[pastry_chef]

Originally Posted by tjs72lemans

My data shows it peaks around 3500. I watched him dyno it, but I have no idea of difference between one from another.

Thank you.
I was curious if it was an engine dyno or chasis dyno measuring at the wheels.
3500 RPM was for peak HP?
How high an RPM did the pull go to?

[tjs72lemans]

Yes, it was an engine dyno. It was taken to 5200 rpm.

[Lee]

I know it bucks conventional "wisdon", but I agree with Sirrotica. In the mid-80's, I helped my cousin installed a CompCam Magnum 268 single-pattern in his stock-block/head '78 T/A (base model engine). With 3.23 gears (we swapped out the stock 2.56's) and 3-tube headers, on Pro-Trac G-60 tires, he was running 14.2's.


About 8 years ago, I had an interesting event. I was helping a guy who had bought a '79 400/4spd SE T/A - the engine was horrible, no power. Larry Navarro referred him to me (thanks Larry!). The owner wanted to as much as he could, so I gave him instructions and let him handle most of the ordering - short block from Len Williams, ported 6X from SD Performance, and I designed a hydraulic roller cam for him. The parts all came in, and he called me to help put it together.

SOMEWHERE, he mis-communicated with the Len and Dave, and he ended up with a 400 with just 8.3:1 compression. I had designed the cam for a 400 having over 9.0. The cam is a 224/236, 115lsa. With the parts right in front of us, we decided to go ahead and put it together, and just see what happened.

Performer intake, Q-jet built by a local dirt track carb guy, R/A manifolds, 2.5" exhaust. Basically a mild low CR 400, but with heads that flowed 265cfm, and a cam designed for more CR. After about 1,000 miles to break the motor in, we put the car on the chassis dyno. Since it was a manual tranny, I was able to start the test at a rather low RPM. I was pleasantly surprised to see it put 312hp/385tq to the wheels!

[Will]

Gonna echo the comments that the 068 is a bad choice. That cam was designed for high compression engines. It has relatively short duration, but the intake centerline is much later than cams designed for lower compression engines and with the lobe centers spread out as far as they are, it's not going to develop much cylinder pressure. Take a look at the specs for the cams the factory was putting in the low compression engines in the '70s, even the '77-'79 W72 engines - they all have much more advanced intake centerlines.

That's what you want in a low compression engine to help it build cylinder pressure. I wouldn't go with a cam with any wider LSA than 112 and would want the ICL to be somewhere between 104-106 if I could choose. The Crower mentioned earlier, and the Summit 2800 come real close. The Comp offerings all should work pretty well as they are good at building cylinder pressure, whether you go with one of the "High Energy" or "Extreme Energy" series cams. Given a blank slate, I'd prefer more compression and a more "traditional" type of cam but in a low compression 400 for street use without steep gears, converter, etc. then something like the Comp XE262 seems to fit the bill pretty well.

Lee - what was the intake centerline of that cam? How much more power would you expect it to make had the compression been where it was intended?

Just looking at the specs you gave, I'd attribute the good power level at that CR to the excellent head flow and I'm just guessing that getting the CR up a point or more would really make a difference.

[Sirrotica]

Originally Posted by Lee

I know it bucks conventional "wisdon", but I agree with Sirrotica. In the mid-80's, I helped my cousin installed a CompCam Magnum 268 single-pattern in his stock-block/head '78 T/A (base model engine). With 3.23 gears (we swapped out the stock 2.56's) and 3-tube headers, on Pro-Trac G-60 tires, he was running 14.2's.


About 8 years ago, I had an interesting event. I was helping a guy who had bought a '79 400/4spd SE T/A - the engine was horrible, no power. Larry Navarro referred him to me (thanks Larry!). The owner wanted to as much as he could, so I gave him instructions and let him handle most of the ordering - short block from Len Williams, ported 6X from SD Performance, and I designed a hydraulic roller cam for him. The parts all came in, and he called me to help put it together.

