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423 SBC prediction

General engine tech -- Drag Racing to Circle Track

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BrazilianZ28Camaro
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Re: 423 SBC prediction

Post by BrazilianZ28Camaro » Sun Jul 28, 2019 11:50 pm

BigBro74 wrote:
Sun Jul 28, 2019 11:38 pm
I agree with Diego- something missing. If I had to choose an easy thing to try it would be to use an actual race fuel.
I have never used av gas- I know it has the octane u need, and I know it is probably easier/less expensive for you but if you are turning it pretty hard it may just work better. Could u just get something like CAM 2 up there To try? Maybe I’m out to lunch on this - if so- please disregard ...
You will find something if you work at it—
Jason

BTW- what were the mph? Same? Rpms through the same?
Good call about the fuel Jason. If I remember correctly the 100LL av gas is just 89 octane. The 100 is just the RON number.

OP have you checked the plugs for signs of detonation?
'71 Z28 street strip car
Pump gas All motor SBC 427
3308 lbs-29x10.5 Hoosiers
NEW BEST ET
1.40 60' / 4.05 330' / 6.32@111.25mph

https://www.youtube.com/watch?v=99p13UK ... ture=share

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Re: 423 SBC prediction

Post by BigBro74 » Mon Jul 29, 2019 12:05 am

BrazilianZ28Camaro wrote:
Sun Jul 28, 2019 11:50 pm
BigBro74 wrote:
Sun Jul 28, 2019 11:38 pm
I agree with Diego- something missing. If I had to choose an easy thing to try it would be to use an actual race fuel.
I have never used av gas- I know it has the octane u need, and I know it is probably easier/less expensive for you but if you are turning it pretty hard it may just work better. Could u just get something like CAM 2 up there To try? Maybe I’m out to lunch on this - if so- please disregard ...
You will find something if you work at it—
Jason

BTW- what were the mph? Same? Rpms through the same?
Good call about the fuel Jason. If I remember correctly the 100LL av gas is just 89 octane. The 100 is just the RON number.

OP have you checked the plugs for signs of detonation?
Well that, and I know that race fuels are for higherRPM engines- piston aircraft are generally not a high rpm deal. I see a lot of pump gas builds where they work fine but then they pour in a race fuel and make a bunch of extra power- often without even adjusting the timing...

About 2002 I had built a compression and vacuum limit stock car engine for my “lil Bro” and we ran it off 92 pump gas for half the season. One time We topped it off with race fuel from the track because we had no other gas that night 🙄 (due to logistical issues)and my brother came in after the race and said “ holy crap- I felt that stuff come through the fuel line—-.”
Even though this was a 9:1 engine—-

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Re: 423 SBC prediction

Post by MadBill » Mon Jul 29, 2019 12:15 am

BrazilianZ28Camaro wrote:
Sun Jul 28, 2019 11:50 pm
Good call about the fuel Jason. If I remember correctly the 100LL av gas is just 89 octane. The 100 is just the RON number...
Not so. Per: https://www.aviationpros.com/fbos-tenan ... s-vs-avgas 100LL is equivalent to 100 Motor Octane Number, probably ~ 110 for the Research Octane Number and thus ~ 105 for the pump label value (R+M/2).

"The autogas (MON) octane number is similar to the aviation rating of octane up to 100 octane, according to ASTM D 2700. When you purchase autogas, the octane rating is the average of the RON and MON, (R+M)/2 and the formula is posted on the gasoline dispenser. However, you have no way of knowing if the (MON) octane number meets the requirements of your aircraft engine unless you have documentation or a means to test gasoline octane on-site."
Felix, qui potuit rerum cognscere causas.

Happy is he who can discover the cause of things.

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Re: 423 SBC prediction

Post by BigBro74 » Mon Jul 29, 2019 12:19 am

I was thinking more of the usage/formulation of the fuel rather than octane/ detonation aspect.

When you search “race gas vs about gas” - a lot of differing info——
Last edited by BigBro74 on Mon Jul 29, 2019 12:41 am, edited 1 time in total.

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Re: 423 SBC prediction

Post by prairiehotrodder » Mon Jul 29, 2019 12:32 am

I'm wondering about the intake and the exhuast.

