Moparts
11.5:1 comp with pump gas?
Posted By: mopar dave
11.5:1 comp with pump gas? - 09/23/09 07:48 PM
this has been talked about on here before, but my situation is alittle different. i will be pulling motor and trans soon for the 8" convertor install and thought it would be a good time to have the ports on the indys cleaned up better and shave the heads for more compression. i have a 408 with indy 360-1 heads with CP dish pistons that are ceramic coated on top and a solid roller cam 258/264@50-.650/.650 on a 108 and 45* of overlap.
if i shave the heads .030" and use a .035" gasket this with give 11.5:1 compression, but do you think i will still be able to use pump gas?
what would be the limit on pump gas with this combo? thanks
Posted By: BobR
Re: 11.5:1 comp with pump gas? - 09/23/09 08:28 PM
Quote:
this has been talked about on here before, but my situation is alittle different. i will be pulling motor and trans soon for the 8" convertor install and thought it would be a good time to have the ports on the indys cleaned up better and shave the heads for more compression. i have a 408 with indy 360-1 heads with CP dish pistons that are ceramic coated on top and a solid roller cam 258/264@50-.650/.650 on a 108 and 45* of overlap.
if i shave the heads .030" and use a .035" gasket this with give 11.5:1 compression, but do you think i will still be able to use pump gas?
what would be the limit on pump gas with this combo? thanks
Detonation can be a silent killer. I wouldn't.
Posted By: rt66jim
Re: 11.5:1 comp with pump gas? - 09/23/09 08:34 PM
My 416 has 72cc W2's Wiseco flattops with 5cc valve reliefs. Calculators figure it at 11.2. It will run on pump gas if you pull the timing back to 30*. It has 185 lbs of cranking compression. Jim
Posted By: Dragula
Re: 11.5:1 comp with pump gas? - 09/23/09 08:40 PM
I run 11.6:1 on the street with pump gas in my hemi and have never had an issue. I run 50/50 race gas when at the track. There is a discussion thread about quench and cranking pressure that can tell you where the sweet spot is if you do a search. I keep a good eye on the tune-up just because of the compression I run, but I would rather have the horse power than not have it. The pistons were the same price either way.
Posted By: emarine01
Re: 11.5:1 comp with pump gas? - 09/23/09 08:43 PM
I think you are real close, eather way ya need to take cranking compression and find what #s you make with that cam, it seems 175-180psi is the upper limit, a lot depends on fuel type and quench, with 12 to 1 and a long duration cam we made 185 psi and ran pump 93 just moving the truck around the shop and yard , we went race fuel under load, same motor with a smaller roller 260@ .50 makes 220 psi so no 93 anymore
Posted By: Big B
Re: 11.5:1 comp with pump gas? - 09/23/09 08:50 PM
I've been running a 493/440 with 12.4:1 compresion for 4 years. Run the hell out of it. It's all about the cam. I have 266/271@.050
Here's the dyno sheet
Posted By: rt66jim
Re: 11.5:1 comp with pump gas? - 09/23/09 09:17 PM
Quote:
I've been running a 493/440 with 12.4:1 compresion for 4 years. Run the hell out of it. It's all about the cam. I have 266/271@.050
Here's the dyno sheet
What heads are on that motor?
Posted By: Von
Re: 11.5:1 comp with pump gas? - 09/23/09 09:22 PM
IMO, I think you will be fine.
I have no quench at all (open chamber heads, .045 gasket, .005 out of the hole), compression comes out to 10.5. Cam is 259/259 duration at .050.
I ran it on pump 91 for a year and a half, without any known issues.
My cranking compression is only 145-150PSI.
Posted By: Dodgem
Re: 11.5:1 comp with pump gas? - 09/23/09 09:26 PM
A good test will be to go to the garage and warm up a bit pull all the plugs and the carb (I like to do it this way) and do a compression test to get an idea where you are cranking now??
Posted By: Big B
Re: 11.5:1 comp with pump gas? - 09/23/09 10:15 PM
It has Indy-1's. Cranking psi is 195
Posted By: mopar dave
Re: 11.5:1 comp with pump gas? - 09/23/09 10:28 PM
heads are indy 360-1's with .039" quench, 10.75 comp and 190 cranking psi. been running pump gas with it for two seasons now without any problems and no black specks on plugs.
i figure that maybe with an aluminum head with .035" quench and coated piston tops i might get away with pump gas at 11.5 comp. dunno?
Posted By: Anonymous
Re: 11.5:1 comp with pump gas? - 09/23/09 10:31 PM
Quote:
It has Indy-1's. Cranking psi is 195
if those are the actual #'s, you'll want a different cam. more static compression will just increase the cranking psi out of sight for pump gas.
