Performance Difference between 8.3:1 & 9.6:1 compression in a 454 - Chevelle Tech

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post #1 of 31 (permalink) Old Jan 5th, 10, 4:26 PM Thread Starter
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Ben
 
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Question Performance Difference between 8.3:1 & 9.6:1 compression in a 454

Doing some contemplation with my Low compression 454 build...

The motor came with stock 781 heads on it... Haven't CC'd them yet so for now we'll assume ~119cc

Contemplating trading for a set of 390 98cc heads.

With this engine setup:

454, 4.370 bore, 4" stroke
Flattop pistons (.080 over) eyebrow valve reliefs)
~.022 DITH
.02 shim head gasket
Lunati 60203 cam 4degrees advanced

Kettbo estimated the 781's would put it ~8.3:1 comp & with the 390's it would be around 9.6:1

------------

The question is- What would the real world performance difference between them be?
How much HP & Torque would i be giving up staying lower Comp. Can anyone crank out a desktop dyno of the two combos so i can see what the differences look like?

idea is that down the road a year or two if i rebuild this motor and change the pistons i might be glad i kept the 781's. A full go through is not in the budget now, and see no reason the motor can't go back together with shim headgaskets & performance cam and be enough to make me happy for a while. Plus it would be nice to run cheap gas in it... However as i said, if the performance difference is significant, then to hell with the cost of gas

Thoughts?

EDIT: Additional

Quote:
Originally Posted by Mike View Post
Couple ???
Carb & intake?
Exhaust ?
Cam's 4°'s over the ground in 4°'s ?
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For cam advance this is what was recommended:
Quote:
Originally Posted by FRYNTYR View Post
X2 on the 60203. Run it on a 103-105 ICL and it'll rip
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post #2 of 31 (permalink) Old Jan 5th, 10, 4:32 PM
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Re: Performance Difference between 8.3:1 & 9.6:1 compression in a 454

Couple ???
Carb & intake?
Exhaust ?
Cam's 4°'s over the ground in 4°'s ?

Rough guestimate is 404hp vs 412 hp @ 4500 & 540tq vs 566 tq @ 2500
Used 750 carb ,dual plane and headers w/muffler's.
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post #3 of 31 (permalink) Old Jan 5th, 10, 4:42 PM Thread Starter
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Re: Performance Difference between 8.3:1 & 9.6:1 compression in a 454

added some more detail to the bottom of my first post...
I'm not really up on the whole cam advance/ICL thing- just posted what Darryl recommended for me..
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post #4 of 31 (permalink) Old Jan 5th, 10, 4:50 PM
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Re: Performance Difference between 8.3:1 & 9.6:1 compression in a 454

OK 3°'s over the 4° already there.
Changed carb ,now get 401/405hp and 541/566tq
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post #5 of 31 (permalink) Old Jan 5th, 10, 4:58 PM
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Re: Performance Difference between 8.3:1 & 9.6:1 compression in a 454

It appears you may be better off with the lower compression engine for now, and as you said later on you can go through the bottom end and up the compression a bit to add onto what you already have. Sounds like an interesting build though, keep us up to date on it!
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post #6 of 31 (permalink) Old Jan 5th, 10, 5:12 PM Thread Starter
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Re: Performance Difference between 8.3:1 & 9.6:1 compression in a 454

I'm surprised the HP peak is only at 4500... sure looks to be a torque monster though...

Just for kicks... what would the HP & toruqe be if it had a domed piston in it- putting it closer to 10.1:1 comp

Also for kicks, 60204 Lunati cam

Thanks for punching this stuff in for me!

Last edited by RAMBO; Jan 5th, 10 at 5:35 PM.
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post #7 of 31 (permalink) Old Jan 5th, 10, 6:15 PM
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Re: Performance Difference between 8.3:1 & 9.6:1 compression in a 454

Rambo, I had the 60204 cam with 10.5:1 compression and my power peak was at 5600 if I recall correctly. I'll check the dyno sheet when I get home.

1968 Camino Custom
468, TKO600, 3.73:1

Pic of Car: http://i52.photobucket.com/albums/g3...5/DSCN0827.jpg
Pic of 468:http://i52.photobucket.com/albums/g3...5/IMG_0233.jpg

1966 Triple Black Chevelle
327, TKO600, EFI, 4.11:1

Pic of Car: http://i52.photobucket.com/albums/g3...5/DSCN1706.jpg
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post #8 of 31 (permalink) Old Jan 5th, 10, 6:22 PM
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Re: Performance Difference between 8.3:1 & 9.6:1 compression in a 454

Quote:
Originally Posted by RAMBO View Post
I'm surprised the HP peak is only at 4500... sure looks to be a torque monster though...

