383 sbc first dyno experience

[steve cowan]

For anyone interested,
Have ran car over last few weeks.
Had a run tonight.
New 255/60/15 R series radials.
Backed up cam timing 4 degrees so cam is straight up 109 - 109 .
Car responded with a mph increase to where it should be .
I have my 950 hp (750) back on as well,still rich will be taking some fuel out for next meeting.
AFR from dyno were 12.3 :1.
At the moment it is 11.4 :1.
Plugs show rich at WOT.
34 DEGREES of timing. 20220730_163643.jpg
Still turning tyres off the hit as shown in the 60ft

Great job Steve! Please tell us your thought process behind the small head & small valve that you are using.

These cast iron heads are what I started learning on 5 years ago when I bought my flow bench and initially I bought 1 x cylinder head as a sacrifice head.
I had no clue where to start in reality, but kept reading the forum here and have been very lucky to talk to some very sharp minds on this forum.
These heads have been through half a dozen 383 combinations starting at running low 12s to where we are now.
After running on the dyno in may this year I think I can get this engine to make 600hp with the cylinder head/ manifold combination but with more duration on the cam at a higher rpm.i would like to retain the 1.94" - 1.5" valve combination.
CSA is a limitation on these heads as they started as a 165cc casting.

[steve cowan]

New 255/60/15 R series radials.
Still turning tyres off the hit as shown in the 60ft

Are you liking the new tires?
I'm assuming those are the Mickey Thompson ET Street R Radial Tires 3553.
I'm in the market for 255/50/16's myself but M/T only offers the SS version in a 16".

First meeting on these new tyres and first time using them.
We can't get MT tyres in Australia and I waited 8 months for this set.
I have had good luck with the SS M/ T and used them for the last 10 years.
I really want to try a radial slick on a good track

[steve cowan]

Hello Steve C. , Did you make the decision on the Camshaft spec.'s ? Great results ! it should carry the mail quite well Mark H.

I didn't pick the lobes CGT off this forum helped me and we communicate from time to time.
The intake lobe was chosen due to valve size,cubic inches and where peak hp / rpm regarding where to close the intake valve.
I am currently using a 1.7 rocker on the intake to increase valve speed.
The longer exhaust duration comes from where Randy331 and CGT (chad) dyno testing has taken them over the years regarding EVO / blow down ,torque etc.
I limited lift on the exhaust valve to 600" lift on this combo.
With the smaller intake lobe and 11.5:1 compression it would not like pumpgas but my intention was to always run MS109 as I am trying to learn .
Maybe with a bigger cam it could/should run pumpgas, but my opinion is if you have to mess up valve events for application just to run pumpgas and have some sort of static compression to make it sound good does not really make sense to me but I am probably wrong on that assumption

[steve cowan]

I forgot to add weather conditions, pretty good air.

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[skinny z]

I forgot to add weather conditions, pretty good air.20220731_100509.jpg

DA 652'!
Man, I miss those days. Around these parts we regularly race at 3000'+. Years ago, back at my old home track, I'd seen days of DA below sea level.
Kind of why I've adopted the corrected ET/MPH approach.

[KnightEngines]

On the dyno the other day we were seeing -400ft elevation.
Correction was at around .98 lol, corrected power was less than observed!
Our old track (adelaide AIR) was the fastest in the country even tho its a goat track for that reason - dyno is across the road from the old track.

[HQM383]

For anyone interested,
Have ran car over last few weeks.
Had a run tonight.
New 255/60/15 R series radials.
Backed up cam timing 4 degrees so cam is straight up 109 - 109 .
Car responded with a mph increase to where it should be .
I have my 950 hp (750) back on as well,still rich will be taking some fuel out for next meeting.
AFR from dyno were 12.3 :1.
At the moment it is 11.4 :1.
Plugs show rich at WOT.
34 DEGREES of timing. 20220730_163643.jpg
Still turning tyres off the hit as shown in the 60ft

Well done Steve. . 3600lb streetable car in the 10's with more to come using under 190cc sbc head and under 2" int valve. No mean feat.

Difference of .9 AFR from dyno to track interesting.