Posted By: Bob_Coomer
Re: 11.5:1 comp with pump gas? - 09/23/09 10:52 PM
What gains are to be had on raising compression, only to pull timing out to compensate for too low a octane fuel rating?
Yes it will run on pump gas after timing changes...
IMO this combo will be counter productive, and wont be optimal..
I wouldnt bother with shaving the heads..
I would rather run optimal timing with a half point to a point less in compression, than run the compression up there and pull timing out, and fight detonation.
Have you thought about E85 which is a pump fuel?
Posted By: Blakcharger440
Re: 11.5:1 comp with pump gas? - 09/23/09 11:01 PM
Quote:
I've been running a 493/440 with 12.4:1 compresion for 4 years. Run the hell out of it. It's all about the cam. I have 266/271@.050
Here's the dyno sheet
So what are the cam specs you are using to run 12.4:1 compression? 
And are you referring to 91 or 93 at the pump? The best gas they sell around here is 91 or else you buy race gas.
Posted By: mopar dave
Re: 11.5:1 comp with pump gas? - 09/23/09 11:11 PM
i'm currently using sunoco ultra 93. what size cam would i have to step up to? how much overlap?
Posted By: 440Jim
Re: 11.5:1 comp with pump gas? - 09/23/09 11:37 PM
Dave,
There are no guarantees. But if I was going to increase your CR, I would add more duration to the cam at the same time.
Posted By: mopar dave
Re: 11.5:1 comp with pump gas? - 09/23/09 11:57 PM
ok, but what size should i be looking at? 268/274@50 on 108? this would be 10* more than i currently have. give me some ideas.
Posted By: mopar dave
Re: 11.5:1 comp with pump gas? - 09/24/09 12:58 AM
i just figure while the engines out it will be a good opertunity to increase compression to get a few more ftlb of torque. if i cant do it with pump gas i'll just have to mix it.
Posted By: Dodgem
Re: 11.5:1 comp with pump gas? - 09/24/09 02:01 AM
Quote:
ok, but what size should i be looking at? 268/274@50 on 108? this would be 10* more than i currently have. give me some ideas.
that would probably be the ticket but may need a 4800 stall
or somewhere in between 264/270 ish??
Posted By: Big B
Re: 11.5:1 comp with pump gas? - 09/24/09 02:26 AM
I use 93 octane
The cam is a Comp solid roller
266/271@50. 112 lobe sep 108 centerline
.680 lift
Pro-charger and fuel injection next
Posted By: Ian
Re: 11.5:1 comp with pump gas? - 09/24/09 03:00 AM
dave if ya machine the heads ,dont forget your intake and push rod holes if got the fat push rods as well ,have ya had it to the track again ,i was thinking the same dave with mine ,bigger cam 272/278 roller 12.1 comp but i said stuff it all and turned the bottle on now i have all the power that i can handle at the track and a car that runs pump on the street and your combo is perfect for nos ,dont even change ya converter and run good fuel at the track and run nines and drive on the street and run 10,s on pump that is sweet in any language . ian
Posted By: mopar dave
Re: 11.5:1 comp with pump gas? - 09/24/09 08:02 PM
the 8" PTC convertor is 4800-5000.
ian, are you sprayin your small block now?
best time so far is an
11.10@123 with a tight convertor. heres some vids.
http://www.youtube.com/watch?v=H-ONEEn5W1chttp://www.youtube.com/watch?v=-LRu0y0HE40http://www.youtube.com/watch?v=OX2Hyge2BP8 first two are with flowmaster 44's and last is with borlas. broke a ball joint on last one also.
Posted By: Ian
Re: 11.5:1 comp with pump gas? - 09/25/09 04:01 AM
your vids show 124 mph thats 10.70-80 what was ya 60 ,s ft do a couple meetings testing ,try taking 2 jet sizes out and play with the timming and tyre presure i picked up 3 mph play with dizzy , jets, the vids i got shows aspirated pass b4 changes then/after changes also took radials off an ran slicks 3rd vid is nos with radials and 4th is nos with slicks
[url=http://www.youtube.com/watch?v=tydI5eF2SXE]http://www.youtube.com/watch?v=tydI5eF2SXE[/url]
[url=http://www.youtube.com/watch?v=PVCrT5G4HIw]http://www.youtube.com/watch?v=PVCrT5G4HIw[/url]
[url=http://www.youtube.com
http://www.youtube.com/watch?v=K11m8i6w6...9hDeKyvXU[/url]
Posted By: b1dartsport
Re: 11.5:1 comp with pump gas? - 09/25/09 04:14 AM
I'm running 11.4 CR with Indy 360-2 230 cc heads, combustion chambers are 65cc. Its set up with zero deck with a 0.40 gasket & JE flat tops. The cam is 260/266 @.050 .675/.675 lift, 108 installed at 104. I run it on the street with 93 pump, at the track with a 50/50 mixture of 101 & 93 just to be on the safe side. So far plugs look good & no problems.
