383 sbc first dyno experience

[steve cowan]

The alloy head had very average mid lift numbers and I used 2 x top cuts as the transition is very average, from the factory they have dug out around the seat ring.
The fix I suspect is a bigger valve but I am not a fan of having a big valve in a small port,I think speed at the seat ring is pretty important.
Remember I am at 7500rpm max at this stage.

[steve cowan]

20240118_185940.jpg

With the Vic Jr it was down to 275 cfm @ 0.800"
This is earlier numbers, I changed the 60 deg cut to a 65 deg under the seat ,I am using no back cuts on these intake valves.
They are Manley Pro - Flow valves and not Race - Flow .

[steve cowan]

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A few port moulds between the 2 heads

[steve cowan]

20240118_193812.jpg

When engine dynoed pinch was 2.10"
There is only 40 - 50 thou thickness on SSR, if I could lay it down more it might pick up some CFM.
What it shows is you do not need a head that flows 300 cfm plus to make 570 ish hp.

[HQM383]

The port architecture between the two heads are very different even though they are both Dart heads.
Cast heads are a Wissota spec head that I originally bought to learn on,$300 AU each head bare delivered from Summit.
The cast iron head has a better top cut to chamber transition and taller SSR so the turn is not abrupt like the alloy 180cc SHP heads (early casting)

The alloy head had very average mid lift numbers and I used 2 x top cuts as the transition is very average, from the factory they have dug out around the seat ring.
The fix I suspect is a bigger valve but I am not a fan of having a big valve in a small port,I think speed at the seat ring is pretty important.
Remember I am at 7500rpm max at this stage.

So your preference of head design and architecture is the iron head. They did perform very well on the first engine. What are your thoughts then on the biggest contributor to the extra hp given the gap between the two engines would likely be greater if both run on the same fuel?
Average csa?
Valve diameters?
Camshaft events?
Total CFM?
Manifold?

I also noted smaller head/cam engine had peak torque 200rpm higher. Seems against conventional wisdom. Did you expect that?

[HQM383]

20221104_210227.jpg20221104_210145.jpg20221104_210105.jpg
A few port moulds between the 2 heads

Excellent visuals thanks for sharing Steve. Some of us hobby guys don’t have that kind of variety on hand for comparison.

[HQM383]

20240118_193812.jpg
When engine dynoed pinch was 2.10"
There is only 40 - 50 thou thickness on SSR, if I could lay it down more it might pick up some CFM.
What it shows is you do not need a head that flows 300 cfm plus to make 570 ish hp.

Smooth, quiet flowing port with appropriately sized cross sectional areas trump flow numbers I suspect?

[steve cowan]

When I was at dyno recently, Russ asked me if I was going to test MS109,I intentionally did not take any fuel with me.
We talked about dart block dyno session with cast iron heads and he showed me a fair amount of data where the better fuel picked up anywhere between 10 - 25 hp .
The strip dominator intake has shorter runners compared to Vic Jr and they are close in CSA between the two.
I think the reason it peaked torque at 5300rpm was all the reasons you mentioned.
It peaked hp at 6600rpm and was only down 5hp at 7000rpm.
It shows as well that in a street car deal that only turns 7500rpm max you can have airspeed faster on the floor at the apex of SSR .
If you automatically make the average airspeed in that area at 280 - 300 ft/ sec the port could end up to big for your intended rpm range.
Got to ask yourself where is your right foot most of the time.
In a street car it is not WOT.

[steve cowan]

20240118_193812.jpg
When engine dynoed pinch was 2.10"
There is only 40 - 50 thou thickness on SSR, if I could lay it down more it might pick up some CFM.
What it shows is you do not need a head that flows 300 cfm plus to make 570 ish hp.

Smooth, quiet flowing port with appropriately sized cross sectional areas trump flow numbers I suspect?

Yes,I agree
I am no expert at all but most of the time now when I use my bench it is more about listening to the port at all depressions and lifts.
I start my lifts at 0.250" and run to 0.100" past max lift on cam I am using.
I like to test at highest depression o can which is 45" on my smaller heads.
My bench has the potential to flow 400cfm @ 28" .
I don't look at overlap flow or low lift flow,I like steeper angles,sinking the valve more.
Less margins on valves,no back cuts.
My opinion is with a 23 degree head you are not valve limited as it's hard to get the throat as the MCSA without going to big on the port for most applications.
The choke is further up stream so making the throat/ valve bigger will only slow air/ fuel down which I don't believe is what you want.
Again it is application specific.

