143 Blueprint Cam Install

[Chevy454]

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I still think its the exhaust .The car has great torque until the revs increase then it just holds back .Its at the paint shop now,when I get it back I will do some more looking .

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Just as a point of reference, our Y-Camaro put down ~370hp to the wheels through the original manifolds & chambered exhaust, on a 10:1 *bone stock* L72 build...went mid-high 12s @ 108 at a 3700-3800 race weight on Polyglass, running pump gas. With a little more compression, the car now runs high-11s @ 117+, through the same original exhaust manifolds , and a Pypes 2.5" transverese muffler...both engines would easily rev to 7k+. Terry Pennington's Camaro runs high 10s @ 130+ through the exact same exhaust manifolds in the F.A.S.T. class...

One problem I've seen before exhaust-wise is, the flapper in the passenger side down pipe get stuck shut & cause some problems. Any idea where your timing/jetting are?

[larry_csa]

Valve springs
Larry

[L78steve]

Valve springs are originals but were checked .Timing is at 36 total,jetting is 70 primary and stock secondarys on a 4557 carb.The engine has 15,000 miles not rebuilt .My next move will be to set it at TDC and check the mark on the balancer to see if it has moved .I get no spark knock with pump premium and 11:1 comp .

[Keith Tedford]

If you plan on running this car, get rid of those stock valve springs. They either (A) broke and dropped a valve, or (B) couldn't keep up with the cam allowing the valve to free fall shut at high rpm. This eventually pounded the keepers through the retainer allowing a dropped valve again. These are the main reasons that there aren't too many original L78s and L72 out there. We didn't seem to have any problem with the L88 springs in the old days.

[Mr70]

That was true to a point.
For 1970 model production,Chevrolet used a more dureable BB valve spring that avoided dropped valves @ higher RPM.
During 1968-9,they started to see an increase in BB warranty claims filed do to unreliable valve springs,so they used the stronger #3970627 to replace the weaker #3859911 spring.
L-88's were exclusive to the #3916164 spring.

[L78steve]

What springs do you guy's recommend ?I baby this thing but would like to twist it up if needed .

[Chevy454]

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What springs do you guy's recommend ?I baby this thing but would like to twist it up if needed .

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Any modern made spring should be fine...they won't have to be anything special for a "stock" cam, so just call Comp/Isky/Bullet/whomever and they'll be able to fix you up. IIRC, in our L72s we're running the springs that came with the Gm/Crane blueprint cam on one engine, and a set of Comps in another...