421 SBC - something holding it back at the track !

[rustbucket79]

The dyno graph shows me a happy little engine. Springs are fine (above 6300 is unknown) carb is fine. Your smaller headers might have actually improved your track times. Dropping your exhaust might help, you'll only know after you try it. The car looks good on the track. You should try jetting up, and if it falls off try going leaner. Try 2 numbers different both front and back. Exhaust on and off can require different jetting too.

[rustbucket79]

Corrrected engine dyno numbers, however relevant for comparison to other dynos, can lead to disappointment on track when there is a big correction. We are routinely 8 percent in the summer months.

[af2]

Your cam is not the problem & the heads are not either. The the intake track size is the reason for the short spread between pt & php. You have to make up your mind if you want to throw money at it or test & tune. For the dyno hp your car is performing in the ball park where it should be.

So wrong in so many ways!

[SBC-68-FIREBIRD]

Am happy with it, just want to test n tune, jetting, Caltrack set up, exhaust, tyre pressures, gear shifts, all the little things.

[F-BIRD'88]

Corrrected engine dyno numbers, however relevant for comparison to other dynos, can lead to disappointment on track when there is a big correction. We are routinely 8 percent in the summer months.

What he said.

[F-BIRD'88]

Going off memory here but I am sure it was the 8019 upgrade I have.
155 seat.
Max lift .650
Cant remember open but am sure it was some around the 400-450 mark.

Consider a-b testing with solid roller lifters (lash set tight) to check confirm high rpm hyd lifter perf.
Would also allow 1.65/1.6 ratio rockers for a bit more net flow.. Ya the cam is small a bit.

With a 5000 stall try moving the cam to straight up 108-108 centers

[levisnteeshirt]

I would go 268/274 @050 on a 108 -109 solid roller , and go up on converter if you need it , may not

[kimosabi]

Probably suggested before but get a custom cam grind from Mike Jones or Straub. It didnt fly like it should. Soften the rear and transbrake it.

[CamKing]

With a 5000 stall try moving the cam to straight up 108-108 centers

That's a good idea, and doesn't cost anything. If it picks up, you know you need a bigger cam.

[F-BIRD'88]

With a 5000 stall try moving the cam to straight up 108-108 centers

That's a good idea, and doesn't cost anything. If it picks up, you know you need a bigger cam.

What he said. If you do go down that road let CamKing spec you a new cam for this.
Then buy it..... You got a lot of room to play on this to go faster.

[67RS502]

you've got a variety of responses.
your mph is showing loss of power, even with different gears and stalls it should mph better.
Since my 420 ( and my car) is similar to your set up, heres the issues I see with your setup:
1. Heads... those heads are just too small, pinch is around 2.1", you need around 2.4-2.5" csa, have them ported! this will be worth a ton of power.
2. Cam is on the small side, which will limit power and rpm, my HR cam is a few degrees bigger, but don't believe all the nonsense of HR cams no power no rpm bs, I shift at 7200-7300, with matching valvetrain hr cams will make good power.
3. its going to want 1 7/8" headers, but 1 3/4" isn't hurting it that bad, about 20hp.
4. make sure your fuel and exhaust system is up to the job.

Dan,
you make some good points of interest, is it fair to say if you have a bigger MCSA being the pinch or the valve throat area and you run a bigger camshaft that all you will do is push peak up higher in the rpm range ?

2 things to consider here: (besides that I don't know what I'm talking about)
Yes, peak power will be pushed up higher if csa is increased, especially if more lobe is thrown at it.
Valve throat can kill power, so it should be around 89%-90% of valve size unless you really know what youre doing.
Also, if csa is too large power can be lost in the intended rpm range, similar to the throat area.
In Scotts case things are sized on the small side... induction, cam and exhaust, all of which are limiting power and rpm.

[67RS502]

I would like Rafel (67RS502) if he could explain what he means by open the pinch up to 2.6'' and let her breathe,i can understand if the thought is to try and keep AVG CSA through the complete intake tract,just grinding the pinch bigger is not the answer because if it was everyone would just do that and pat it on the head and call it good.
i am not here to criticize or question anyone's ideas i am here to learn

2.6" is the csa on my heads, I believe Scotts should be around 2.4-2.5" ( as my 1st post states) assuming he wants more rpm too to make more power, as he has the gear and stall to use it, and a shift point of 7000 would be good.
In a way everyone does do that, in better head designs the pinch is eliminated altogether, its just a design flaw we now need to work around with a 23 degree head that's was designed for small cube engines.
I believe that the pinch is more critical as CID goes up, on a small cube engine its something that isn't as critical because a decent aftermarket head isn't hurting it much and you have lots of valve curtain area. Stroke eats up heads fast, hence 400+ cube engines need some head.
Agreed, those heads go turbulent anyway so opening up the pinch isn't all that needs to be done, the whole port needs work, not just the pinch, but there is a bunch of power there.

[F-BIRD'88]

Still waiting for the dyno test power correction factor.

[randy331]

is it fair to say if you have a bigger MCSA being the pinch or the valve throat area and you run a bigger camshaft that all you will do is push peak up higher in the rpm range ? all things been equal as in intake and exhaust ports been optimized for the MCSA.

It depends on where your currently at. Average CSA vs MCSA current cam etc.
On the OP engine I'd bet on opening up the MCSA to be a win no matter what the flowz bench says after the change.
It's peaking kinda low, but about where you'd expect for the sum of parts vs cubes.

Randy

[Frankshaft]

is it fair to say if you have a bigger MCSA being the pinch or the valve throat area and you run a bigger camshaft that all you will do is push peak up higher in the rpm range ? all things been equal as in intake and exhaust ports been optimized for the MCSA.

It depends on where your currently at. Average CSA vs MCSA current cam etc.
On the OP engine I'd bet on opening up the MCSA to be a win no matter what the flowz bench says after the change.
It's peaking kinda low, but about where you'd expect for the sum of parts vs cubes.

Randy

I agree. The Afr 195's are overrated heads. I could pick that thing up 40 hp EASY without even putting them on the flow bench. They are way to small, and way to fast for that combo. Even with the camshaft that's in it. I just re read the first post. The Afr 210's are overrated too. I could pick that thing up 40 hp with those too. Probably closer to 100 with the right camshaft.