The exhaust is hooker super comp 1.75" headers with 3" exhaust and flowmasters. Always run through the mufflers.

The air cleaner is a tall base K&N with a short 9" dia. element and a breathable lid.

I'm helping a friend with this and hoping to try a few things. I think the fuel is not the problem but we will keep trying stuff.

Brian
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www.therocketshop.blogspot.com

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Re: 423 SBC prediction

Post by BigBro74 » Mon Jul 29, 2019 12:44 am

Simple to remove the exhaust and the air cleaner to test I guess.....

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Re: 423 SBC prediction

Post by 408 Nova » Mon Jul 29, 2019 2:10 am

Are you sure your converter is flashing at 5500? And also, your engine isn't "blowing through" your converter, is it? By that I mean it doesn't have a lot of slippage now with the bigger, more powerful engine?

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Re: 423 SBC prediction

Post by GARY C » Mon Jul 29, 2019 2:40 am

MadBill wrote:
Mon Jul 29, 2019 12:15 am
BrazilianZ28Camaro wrote:
Sun Jul 28, 2019 11:50 pm
Good call about the fuel Jason. If I remember correctly the 100LL av gas is just 89 octane. The 100 is just the RON number...
Not so. Per: https://www.aviationpros.com/fbos-tenan ... s-vs-avgas 100LL is equivalent to 100 Motor Octane Number, probably ~ 110 for the Research Octane Number and thus ~ 105 for the pump label value (R+M/2).

"The autogas (MON) octane number is similar to the aviation rating of octane up to 100 octane, according to ASTM D 2700. When you purchase autogas, the octane rating is the average of the RON and MON, (R+M)/2 and the formula is posted on the gasoline dispenser. However, you have no way of knowing if the (MON) octane number meets the requirements of your aircraft engine unless you have documentation or a means to test gasoline octane on-site."
Min required for that engine, how do you think it would effect timing and power?
VP110, Specific Gravity =0.7050, MON =109, RON =110, (R+M/2) = 109.5
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Re: 423 SBC prediction

Post by BigBro74 » Mon Jul 29, 2019 4:06 am

BigBro74 wrote:
Mon Jul 29, 2019 12:19 am
I was thinking more of the usage/formulation of the fuel rather than octane/ detonation aspect.

When you search “race gas vs about gas” - a lot of differing info——
My autocorrect function was on—- I meant
“Race gas vs AV gas”

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Re: 423 SBC prediction

Post by 6.50camaro » Mon Jul 29, 2019 9:06 am

prairiehotrodder wrote:
Mon Jul 29, 2019 12:32 am
I'm wondering about the intake and the exhuast.

The exhaust is hooker super comp 1.75" headers with 3" exhaust and flowmasters. Always run through the mufflers.

The air cleaner is a tall base K&N with a short 9" dia. element and a breathable lid.

I'm helping a friend with this and hoping to try a few things. I think the fuel is not the problem but we will keep trying stuff.

Brian
IMHO this is your problem . Both ends of the engine are being restricted . My engine combo is very close to this but slightly less 4.165 bore x3.875 stoke flat top pistons, Dart 220 race series 60/40 offset Heads . 11.6 to1 CR, 3° less @.050 intake lobe 4°less @.050 ex. lobe, lift @valve .675 in .645 ex with1.6 in rocker 1.5 ex rocker . the same stall converter , 50 lbs more total weight with fuel and driver . 100LL fuel at the present using a 70's era holley 750 DP carb to slow the car to 6.50 index class . The difference is 1-7/8 x 3-1/2 collector hooker super comp header open with turn downs, and a K&N 14x4 filter . Still have water pump , alt. and PS Pump belt driven. Saturday off the trailer in 90° heat humidity in the high 80's went 1.40-60' 4.12-330' ,6.45 @104+ in the 1/8 , my mph is off 1-2 mph from what it normally was after switching from a 30" tire to a 28.5 tire . Plus the 750 cfm carb is restricting the top end slightly i believe . The car has been 6.31@108 with a 850 holley street hp carb .
I reallly believe a 3.875 stroke small block needs a minimum of 1-7/8 primary for good performance, anything less and you'll be hunting for the lost power . Dan