I removed the towbar a couple of weeks ago and weighed car at track last week 3620 with me
Going back through my notes-
Last weekend test and tune car ran 11.07 - 121.36 with wheel spin 1.73 in 60 ft ,week before that it ran 10.97 @ 121.34 .
Looking back now when I ran 11.13 @ 118 last year with similar combo with 010 block the 950 hp carb jetting will end up around there.
Initially I set up 950 hp for last weekend-
Front- 82 MJ 79 PVRC using my 3 hole cast metering blocks
31 - block - 31.
The PVRC is drilled no jet.
Transfer slot jet - 69" x 4
Drives up return road around 15 AFR. idle is afr of 12.3.
7.5 powervalve in front rear is blocked. 31 squirter.
Rear is 88 MJ , 31 squirter.
WOT AFR was 10.8 and showed rich on plugs.
So for this weekend I dropped 4 x jet sizes all round which is approx 8% calculations on pin size.
Front - 78 MJ pvrc fixed 79.
Rear - 84 MJ
Plugs show rich WOT with afr of 11.4.
I am thinking of going down another 4 jet sizes depending on pin gauge calculations.
Thoughts ?

You may need to tap pvcr and drop to around .063” to see how that affects WOT.

[steve cowan]

Well done Steve. . 3600lb streetable car in the 10's with more to come using under 190cc sbc head and under 2" int valve. No mean feat.

Difference of .9 AFR from dyno to track interesting.

I removed the towbar a couple of weeks ago and weighed car at track last week 3620 with me
Going back through my notes-
Last weekend test and tune car ran 11.07 - 121.36 with wheel spin 1.73 in 60 ft ,week before that it ran 10.97 @ 121.34 .
Looking back now when I ran 11.13 @ 118 last year with similar combo with 010 block the 950 hp carb jetting will end up around there.
Initially I set up 950 hp for last weekend-
Front- 82 MJ 79 PVRC using my 3 hole cast metering blocks
31 - block - 31.
The PVRC is drilled no jet.
Transfer slot jet - 69" x 4
Drives up return road around 15 AFR. idle is afr of 12.3.
7.5 powervalve in front rear is blocked. 31 squirter.
Rear is 88 MJ , 31 squirter.
WOT AFR was 10.8 and showed rich on plugs.
So for this weekend I dropped 4 x jet sizes all round which is approx 8% calculations on pin size.
Front - 78 MJ pvrc fixed 79.
Rear - 84 MJ
Plugs show rich WOT with afr of 11.4.
I am thinking of going down another 4 jet sizes depending on pin gauge calculations.
Thoughts ?

You may need to tap pvcr and drop to around .063” to see how that affects WOT.

I can use my billet metering blocks with adjustable emulsion jets,and adjustable PVRC jets.

[steve cowan]

For anyone interested,
Have ran car over last few weeks.
Had a run tonight.
New 255/60/15 R series radials.
Backed up cam timing 4 degrees so cam is straight up 109 - 109 .
Car responded with a mph increase to where it should be .
I have my 950 hp (750) back on as well,still rich will be taking some fuel out for next meeting.
AFR from dyno were 12.3 :1.
At the moment it is 11.4 :1.
Plugs show rich at WOT.
34 DEGREES of timing. 20220730_163643.jpg
Still turning tyres off the hit as shown in the 60ft

You've done your homework no doubt. Nice work!

You get that baby to hook up, it's really going to run.



It seems to me that if the open spacer lost some on the dyno, that it would lose on the dragstrip also, assuming the same engine speeds. However, damned if I wouldn't try it.

Seems to me that the reverb pulse hurts the carb signal?
Just thinking out loud but maybe shear plate on top of a 2 " spacer

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[RevTheory]

I think that's a great test, Steve. I've spent quite a bit of time thinking through and setting in motion as many ways as I can think of to make air only go one direction to the best of my $$$ and ability.

[408 Nova]

For anyone interested,
Have ran car over last few weeks.
Had a run tonight.
New 255/60/15 R series radials.
Backed up cam timing 4 degrees so cam is straight up 109 - 109 .
Car responded with a mph increase to where it should be .
I have my 950 hp (750) back on as well,still rich will be taking some fuel out for next meeting.
AFR from dyno were 12.3 :1.
At the moment it is 11.4 :1.
Plugs show rich at WOT.
34 DEGREES of timing. 20220730_163643.jpg
Still turning tyres off the hit as shown in the 60ft

You've done your homework no doubt. Nice work!

