Highest compression on pump gas?
#1286170
08/16/12 01:03 AM
08/16/12 01:03 AM
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Joined: Mar 2003
Posts: 4,929
Tri-Cities, Washington
VITC_GTX
OP
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OP
master
Joined: Mar 2003
Posts: 4,929
Tri-Cities, Washington
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I imagine this has been asked many times in different forms, iron heads, aluminum heads, w/quench, w/o quench, overlap, etc, but my question is assuming you have no quench and you use crappy 87 octane gas what's the highest compression you can run with stock iron heads and any cam?
I'm putting together a very mild 383 and I don't want any issues with detonation, don't even want to consider having a problem.
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Re: Highest compression on pump gas?
[Re: VITC_GTX]
#1286171
08/16/12 01:50 AM
08/16/12 01:50 AM
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Joined: Mar 2003
Posts: 4,848
Memphis
HemiRick
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Memphis
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You really need to know the cam size and optimize the compression to it.....As cam size has huge effect on when it will ping.
Take care,
Rick
68 Coronet R/T 440 & 68 Charger 528 Hemi,and 5 Challengers! 6 cyl, 318, 360, 383, 451
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Re: Highest compression on pump gas?
[Re: DaytonaTurbo]
#1286174
08/16/12 07:50 AM
08/16/12 07:50 AM
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Joined: Jun 2008
Posts: 3,916
usa
lewtot184
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usa
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Quote:
I don't think I'd want to exceed 8.5.
x3. there is an 8:1 piston out there. the engine will drive fine with this piston but will be very lazy performance wise.
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Re: Highest compression on pump gas?
[Re: lewtot184]
#1286176
08/16/12 12:18 PM
08/16/12 12:18 PM
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Joined: Jan 2003
Posts: 75,017
U.S.S.A.
JohnRR
I Win
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I Win
Joined: Jan 2003
Posts: 75,017
U.S.S.A.
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Quote:
Quote:
I don't think I'd want to exceed 8.5.
x3. there is an 8:1 piston out there. the engine will drive fine with this piston but will be very lazy performance wise.
All the available 383 pistons , except the KB400, are 8:1ish pistons
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Re: Highest compression on pump gas?
[Re: dogdays]
#1286178
08/16/12 08:46 PM
08/16/12 08:46 PM
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Joined: Feb 2003
Posts: 21,318
Manitoba, Canada
DaytonaTurbo
Too Many Posts
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Too Many Posts
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Manitoba, Canada
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Quote:
The Prius engine runs at 13:1 compression on regular gas using this principle. Also Mazda's SkyActiv gasoline engine uses something similar.
No idea on the prius, but I think the mazdas get away with this because they use direct injection so there is no such thing as ping when you're compressing only air. However tough to compare new cars with variable valve timing to our old clunkers.
The idea of using high compression with a cam made to bleed off pressure sounds like it would deliver poor fuel mileage. Even with a late intake valve closing and efi to keep it in check, I just don't see it working all that well. However I would love to read about someone trying it.
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Re: Highest compression on pump gas?
[Re: Blakcharger440]
#1286180
08/16/12 11:36 PM
08/16/12 11:36 PM
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Joined: Feb 2003
Posts: 21,318
Manitoba, Canada
DaytonaTurbo
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Too Many Posts
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Posts: 21,318
Manitoba, Canada
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Quote:
So...what about all the Pump Gas Drag guys that claim to run pump gas with 12.5 compression? Are they running cams with alot of duration?Probably adjusting their timing back and forth all the time?
Pump gas like the pump premium I can buy at 94 octane? Big difference between that and 87! 12.5 with a big cam and 94 could work.
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Re: Highest compression on pump gas?
[Re: DaytonaTurbo]
#1286181
08/17/12 12:02 AM
08/17/12 12:02 AM
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Joined: Jan 2003
Posts: 2,402
Wichita,KS
Blakcharger440
top fuel
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top fuel
Joined: Jan 2003
Posts: 2,402
Wichita,KS
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Quote:
Quote:
So...what about all the Pump Gas Drag guys that claim to run pump gas with 12.5 compression? Are they running cams with alot of duration?Probably adjusting their timing back and forth all the time?
Pump gas like the pump premium I can buy at 94 octane? Big difference between that and 87! 12.5 with a big cam and 94 could work.
Wow!!! The best I can get around here is 91. 
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Re: Highest compression on pump gas?
[Re: DaytonaTurbo]
#1286183
08/17/12 12:48 PM
08/17/12 12:48 PM
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Joined: Jan 2003
Posts: 16,376
dogdays
I Live Here
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I Live Here
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Posts: 16,376
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Back to Mazda. The major thing they did to allow that high compression ratio, up to 14:1 in Europe on premium pump gas, was to decrease the temperature of the incoming air charge.
They do this two ways: first, some fuel is injected on the intake stroke, evaporation cools the incoming air, then more fuel is injected during the compression stroke.
Second, the exhaust gas residual in the chamber was found to have a major heating effect on the intake charge, so they cut it in half by using a 4-2-1 header. There is also some business about the piston top, which features a nice hole right in the center. I did not understand the explanation they gave, something about not heating the top of the piston.
It's fascinating to see developments like this.
R.
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