Just for kicks... what would the HP & toruqe be if it had a domed piston in it- putting it closer to 10.1:1 comp

Also for kicks, 60204 Lunati cam

Thanks for punching this stuff in for me!
W/781's it's 467hp @5000 & 565tq @2500
That's w/cam at 4°'s.
W/your additional 3°'s it's 450hp @5000 & 568tq @2500.
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post #9 of 31 (permalink) Old Jan 5th, 10, 6:42 PM Thread Starter
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Re: Performance Difference between 8.3:1 & 9.6:1 compression in a 454

Quote:
Originally Posted by Mike View Post
W/781's it's 467hp @5000 & 565tq @2500
That's w/cam at 4°'s.
W/your additional 3°'s it's 450hp @5000 & 568tq @2500.
is that the 60204 cam or with the domed pistons?
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post #10 of 31 (permalink) Old Jan 5th, 10, 6:43 PM
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Re: Performance Difference between 8.3:1 & 9.6:1 compression in a 454

different cam & c/r.
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post #11 of 31 (permalink) Old Jan 5th, 10, 6:44 PM Thread Starter
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Re: Performance Difference between 8.3:1 & 9.6:1 compression in a 454

Quote:
Originally Posted by Mike View Post
different cam & c/r.
can you show me the cam with the lower comps?
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post #12 of 31 (permalink) Old Jan 5th, 10, 8:14 PM
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Re: Performance Difference between 8.3:1 & 9.6:1 compression in a 454

With your numbers and the 781's, DynoSim came up with 8.47 to 1 compression. 60203 cam made 408 HP @ 5000 and 504 TQ @ 3500. 60204 cam made 420 HP @ 5000 and 486 TQ @ 4000.

With the 390's it came up with 9.92 to 1 compression, which seems high but with the big bore it could be right. 60203 cam made 441 HP @ 5000 and 537 TQ @ 3500. 60204 cam made 449 HP @ 5000 and 516 TQ @ 4000.

Just for fun either heads (don't have different flow numbers) with 2.19/1.88 valves and 10.5 to 1 compression came in at 495 HP @ 5500 and 540 TQ @ 4000 with the 60204.
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post #13 of 31 (permalink) Old Jan 5th, 10, 10:52 PM
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Re: Performance Difference between 8.3:1 & 9.6:1 compression in a 454

Quote:
Originally Posted by Twins Fan View Post

Just for fun either heads (don't have different flow numbers) with 2.19/1.88 valves and 10.5 to 1 compression came in at 495 HP @ 5500 and 540 TQ @ 4000 with the 60204.
Considering thats basically my combo but my heads are ported and that was just about right on the money.

EDIT: Dyno sheet calculates out 483 hp and 570 ft -lbs assuming 15% loss.

I had 484 RW ft-lbs at 3800RPM and 411RWHP at 5200RPM. Remember you have a couple more cubes on me...

I wonder how my current pistons and cam compare...

1968 Camino Custom
468, TKO600, 3.73:1

Pic of Car: http://i52.photobucket.com/albums/g3...5/DSCN0827.jpg
Pic of 468:http://i52.photobucket.com/albums/g3...5/IMG_0233.jpg

1966 Triple Black Chevelle
327, TKO600, EFI, 4.11:1

Pic of Car: http://i52.photobucket.com/albums/g3...5/DSCN1706.jpg

Last edited by Brettd85; Jan 5th, 10 at 11:13 PM.
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post #14 of 31 (permalink) Old Jan 6th, 10, 12:21 AM Thread Starter
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Re: Performance Difference between 8.3:1 & 9.6:1 compression in a 454

Quote:
Originally Posted by Twins Fan View Post
With your numbers and the 781's, DynoSim came up with 8.47 to 1 compression. 60203 cam made 408 HP @ 5000 and 504 TQ @ 3500. 60204 cam made 420 HP @ 5000 and 486 TQ @ 4000.

With the 390's it came up with 9.92 to 1 compression, which seems high but with the big bore it could be right. 60203 cam made 441 HP @ 5000 and 537 TQ @ 3500. 60204 cam made 449 HP @ 5000 and 516 TQ @ 4000.

Just for fun either heads (don't have different flow numbers) with 2.19/1.88 valves and 10.5 to 1 compression came in at 495 HP @ 5500 and 540 TQ @ 4000 with the 60204.

Gotta be an error with the 390's... 9.9:1 seems too high of a jump between 119cc heads and 98cc heads.

thanks for running them though!
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post #15 of 31 (permalink) Old Jan 6th, 10, 12:41 AM
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Re: Performance Difference between 8.3:1 & 9.6:1 compression in a 454

Ben, I know you havent CC'd your heads but using stock head specs, haven't you run the compression calcs? That will tell you what it really is... I probably wouldnt run the 60204 if under 9.5:1 compression. I would think a better flowing head is more important than higher compression, I'm sure theres a happy balance there though.

1968 Camino Custom
468, TKO600, 3.73:1

Pic of Car: http://i52.photobucket.com/albums/g3...5/DSCN0827.jpg
Pic of 468:http://i52.photobucket.com/albums/g3...5/IMG_0233.jpg

1966 Triple Black Chevelle
327, TKO600, EFI, 4.11:1

Pic of Car: http://i52.photobucket.com/albums/g3...5/DSCN1706.jpg

Last edited by Brettd85; Jan 6th, 10 at 12:56 AM.
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