SBC 421 combo advice

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raynman1969
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Re: SBC 421 combo advice

Post by raynman1969 »

Foot braked, left around 2000 rpms , shifted at 6500 and went through the lights at 6700-6800
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Re: SBC 421 combo advice

Post by steve cowan »

hi Ray,
if your car is set up well i believe it would run mid 10s @ 125 -126mph
i understand it is early days and i dont want to sound critical at all about your combo as for myself it is about learning from other people as well.
i looked at your dyno sheet,i would of liked to see where power would be at around 7000rpm
was that a dyno carb you used and what carb did you decide to use when on the track,i ask because the dyno sheet says braswell 900 ??
i would expect if you ran a 50 series drag radial (26'') with a 4.30 rear gear it would rpm at the stripe well over 7000 rpm,the reason i say this is i believe you need to turn the engine rpm 500-1000 past peak on the shift and well past peak at the stripe,if your peak is 6500rpm and you are shifting at 6500 you are leaving plenty on the table as far as power.
i see earlier camking says your cam will peak at 6800rpm and i am sure Mike is correct,my calculations say you need a MCSA area of 2.44'' at 6500rpm and i see the 220 AFR are at 2.18'' at the pushrod,are those heads out of the box ?? are they the competition head ??
i am a big fan of bigger converters as well 5500rpm plus as i have had good results.
Ray,
i hope we can have a good discussion about your combo as you have good parts that need to be optimized for max performance.
steve c
"Pretty don't make power"
raynman1969
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Re: SBC 421 combo advice

Post by raynman1969 »

It was run on the dyno with a BLP carb, street version that flowed 950 but it seemed to be a restriction according to the dyno, pulling 1.8 inches of vacuum. It sent the carb back and they installed a billet main body that flowed 1050. Tires are a street R 325/50/15, diameter is 28.3. Haven’t done any tuning yet just working on the suspension, best sixty foot was 1.56. Another friend of mine was checking a calculator and figuring the da and on a good air day the car should run 10.6 or 7 at 126,127. Haven’t been on the drag strip for years. So knocking the rust out of the driver was a priority, lol. The AFR 220s are the comp version , any advice or ideas are greatly appreciated.
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Re: SBC 421 combo advice

Post by steve cowan »

Ray,
thanks for the clarification on the tyre size as i should of researched better,my bad
makes more sense with the rpm you stated.
the biggest problem we have is trying to tune and run fast when the weather is crap and it just dont work as you know.i stand by my statement on overrunning the engine past peak power but there is alot to experiment with shift points,launch rpm etc,i have been reading a lot of old threads here on short shifting a 3 speed auto 1-2 shift and overrun the 2-3 shift and this is due to gear multiplication etc,very complex subject but worth investigating.
i think you have a great base to work with and the engine looks to make some power and i am not going to sit here and say you need to change this and that as we need to work with and try and optimize what we have,it comes to a point where we all get tired of throwing money at this stuff as you can probably agree.
A good converter should be on the christmas list though,the car will pick up straight away,my streeter @ 3650 pounds picked up 3 tenths going from a 9'' 4000 rpm to a 8'' 5600 converter,i drive my stuff on the street alot and i am not buying into the big converter drama on the street deal,i would have not problem using a 6000 stall on the street if need be.
my cars street manners are exactly the same with both converters.
your car should dip into 1.47 sec 60 ft easily with footbrake but the cars suspension tuning is the key as has been stated and you know that already.
i would be interested in hearing your setup as in shocks,caltracs,leafsprings ? etc
steve c
"Pretty don't make power"
raynman1969
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Re: SBC 421 combo advice

Post by raynman1969 »

I have Smith racecraft bars in the rear with double adj. Qa1 shocks, Smith racecraft control arms and santuff springs with Qa1 drag r shocks, went with a 4200 stalk because of the nos, when I do spray it it will stall higher.
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Re: SBC 421 combo advice

Post by steve cowan »

Looks like you have all the fruit
What is the quickest and fastest the car has been previously?
You could be correct with stall speed and nitrous but my last hot rod that was not the case with converter,stall was very similar.
I ran a single stage 300 shot
460 BBC tunnel ram
Powerglide 5000 stall tranabrake
9 inch 3:9 rear gear
28 x 11 Mt slick
1.25 60ft
5.50 @ 125 mph 1/8 mile
8:90 @ 150 mph 3150pounds with me
Using vp 103 fuel
9:90 - 10:0 @ 135 MPH N/A
With the gas
8000 rpm on the stripe
254 -260 @ 0.050 cam 106 LSA
10.5:1 compression
I tried a different cam with more exhaust duration and wider LSA but didn't develope enough data to give a correct assessment
Not trying to compare anything here, just showing you a combination I ran some years ago, with good results and never had a nitrous failure either.
steve c
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raynman1969
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Re: SBC 421 combo advice

