383 sbc first dyno experience

[steve cowan]

Kevin,
My opinion is it is to hard to lock in a definite answer to your question.
This is where Larry's program gives a really good starting point on induction size including headers etc.

I wanted to test open headers this weekend compared to full 3" exhaust but we got rained out.

I think that last sentence is key to my question.
Certainly changes in the tune would be expected especially if scavenging is improved regardless of the shape of your combustion chamber But as suggested, improvements in chamber shape have shown improvements in VE by way increased high lift flow (as in Vortecs).

Regarding the induction, yes most definitely. That side of the cylinder head is every bit as important in tuning as witnessed by your extensive testing with spacers. I'll be going there as well however my immediate interest, once I'm back on track, is to get into this exhaust. It's always been crippling and there certainly are better results to come.

Anyway, hoping for sunny skies down under and some testing and analysis from you.

Thanks as always Steve.

One test I want to do before engine comes out at end of year is go back to the 1 5/8" tri-y headers that are port matched to these cast iron heads.
I ran those headers against my 1 3/4" 4 into 1 headers when combo was running 11.7s @ 114.
No difference was found.
I would like to see if the smaller header kills top end power
I run from 6000rpm- 7500rpm at the track,does not fall under 6000rpm on the shift.
At a guess I think they might help in the first 330ft but fall off after that.
The 4 into 1 is 1 3/4" to a 3" collector 19" long with bolt on extensions.
I have a set of 1 3/4" tri-y but got to get them to fit in the car.

[HQM383]

It's a simple time/area thing.
Without changing capacity to make more power you either gotta cram more air in per rev or turn more rpm, or both.
Once you get much above 110% ve it's far easier to turn more rpm that to improve ve%.
To go from say 6500 to 7000rpm peak power requires about 8% more time/area, which doesn't sound like much, but actually requires quite a lot more cam!
Add in your intake lag at higher rpm & the cam requirements get bigger again.

In the 260's is where experience tells me steve wants to be.

I've put 278/284 in a 355 cube engine - not near as cranky as you'd expect.

Thanks Tony. I was interested in the large jump from 240* to suggested up in the 260* @ .050”.

So cfm being volume over time the small valve needs a lot of open exposure time v a larger valve for effective cylinder fill to get the rpm and therefore hp. Simple really. I was thinking if 7k+ is past choke point of 1.94” valve would there be diminishing returns. No doubt your experience knows what works.

[1980RS]

Kevin,
My opinion is it is to hard to lock in a definite answer to your question.
This is where Larry's program gives a really good starting point on induction size including headers etc.

I wanted to test open headers this weekend compared to full 3" exhaust but we got rained out.

I think that last sentence is key to my question.
Certainly changes in the tune would be expected especially if scavenging is improved regardless of the shape of your combustion chamber But as suggested, improvements in chamber shape have shown improvements in VE by way increased high lift flow (as in Vortecs).

Regarding the induction, yes most definitely. That side of the cylinder head is every bit as important in tuning as witnessed by your extensive testing with spacers. I'll be going there as well however my immediate interest, once I'm back on track, is to get into this exhaust. It's always been crippling and there certainly are better results to come.

Anyway, hoping for sunny skies down under and some testing and analysis from you.

Thanks as always Steve.

One test I want to do before engine comes out at end of year is go back to the 1 5/8" tri-y headers that are port matched to these cast iron heads.
I ran those headers against my 1 3/4" 4 into 1 headers when combo was running 11.7s @ 114.
No difference was found.
I would like to see if the smaller header kills top end power
I run from 6000rpm- 7500rpm at the track,does not fall under 6000rpm on the shift.
At a guess I think they might help in the first 330ft but fall off after that.
The 4 into 1 is 1 3/4" to a 3" collector 19" long with bolt on extensions.
I have a set of 1 3/4" tri-y but got to get them to fit in the car.

