[JKrull66]

Changed directions a bit on the now 541. Dropped the compression to 11-1 from 15.6 -1 to aid in head gasket life. Pulled 917 @ 6900 on a mix of C12 and 93 pump gas. Last pull backed off the timing a bit and run just the 93 Pump gas, still pulled a bit over 900 with out issues. Thanks go out to Jim Robertson and Mark Samford out of Abilene Tx for their efforts.
I don't have the sheets to post at this time, may be later in the week, or Jim might chime in.
Engine
IA 2
4.5 Billit Crank
GRP Rods
Diamond Dish pistons
1st gen E head & victor heavily modified By R.A.C.E.
1200 pro Systems
Big Roller cam
Time to put the Antique tags on the 63... Looks kind of stock Heh Heh
John

[Apache Warrior]

How big of a cam with only 11-1 compression?

Do you know the duration @.050?

I'm curious to know because I had a 280@.050 intake duration cam selected for my combo and I am only at 12.5-1 and some have told me I'm way low on compression for that size cam (280/284).

Curious where you're at?

[JKrull66]

Originally Posted by Apache Warrior

How big of a cam with only 11-1 compression?

Do you know the duration @.050?

I'm curious to know because I had a 280@.050 intake duration cam selected for my combo and I am only at 12.5-1 and some have told me I'm way low on compression for that size cam (280/284).

Curious where you're at?

I had good luck with a 280 284 butler cam back in my 462. This cam is bigger than that, a few more degrees on the intake and quite a bit bigger on Exhaust but it is custom for my combo. Call Jim and he can help pick one out for you.
John

[Gach]

Holy chit....917 hp with E-heads pump gas. Congrats. Smart move on droping
The compression...but I don't have to tell you that. Wow! With e-heads. So much for the High Ports being king. LOL

[Apache Warrior]

JKrull - thanks for the PM!

[JKrull66]

Originally Posted by Gach

Holy chit....917 hp with E-heads pump gas. Congrats. Smart move on droping
The compression...but I don't have to tell you that. Wow! With e-heads. So much for the High Ports being king. LOL

Yes gave up a little over 100 HP (1022HP@ 15.6-1) for what should be a durable, low maintenance combo.
John

[GREATGTO]

Robertson does really nice work, hope you enjoy it, very nice setup

[rad400]

Great numbers John.

[Lloyd-TX]

Nice #'s, John!

Smart move going to a lower compression combination. Changing head gaskets every few passes has to SUCK!

If you don't mind, can you post some head flow numbers?

[R 70 Judge]

917hp with 11-1 and E-Heads is pretty damn amazing!

I'm waiting to hear from Patrick at Prosystems on the status of my carb. I sent my 1150 Dominator off to be reworked last week. Once I get it back I think I have just about everything I need to ship my engine off to Jim for machining, assembly, and dyno


With results like this I better hurry before the line for a RACE engine gets too long

[JKrull66]

Originally Posted by Lloyd-TX

Nice #'s, John!

Smart move going to a lower compression combination. Changing head gaskets every few passes has to SUCK!

If you don't mind, can you post some head flow numbers?

Sent you a PM.

[bankbook]

Thats one hell of a motor. Smart move in the end making it last longer.

[Lloyd-TX]

Originally Posted by JKrull66

Sent you a PM.

Got it.

Thanks, John.

[Gach]

Sucks changing head gaskets every 10-15 runs.

[GREATGTO]

Hmm with only a 1200 cfm carb too, nice!

[GOAT490]

CUBIC HP. NICE!!!!!

PHILLYGOAT

[60man]

Very nice John...after shopping around for C12 today pump gas friendly bigger inch motor sounds good in my book..!! $$$$

[BruceWilkie]

Originally Posted by Apache Warrior

some have told me I'm way low on compression for that size cam (280/284).

At 12.5:1 I dont think so unless you are looking for 5500 rpm shift points and rev limit around 6000


FWIW the intake closing point fully determines the number of degrees you are in compression. 100% valve closed is the only time you have full compression although you DO have considerable cylinder pressure rise before that occurs. This is but one reason why duration at .050" lifter rise is not how you should be judging a cams characteristics.

The .050" numbers are best used for cam timing and checking purposes!!!

A cam with 284 degrees intake duration at .050" cam lift could have an actual valve seat duration from 309 to 324 degrees(typically).

Suppose this 284 at .050 intake lobe is installed with a 106 degree intake centerline. Using the .050 number, the intake closing is 68 deg ABDC. Yet the valve is still open .075" (1.5 rocker) to .085" (1.7 rocker). Obviously still open, you are NOT in full compression the next 112 degrees btdc.

If seat time duration is 309 degrees then the intake is sealed closed at 80.5 degrees abdc giving you 99.5 degrees of 100% compression.

If Seat time duration is 324 the intake closes at 88 deg atdc. You are only going to have 100% compression for 92degrees.

Advancing the cam x degrees closes the valve the same number of degrees sooner for a equal degree gain in compression duration. Retarding would be a compression duration loss.

Higher engine speeds raise dynamic compression(but dynamic cant exceed static NA) and higher speed also allows inertia to fill the cylinder more beyond bdc than it would at lower speed. This creates a denser fill that usually more than offsets the compression loss. Regardless the cam with 309 seat duration and 284 at .050 is likely to have more power through the mid range and up than with 324 degrees seat duration and 284 at .050 duration. More often than not the 309/284 indicates more area through the valve lift curve and more power everywhere compared to a cam with the 324/284 numbers same net valve lift.

Duration and timing points of your intake lobe greatly affect the rpm band where it makes power. Compression greatly determines how much power and has minor affect to the rpm band where it makes power.

LSA and ICL are also best used for checking and reference. LSA is the COINCIDENTAL centerline of the intake/exhaust timing points. ICL is the COINCIDENTAL centerline of the intake open/close points.

Its the actual TIMING POINTS, AMOUNT of VALVE lift and RATE of VALVE lift combined with THRU-FLOW capabilities of your engine that matter. Cylinder heads and stroke are the big influences on actual cam requirements.

BACK TO TOPIC

John,
Thats not a bad trade off at all. 93 octane is sure cheaper than race gas. The other option would have been cheaper E85 and only drop compression 2 points for less power loss yet still improve reliability vs 15.6 compression and race gas. Of course if you street drive alot the e85 costs more in the long run than 93. Tough decision for sure.(I'm in that decision mode with my turbo project. Its available locally and cheap as regular 87. In my case its definately going to be less detonation/preignition prone if I run E85)

I suspect adding a tid of spray to get your 105 hp back it would still be more reliable than the 15.6 compression.

[JKrull66]

Spray? Who said anything about spray...

May be someday, This will get me going for now... Just because I have a plate and bottles in the shed doesn't mean I don't have the will power not to use it!

[Dragncar]

Nice numbers Krull.
Gach, the 937 HP on 93 octane High Port engine is still king of the Pontiac pump gas dyno wars, but you already know that.
And I think it was the same guy, Robertson who did the head work on both engines. The man knows a thing or two.