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Re: 423 SBC prediction

Post by BigBro74 » Mon Jul 29, 2019 9:59 am

If you think the air cleaner is restricting- just put a vacuum gage on it and see what happens when you run it WOT - then take the air cleaner off and run it again and see if the vacuum goes down at wide open. Tape the gage to the dash and film it with your phone or something. The test will be worth a thousand expert opinions—-. As for the headers- do you think going to 1-7/8” over 1- 3/4” will make a big difference with FULL exhaust system? I have not done this test personally......
The fuel thing would be real easy to test also..... especially with one of those performance apps the guys are talking about- just need a country road for all that testing-😉

BTW Race gas vs av gas - http://www.rockettbrand.com/downloads/t ... 0AvGas.pdf

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Re: 423 SBC prediction

Post by prairiehotrodder » Mon Jul 29, 2019 11:02 am

thanks for that article on avgas. I have been using it for 1.5 seasons now. First in a 10-1 CR 540 and now in a 12.9 CR 555 and it has worked awesome. I'm using the 100LL that is died blue. It is convenient to me and cheap at $1.52 per liter. All the dirt bike and snowmobile racers in my area are using it as well. I have not heard anything negative about it until i read that article.
I do not think header primary size is the problem with this motor but i could be wrong. I would be more inclined to think the mufflers or the air cleaner are a restriction. They are easy thing to test. We will keep working at it. Thanks for all the suggestions.
Brian
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www.therocketshop.blogspot.com

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Re: 423 SBC prediction

Post by 6.50camaro » Mon Jul 29, 2019 11:14 am

Really what I'm saying is 1-7/8 open system. If you want or have to run a full system then you need to design and size it to not hinder the performance of the engine . We all have to make compromises at times be it from $ , time , chassis layout or what ever reason . A full system designed for a 383 will not perform at peak for a 423 unless it was over designed to start with . I believe the system he has now is one reason they only saw a .10 time change , along with the air filter.
I have made the change from 1-3/4 headers to 1-7/8 header open system and pickup alot . When i had a 383 in the car with1-3/4 headers and i dropped the 2-1/2"X pipe with no mufflers to 3"x12" header extension i picked up .25 with that alone.
This has been a subject of many threads in the past and I'll say again . Who would build a 600to700 hp big block 427 chevy and try and use 1-3/4 headers on that. Its more displacement and horsepower than engine architecture. Again my opinion .Dan

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Re: 423 SBC prediction

Post by prairiehotrodder » Mon Jul 29, 2019 11:29 am

6.50camaro wrote:
Mon Jul 29, 2019 11:14 am
Really what I'm saying is 1-7/8 open system. If you want or have to run a full system then you need to design and size it to not hinder the performance of the engine . We all have to make compromises at times be it from $ , time , chassis layout or what ever reason . A full system designed for a 383 will not perform at peak for a 423 unless it was over designed to start with . I believe the system he has now is one reason they only saw a .10 time change , along with the air filter.
I have made the change from 1-3/4 headers to 1-7/8 header open system and pickup alot . When i had a 383 in the car with1-3/4 headers and i dropped the 2-1/2"X pipe with no mufflers to 3"x12" header extension i picked up .25 with that alone.
This has been a subject of many threads in the past and I'll say again . Who would build a 600to700 hp big block 427 chevy and try and use 1-3/4 headers on that. Its more displacement and horsepower than engine architecture. Again my opinion .Dan
i value your opinion and i'll mention these things. thanks
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Re: 423 SBC prediction

Post by PRH » Mon Jul 29, 2019 12:32 pm

20+ years ago I built a high CR 406 with AFR 210’s, roller. Vic jr, Etc.

Went in a 65 Chevy II street car.
4.30’s, 9”, glide, 28” tires iirc.

Had 1-3/4x3 headers, 3” pipes into 3” flow masters coming out in front of the rear tires.
Mid-10 second car.
Remove pipes and muffs...... picked up .3 in the 1/4.
Somewhat handy with a die grinder.

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