On my Vortec 406 I had el-cheapo 1 5/8" headers and the car ran 120mph, I switched to my 1 3/4 Hooker S/C's and the car picked up nothing, natta, 0.

[skinny z]

On my Vortec 406 I had el-cheapo 1 5/8" headers and the car ran 120mph, I switched to my 1 3/4 Hooker S/C's and the car picked up nothing, natta, 0.

Many times there's been a demonstration of how effective a small tube primary header is.
What would have been the secondary specs in that back to back? Open headers I presume?

[1980RS]

On my Vortec 406 I had el-cheapo 1 5/8" headers and the car ran 120mph, I switched to my 1 3/4 Hooker S/C's and the car picked up nothing, natta, 0.

Many times there's been a demonstration of how effective a small tube primary header is.
What would have been the secondary specs in that back to back? Open headers I presume?

1st run was with them closed and ran 11.06@118mph
2nd run was aborted after the tracks surface went to crap that day.

[steve cowan]

I think that last sentence is key to my question.
Certainly changes in the tune would be expected especially if scavenging is improved regardless of the shape of your combustion chamber But as suggested, improvements in chamber shape have shown improvements in VE by way increased high lift flow (as in Vortecs).

Regarding the induction, yes most definitely. That side of the cylinder head is every bit as important in tuning as witnessed by your extensive testing with spacers. I'll be going there as well however my immediate interest, once I'm back on track, is to get into this exhaust. It's always been crippling and there certainly are better results to come.

Anyway, hoping for sunny skies down under and some testing and analysis from you.

Thanks as always Steve.

One test I want to do before engine comes out at end of year is go back to the 1 5/8" tri-y headers that are port matched to these cast iron heads.
I ran those headers against my 1 3/4" 4 into 1 headers when combo was running 11.7s @ 114.
No difference was found.
I would like to see if the smaller header kills top end power
I run from 6000rpm- 7500rpm at the track,does not fall under 6000rpm on the shift.
At a guess I think they might help in the first 330ft but fall off after that.
The 4 into 1 is 1 3/4" to a 3" collector 19" long with bolt on extensions.
I have a set of 1 3/4" tri-y but got to get them to fit in the car.

On my Vortec 406 I had el-cheapo 1 5/8" headers and the car ran 120mph, I switched to my 1 3/4 Hooker S/C's and the car picked up nothing, natta, 0.

I think headers are a blackhole for time.

[steve cowan]

For anyone interested,
I put half a turn pre- load on caltracs,tight extension on front shocks and soft extension on rear shocks, car responded.

20220827_171600.jpg

20220827_163642.jpg

20220827_155249.jpg

[BobbyB]

Good job!

[1980RS]

For anyone interested,
I put half a turn pre- load on caltracs,tight extension on front shocks and soft extension on rear shocks, car responded. 20220827_171600.jpg20220827_163642.jpg20220827_155249.jpg

Good job Steve, you got me beat.

[i82much]

what a cool ride.

[steve cowan]

For anyone interested,
I put half a turn pre- load on caltracs,tight extension on front shocks and soft extension on rear shocks, car responded. 20220827_171600.jpg20220827_163642.jpg20220827_155249.jpg

Good job Steve, you got me beat.

Ah,but for how long Bob

[steve cowan]

what a cool ride.

20220906_160530.jpg

20220906_160536.jpg

[408 Nova]

what a cool ride.

20220906_160530.jpg20220906_160536.jpg

Fast and nice ride!

[1980RS]

what a cool ride.

20220906_160530.jpg20220906_160536.jpg

Me likes

[Erland Cox]

Hi Steve!
Did you dyno with that air filter?
I did a test on a 350 in one of my road racing Camaros with filters.
Frome bare carb to a Summit aluminum fitler base with 14" filter and a nice radius from filter to carb was +25hp.
Best hp was 445 with 4779 Holley.
Your filter base does not look like it has a good radius.

Erland