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Combustion chamber comparisons

General engine tech -- Drag Racing to Circle Track

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BradH
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Combustion chamber comparisons

Post by BradH » Wed Oct 30, 2019 8:45 am

Pics or original Edelbrock BBM Victor chambers ("Gen 1") vs pics of more compact later style ("Gen 2") vs "Gen 2" that's been reworked to reduce valve shrouding, etc.

The "Gen 1" chamber always looked odd to me, probably because the transition from the valve seats into the chamber didn't appear to offer much in pressure recovery benefits (very "flat" from top of valve seats towards quench pad).
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aluminum-cylinder-head-stage-vii-raised-port-30.jpg
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MP Stage-VII chamber.jpg
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The "Gen 2" chamber went the other direction to a bit of an extreme, which is why the heads benefit from additional work beyond the revised as-cast form.
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victor_72cc_chamber-Edelbrock seat config.jpg
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After 1.jpg
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I'm working with "Gen 2" stuff now (the heads done for my current engine and a spare set of castings on hand), but am curious what others' opinions of the "Gen 1" chamber is. I had "Gen 1" heads and cut 'em loose because of what I thought was a much better chamber w/ the "Gen 2", but admit it could have been a poorly thought-out (and money-losing) decision if the originals weren't as bad as I believed them to be. - Brad
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Powertrip
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Re: Combustion chamber comparisons

Post by Powertrip » Wed Oct 30, 2019 10:53 am

I don't like the Gen 1 Victor combustion chamber, I believe the Gen 2 is a better design. If you mount a BBM head on a cylinder fixture, flip it upside down, and blow through the intake, you can learn some things by probing the combustion chamber. What I have found is that there is very little flow coming out the short side and cylinder wall side of the valve, regardless of bore size and if you unshroud to the gasket. What DOES happen is the flow travels across the spark plug, the exhaust valve, the quench side, and actually gets sucked BACK IN to the short and cylinder wall sides of the valve at high lifts! For this reason, I believe unshrouding the intake, like you have, may help low lift flow but also worsens reversion. I do like the way you have modified the quench side of the exhaust, but would have left the intake side alone.
It will be interesting to see if the changes you have made are noticeable once you take it to the track.
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mag2555
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Re: Combustion chamber comparisons

Post by mag2555 » Wed Oct 30, 2019 12:30 pm

I would love to see the gen 1 on the dyno with a rework of the chamber moved a little more deeper into the chamber, but from what I have seen in regards to most full on racing motors is that the chamber shape that promotes the highest level of Intake flow at .250" to .350" lift will in the end make the most average power.

BradH
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Re: Combustion chamber comparisons

Post by BradH » Wed Oct 30, 2019 2:28 pm

mag2555 wrote:
Wed Oct 30, 2019 12:30 pm
I would love to see the gen 1 on the dyno with a rework of the chamber moved a little more deeper into the chamber...
As in sinking the valves to create more of a bowl around them from which to transition into the flatter area of the chamber?

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Re: Combustion chamber comparisons

Post by mag2555 » Thu Oct 31, 2019 6:15 am

As in a bit of a heart shape to bring the plug closer to the center of the chamber which will by nature make the chamber more bowl shaped.

BradH
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Re: Combustion chamber comparisons

Post by BradH » Thu Oct 31, 2019 10:21 am

mag2555 wrote:
Thu Oct 31, 2019 6:15 am
As in a bit of a heart shape to bring the plug closer to the center of the chamber which will by nature make the chamber more bowl shaped.
Almost sounds like you're describing the old Chapman Stage VI head's chamber:
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Powertrip
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Re: Combustion chamber comparisons

Post by Powertrip » Thu Oct 31, 2019 4:35 pm

What are the CC's on those chambers, they look huge!
Still think the 2nd gen Edelbrock chamber are pretty damn good.
The price of progress is trouble.

BradH
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Re: Combustion chamber comparisons

Post by BradH » Fri Nov 01, 2019 6:24 am

Chapman 260 with 2.18 intake is listed as 78 cc
Victor Gen1 are listed as 75 cc
Gen2... 72 cc

Mine have both the additional chamber work & have been milled .030; I measured one at 72.8 cc.

