423 SBC combo help

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prairiehotrodder
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Re: 423 SBC combo help

Post by prairiehotrodder »

thanks guys, this seems like some very valuable info about the heads. How does a guy correct a "to fast" Head ? What does that even mean ?
Thankyou very much.
Brian

Also note - Allen purchased a back half kit with a 4 link and 14 x 32 tires that we were planning to install this winter. If the heads were ported and the car could be geared accordingly.
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Re: 423 SBC combo help

Post by PRH »

i calculate it would make = 507.9 Peak on my Dyno @ 600 RPM/SEC test rate
Larry, thanks for the response.

I guess for me....... I look at that combo of parts...... and just can’t imagine how you could end up with only a nominal 500 STP corrected hp.

As a result of that train of thought...... my mind looks at potential issues with the car..... converter, headers, tuning, etc, that would lead to the numbers “looking” that bad.

I will say this........ before I spent any money on upgrades to the motor in a search for more power...... I’d dyno the motor just as it is, with the headers that are being used on the car........ if for nothing else, as a baseline.

We had a 422 here recently....... easy on parts .630 lift cam, ootb SV, ootb afr220’s, qft 850....... Street use....... made just under 600hp.
9535C7EF-371F-43D0-94EE-2BB2C982E3EF.png
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Re: 423 SBC combo help

Post by 77cruiser »

With an 11-1 AFR what do the plugs look like after a pass?
Jim
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Re: 423 SBC combo help

Post by 6.50camaro »

Brian you correct to small of head by porting giving it more cross section area (csa) iin the correct spots . What it means is your trying to force to much air (cfm) thru to small an area . You can do it but the outcome is increased velocity which then does not like to turn and follow the port contour over the short turn or thru the bowl under the valve . AFR states the minium csa for those heads is 2.34 csa my calculation show on allens motor air speed goes to mach .60 or 690 fps, which is choke at just over 6800 rpm . There is more to it but thats a quick example . Hope it helps .Dan
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Re: 423 SBC combo help

Post by allens »

77cruiser wrote: Wed Aug 19, 2020 10:57 am With an 11-1 AFR what do the plugs look like after a pass?
I don't think we've ever removed them after a single pass, although the last time they were out were slightly black.
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Re: 423 SBC combo help

Post by allens »

Can anyone provide more input on tuning with Avgas 100 octane?

We changed the shortblock (more compression than the old 383), cam and carb all at the same time last year.
AFR has always read rich since then, and quite a ways off what would likely be ideal.

I emptied out all of the avgas last year and ran 10 gallons of C12, and it ran exactly the same times, temps and AFR readings as with the avgas, other than a slightly different smell, there was no noticeable difference.

Last weekend, tried changing 2 sizes smaller on all of the main jets, and picked up what looks like on average a tenth. AFR only changed about .1

Can I safely assume based on the above that the AFR gauge is likely close to correct?

It's been suggested to take out some timing and then remove fuel until the MPH stops increasing, I think we'll likely change to 1.75 headers and remove the mufflers and try to get the carb changed so the AFR is more reasonable and then re-assess possibly changing heads or having some porting done over the winter.

Thanks to everyone for your input so far :)
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Re: 423 SBC combo help

Post by PRH »

If you’re suspicious of the A/F reading...... replace the O2 sensor and see if the readings change.

It’s hard to imagine that combo making its best power at an A/F ratio that would be on the edge of hurting parts.
It went quicker leaning it out....... I’d keep going with that until it slows down.
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Re: 423 SBC combo help

Post by maxracesoftware »

"If O2 Sensors are correct ???? "
then the very last thing you want with an Intake Port that has local areas with way too much FPS velocity
is a "Rich Mixture" :twisted:

a very rich mixture will just cause the Intake Port to go into pumping choke condition sooner in RPM Range
and more severe .
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Re: 423 SBC combo help

Post by 6.50camaro »

I use 100LL avgas . Its was only a slight change for 110 race gas jetting wise for me . Your graph said 10.86 afr. which is about 14% rich from where you want to be 12.8 or so. If 1 jet size is 2% 4 jet sizes is about 1/2 way to where you want to be . If it goes quicker and the mph is icreasing your going in the right direction . Then drop 2 sizes at a time till the mph slows then go back to the jet it had the best mph at .this with timing at about34* which shouldbe safe . Then put in a new set of plugs . The ground strap should have a color change from heat on the bend . If its on the flat near the center electrode add timing .if its nearer the plug body take timing out . Dan
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Re: 423 SBC combo help

Post by prairiehotrodder »

thanks guys, this was a helpful discussion. Wish we would have had more test & tune time this year.
Brian
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Re: 423 SBC combo help

Post by 77cruiser »

Bet you have some back roads, you could get a couple plug readings.
Jim
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Re: 423 SBC combo help

Post by rustbucket79 »

allens wrote: Wed Aug 19, 2020 12:31 pm Can anyone provide more input on tuning with Avgas 100 octane?

