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Old 04-29-2011, 04:42 PM
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Pump Gas Versus Race Gas / dyno results ??

Hi guys; question at hand about octane and dyno runs; Any input on my situation talked about below will be appreciated!
we're doing a 69 camaro/4spd/3:73 -12bolt; now and just finished a 383 stroker build with the following build list:

-New GM 1pc main roller block bored .030" over
-internally balanced and blueprinted
-The engine was assembled using only ARP studs and bolts
-Eagle forged crank w/eagle forged H-beam rods
-Mahle forged -16 dish pistons 9.8:1 with file fit rings
-melling select 10% higher volume oil pump and matching 3/4" pick-up
-Dart pro1 platinum 200cc heads w/64cc chambers
-Dart dual plane intake port matched to heads
-Holley 650 HP/Street / double pumper / mech. secondaries
-Comp cams pro magnum rocker arms, pushrods, and hydraulic roller lifters
-Cloyes aluminum timing cover with true roller timing chain
-Comp Cams XR282 Roller cam for 87 and up blocks. .510/.520 lift 230* 236* Duration
-Powermaster high torque mini starter
- Holley #HLY-12-327-11 (110 gph) mechanical fuel pump w/bronze tip pushrod
-ATi super damper
-Ram Clutches: #1531 billet steel flywheel 1-pc. inter. bal. to nuetral / 168 th.
-CenterForce II pressure plate #CFT165552 / CF. #383735 (11") disc / CF. #N1716 throwout brg.
-The block, valve covers and intake are powder coated satin black
Note: machine/speed shop; balanced rotating assembly to "0" neutral; and require a (1-pc. internal balanced to "0" nuetral 168 th. flywheel )

Just had it dynoed; full day; made 12 to 15 pulls through out; with changes of jets, adding 1" spacer, timing changes; etc, to get good air-fuel ratios and even hp / torq. curves; finally pulled 443hp and 465 torq. at 4600rpm and that thing sounded a bit "nasty" My only concern is dyno; all timing and adjustments were made with racing fuel and 1 3/4" headers; 38 deg. total timing; I'll be running 92-93 pump gas with 1 5/8" headers; will all the jet changes, adustments and timing be off when I run it in the car? I hope all adjustment aren't a waste; due to high octane fuel not burning completely on a lower comp. pump gas engine. thanks imput appreciated. John sr&jr

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Old 04-29-2011, 05:34 PM
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Quote:
Originally Posted by fastlaners
Hi guys; question at hand about octane and dyno runs; Any input on my situation talked about below will be appreciated!
we're doing a 69 camaro/4spd/3:73 -12bolt; now and just finished a 383 stroker build with the following build list:

-New GM 1pc main roller block bored .030" over
-internally balanced and blueprinted
-The engine was assembled using only ARP studs and bolts
-Eagle forged crank w/eagle forged H-beam rods
-Mahle forged -16 dish pistons 9.8:1 with file fit rings
-melling select 10% higher volume oil pump and matching 3/4" pick-up
-Dart pro1 platinum 200cc heads w/64cc chambers
-Dart dual plane intake port matched to heads
-Holley 650 HP/Street / double pumper / mech. secondaries
-Comp cams pro magnum rocker arms, pushrods, and hydraulic roller lifters
-Cloyes aluminum timing cover with true roller timing chain
-Comp Cams XR282 Roller cam for 87 and up blocks. .510/.520 lift 230* 236* Duration
-Powermaster high torque mini starter
- Holley #HLY-12-327-11 (110 gph) mechanical fuel pump w/bronze tip pushrod
-ATi super damper
-Ram Clutches: #1531 billet steel flywheel 1-pc. inter. bal. to nuetral / 168 th.
-CenterForce II pressure plate #CFT165552 / CF. #383735 (11") disc / CF. #N1716 throwout brg.
-The block, valve covers and intake are powder coated satin black
Note: machine/speed shop; balanced rotating assembly to "0" neutral; and require a (1-pc. internal balanced to "0" nuetral 168 th. flywheel )

Just had it dynoed; full day; made 12 to 15 pulls through out; with changes of jets, adding 1" spacer, timing changes; etc, to get good air-fuel ratios and even hp / torq. curves; finally pulled 443hp and 465 torq. at 4600rpm and that thing sounded a bit "nasty" My only concern is dyno; all timing and adjustments were made with racing fuel and 1 3/4" headers; 38 deg. total timing; I'll be running 92-93 pump gas with 1 5/8" headers; will all the jet changes, adustments and timing be off when I run it in the car? I hope all adjustment aren't a waste; due to high octane fuel not burning completely on a lower comp. pump gas engine. thanks imput appreciated. John sr&jr
I think there will be couple tuning differences with race gas against unleaded pump premium:

1) Race gas will let you get away with more ignition advance, sooner and against a relatively leaner mixture simply because of the octane difference will tolerate more advance and a dryer mixture before detonation occurs. So you'll see more power overall against a lower specific fuel consumption. Pump unleaded will probably want a little less ignition advance, or at least putting it in a little slower. And or a richer mixture, the richer mixture isn't for burning per se, it is there to use the phase change from liquid to gaseous to absorb heat from the combustion process which delays the onset of detonation.

2) Is temperature tolerance to detonation. Race fuel tends to be more stable with changes to temperature in the intake system. That is to say the octane rating doesn't degrade so much with increasing temps as happens with pump fuel (some brands are worse than others). This can push you toward a cool air source for intake air, the termination of exhaust heat under the intake if it is so equipped. Again the reduction of total timing and or slowing the rate of advance, and or richening the mixture.

The root issue is the detonation limit with pump fuel and another point will be how ard the engine has to work against vehicle resistance to movement. That will also be affect by gear ratio which includes the specific ratio of each transmission ratio. This alone will cause tuning differences from those of the dyno as it is set to a test standard which is probably different from the forces the vehicle will dictate.

This is not to say that dyno tuning isn't useful, but it is just another information blip on the road to the best tuning condition. So the changes you make shouldn't have to be major, just fine tuning the integrated result.

Bogie
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Old 04-29-2011, 06:57 PM
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Pump Gas Versus Race Gas / dyno results ??

Thanks for reply; Bogie; some good technical info; so when I run engine in car with pump gas; hopefully I can pull 2 or 3 degrees from 38 deg. high-octane dyno results; and not have to rejet or change other things and loose time and money spent on dyno. thanks Johns
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Old 04-30-2011, 01:39 AM
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You don't mention the compression ratio so unless you have to back the timing down to eliminate detonation with pump gas I doubt you will see any difference at all.

Fuel is fuel, its still gasoline.
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Old 04-30-2011, 08:38 AM
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1.21 giga-watts???!!!!
 
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OP,
Use one of the online compression calculators and get back to us with what compression ratio your engine has.

High Octane gas just "burns" a bit slower and lets you run more advance without detonation. Same amount of BTUs in a gallon of Racer Blue and Shell regular.

Modern cylinder heads are usually happier at less timing than the good old standby 36 degrees. More like 34-36 degrees. Of course, every engine is different.
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Old 04-30-2011, 10:31 AM
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I'm not meaning this as a jab or trying to be a jerk or anything

but, I'm curious as to why you used race gas for the dyno work, if you planned on running the car on pump gas?

did you not realize they had race gas in the tank, or just change your mind, or?

I'm just trying to learn what happened here for the education, as i have never been around any dynos before, and plan on some day getting the chance to tune my motor when its done.
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Old 04-30-2011, 12:51 PM
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1.21 giga-watts???!!!!
 
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"but, I'm curious as to why you used race gas for the dyno work, if you planned on running the car on pump gas?"

Was wondering the same thing myself. Good bench racing info to say "I got a such and such HP engine in my Camaro" but not so good for real driving on the street. He'll get it figured out.
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Old 04-30-2011, 06:43 PM
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dyno and build notes

Hi I didn't relize the operator was using race fuel 112; until after session; he said he uses it so no chance of detonation; that would be impossible to hear in noisey chamber; while running. He has been doing them for a long time and he says I shouldn't have to change anything when I switch to pump gas; I hope he's right! The build specs are listed above in my post; I called cnc motorsports; that supplied and did the balancjng of the rotating assembly in a new 383 stroker block; clearanced to "0" and they advertised 9:8 to 1; with -16 dish and eagle forged rotating assembly package and heads, cam, I metioned in build list; that they have got 9:7 to 1 on similar engine they build complete.
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Old 04-30-2011, 11:51 PM
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Race gas comes in several variety's and should not be compared to each other without regard. Some carry their own oxygen while others are mostly methanol.

Pump gas is very inconsistent and any quality blends made specifically for racing would make a better choice when trying to control variables in a Dyno room.
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