SOMEWHERE, he mis-communicated with the Len and Dave, and he ended up with a 400 with just 8.3:1 compression. I had designed the cam for a 400 having over 9.0. The cam is a 224/236, 115lsa. With the parts right in front of us, we decided to go ahead and put it together, and just see what happened.

Performer intake, Q-jet built by a local dirt track carb guy, R/A manifolds, 2.5" exhaust. Basically a mild low CR 400, but with heads that flowed 265cfm, and a cam designed for more CR. After about 1,000 miles to break the motor in, we put the car on the chassis dyno. Since it was a manual tranny, I was able to start the test at a rather low RPM. I was pleasantly surprised to see it put 312hp/385tq to the wheels!

Lee, I used the 260 HE cam in a basically stock, freshened up 75 T/A 400 (advertised compression ratio is 8.0 to 1) that ended up in in a oval track car. That car would run just as fast as all the SBCs that needed race gas to run whatever compression ratios they were running. I was extremely happy with how it ran, even with less than impressive compression.

Two other cars I've used a 268 HE were a 455 T/A with 197 HO heads (8.4 advertised compression ratio), and another 455 in a T/A with 6X, 400 (roughly 9.3 to 1) heads. At 9.3 with the 268 you have to run premium fuel, and you're on the edge of detonation with that combination. This engine should probably have a larger cam to be less prone to detonation, and would probably make more power on the top end, currently runs out of steam at around 5000 RPM.

[Lee]

Will - The software model predicted that the motor would have made 30+ more HP with the CR over 9. The ICL was around 109 to 111. I moved recently, and don't have all my old notes immediately available. I was really surprised to see the TQ as high as it was, when I began the dyno pull. - I had expected the low-end to be a bit soggy with that cam.

[77 TRASHCAN]

Originally Posted by Sirrotica

Lee, I used the 260 HE cam in a basically stock, freshened up 75 T/A 400 (advertised compression ratio is 8.0 to 1) that ended up in in a oval track car. That car would run just as fast as all the SBCs that needed race gas to run whatever compression ratios they were running. I was extremely happy with how it ran, even with less than impressive compression.

Two other cars I've used a 268 HE were a 455 T/A with 197 HO heads (8.4 advertised compression ratio), and another 455 in a T/A with 6X, 400 (roughly 9.3 to 1) heads. At 9.3 with the 268 you have to run premium fuel, and you're on the edge of detonation with that combination. This engine should probably have a larger cam to be less prone to detonation, and would probably make more power on the top end, currently runs out of steam at around 5000 RPM.

I sold 3 of the High Energy 260H cams, back then. The low compression 400's all ran great, the owners were thrilled. I sold one or two of the 268H's, got good feebdack, but don't remember what size engines they went in.
THe 268H is very close to the 068, but the 068 has slower opening lobes that might help with octane sensitivity...

[Will]

Originally Posted by 77 TRASHCAN

...
THe 268H is very close to the 068, but the 068 has slower opening lobes that might help with octane sensitivity...

In what way is it "very close?"

Certainly not the lobe centerlines - 068 has 116 LSA with I think either 112 or 114 ICL vs. the Comp with 110LSA and 106 ICL (like just about every Comp shelf grind).

.050" duration on the intake for the Comp is 218, 068 is 212. Comp is a single pattern so same exhaust, 068 is 225.

Rated duration for the Comp is 268, for the 068 is 288/296, but I don't know what lift those are at so might not be the best comparison.

lift for the comp is .454, 068 is .407.

So other than that the .050" duration on the intake side is within 6 degrees of each other, and that they have lobes that push lifters up and down and fit in a Pontiac block, I'm not seeing a whole lot of similarities here.

If I had a low compression engine, I'd definitely want the Comp cam. If I had 10+:1, the 068 would be a better choice for running on pump gas.

[455abody]

I used a Comp XE262 cam is a low comp 400 8.1 with mild porting on 6x heads. I was pleased ran really well. Nice idle as well. Brian