[LaminarTurbulence]

20240118_193812.jpg
When engine dynoed pinch was 2.10"
There is only 40 - 50 thou thickness on SSR, if I could lay it down more it might pick up some CFM.
What it shows is you do not need a head that flows 300 cfm plus to make 570 ish hp.

Steve, way back when, the BEST A/S Chev engines in the early / mid 90’s utilised “fuellies”, depending on porting styles made 620-630 and the minimum CSA (at the S/T) was about 2.2”. And flow backed up/ flattened out @ .600. Peak power rpm was right about 6800. And flow wasn’t @ 300 CFM

More than one way to skin a cat but the laws of physics and engine demand/engine speed/supply don’t change within reason. The smart ones didn’t open the pinch with the architecture being utilised because I guess you know why…

The best MS engines are now at the minimum, 310” instead of 350” for reasons including demand and available supply with appropriate velocities…

Like you said, application specific AND just a stack of compromises… The price of progress is trouble

[skinny z]

1.5 on the exhaust...

That raises a question I've had since the first I read about someone using less ratio on the exhaust as opposed to the intake.
What's the logic there? Is it compensating for a cam spec or working with the specifics of a particular port?

I'm the seeing the answer is in all of the above.
A guy like Steve, who's constantly experimenting on the flow bench, is seeing an advantage (or not) when moving the rocker ratio around. That's with a given cam and an unspecified cylinder head, Unspecified in that it's constantly evolving. The ratio that may have worked yesterday isn't necessarily the ratio of today.
Now, to bring that around to a fellow like myself, who hasn't got a flow bench (or ready access to an engine dyno for that matter ) but I've a set of heads, done and dusted as it were. I've an engine spec pre-decided. That is, these are the parts I've got. Rocker arm ratio included (1.6 all around). I send that off to my cam designer and what he delivers to me is what is best suited to that pile of parts.
At least that's how I see it.
I can't say what changing my engine spec might do to what is an otherwise optimum cam. A change to a single plane from the dual plane I've always run or a move to large headers will undoubtedly have some sort of cascading effect. Even on a more basic level, my spec is based on an open header. It's reasonable to assume that the cam isn't best suited to a fully mufflered car. Might the rocker ratio come into play here?
Anyway, just musing on my part.

[steve cowan]

1.5 on the exhaust...

That raises a question I've had since the first I read about someone using less ratio on the exhaust as opposed to the intake.
What's the logic there? Is it compensating for a cam spec or working with the specifics of a particular port?

I'm the seeing the answer is in all of the above.
A guy like Steve, who's constantly experimenting on the flow bench, is seeing an advantage (or not) when moving the rocker ratio around. That's with a given cam and an unspecified cylinder head, Unspecified in that it's constantly evolving. The ratio that may have worked yesterday isn't necessarily the ratio of today.
Now, to bring that around to a fellow like myself, who hasn't got a flow bench (or ready access to an engine dyno for that matter ) but I've a set of heads, done and dusted as it were. I've an engine spec pre-decided. That is, these are the parts I've got. Rocker arm ratio included (1.6 all around). I send that off to my cam designer and what he delivers to me is what is best suited to that pile of parts.
At least that's how I see it.
I can't say what changing my engine spec might do to what is an otherwise optimum cam. A change to a single plane from the dual plane I've always run or a move to large headers will undoubtedly have some sort of cascading effect. Even on a more basic level, my spec is based on an open header. It's reasonable to assume that the cam isn't best suited to a fully mufflered car. Might the rocker ratio come into play here?
Anyway, just musing on my part.

I ran those cast iron heads as stock on my 010 383 block several years ago.
10.6 comp
Comp SFT 235 - 242 @ 0.050
500" lift
106 lsa in at 106 but did move around.
Car ran 11.70 - 114 mph
As cast Vic Jr.
I tested rockers on the exhaust
From 1.3 break in rockers
Up to 1.6.
I had 1.7 rockers but never run on exhaust.
I tested tight lash ,loose lash etc
I will be honest that there was really no excessive change at the track,as you know there is a ton of variables.
In my opinion and testing -
For what we are doing, street car application, 6000rpm- 7500rpm operating range I don't think these style of engines care that much.
I have had more rewards by moving the cam close to straight up most times and picked up ET and mph across the whole run.
This might make some guys laugh but I take my moroso speed calculator pretty seriously and make my car run to those increments.

[skinny z]

This might make some guys laugh but I take my moroso speed calculator pretty seriously and make my car run to those increments.

