423 SBC prediction

[prairiehotrodder]

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.

Well that makes sense because on the 383 we didn't gain much from going to the bigger heads and cam. Same exhaust system then and now.
I'm having a tough time getting my friend to give it a try with open headers.

[BigBro74]

Well you can carefully explain why open exhaust may help, and then- if that doesn’t work-(provided your friend is a guy...) take the masculine approach and call
“no balls”
(BTW-Sarc..)
(And If your friend is female- I’ve got nothing—....)

I’m sure you will find your power- stay happy!
J

[prairiehotrodder]

looked at the timeslips. All gains were in the 1/8th. Same mph as the old combo. It runs 6.62 in the 1/8 th. and 10.53 best in the 1/4 at 126 mph.

[BigBro74]

looked at the timeslips. All gains were in the 1/8th. Same mph as the old combo. It runs 6.62 in the 1/8 th. and 10.53 best in the 1/4 at 126 mph.

I guess this makes senses really if it is same cam and heads on a bigger shortblock, and the cam is 4 degrees farther advance than in the other engine. The extra compression is probably helping out otherwise so the top end didn’t drop off—— just rambling....

[econo racer]

Try that 850 carb you have and see if it runs faster. What are you shifting it at? There is at least 3 more tenths there. You just got to find it. And you will

[GARY C]

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.

Well that makes sense because on the 383 we didn't gain much from going to the bigger heads and cam. Same exhaust system then and now.
I'm having a tough time getting my friend to give it a try with open headers.

That may be the Flow Masters them selves, I did a test with my nitrous 382 by adding exhaust to see if it slowed down, it never did.

1 7/8 header with 3.5 collector, straight pipe alone, added bullets, replaced with 3.5 X pipe system no mufflers, added tapered pipe from 3.5 to 3" about 2'. 6" long and Dyno Max muffler then added 3" tail pipes... no difference. The guy that bought it from me ran a 421, with and without tail pipes ran the same ET.
421 no tail pipes.

[prairiehotrodder]

That Nova really boogie's.

We made up some 3" collector extensions to replace the exhaust system at the next race. These will allow my friend to mount his O2 sensor and keep data-logging. We are also going to make a hold down to so he can keep the deep air cleaner base on the carb but try a run without the filter.

The funny thing about all this is that on last Saturday with the brand new engine he was runner-up in pro class and won money for the very first time. The motor was consistent and going rounds and thats why he didn't touch anything as far as trying to make it go faster.

Brian

[67RS502]

1. I think your heads are too small for the cubes, cam and comp.
2. Headers are too small. 1 7/8" is what you need. Pipemax will verify this. (my 420 picked up 1.5mph from 1 3/4" to 1 7/8")
3. Need more info on the exhaust, but flowmasters may not be the best choice especially if theyre not places in the correct place.
4. Tiny air filter is choking it, and that lid is not helping.

If you try open headers you need header extensions, or the test is meaningless.

[prairiehotrodder]

The heads are the fully CNC version of the AFR 227 with the 60/40 valve spacing and offset T&D shaft rockers. They were to big for the 383 now they are to small for the 423 ???

In my experience header tube primary size hasn't made as much difference as i expected. On a 700 hp 540 i was told the 2" tubes were choking it according to pipemax so i went to a set of 2.25" lemons and gained nothing. I'm not saying you are wrong and if we don't find any other solutions that may eventually be worth a try.

We have header extensions that i think are about 14" long.

[67RS502]

I don't really care for afr heads, as they tend to have some velocity issues. I assume they are around 2.25 csa which is on the small side for a 423, especially with the cam, rpm and comp you have, and the car isn't too heavy.
I'm also not the only one who pointed this out.
Heads need to be around 2.5" csa which will end up around 240cc+/-
Header are worth 1.5mph on my deal (20+hp) shifting around 7200, if I remember right it was with a tight verter, so it may be a bit more with an 8"
Don't forget the air filter, its a cheap fix.
Good deal on the header extensions.
Whats the fuel system like in the car?

[BrazilianZ28Camaro]

If your friend have the flowmasters with the funny sound, they're costing you 50-60 RWHP.

Open headers plus extensions will wake up this combo. Keep two eyes on the plugs too.

Good luck.

[prairiehotrodder]

gonna find out this week hopefully.

[BrazilianZ28Camaro]

I don't really care for afr heads, as they tend to have some velocity issues. I assume they are around 2.25 csa which is on the small side for a 423, especially with the cam, rpm and comp you have, and the car isn't too heavy.

The AFR 227s are more like 2.4 CSA at the pinch, should feed this engine at 6500-6800 I believe. They always can be ported.

[prairiehotrodder]

we made up some 16" collector extensions that have an O2 sensor in them and hopefully i can report later tonight on the progress. The owner also thinks the timing pointer is not accurate so that may be an issue. He thinks the timing is way retarded but since he doesn't know for sure he is scared to advance it with this new high CR engine. He bought a piston stop to check the pointer.
He says it starts to easy and runs to smooth for the timing to be right. We were planning to start with the timing at about 36.
Brian

[ClassAct]

we made up some 16" collector extensions that have an O2 sensor in them and hopefully i can report later tonight on the progress. The owner also thinks the timing pointer is not accurate so that may be an issue. He thinks the timing is way retarded but since he doesn't know for sure he is scared to advance it with this new high CR engine. He bought a piston stop to check the pointer.
He says it starts to easy and runs to smooth for the timing to be right. We were planning to start with the timing at about 36.
Brian

The spark plug will tell you when the timing is correct. What the light says is what it says.