We changed the shortblock (more compression than the old 383), cam and carb all at the same time last year.
AFR has always read rich since then, and quite a ways off what would likely be ideal.

I emptied out all of the avgas last year and ran 10 gallons of C12, and it ran exactly the same times, temps and AFR readings as with the avgas, other than a slightly different smell, there was no noticeable difference.

Last weekend, tried changing 2 sizes smaller on all of the main jets, and picked up what looks like on average a tenth. AFR only changed about .1

Can I safely assume based on the above that the AFR gauge is likely close to correct?

It's been suggested to take out some timing and then remove fuel until the MPH stops increasing, I think we'll likely change to 1.75 headers and remove the mufflers and try to get the carb changed so the AFR is more reasonable and then re-assess possibly changing heads or having some porting done over the winter.

Thanks to everyone for your input so far :)
Other than minute jetting differences in different fuel types, rich is rich. There is nothing wrong with doubting your A/F gauge (lead eventually poisons oxygen sensors) and your car has already responded positively will leaner jetting. Continue down that path until the change is negative or not improving. If the gauge reads proper you can trust it, if not you probably need to replace the sensor.

The car didn’t pick up with C 12 because it’s happy with the AV gas. That might change once the carb is tuned. Better fuel doesn’t mean more power.

Run collector extensions with the open headers, bare headers are always down from headers with collector extensions on the dyno.

Big tires are great for marginal tracks, but plan to run slower with them.

Honestly, if the season is over for you now, gather up all your parts and head to the dyno, you’ll learn a bunch plus it’s great fun.

Find out the best timing, jetting, shift points, peak torque and horsepower RPM’s, etc. Oh, and it’s actual corrected and measured torque and horsepower too. (Useful when problem is in the car rather than engine)
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Re: 423 SBC combo help

Post by F-BIRD'88 »

If you are going to tune by a afr guage.. You also need to visually keep track of the leanest and or hottest running cylinders. All 8 don't run the same.
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Re: 423 SBC combo help

Post by maxracesoftware »

i ran your Engine Data thru 3 Simulation programs and you should be able to make
about 614 Peak HP to 620+ Peak HP anywhere at 6600 RPM to 6800 RPM max with your current combo
sorted out .... meaning after problem areas are fixed !

get on a properly calibrated Dyno that has
1]= Fuel Consumed Lbs/Hour readings / data
2]= Air / Fuel Ratio from O2 Sensors
3]= EGT exhaust gas temps
4]= preferribly a Dyno Room setup to where you can run your actual Headers

if its a SuperFlow Dyno ,
tell the Operator to set TQ/HP smoothing Filter to ZERO 0
or disable ProFilter, normally , Filter is Default = 3
but you want to see unfiltered/unsmoothed Data,
not worried about smooth looking Graphs ,
instead looking for dips or peaks in TQ/HP Curves/Data

AFR 227CC CNC'd out-of-box-shape Port Specs :
Intake Port CenterLine Length = 5.488
Exhaust Port CenterLine Length= 2.888

Flow Tests from 3 different pairs of AFR 227CC

1 Pair Ported to 231.0 CC Intake Ports
Flow tested on 4.000 Bore Fixture
Angle-milled + straight cut

other 2 Pairs, Flow tested on 4.125 Bore Fixture
out-the-box shape
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Re: 423 SBC combo help

Post by maxracesoftware »

i ran your Engine Data thru 3 Simulation programs and you should be able to make
about 614 Peak HP to 620+ Peak HP anywhere at 6600 RPM to 6800 RPM max with your current combo
sorted out .... meaning after problem areas are fixed !
i forgot to mention :
in all 3 Engine simulations i used :
285.0 Intake Flow CFM
207.0 Exhaust Flow CFM
... those were approx CFM numbers for "out-the-box" AFR 227CNC'd
at your current Cam's Valve Lifts
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