SBC 421 combo advice

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raynman1969
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SBC 421 combo advice

Post by raynman1969 » Sun Jan 07, 2018 10:49 am

Looking for some combo advice for my build. Engine is going in a 1969 Camaro, auto trans turbo 400 3500-4000 stall approx. This will be street driven very little and drag raced. 3 7/8 stroke x 4.155 bore, flat top pistons looking to run 11 to 11.5 comp. when i was shopping for cylinder heads i was told the cam i purchased would not be correct for my engine. Cam specs 626 626 lift, 262/271 duration at .050 lsa 106 icl 102. I was looking at afr 220 or afr 235's, edelbrock cnc super victor with a holley 950xp. Lemons 1 7/8 headers. I need some advice on this cam, if it will not work nows the time to change before i complete the engine assembly and which heads would people recommend? I plan on running 100 octane on the street and 110 race gas on the strip. One last thing i have a nos kit with up to a 250 hp shot.

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Re: SBC 421 combo advice

Post by bigjoe1 » Sun Jan 07, 2018 11:40 am

I build engines similar to what you are doing. I always use AFR heads, and the cam you have will be just fine-- Put as much rocker ratio as you can get on the intake ONLY.



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Re: SBC 421 combo advice

Post by CamKing » Sun Jan 07, 2018 11:51 am

That cam will make peak HP at about 6,800rpm.
If you go with that cam, you'll need a 4,500 stall.
If you're going to run the NO2 a lot, you'll want a wider LSA to reduce overlap
If you want to stay with your stall, you'll need a shorter duration cam.
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Re: SBC 421 combo advice

Post by raynman1969 » Sun Jan 07, 2018 12:40 pm

bigjoe1 wrote:
Sun Jan 07, 2018 11:40 am
I build engines similar to what you are doing. I always use AFR heads, and the cam you have will be just fine-- Put as much rocker ratio as you can get on the intake ONLY.



JOE SHERMAN RACING
Would you use the 220 or 235's ? So you would recommend 1.6 rockers on the intake and 1.5 exhaust? I appreciate the advice.

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Re: SBC 421 combo advice

Post by bigjoe1 » Sun Jan 07, 2018 1:06 pm

The AFR 220 do not need shaft rockers, but ,the 235 heads will require them-The 235 with shaft rockers will be considerably better, but cost a lot more If you get shafts, use 1.70 on the intakes only--forget the NOS



JHOE SHERMAN RACING

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Re: SBC 421 combo advice

Post by raynman1969 » Sun Jan 07, 2018 1:51 pm

CamKing wrote:
Sun Jan 07, 2018 11:51 am
That cam will make peak HP at about 6,800rpm.
If you go with that cam, you'll need a 4,500 stall.
If you're going to run the NO2 a lot, you'll want a wider LSA to reduce overlap
If you want to stay with your stall, you'll need a shorter duration cam.
I will not be using the NOS much and it will probably be in the lower hp levels (150).
Trying to make 650 hp without the NOS.

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Re: SBC 421 combo advice

Post by rfoll » Sun Jan 07, 2018 1:53 pm

I have a similar combination. My cam is about 5 degrees smaller, and at 10.5:1 compression it runs well on pump gas. I ran a 4400 stall converter for several years, but as my car spends 90 percent at the strip, I went to a 5000+ converter. The car/motor loves it, but is a real nuisance to run on the street. I started out with a mild 350 running 14 flat at 100 mph, and through a progression of changes, I now run high 10s at over 120. Every time I did something to make the car faster at the track, the fun factor on the street took a hit. If you are truly wanting to drive on the street I recommend you back down on the compression, cam, and converter. A 72 cc chamber head with the flat tops will put your compression in the high to mid 10s. It will sound nasty, and In it's mildest form, a 421 will boil the tires for blocks and live a long time. The nitrous can easily make up for any lost performance when you are at the track.
So much to do, so little time...

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Re: SBC 421 combo advice

Post by CamKing » Sun Jan 07, 2018 2:25 pm

raynman1969 wrote:
Sun Jan 07, 2018 1:51 pm
CamKing wrote:
Sun Jan 07, 2018 11:51 am
That cam will make peak HP at about 6,800rpm.
If you go with that cam, you'll need a 4,500 stall.
If you're going to run the NO2 a lot, you'll want a wider LSA to reduce overlap
If you want to stay with your stall, you'll need a shorter duration cam.
I will not be using the NOS much and it will probably be in the lower hp levels (150).
Trying to make 650 hp without the NOS.
That cam will get you close to the HP goal. You'll just need to change your stall speed to at least 4,500.
It won't be very fun to drive on the street, but if you want the HP, you have to deal with the lack of low-end power.
Mike Jones
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Re: SBC 421 combo advice

Post by steve316 » Sun Jan 07, 2018 4:29 pm

You should be able to 650 hp out of that combination. I would want to base line it on a Dyno.

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Re: SBC 421 combo advice

Post by cottonwood green » Sun Jan 07, 2018 4:36 pm

Carl from CNC Blocks N/E did a similar pump gas build and posted the results at chevelle's.com http://www.chevelles.com/forums/13-perf ... sults.html
It made 574 lb ft at 4800 and 606 hp at only 6400.

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Re: SBC 421 combo advice

Post by raynman1969 » Mon Jan 08, 2018 3:31 pm

CamKing wrote:
Sun Jan 07, 2018 11:51 am
That cam will make peak HP at about 6,800rpm.
If you go with that cam, you'll need a 4,500 stall.
If you're going to run the NO2 a lot, you'll want a wider LSA to reduce overlap
If you want to stay with your stall, you'll need a shorter duration cam.
I am not going to use the nitrous alot but just once in awhile, without wider overlap what is the down side?

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Re: SBC 421 combo advice

Post by Newold1 » Mon Jan 08, 2018 3:47 pm

There you go! Good info and advise from two very experienced and successful people here on Speedtalk!

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Re: SBC 421 combo advice

Post by kimosabi » Tue Jan 09, 2018 9:36 am

raynman1969 wrote:
Mon Jan 08, 2018 3:31 pm
CamKing wrote:
Sun Jan 07, 2018 11:51 am
That cam will make peak HP at about 6,800rpm.
If you go with that cam, you'll need a 4,500 stall.
If you're going to run the NO2 a lot, you'll want a wider LSA to reduce overlap
If you want to stay with your stall, you'll need a shorter duration cam.
I am not going to use the nitrous alot but just once in awhile, without wider overlap what is the down side?
Depends what you mean about downside. More nitrous flow right through the combustion and more fire in the exhaust. Some would call that an upside. :D

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Re: SBC 421 combo advice

Post by jmarkaudio » Tue Jan 09, 2018 9:57 am

If you have not bought a carb yet make sure you don't get the Ultra 950 with a 1.600 venturi. The 850 version will actually flow more air, cleaner, or go with a Quick Fuel 1050 4150 annular. Or best a custom 4150...

And with that cam you want more stall, 5000-5500 at least...
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Re: SBC 421 combo advice

Post by rfoll » Tue Jan 09, 2018 1:45 pm

I can tell you from the current setup on my car with a well built 415, you will not like a 5000 rpm converter on the street. At the track it is a serious yahoo.
So much to do, so little time...

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