What is the biggest I can run without risking detonation/

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Bright red 87 GTA with 350 tuneport. Basic mods such as K&N filter, Flowmasters, Wells MAF, TPIS air foil, Accel 8.8mm plug wires with , Accel distributor cap and rotary buttons.Gutted cat. B&M Shift kit, 100HP shot Nitrous, soon to change over to carburator.

 

Many factors will determine the limits of 92 pump gas. A properly designed engine could go to 12:1. A rule of thumb is only 9:1 at sea level. Higher altitudes can get away with higher compression ratios as can the use of aluminum heads.

Using flat top pistons and modern electronic fuel management systems, it's not uncommon for an engine to be at 10 or 11:1 without experiencing detonation.

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Stephen's racing page

87 IROC-Z Pro ET Bracket Race Car and knocking on the SuperPro ET class
383 stroker (carbed) with double hump cast iron heads and pump gas
LS6 Big Block buildup now in progress

Best results before the engine blew up
Best ET on a time slip: 11.857
Best corrected ET: 11.163
Best MPH on a time slip: 117.87
Best corrected MPH: 126.10
Best 60 foot: 1.662

Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!

Member of the Calgary Drag Racing Association

 

I have heard that 10.0:1 is the highest you can go on 93 octance fuel.

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1987 Chevy Camaro IROC-Z
L98 TPI 350 (5.7L)
TH 700R-4 Transmission with 2.77:1 Rear End

Current Mods: Edelbrock TES 1 5/8" Headers, Hooker Aerochamber Cat-Back System, Performance Resource Chip with 160* Thermostat, Accel Ignition Components, K&N Filters, All Free Mods, Falken ZIEX Z-Rated Tires.

Best ET : 14.3 @ 97mph
(corrected for elevation)

 

87,

I have a 355 at 11:1 and was running 93-94 octane without noticable detonation. I'm guessing a knock module on an ECM might have found a few "pings" here and there, but my old ears couldn't hear anything at 10° BTC idle timing with an old mechanical distributor. I did have a lot of "fun" getting the spark curve right with weights and springs, but once it was dialed in, I could drive it all day long.

It would still run, if I ever got the truck body replaced/repaired.

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Later,
Vader
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"Make Me Bad"
Adobe Acrobat Reader 4.0

 

I think I am going to stick with 10:1 to play it safe. Thanks guys

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Bright red 87 GTA with 350 tuneport. Basic mods such as K&N filter, Flowmasters, Wells MAF, TPIS air foil, Accel 8.8mm plug wires with , Accel distributor cap and rotary buttons.Gutted cat. B&M Shift kit, 100HP shot Nitrous, soon to change over to carburator.

 

I build engines that will run without pre-detonation on 90 octane gas and those occasions when your in the "back country" and 87 is as good as it gets. 9.5-steel head, 10.5-aluminum head has kept me out of trouble (no pissed of clients). If you have muti-point fuel injection, that can be bumped up a full point. The new vettes are running 11/1.

It's always better to error on the conservative side. A half a point wont get you that much extra hp.

Here's an excellent article on gas/octane. Just ignore the Pontiac verbiage.
http://www.wauknet.com/douthitt/pumpgas.htm

 

they have cars out there that are running on 11:1

just depends on the shape of the piston, head, timing, volumetric efficeny( dynamic compression ), and a lot of other things

**** don´t the s2000 use 11:1 and I have seen then running around wiht 6psi on the stock compression

 

It all depends on the cam duration too. The bigger the duration the more fuel you'll get. Im running 11.5:1. See sig for other specs.

 

i think they are probably loosing some hp bc of limited ignition timing..

The hp increase when going from 11 to 12 to 1 is about 2.5percent. Is it worth it?

 

You amaze me, why don't you bring back the very first post.

 

If you want to invest in 6" rods and matching pistons you can go 11:1 easily without detonation probs and use pump gas, too.

 

I am running 10.8:1 on my LT4. that is the stock CR on that motor.

 

Things like reducing heat risers (polishing the combustion chambers), (profiling) and such help reduce the risk of predetonation. Also you can get away with using pump gas on high comp. by using large duration camshafts. The compression is bled off at lower rpms because of the large overlap.

 

So, you're saying that if I run 10.6:1 with a 58cc head and a Comp XE268 cam, I'll be great on 92/93 gas? The only reason I'm going so high is cuz I'm going to be switching to a 64cc head (not sure which ones, yet) and I'm not gonna rebuild the whole engine just for a head change to keep compression up.

 

I think I will try that


and hey whats wrong with finding all the old as hell post man


least it gives us something to talk about that hasn't been done in a while

 

someone was telling me that if i run over a 100 shot (NOS) on my car, that i need to get racing gas. is this true? or will the regular 87 oct. work just fine? (look at sig for motor)

 

87 octane? I can't believe someone would put that in an f-body
Use 91 octane, especially if you've done anything to the car as far as mods

 

why put the higher octane in there if you dno't need it

your not going to get mroe power just by putting in higher octane unless you need it

if you don't need it you are going to have a LOSS of power

 

his sig says 8.5:1 compression.. 87 is just fine for that (why's your compression soo low man? you plan on a supercharger or turbocharger soon?)
i say use 91-92 octane if you plan on using your nitrus oxcide, but otherwise spending the extra few dollars on higher octane won't help you out in the HP/TQ department.

 

i've got aluminum heads and ~9.6 or 9.7:1 CR and my car is fine on 89 gas, runs the same on 92. Never tried 87, though. i think that's asking for trouble

 

if i put any higher octane in.. im jsut wasting my money, there is no differnace at all....


im running 8.5 casue i didnt build the engine, nor did i tell the guy waht to do to it. my friends dad was having it built for him, and he desided he didnt want it so he sold it to me for 800 bucks..thats y its so low. im thinkin bout changing the heads on it in the future, but not to sure.

 

also just as a side note

static compression is not the best way to figure out how much octane you need

dynamic compression is the best way

you cat get a car that runs 16:1 static compression to run on 87 octane if you want

but then again you can make a car that only has 5:1 NEED 100+ octane fuel

all depends on how much air/fuel you get in there


if you take a car that has 100ci per cyl and runs 10:1 that that means if you are pulling in a full 100ci of air and fuel then you have a dynamic 10:1 compression ratio... but most all the tiem you don't do that.... if you only pull in 50ci of air then your static compression is still 10:1 but dynamic compression is now 5:1


bigger cams, better flowing heads, intakes, exhuast, all that help VE which in turn will make a higher dynamic compression


again though shape of the comb chamber, how well the fuel is atomized, even distro of the a/f, proper a/f ratio, ignition timing, as well as various other things can change that also