At one time I was involved in a chassis shop. Drag racing stuff 90% of the time. Gassers, dragsters, back halved cars, etc.
Tom, the shop owner and craftsman also used his Moroso slide rule to great effect. My engineering friend laughed and commented on how his DragSim program (now over thirty years dated) was far superior. But at the end of the day, Tom's cars always ran the numbers. My friend's...not so much.
Sometimes math is simple.
I have a Moroso calculator too.

[HQM383]

20240118_193812.jpg
When engine dynoed pinch was 2.10"
There is only 40 - 50 thou thickness on SSR, if I could lay it down more it might pick up some CFM.
What it shows is you do not need a head that flows 300 cfm plus to make 570 ish hp.

Smooth, quiet flowing port with appropriately sized cross sectional areas trump flow numbers I suspect?

Yes,I agree
I am no expert at all but most of the time now when I use my bench it is more about listening to the port at all depressions and lifts.
I start my lifts at 0.250" and run to 0.100" past max lift on cam I am using.
I like to test at highest depression o can which is 45" on my smaller heads.
My bench has the potential to flow 400cfm @ 28" .
I don't look at overlap flow or low lift flow,I like steeper angles,sinking the valve more.
Less margins on valves,no back cuts.
My opinion is with a 23 degree head you are not valve limited as it's hard to get the throat as the MCSA without going to big on the port for most applications.
The choke is further up stream so making the throat/ valve bigger will only slow air/ fuel down which I don't believe is what you want.
Again it is application specific.

What do you think is more important, minimum cross sectional area or average cross sectional area? Local velocities in specific areas to get right or average velocity to targeted application?

[HQM383]

1.5 on the exhaust...

That raises a question I've had since the first I read about someone using less ratio on the exhaust as opposed to the intake.
What's the logic there? Is it compensating for a cam spec or working with the specifics of a particular port?

I'm the seeing the answer is in all of the above.
A guy like Steve, who's constantly experimenting on the flow bench, is seeing an advantage (or not) when moving the rocker ratio around. That's with a given cam and an unspecified cylinder head, Unspecified in that it's constantly evolving. The ratio that may have worked yesterday isn't necessarily the ratio of today.
Now, to bring that around to a fellow like myself, who hasn't got a flow bench (or ready access to an engine dyno for that matter ) but I've a set of heads, done and dusted as it were. I've an engine spec pre-decided. That is, these are the parts I've got. Rocker arm ratio included (1.6 all around). I send that off to my cam designer and what he delivers to me is what is best suited to that pile of parts.
At least that's how I see it.
I can't say what changing my engine spec might do to what is an otherwise optimum cam. A change to a single plane from the dual plane I've always run or a move to large headers will undoubtedly have some sort of cascading effect. Even on a more basic level, my spec is based on an open header. It's reasonable to assume that the cam isn't best suited to a fully mufflered car. Might the rocker ratio come into play here?
Anyway, just musing on my part.

In my quest for knowledge and understanding and a bank account that can not afford a dyno or infinite amount of parts to swap out, running some sims returns interesting feedback on reduced rocker ratio on exhaust. Two patterns emerge

1. If the exhaust lobe is tailored closer to what the engine likes (not duration, this was held reasonably constant) changing exh R/R has reduced effect. The opposite is true. It seems to equate to engine wanting specific exh valve movment for targeted rpm gains ie peak tq or peak hp.

2. If the combination yields fast exh movement off seat such as TK lobe with 1.6 R/R then low torque is enhanced below peak. Going extreme to 1.3 R/R lowers tq below peak ans conversely raises tq above. this leads to higher peak hp.

On test engine:

Intake lobe Comp 12558 and 1.6 R/R

TK lobe 4616 on exhaust ratio change effect
1.3 R/R
3500rpm = 403ft/lb and 268hp
5000rpm = 525ft/lb and 500hp
6500rpm = 448ft/lb and 555hp

1.6 R/R
3500rpm = 412ft/lb and 275hp
5000rpm = 522ft/lb and 497hp
6500rpm = 422ft/lb and 547hp

High Energy lobe 4221 on exhaust ratio change effect
1.3 R/R
3500rpm = 392ft/lb and 261hp
5000rpm = 524ft/lb and 499hp
6500rpm = 447ft/lb and 554hp

1.6 R/R
3500rpm = 394ft/lb and 263hp
5000rpm = 524ft/lb and 498hp
6500rpm = 445ft/lb and 551hp

Get exhaust lobe right and rocker ratio change is almost margin of error stuff.