Chamber size for iron head stroker

[yellow rose]

Egr puts heat into the chamber. Heat burns more. GM went crazy in that and ran all their temps way up in over 200-230 ish

Dont take and railroad the thread with emissions talk.
Quench is great, smaller compact chambers burn faster, less timing squeeze it all central to the plug and watch the power go up.
As long as you can unshroud the closed chamber.. it's not really behind the open one..its the flow that is slightly hindered from valve shrouding of closed chambers.
Really small down-to-earth example would be a 273 head closed chamber 920 casting. They flow around 170 CFM. If you unshroud that chamber all the sudden they flow around 183 CFM, allowing more signal to the straight side of the port ,therefore carrying the flow up higher in the lift than would normally carry. Same for all heads. While some chambers ARE so compact it's hard to unshroud them enpugh... there in lyes the idea getting a better port attached to that chamber to realize the advantage. Though there may always be a trade off...you just have to exploit the flow potential to offset that when comparing heads. Regardless..
It's all just planning and more or less work depending on the path you take. I pushed 91 octane california gas on heavily ported open chamber j hesds to 188 cranking psi /high 8's dynamic, I used kb 356 milled them about .046 off the quench pad...and milled the open chambers about .050ish for a depth of .030 and 60cc.. so the piston took up the gasket and the chamber gave the clearance. Heads flowing a hair better than those/op's.. a beast that rpm'd just fine and would just leave behind any car at speed...hardly, if at all, hooked from a light.
Just do it right and it wont matter either way.

If you look and see what most of the newer combustion chambers look like, even for N/A stuff, you can see they are going back to way "softer" chambers. Softer is hard to describe, but you know it when you see it.

And again, I'm asking how much timing do you run with a Hemi or a magnum? Every magnum headed deal I've done is 34-36 just like any other wedge with decent plug location.

 

[yellow rose]

Which makes a lot of sense.... the combustion process goes no faster at 6k rpm versus 3k, but the piston moves away from TDC a lot faster at 6k, and so the peak pressures have no chance to build as high when you get the rev's up. So less chance for detonation from that particular factor.... which jives with common observations.

I'm gradually learning that you have to look at things differently in the 3k and lower RPM range versus the higher RPM ranges. Things like this, and intake breathing and cylinder filling mechanisms, change a LOT from low to high RPM ranges, and your thinking needs to change if you emphasize one vs the other. The broad RPM range engines that I like have to be a compromise of factors.

Reading a lot of sources of info, both gearhead and research papers, and hearing the ideas of others here, have been invaluable to me getting a better grip on this stuff. I really appreciate the ideas expressed, even if they challenge my thinking.

Well, the timing requirement at peak torque is much different than what you need at peak HP. Cylinder fill is less past peak torque. And that should require less timing, or maybe even the same timing...as in flatten out the curve past peak torque because even though the cylinder has less volume, it also has less time to burn it.

I'm planning on testing this year (if I can) where I'm going to leave on 42-44 total and bring it back to 35 total in high gear and stepping in down some from first to second and second to third.

Even if I have to use an analog box I have with an external 3 step retard.

 

[MOPAROFFICIAL]

If you look and see what most of the newer combustion chambers look like, even for N/A stuff, you can see they are going back to way "softer" chambers. Softer is hard to describe, but you know it when you see it.

And again, I'm asking how much timing do you run with a Hemi or a magnum? Every magnum headed deal I've done is 34-36 just like any other wedge with decent plug location.

