423 SBC prediction

[Steve.k]

Prairiehotrodder did you flow intake? Maybe with the extra cubes your intake is holding you back. 1/10 of a second is likely 30hp gain or so, so that would explain close to cube jump. What rpm was it liking for shift.

[prairiehotrodder]

without the exhaust it went 10.39 at 127.9 last night so that was a gain. Not to scientific yet but will learn more this week.

[Steve.k]

Gaining ground thats good news. I've been running these intakes built for 350ish cubes. Now after moving to 434 really had to open them up.

[PRH]

To revisit the exhaust thing.......

On a 383 Mopar with unported stock heads(230’s cfm) and a .560 lift flat tappet cam, with a RPM intake manifold....... a motor making in the 475hp range.......
Tested back to back on the dyno, going from 1-3/4 x 3 headers to 1-7/8 x 3 headers was worth 13hp, and the peak occurred 300rpm higher.
TQ output was the same.

1-3/4” tubes seems on the small side to me for a 650hp 423” motor.

[Monza355]

Did you verify that the tdc is correct in relation to damper/timing pointer ?

[prairiehotrodder]

changed the cam back to the -2 setting ( 4 retarded from where it has been since we put the new short block in) The -2 is where the cam was in the 383. Now we have more of an apples to apples test. Only difference is the carb and short block. The 383 had a 850 and the 423 has a 1050. Everything else is the same. Also bought a set of 1 7/8 headers but we will leave them for the next test. So far i think the 423 high CR short block has gained a total of -15 - .2 in the quarter. Then maybe another .1 from dropping the exhaust system which may have been more to do with the weight reduction. My current math tells me that going from the 11-1 383 short block to the 13.3-1 423 short block gained around 30 - 40 hp. Basically the cubic inches and nothing for the compression.


this weekend hopefully we will learn more with the cam back to where it was in the 383. Advancing it was a dumb idea considering the car has 4.56 gear, a 5500 stall, weighs around 3000 pounds with a small tire and is drag race only. I expect it to go faster just because of the september air.

Brian

[prairiehotrodder]

the owner put the exhaust back on and went 10.36 so total gains in a fair comparasin was about .25 total. Retarding the timing seemed to help about as much as dropping the exhaust with the cam timing as was before. I would have left the exhaust off but its not my car. Tomorrow he is going to drain the AV GAS out and put in VP C12. Might be interesting to see what that will do. The carb is completely out of the box stock which i would expect to be calibrated better for C12 than for av gas.
Brian

[prairiehotrodder]

C12 race gas made zero difference over avgas other than emptying the wallet by 4 times as much. This is a 13.3 -1 CR motor.

Brian

[prairiehotrodder]

changed the cam in this motor and now we are back to 10.60's at 124. Its a mystery to me why this motor isn't responding and going high 9's by now.

[JES]

What did you change it to ?