Octane question?
Thread Starter
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,444
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Octane question?
for a 420 ci with race flowed AFR195 cc Ported superram 58mm. 1 3/4 full
How much compression do you guys run with small type LPE219 cams that have no overlap? Crane has an H-roller with 222/230 112 lc that recomends max of 10.75
In the past I ran near the limit of what Crane had to say and it kept so much trapped presure that I had ping on a level highway at 70 mph at light throttle with 92 octane. Cranking pressure was @ 190 lbs. So in later motors I went to higher overlap to get dynamic pressure down.
What are you guys doing without retarding the ignition to use pump gas
How much compression do you guys run with small type LPE219 cams that have no overlap? Crane has an H-roller with 222/230 112 lc that recomends max of 10.75
In the past I ran near the limit of what Crane had to say and it kept so much trapped presure that I had ping on a level highway at 70 mph at light throttle with 92 octane. Cranking pressure was @ 190 lbs. So in later motors I went to higher overlap to get dynamic pressure down.
What are you guys doing without retarding the ignition to use pump gas
Melting Slicks
Joined: Jun 2001
Posts: 2,429
Likes: 14
From: CA
Re: Octane question? (gkull)
One way to bring down the cranking compression & reduce ping would be to go with a wider LSA, like 114 to 116 deg - if you don't already have the cam yet.
If you have a vac advance dist try adjusting it down (too much vac advance will give part-throttle ping that goes away at WOT)
If you have a vac advance dist try adjusting it down (too much vac advance will give part-throttle ping that goes away at WOT)
Melting Slicks
Joined: Mar 2002
Posts: 3,107
Likes: 126
From: S.L.C. UT
Re: Octane question? (71coupe)
That is almost the same combo my 420 was when I first built it.I had AFR195 competetion package heads with the Crane 222/230 powermax hyd roller cam.
I ran 10.9:1 compression, but I am at 4400 ft (SLC).Even with a miniram it made a ton of torque.It had over 400 rwtq from 1800rpm on up.It peaked at 440 rwtq and 415 rwhp.I don't know what kind of computer you using, but careful tuning should allow you to go to 10.25-10.5:1. The one thing I do to help against pre-detonation is run a real tight quench, about .036-.038
That combo with a Superram is going to be a torque monster.
[Modified by tpi 421 vette, 8:03 PM 10/2/2002]
[Modified by tpi 421 vette, 8:07 PM 10/2/2002]
I ran 10.9:1 compression, but I am at 4400 ft (SLC).Even with a miniram it made a ton of torque.It had over 400 rwtq from 1800rpm on up.It peaked at 440 rwtq and 415 rwhp.I don't know what kind of computer you using, but careful tuning should allow you to go to 10.25-10.5:1. The one thing I do to help against pre-detonation is run a real tight quench, about .036-.038
That combo with a Superram is going to be a torque monster.
[Modified by tpi 421 vette, 8:03 PM 10/2/2002]
[Modified by tpi 421 vette, 8:07 PM 10/2/2002]
Race Director
Joined: Dec 1999
Posts: 10,230
Likes: 885
From: Alexandria, Virginia, USA VA
Re: Octane question? (tpi 421 vette)
also considering limiting the vac advance or going without.
source of alot of light throttle pinging. I ran a 427 with alum heads at 11-1 on pump gas with a Unilite dist. with no vac advance and although gas mileage suffers, no light throttle pinging.
cya.
source of alot of light throttle pinging. I ran a 427 with alum heads at 11-1 on pump gas with a Unilite dist. with no vac advance and although gas mileage suffers, no light throttle pinging.
cya.
Team Owner
Joined: Apr 2000
Posts: 27,818
Likes: 8
From: CT
CR
Mine's 11:1...I've had a time or two(like now) with tuning trouble on the stock ecm. It ran for a LONG TIME on 92 octane and ZERO PING. I'm switching over to a DFI now. A friends 434 LPE(18*heads) SBC runs similar compression, spins it to 67-6800 and NO PING. Tuning obviously is critical.
Le Mans Master
Joined: Jan 2000
Posts: 8,721
Likes: 108
From: Canada
Re: CR (JD 90 383)
I can run fine with 92 octane, no ping (10.5 cmpression). My cam brings on the hp from 3800 - 6800 and at those rpm's it runs fine. I used to run 94 octane but why spend the extra $ when I get no performance increase. Things may change when I swap cams though.