I imagine what you mean by "softer chambers". A lot of **** out there ...and I haven't seentit'tall...but not much softer than a 273 or mag before it's an open chamber again, that is in the wedges we're working with here. Dont run a hemi or a mag outside a stock 5.9 in my pickup.
Example: I ran 28 total timing max with 25 being ideal/smoother on pump 91...100 octane was more like 28-30 total in my 410,l cid small block
9.9 comp 8.8 dynamic. Cranked near 190psi
It hated over 30 degrees no matter if the octane was there.
Just enough octane the motor requires is all you need. Thats example is a lil outside the box but it's the same dictating chamber. Before I forget to say this.. just build for the octane anymore if you trying go for it... focus there so you end up fkd and rattling when you put your foot into it....but really.. anymore octane than the tune requires is going to burn slower...and need "more timing" .Maybe that's what's happening, maybe not... but if the designed chamber is happy with around 30 degrees when all is right "stars aligned" ..then you wont need that much.
Stock stuff likes 35-36 ime, but we all know that motor is not a true blueprint piece and definitely not optimized for that chamber/head nor its potential even in stock as cast form.

 

[yellow rose]

I imagine what you mean by "softer chambers". A lot of **** out there ...and I haven't seentit'tall...but not much softer than a 273 or mag before it's an open chamber again, that is in the wedges we're working with here. Dont run a hemi or a mag outside a stock 5.9 in my pickup. I ran 28 total timing max with 25 being ideal/smoother on pump 91...100 octane was more like 28-30 total in my 410, 9.9 comp 8.8 dynamic. Just enough octane the motor requires is all you need. Thats example is a lil outside the box and yes more octane can raise it up to the point of hurting performance. Before I forget to say this.. just build for the octane anymore if you trying go for it... focus there so you end up fkd and rattling when you put your foot into it....but really.. anymore octane than the tune requires is going to burn slower...and need "more timing" .Maybe that's what's happening, maybe not... but if the designed chamber is happy with around 30 degrees when all is right "stars aligned" ..then you wont need that much.
Stock stuff likes 35-36 ime, but we all know that motor is not a true blueprint piece and definitely not optimized for that chamber/head nor its potential even in stock as cast form.

I'll look and see if I can find some pictures of the softer chambers. They aren't really closed or open.

If I find them, I'll see if I can post them. That may be harder than finding them.

 

[RAMM]

I'll look and see if I can find some pictures of the softer chambers. They aren't really closed or open.

If I find them, I'll see if I can post them. That may be harder than finding them.

LOL ^^^^^ You haven't posted a picture of anything, EVER. J.Rob

 

[RAMM]

I'll look and see if I can find some pictures of the softer chambers. They aren't really closed or open.

If I find them, I'll see if I can post them. That may be harder than finding them.

"Softened chambers" I really don't like that terminology, it's dumb but its actually really easy to describe. When the nitrous gurus are talking about "softened " chambers they are describing a conical dish cut into the deck surface-simple and yes you will need a CNC in order to do it. Yes it makes more power just like a conical dish in a piston. Quench is slowly going out of style. J.Rob

 

[360duster]

Impressive. Not a stroker, correct? I hope to avoid machining.

4" Crank, 408 cui.

Michael there is alternative part number for a version that's meant for closed chambers. Kb 416 it needs no milling.

correct, forgot about these.....when i built this engine only the KB were available...would have saved me some work!

Michael

 

[yellow rose]

LOL ^^^^^ You haven't posted a picture of anything, EVER. J.Rob

I actually have posted some pictures. So you are wrong again. Nice to see you are using your other name today.

And yes, I found a better picture of what I'm talking about. I can email it to someone if they want to post it.

The thing is, you are actually AGREEING with me and you don't get it.

Even in N/A applications the chambers are moving away from all the quench and pulling the chamber away from the valves. If the chamber walls are vertical (or close to it) it's bad for flow, even if you use a 55 degree valve job.

Also, the picture I found shows how important it is to get the chamber away from the exhaust valve on the roof (if I'm thinking correctly...) so you are using as much of the valve diameter on blow down and reduce pumping losses on the exhaust stroke. You can use a smaller valve and port on the exhaust and make more power.

As I've said...quench is highly overrated. That doesn't mean run the piston a .100 down the hole either. It means closing the quench from .080 to .040 will net maybe, maybe a few HP. It won't reduce net timing a single degree.

Overrated.