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Re: Combustion chamber comparisons

Post by mag2555 » Fri Nov 01, 2019 6:44 am

This stuff can get to be a can of worms!

Lets see now,more open chambers lends themselves to better high lift flow 90% ofthe time depending on the heads valve inclination angle, it lends itself to needing less lead time needed and also makes for better BSFC numbers.

On the other side of the coin you get all the opposite to one degree or another, plus a notable increase in octane tolerance.

Finding that happy middle of the road is the headache!

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Re: Combustion chamber comparisons

Post by randy331 » Fri Nov 01, 2019 10:56 am

mag2555 wrote:
Wed Oct 30, 2019 12:30 pm
from what I have seen in regards to most full on racing motors is that the chamber shape that promotes the highest level of Intake flow at .250" to .350" lift will in the end make the most average power.
Ideal chamber shape has little to do with flow as seen on a flow bench, and absolutely not in that lift range.
Blowing the chamber out chasing flow in the .250-.350 lift range is a bad idea.

At least on "full on racing motors" whatever that describes .
mag2555 wrote:
Fri Nov 01, 2019 6:44 am
This stuff can get to be a can of worms!

Lets see now,more open chambers , it lends itself to needing less lead time needed and also makes for better BSFC numbers.
This is backwards. Open chambers need more timing and produce worse BSFC numbers.

Randy

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Re: Combustion chamber comparisons

Post by Elroy » Fri Nov 01, 2019 12:29 pm

On all those chambers it would be nice to have the spark plug further inside the chamber////
mag2555 wrote:
Fri Nov 01, 2019 6:44 am
This stuff can get to be a can of worms!

Lets see now,more open chambers lends themselves to better high lift flow 90% ofthe time depending on the heads valve inclination angle, it lends itself to needing less lead time needed and also makes for better BSFC numbers.

On the other side of the coin you get all the opposite to one degree or another, plus a notable increase in octane tolerance.

Finding that happy middle of the road is the headache!
Is this satire?//or are you serious? I would tend to think you were joking but if not do you have an instance or test to support this?/sorry if I am not picking up on the whole picture here.

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Re: Combustion chamber comparisons

Post by rebelrouser » Fri Nov 01, 2019 5:24 pm

I have a pair of pro comp heads, which should be a copy of the gen1 Edelbrock victor Chrysler heads. One chamber got smacked with a piston, so I need to do something to the chambers anyway. Do you guys think the modification in the thread would be worth doing to these? I has a .740 lift cam, the engine made 720 HP before it blew up. I am taking the bore from 4.440 to 4.50, and raising the compression from 12 too 13 to 1. The heads flow around 325 cfm on the intake @ 28 inches .700 lift.

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inline6
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Re: Combustion chamber comparisons

Post by inline6 » Fri Nov 01, 2019 9:15 pm

I'm no expert but wanted to give my opinion. First thing is way less shrouding in the second generation on both exhaust and intake. Also and this seems to be a common trend in heads in the last 10 years or so, is the typical bridge area finish down to the quench. What I am trying to describe is the transitions from the bridge to the quench area is divided between the exhaust and intake and feathered while maintaining that a slightly sharp bridge. The second just looks like it has better overall air flow, better burn charistictics and possibly better swirl.
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BradH
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Re: Combustion chamber comparisons

Post by BradH » Sat Nov 02, 2019 9:14 am

Misc comments...

The big advantage to the Gen 1 heads was they came cast with more "ready to run" intake & exhaust bowl sizes. Along with the chamber redesign, Edelbrock cast the Gen 2 bowls far smaller and lost a solid 20-25 CFM.

Not hearing much debate about the Gen 2 chamber being the better design. How much the chamber difference alone improves performance I can't say since I never finished my engine with the Gen 1 heads before deciding to go Gen 2.

From the porting work that Dwayne at Porter Racing Heads (member PRH) and I did on a Procomp Gen 1 "clone" and Dwayne's work on my Gen 2 heads, the chamber difference doesn't really show up in terms of raw flow #s. With the runners and bowls done the same, they both can go 350-ish on the intakes while staying with standard size (not Max Wedge) port entrances.

Re the question of modifying the Gen 1-style chamber like the Procomp pictured has, not sure what can be done short of welding in the transition to the quench pad and reshaping it. "It is what it is" really applies here, IMO.

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