torque, and priced very well

[70c10]

Jay can you post the part numbers of your cam, your rear gear ratio, stall speed, and anything else you did to the truck?. Maybe your truck needs more gear ratio to turn those 20" tires? Maybe your cam you installed is too big? Pull the valve cover off and look on the head to see what numbers are casted on them. It might be something simple. Your truck sounded healthy when I heard it! As a last resort, you may want to take to a speed shop that works on muscle cars. Here is a sample pic of a sbc head casting number:

[Jcentsr6]

Originally Posted by 70c10

Jay can you post the part numbers of your cam, your rear gear ratio, stall speed, and anything else you did to the truck?. Maybe your truck needs more gear ratio to turn those 20" tires? Maybe your cam you installed is too big? Pull the valve cover off and look on the head to see what numbers are casted on them. It might be something simple. Your truck sounded healthy when I heard it! As a last resort, you may want to take to a speed shop that works on muscle cars. Here is a sample pic of a sbc head casting number:

The cam is good. I have gone over that part prior....Good thinking though.
The truck would not spin the wheels when I had my small 15inch wheels. I dont know my gear ratio..I think 373?? What was stock in these anyways?
But other than not spinning wheels...it doesnt have pickup power...no accel. It sounds great like before...it just has never had any POWER. Even when you saw it.....Just all sound. Sounds like a drag car or something.............If I could get it to run like it sounds, Ill be happy.

And I could not see your pic for some reason. Thanks i hope to see ya soon!

[Jcentsr6]

I see the pics now.....If I post the casting #s, can someone translate them for me?

[70c10]

Mortec.com has all the casting numbers. Have you checked your fuel pressure to make sure there are no kinks or clogs in the lines/filters?? Are you getting wide open throttle?. Make sure nothing is binding your linkage anywhere! What is the part number for the cam? Gear ratio varied on these trucks. You should check it.

[Jcentsr6]

Originally Posted by 70c10

Mortec.com has all the casting numbers. Have you checked your fuel pressure to make sure there are no kinks or clogs in the lines/filters?? Are you getting wide open throttle?. Make sure nothing is binding your linkage anywhere! What is the part number for the cam? Gear ratio varied on these trucks. You should check it.

http://store.summitracing.com/partde...K&autoview=sku

Lunati 60203lk i think.
I have new stainless fuel lines...pressure good. No linkage bind. Pro Performed intake manifold..and a Holley Street avenger 670cfm carb

[c10crazy]

Do you have a stock stall converter in your truck?. If your truck has less than 3:73 gears it will feel like it has no power with that cam. Another thing to check is your timing! This can really make a huge difference! If the motor appeared all stock when you bought it, it may be. You may have overcammed it for the gear, stall and heads it has.

[Jcentsr6]

Originally Posted by c10crazy

Do you have a stock stall converter in your truck?. If your truck has less than 3:73 gears it will feel like it has no power with that cam. Another thing to check is your timing! This can really make a huge difference! If the motor appeared all stock when you bought it, it may be. You may have overcammed it for the gear, stall and heads it has.

I dont know what gears are in it...and no stall. BUT in ran the same before I put everything on it. Exactly the same...no diff. I checked the timing 3 diff times...pulling the cover off and everything. Thought I was going to loose my mind. I would think you were right about the stall and everything...but when it was all stock...it never had any power.

[Jcentsr6]

I checked the web for casting #s...it looks like only 4 diff #s can apply to that motor. 6722292, 3975950, 330864, and 330865. Is this right. I have a 1970 402 motor...engine code TBG. Oval port.

So If the heads are diff than those Im screwed?

[67shortie]

That cam (to me anyway) is not to big for a 402, that is not your problem.

125 psi in the chamber on a compression check (was this done correctly?) is a sign that you have either a flat top style piston and an open chamber head. This would lower your compression to the 8/1 range and kill power.

Did you ever get those casting numbers yet? That will tell us allot right now.

[Jcentsr6]

Originally Posted by 67shortie

That cam (to me anyway) is not to big for a 402, that is not your problem.

125 psi in the chamber on a compression check (was this done correctly?) is a sign that you have either a flat top style piston and an open chamber head. This would lower your compression to the 8/1 range and kill power.

Did you ever get those casting numbers yet? That will tell us allot right now.

Its raining its butt off right now...Im working on getting those casting #s right away. Thank you everyone for the input. Also I have had others say the cam is okay that also have a 402..so Prob okay

[neonlarry]

With that cam your compression might be fine, you are going to get some bleed off of dynamic compression from what a stock cam would give you.
On gear ratios a lot of these trucks with an auto came with 3.07 rear gears. Not your best for laying down that black stuff or instant acceleration. A bigger cam would just make it worse instead of better except on the top end.
You said you checked timing, but it sounded like you were talking about cam timing. Where is your ignition timing set and what is your max overall timing with vacuum advance plugged?
Is your vac advance hooked to ported or manifold vac?

[70c10]

Jay, according to Lunati's site, they recommend 2400 stall for that cam. I would definitely verify rear gear ratio. These two things could make the truck sluggish. Are your vacuum secondaries working properly? What is your initial and total timing set at? I'm just throwing some things out there.
Edit- Larry beat me to it on the gears and timing

[straitnate14]

and is your advanvce working? that was happening to mine before I put the blower on and it killed the power

[Pont406]

I would try and advance the cam before spending any more money on it. It sounds like a cam is installed wrong.