Post by raynman1969 »

New car just finished it midsummer, it weighed 3530 with me in it. I will keep you updated on its progress. Can’t wait to take it back to the track.
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Re: SBC 421 combo advice

Post by steve cowan »

Ray,
Sounds like a sweet deal
Yes I would really enjoy some follow up down the track, good luck and enjoy
steve c
"Pretty don't make power"
raynman1969
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Re: SBC 421 combo advice

Post by raynman1969 »

The Camaro did go 11.00 at 123.4 mph with out the NOS. The car seems to leave fairly decent but seems to flatten out then go again, not a bog by any means but you can visually see in a video that it goes then flattens out then goes again. My big question is how fast should this be with out the NOS.
The engine made 615 hp at 6400 rpm, weighs 3500 lbs with me in it and best 60 foot is a 1.54. I am thinking that the converter is a little tight but will be better when i spray it. Could i be losing too much through the drive train? In the spring i will try the 150hp nos shot and see what happens.
4.30 gear with a turbo 400.
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Re: SBC 421 combo advice

Post by KnightEngines »

Drop the front float level to about .060" below middle of sight glass, check your accel pump plunger travel.
A launch, then mild stumble & go again is usually a light flood or lean spot coming on to the main circuit.
615hp & 3500lb should be well into the 10's & in the high 120's for mph.
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Re: SBC 421 combo advice

Post by GARY C »

If you carb has a rear power valve that could cause the flat spot by uncovering it when it leaves.
Please Note!
THE ABOVE POST IN NO WAY REFLECTS THE VIEWS OF SPEED TALK OR IT'S MEMBERS AND SHOULD BE VIEWED AS ENTERTAINMENT ONLY...Thanks, The Management!
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Re: SBC 421 combo advice

Post by SBC-68-FIREBIRD »

Hey Mate,
Just to give some comparison I run a 68 Firebird with a 421SBC in it. Car weighs 3620 with me in it, Turbo 400, 8" x 5000 stall, 3.73 gears, 275/50/15 MT drag radials. It only makes it to the track a few times per year but goes cruising most weekends.
Engine made 580HP@6000rpm & 550TQ@5000rpm.
Dart Little M - 3.875 stroke - 4.155 bore - 11.6 comp - AFR210 comp heads untouched - Super Victor with plenum work & port matched - 850QFT carb - 246/250@50 on 108LSA hydraulic roller - crappy 1.75" long tube headers with press bends.
It has run quite a few 10.9's & ran one 10.87@122.18mph.
I want to change my headers for a better set & still deciding which way I am going to go but over the years lots of little things have got me some pretty decent improvements - better converter, Calvert shocks, aluminium rims instead of steel, smaller diameter tyre to suit my 3.73 gears, Caltrack adjustments.
I agree with the previous comments about 5000 converters, get a good one & no problems on the street.
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Re: SBC 421 combo advice

Post by raynman1969 »

GARY C wrote: Thu Feb 21, 2019 3:22 am If you carb has a rear power valve that could cause the flat spot by uncovering it when it leaves.
No power valve front or rear.
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Re: SBC 421 combo advice

Post by MadBill »

There's a great video somewhere in the depths of S/T showing the fuel in the rear bowl going way higher than 45°on a hard launch, exposing the jets to air.. Ryan Brown Racing I think...

PS: Most guys would say a primary PV keeps the plugs a lot cleaner.
Felix, qui potuit rerum cognscere causas.

Happy is he who can discover the cause of things.
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Re: SBC 421 combo advice

Post by cjperformance »

MadBill wrote: Sun Feb 24, 2019 6:53 pm There's a great video somewhere in the depths of S/T showing the fuel in the rear bowl going way higher than 45°on a hard launch, exposing the jets to air.. Ryan Brown Racing I think...

PS: Most guys would say a primary PV keeps the plugs a lot cleaner.
Yes in general most certainly and the bores less glassy! Of course all depending on exactly how its tuned and driven/used, i have seen many improperly set up non PV carbs damage bores.
Craig.
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