In general, how much compression can safely be run on 93 octane? I plan on a 408 build and trying to decide on pistons. Looking at around 11.0:1. Later down the road, I possibly plan on a 200 shot of nitrous to the equation. Although nitrous doesn't really raise the compression. Engine will be carbed with aluminum heads.
Brian
The design of the camshaft can blead of cylinder pressure altering the *dynamic* compression ratio. The efficiency of the combustion chamber also plays a role in how much compression can be ran with pump gas.
I believe there is more to the answer to the question you posed than just blurting out some number because someone's uncle's nephew ran this much compression in his "motor".
2011 Mustang GT, MT-82, 3.73's :
BONE STOCK 12.223@115.18
Points taken. Although neither of the answers I can give unfortunately. I would hate to go out and choose a 9.1:1 and leave alot on the table than if I would have chosen a high 10, low 11 ratio. Although I DON'T want to get stuck with having to use a race/gas mix all the time.Originally Posted by Pure Stock
10.5 is always safe, but i have had 12:1 on pump gas, cam over lap is a big factor, but i have personally seen that on a n2o motor with lower static compression and hefty shot like a 200hp shot, they seem to react better to the spray better than higher comp motors, this is kinda hard to explain, i hope this makes sense... But i would say you would be plenty happy with a mid 10:1 motor and later add some juicey juice... A motor like that will easily propel you into the 9s, of course with the right susp, tranny, etc etc..
2015 A6 Mustang GT that so far has gone 9.48@147 but still the fastest prochargerd S550 in the world aside from Tim Essick's!
www.Rodeheavershotrod.com
Plus is it going to be driven on the street because the higher the compression the less streetable it becomes 10.5 is ideal I think.
Last edited by Balaska347; 02-19-2008 at 10:02 PM.
What exactly do you mean by "streetable"?
Plus is it going to be driven on the street because the higher the compression the less streetable it becomes 10.5 is ideal I think.
That's alot of juice to run with pump on 11. anything. Like previuosly stated combustion chamber design is the most important part of how much compression you can run on any octane. As far as not wanting to have to mix fuel, you can always take timing out, to run straight pump gas. On a pushrod motor it's so quick and easy to do that it seems like your best bet.
ive seen many 10.5 and 10.8 to 1 cars running around i dont see 11 to 1 being a big problem. alot of it is combustion chamber design but i think u will be alright just keep the timing back a little when out cruisin
Nitrous is forced induction. The compression will raise while on the spray.
Seems like 10-10.5:1 is a nice safe number (considering a 200 shot) without worrying about being on the border of detonation while still utilizing enough timing for max power.
A cam in the 240+ dur. @ .050 would be a good idea. Don't forget a tight quench and a piston that is as high as the deck or a little out of the hole.
FWIW I'm running 10.5:1 on factory iron heads and a 230 dur cam..all 1968 stock stuff.
-JOHN
Carburetors and SAE wrenches.................
Buy Made in the USA - It Matters.
Chevy's LS7 is 11:1 so it's obviously possible to have a very streetable 11:1 motor with the right combination of parts. And that motor had to be designed for 91 octane too.
Last edited by Stangman701; 02-20-2008 at 05:12 PM.
2015 Charger Hellcat
2.4" upper pulley, ID1300 injectors, BAP, E85 tune, Cat Delete Pipes, One Piece Drive Shaft, Diff Brace, 305/35/20 555R's for the street and 305/45/18 MT ET Street R's for the track. 9.97@142 Best ET
85 GT
Heads and Cam plus other bolt ons
73 F250
Lifted, 35's, 460 4spd
Real name = Ray
Well since were throwing some numbers out there, a member of this site has a 302 based stroker that has a static compression ratio of approx. 11.29:1, give or take a couple of hundreths. Ingests a steady diet of Sunoco 93 octane. No audible detonation can be detected. Of course, a top-of-the-line cylinder head is employed that has a super-efficient combustion chamber. This is a naturally aspirated example.
2011 Mustang GT, MT-82, 3.73's :
BONE STOCK 12.223@115.18
Tim, you're in luck cause you're going to get to assemble the heads, cam and valvetrain for the 2nd time when Brian brings this up to you. Funny, both engine builds will be for a guy named Brian. Only diference will be one was a 393 and this one will be a 408.
My old GSXR 1000 had 12.?:1 compression and ran on pump 93.
Rob
1 Monte SS. White.
Banned dates
11/27/08
4/25/11
3/28/12
12/1/12
There are more but that's all that was logged!!!
I always wondered this too. I know these sportbikes have really clean innards. As far as their castings go. My cbr had stupid compression and redlined at something like 13k!
I appreciate all the great feedback!
Yeah, they do rev.I always wondered this too. I know these sportbikes have really clean innards. As far as their castings go. My cbr had stupid compression and redlined at something like 13k!
I appreciate all the great feedback!
Rob
1 Monte SS. White.
Banned dates
11/27/08
4/25/11
3/28/12
12/1/12
There are more but that's all that was logged!!!
Bikes can run more compression because of how they are camm'd.
Last edited by somethingclever; 02-21-2008 at 03:29 PM.
-JOHN
Carburetors and SAE wrenches.................
Buy Made in the USA - It Matters.
my rollback had 21:1 and it would not run on pump gas....lol
2015 A6 Mustang GT that so far has gone 9.48@147 but still the fastest prochargerd S550 in the world aside from Tim Essick's!
www.Rodeheavershotrod.com
Yeah,and the lack of rocker arms allowes them to rev to the moon!!!
HAHAHAH and the redline is alos like 2000 rpm. HAHA
Rob
1 Monte SS. White.
Banned dates
11/27/08
4/25/11
3/28/12
12/1/12
There are more but that's all that was logged!!!
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