Posted By: Ian
Re: 11.5:1 comp with pump gas? - 09/25/09 04:42 AM
Quote:
I'm running 11.4 CR with Indy 360-2 230 cc heads, combustion chambers are 65cc. Its set up with zero deck with a 0.40 gasket & JE flat tops. The cam is 260/266 @.050 .675/.675 lift, 108 installed at 104. I run it on the street with 93 pump, at the track with a 50/50 mixture of 101 & 93 just to be on the safe side. So far plugs look good & no problems.
looks like a nice pump gas combo what does she weigh and what times are you getting out of her thanks
Posted By: b1dartsport
Re: 11.5:1 comp with pump gas? - 09/25/09 05:03 AM
Car is a '73 dart sport. 3080# with me in it. Dana with 4.56 & 29.5 Hoosiers. Cal Traks,BG Racing 904, 8" A-1 vert flashes at 5200, Ported Indy intake with 1050 race Demon. Restoblock at 4.030, callies 4.00 dragonslayer & h-beams (408). Car has less than 200 street miles, has only been to 2 test & tunes. Best time so far was 9.87 at 136.53 with a 1.39 60ft & I think it was running fat.
Posted By: Ian
Re: 11.5:1 comp with pump gas? - 09/25/09 05:27 AM
thats one bad small block tuff azz well done .
Posted By: mopar dave
Re: 11.5:1 comp with pump gas? - 09/25/09 12:22 PM
ian, my best 60 was a 1.63, thats the reason for the vert change.
b1dartsport, nice combo, looks like its workin.
Posted By: Anonymous
Re: 11.5:1 comp with pump gas? - 09/25/09 12:27 PM
My 416 had 11.9 to 1 compression it ran just fine on 93 pump gas..
Posted By: mopar dave
Re: 11.5:1 comp with pump gas? - 09/25/09 01:42 PM
what does your combo look like 340srule?
i'm thinking with an aluminum head, coated piston tops and .035" quench 11.5 should work. i was trying to get an idea how far i could go or wheres the limit, because i want to go there on pump gas.
Posted By: b1dartsport
Re: 11.5:1 comp with pump gas? - 09/25/09 04:20 PM
Dave,make sure you do a good job of getting rid of edges & angles on your pistons. I used a Dremel with a light grit stone to get rid of any edges on valve reliefs & put a very slight radius on edges of pistons. Followed this up with a good polish with 1200 grit sandpaper. If I were you, I would also consider going to a flat top instead of cutting those heads. In my experience I have always seemed to get very good performance out of lower compression race combos using flat tops. I know money is an issue here, but in the long run those heads are very expensive & I think you will be limiting your future options. Good luck with whatever you decide, let us know what the end result is. Randy
Posted By: mopar dave
Re: 11.5:1 comp with pump gas? - 09/25/09 04:56 PM
thanks for the info. i'v got $800 into the CP dish pistons plus the coating, so i will be using those. as far as shaving the heads, indy says .100" max. i will be shaving .030 to make a 60cc chamber. i'll let ya know the results.
Posted By: BBR
Re: 11.5:1 comp with pump gas? - 09/25/09 05:06 PM
Your elevation above sea level plays a big part in what CR you can get away with.
Posted By: Ian
Re: 11.5:1 comp with pump gas? - 09/25/09 05:38 PM
dave stuffed up me post go to youtube and search ap6 angree seemed like you are spinning out of the hole ,in one of ya vids i can here your car spinning shifting to second for a bit ,not trying to talk ya out of anything mate just just play some more before pullin it down ,i was told 080 th for 1 pint of comp good luck
Posted By: mopar dave
Re: 11.5:1 comp with pump gas? - 09/25/09 05:57 PM
ian, if i shave off .30" it will get me 3/4 of a point, so .040" may get one full point.
Posted By: Ian
Re: 11.5:1 comp with pump gas? - 09/25/09 06:08 PM
dave just double check ryan told me this To gain a point? You'll need to probably take around .080" at least off the heads. Usually can't take that much off an INDY head, the seat depth is too shallow.my heads are cnc-1
Posted By: mopar dave
Re: 11.5:1 comp with pump gas? - 09/25/09 08:04 PM
ok ian, but why .080", indy days .006" off = 1cc reduction. i have 65cc and need to get to 60cc to get 11.5:1 comp.