Compression VS H.P.
#2596824
12/25/18 05:31 PM
12/25/18 05:31 PM
|
Joined: Aug 2003
Posts: 5,020 new jersey usa
11secdart
OP
master
|
OP
master
Joined: Aug 2003
Posts: 5,020
new jersey usa
|
I am considering lowering the compression in my 363 ( 30over 360 magnum block, W2 heads, 590 lift M/P mech. cam) from 11.5 to 1 to 9.5 to 1 so i can use pump gas. It made 549 hp and 450 tq on the dyno and went 10.60s at 125 in my Dart. 3150 lbs, 4.30 gear, 4800 stall Converter, 904. How much power will i loose? I stopped it down to run 11.50s. will it run high 10s-low 11s? Don't mind losing a little but still want to be able to run 11.40s in bad air.
Last edited by 11secdart; 12/25/18 05:35 PM.
68 Dart 410 / 904 92 D150 original owner 21 Ram 1500 Quad Cab, Big Horn , Hemi ,4x4 23 Audi Q5 16 Honda HRV
|
|
|
Re: Compression VS H.P.
[Re: 11secdart]
#2596918
12/25/18 09:13 PM
12/25/18 09:13 PM
|
Joined: Sep 2014
Posts: 4,457 Washington
madscientist
master
|
master
Joined: Sep 2014
Posts: 4,457
Washington
|
I'd spend my money on a cam from a custom grinder long before I dumped the compression and no way in hell would I ever drop it that far.
It's 2019 and you can easily run that compression ratio on pump gas. The issue isn't your compression ratio. It's the cam. I like the MP cams but I'd say look at a different cam, preferably one that isn't in a catalog or on someone's shelf.
Me? I'd call Jim at Racer Brown and tell him what you are doing and see what he says. I run the same CR as you on pump gas. I don't have detonation issues. I also have a dome. It's not an issue.
I've also used Cam Motion for relatively high CR pump gas stuff and never had an issue.
I'm not a fan of giving up CR when you don't need to.
Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
|
|
|
Re: Compression VS H.P.
[Re: KOS]
#2597069
12/26/18 09:42 AM
12/26/18 09:42 AM
|
Joined: Aug 2003
Posts: 5,020 new jersey usa
11secdart
OP
master
|
OP
master
Joined: Aug 2003
Posts: 5,020
new jersey usa
|
Thanks for great advice guys, Happy Holidays ! Yes I run some N.E. index races.
68 Dart 410 / 904 92 D150 original owner 21 Ram 1500 Quad Cab, Big Horn , Hemi ,4x4 23 Audi Q5 16 Honda HRV
|
|
|
Re: Compression VS H.P.
[Re: 11secdart]
#2597164
12/26/18 03:04 PM
12/26/18 03:04 PM
|
Joined: Jan 2003
Posts: 6,266 Renton Washington
Triple Threat
master
|
master
Joined: Jan 2003
Posts: 6,266
Renton Washington
|
I ran my old Aluminum headed SB @ 11.3:1 on 92 octane pump gas.
If you could get to 10:1 i think you'd be pretty safe as long as you dont get greedy with timing.
-Dustin 67 Dart, 9 second, 392" G3 Hemi 68 Barracuda 340 F/SA
|
|
|
Re: Compression VS H.P.
[Re: 11secdart]
#2597206
12/26/18 04:27 PM
12/26/18 04:27 PM
|
Joined: Jan 2005
Posts: 12,472 Kalispell Mt.
HotRodDave
I Live Here
|
I Live Here
Joined: Jan 2005
Posts: 12,472
Kalispell Mt.
|
I run 11 to 1 with iron magnum heads, some thought into keeping the air cool and some other tricks should be able to make it live just fine on pump premium as is. 9.5 is very low these days.
I am not causing global warming, I am just trying to hold off a impending Ice Age!
|
|
|
Re: Compression VS H.P.
[Re: 11secdart]
#2597241
12/26/18 05:55 PM
12/26/18 05:55 PM
|
Joined: Oct 2007
Posts: 4,217 New York
polyspheric
master
|
master
Joined: Oct 2007
Posts: 4,217
New York
|
Sorry if some of this is obvious? Tighten your quench to .035". Reduce your initial spark lead. Slow up and lengthen your spark advance curve. Consider a high gear only 2-4° spark retard (45 years old, H/T Bill Jenkins) Higher number PV. Step up the mains 1 number. Bigger ATF cooler. Retard the cam 4° (watch your exhaust P-V!).
Boffin Emeritus
|
|
|
Re: Compression VS H.P.
[Re: polyspheric]
#2597276
12/26/18 07:28 PM
12/26/18 07:28 PM
|
Joined: Sep 2014
Posts: 4,457 Washington
madscientist
master
|
master
Joined: Sep 2014
Posts: 4,457
Washington
|
Sorry if some of this is obvious? Tighten your quench to .035". Reduce your initial spark lead. Slow up and lengthen your spark advance curve. Consider a high gear only 2-4° spark retard (45 years old, H/T Bill Jenkins) Higher number PV. Step up the mains 1 number. Bigger ATF cooler. Retard the cam 4° (watch your exhaust P-V!). All these are much better options for the OP than his original idea.
Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
|
|
|
Re: Compression VS H.P.
[Re: 11secdart]
#2597681
12/27/18 06:05 PM
12/27/18 06:05 PM
|
Joined: Aug 2003
Posts: 4,736 On the parachute mount
n20mstr
master
|
master
Joined: Aug 2003
Posts: 4,736
On the parachute mount
|
WHy not consider a head swap? get some magnum type heads to replace the W2 . Also you have a magnum block, get an up to date roller hydraulic cam and you probably be fast enough for 10.00 index....
just a thought, im like that...I rather speed up than slow down lol
Last edited by n20mstr; 12/27/18 06:07 PM.
....BAD A$$ STREET CAR.....
|
|
|
Re: Compression VS H.P.
[Re: 11secdart]
#2597702
12/27/18 07:25 PM
12/27/18 07:25 PM
|
Joined: Aug 2003
Posts: 43,637 Bend,OR USA
Cab_Burge
I Win
|
I Win
Joined: Aug 2003
Posts: 43,637
Bend,OR USA
|
You may loose 30 HP but gain more torque with lower compression on pump gas All the iron headed pump gas motors I've dyno that had less than 10.5 to 1 compression, aluminum head motors also, made more torque than HP by 30+ Ft Lbs. I wouldn't hesitate to run the pump gas with 9.5 to 1 compression ratio as long as you retune the motor for it Torque moves the mass, not HP HP make it MPH
Last edited by Cab_Burge; 12/28/18 12:47 AM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
|
|
|
|
|