[Nitebird]

I will be ordering a roller cam,lifters and distributor for my engine tomorrow from SD performance. I have another question to ask you guys.

For my engine combo which cam would run safer and better with 87 or 91 pump gas?
Would it even be safe to even try 87 pump gas?

The combo

1979 TA/SE 4spd,AC,power 4wheel disc
Pontiac 455 .030 at 10.1 compression
Tomahawk forged I beam rods
950 Holley
RPM or Tomahawk intake...I have both
Edelbrock D Port heads 87cc with 1.5 rockers
1 5/8 headers

The cam choices : both hydraulic roller

Stump Puller 230/236 duration 567"/.578" lift 112
Old Faithful 236/245 duration 578"/.582" lift 112

Any feedback is appreciated! Thanks!

[Cliff R]

With tight quench you could easily run the lower octane using the larger of those two camshafts. The Stump Puller yanks power down in the rpm range, and this will produce high cylinder pressure early, when the events are happening slower, so it will be more octane sensitive at any given compression ratio compared to the OF cam.

Where you put the cam has a MAJOR impact on that deal as well.

My 455 is right at 11 to 1 static compression, using the OF cam and high ratio rockers. It gets a steady diet of 89 octane, and I've ran 87 octane in it many times on the street. On race days I blend in 1/2 a tank of 92-93 octane. Never once heard this engine ping on any type of pump fuel, even on the hottest summer days fully heat soaked.

It will on occasion "run-on" for a few seconds on 87 octane, but only when outside temps are over 90 degrees and the engine is fully warmed up and heat soaked.

For what you are doing, I'd make sure to deck/square the block for zero and use .039" head gaskets, especially if you are concerned about octane tolerance. The engine will require less total timing for most power, and less octane sensitive, at least from what we've seen here.....Cliff

[ta man]

I run 87 octane quite often with mine...my heads are KRE though with an OF cam approximately 10.25 to 1..

[GTOLou]

Nice combo - I'd like to see bigger than 1 5/8 headers for a 455+ build.

[Nitebird]

Originally Posted by Cliff R

With tight quench you could easily run the lower octane using the larger of those two camshafts. The Stump Puller yanks power down in the rpm range, and this will produce high cylinder pressure early, when the events are happening slower, so it will be more octane sensitive at any given compression ratio compared to the OF cam.

Where you put the cam has a MAJOR impact on that deal as well.

My 455 is right at 11 to 1 static compression, using the OF cam and high ratio rockers. It gets a steady diet of 89 octane, and I've ran 87 octane in it many times on the street. On race days I blend in 1/2 a tank of 92-93 octane. Never once heard this engine ping on any type of pump fuel, even on the hottest summer days fully heat soaked.

It will on occasion "run-on" for a few seconds on 87 octane, but only when outside temps are over 90 degrees and the engine is fully warmed up and heat soaked.

For what you are doing, I'd make sure to deck/square the block for zero and use .039" head gaskets, especially if you are concerned about octane tolerance. The engine will require less total timing for most power, and less octane sensitive, at least from what we've seen here.....Cliff

Thanks for the information Cliff! My 455 short block was zero decked and I am using a felpro .039 gasket.

Could you give a example of what degee to put the OF cam in order to be more pump 87 friendly?

[Cliff R]

At 10 to 1 compression set the ICL 108 or close to it. If it comes up where the ICL is going to be 108.5 (for example), do NOT under any circumstances advance the cam an additional 2 degrees with a 9 keyway set, or 4 degrees with a 3 keyway set to compensate for chain stretch, improve low end power, etc. That is all HORSECRAP, and can/will get you into trouble when it comes to power production, and managing pump fuel at any given compression ratio.

Here's a real World example of what I'm talking about. A few years ago we supplied a set of KRE heads that we prepared and a custom ground 230/242/112 HR camshaft. Solid set-up and proven to work on pump fuel with 85cc KRE heads, zero deck, .039" gasket. The owner/engine builder installed the cam and it came up at 109ICL, so he left it there. For several years he drove, raced, and flogged the engine pretty hard with zero issues. For some reason that I will never know, one day he decides to advance the cam 2 degrees with his 9 keyway Rollmaster timing set.

He did mention this to me, and also said that he immediately started to hear light pinging at part throttle cruising, and a little detonation at full throttle.

The next email I get says that he has the engine out, apart, and two of his forged pistons have the ring lands busted out of them!......Cliff

[Nitebird]

Originally Posted by Cliff R

At 10 to 1 compression set the ICL 108 or close to it. If it comes up where the ICL is going to be 108.5 (for example), do NOT under any circumstances advance the cam an additional 2 degrees with a 9 keyway set, or 4 degrees with a 3 keyway set to compensate for chain stretch, improve low end power, etc. That is all HORSECRAP, and can/will get you into trouble when it comes to power production, and managing pump fuel at any given compression ratio.

Here's a real World example of what I'm talking about. A few years ago we supplied a set of KRE heads that we prepared and a custom ground 230/242/112 HR camshaft. Solid set-up and proven to work on pump fuel with 85cc KRE heads, zero deck, .039" gasket. The owner/engine builder installed the cam and it came up at 109ICL, so he left it there. For several years he drove, raced, and flogged the engine pretty hard with zero issues. For some reason that I will never know, one day he decides to advance the cam 2 degrees with his 9 keyway Rollmaster timing set.

He did mention this to me, and also said that he immediately started to hear light pinging at part throttle cruising, and a little detonation at full throttle.

The next email I get says that he has the engine out, apart, and two of his forged pistons have the ring lands busted out of them!......Cliff

That is just awesome good stuff to read!....except for that guys misfortune with his engine of course.

Thanks again

[Nitebird]

Originally Posted by GTOLou

Nice combo - I'd like to see bigger than 1 5/8 headers for a 455+ build.

I would like to run some 1 3/4 but cant find any that fit the budget as I cant afford the Dougs headers.