You get that baby to hook up, it's really going to run.



It seems to me that if the open spacer lost some on the dyno, that it would lose on the dragstrip also, assuming the same engine speeds. However, damned if I wouldn't try it.

Seems to me that the reverb pulse hurts the carb signal?
Just thinking out loud but maybe shear plate on top of a 2 " spacer 20220731_150749.jpg
20220731_150721.jpg

That's what I've always heard. An open spacer cuts signal to the carb. That shear plate should help bring a little signal back to the carb.

Did the 2" open spacer lean your engine out on the dyno?

[steve cowan]

You've done your homework no doubt. Nice work!

You get that baby to hook up, it's really going to run.



It seems to me that if the open spacer lost some on the dyno, that it would lose on the dragstrip also, assuming the same engine speeds. However, damned if I wouldn't try it.

Seems to me that the reverb pulse hurts the carb signal?
Just thinking out loud but maybe shear plate on top of a 2 " spacer 20220731_150749.jpg
20220731_150721.jpg

That's what I've always heard. An open spacer cuts signal to the carb. That shear plate should help bring a little signal back to the carb.

Did the 2" open spacer lean your engine out on the dyno?

The 2" spacer dropped power and messed up A/F through the pull,swapping to the 4 hole with nothing else was a day / night win.
Picked up 15 hp at top but picked up through the curve,AFR stabilised and engine sounded better from the get go.
I would say every combination is different but worth investigating.
I can not fit 2" open with shear plate as it hits the hole cut in the hood.i am going to keep running the mismatched 4 hole spacer .
Time to start playing suspension

[408 Nova]

Heck, you've got me wanting to try one of those tapered spacers on these engines I'm messing around with around here.

[Bob Hollinshead]

Great results and thanks for sharing but it has me questioning a lot LOL. With a 1.94" valve shrouding is not an issue, and I expect with the 50* seat angle the chamber is probably shaped well to compliment it. Throat size and bowl size must work well. And if I remember right Randy331's philosophy was always concentrating on airflow at the bottom of the intake stroke. But I don't know if there is magic happening here or if the same numbers could be hit with a 2.05 or 2.08" valve? Or would it make more power?

[steve cowan]

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Great results and thanks for sharing but it has me questioning a lot LOL. With a 1.94" valve shrouding is not an issue, and I expect with the 50* seat angle the chamber is probably shaped well to compliment it. Throat size and bowl size must work well. And if I remember right Randy331's philosophy was always concentrating on airflow at the bottom of the intake stroke. But I don't know if there is magic happening here or if the same numbers could be hit with a 2.05 or 2.08" valve? Or would it make more power?

Thanks Bob,
The chamber on those heads are really untouched, I have done zero unshrouding and have not taken the chamber to the bore wall .if I was going to angle mill the heads I would work the chamber and still might when I do upgrades next year.
Both intake and exhaust seats have a 0.100" 40* top cut I blended as best as possible for a 23 deg head without scooping out around the valve.i am not saying what other people are doing is wrong, just saying what I did/ didn't do.
I am sure in the hands of someone that knows what they are doing they could be improved.
So looking at a bigger valve scenario and this is just my opinion and I am sure plenty don't agree but that's fine.
I look at the CFM/ IN2 at the throat,valve and pinch and these all have different percentages to work towards.
If you do some area measurements on different valve sizes,throats but the port stays the same size in CSA does it pick up flow ??
If it does not then the cfm/ in2 must be lower.
Now most have read where Larry has put bigger valves in older style OEM heads and picked up power and gone faster but I doubt Larry just put a bigger valve in only.
It's like the spacer deal,every combination is different and you have to try for yourself.
I had a few guys at the track Saturday night say to me that I picked up 30hp so now it makes 600hp lol.
I said backing up the cam timing has pushed potential power up in a more useful rpm range and the mph/ weight is showing 540 hp.
I have shown combustion chamber before but will show again, valve job is -
TC - 40*
SEAT - 50*
BOTTOM CUTS - 60* - 70*- 82*
1.94" intake @ 89% throat that is concentric to the stem.
1.5" exhaust
TC - 40*
SEAT - 50*
radius under. Throat is approx 87%
But I don't set throat size to valve ratio on the exhaust.

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