What makes a head "fastburn"?

[SWB]

If someone wants to PM or e-mail me I have some limited info on the v-12 jag from an undisclosed engineeer there. Key word is limited.

SWB

[putztastics]

What are some other heads besides the vortech heads that are faster burn?

The stock Dodge Magnum heads have the same "fast burn" ideas built into them, small double quench chambers, and a swirl inducing intake port. The intake port is interesting, right past the pushrod pinch the port is narrow on the top 1/3 or so and wide on the bottom 2/3rds. Many people look into a Magnum intake port and think that the narrower upper half of the port is that way for rocker pad support. I don't think that is the reason. In theory there would be a flow to the narrow higher velocity (lower pressure) part of the port thus inducing swirl in the port.

This port design is a major difference between the Dodge 4448308 casting which is sometimes called "high swirl".

[liquigas]

viewtopic.php?t=1396

This thread covers a way to get the swirl and it's benefits from your existing set of heads without leaving unburnt mixture on the cylinder walls.

You cut a groove in the cylinder head.

Seems simple.

[526FIREHAWK]

Ok, from everything you guys are saying swirl has alot to do with the burn speed? But from other things ive read on this board too much swirl can cause problems. But the basics are compact chambers, some swril, and generous quench areas. Thats alot to comprehend for a novice.

[Ape]

If its also of theoretical didactic interest, and not just hands on practical "US engine" related, you might want to take a trip to your local mercedes breaker / junkyard and let him show you a 250 / 280 (of the 250S / SE from the 70´s) cylinder head.
Those have a combustion chamber solely underneath the exhaust valve with the spark plug right by, for named reasons.

[10.90streetcar]

Would an sb2.2 be considered a Fast Burn Head? And if so how much faster? 10%, 20% or what?

[526FIREHAWK]

Yeah, What about the SB2.2 heads, EA pro has them listed as a fastburn head.

[liquigas]

What about those crucial moments when valve is closing and port swirl is just coming to a standstill before spark? There is a considerable gain from promoting swirl in the combustion chamber at TDC. Ports can't do that once closed.

[Ape]

thats where asymetric ore specifically shaped squish areas come to play, in order to make the mixture more homogenous and the fuel droplets smaller in diameter.
Try to find pic´s of the suzuki S-rad chamber to see how they swolved the problem, also the article on the endyn softheads is quite interesting, cuz´of the pictures: www.theoldone.com

[liquigas]

Yes but...

Isn't the chamber closed off for the most crucial part of combustion?

Seems like squish areas create a flat plate effect, like water over a wide spillway, as soon as the compressed gasses creep out as the cylinder begins to drop.

The groove making a jet of motion towards the cylinder wall seems like a sure way to get more burn going on, sooner, and in a more turbulent fashion.

swirl from the port and assymetrical chambers have an established benefit to a point. Doesn't the groove act in those moments between the end and restart of the chamber's influence on combustion?

I'm trying to figure it out too, so thanks for the input Ape.

[MadBill]

Swirl is just a way of introducing energetic mixture movement into the cylinder. It degenerates into chaotic turbulence approaching TDC and contributes to the 'wrinkled' (long) flame front that speeds combustion.

[Ape]

Yes but...

Isn't the chamber closed off for the most crucial part of combustion?

*)
Yes and thats good that way that way the squished Gas is where it belongs..int he chamber if the squish stays open too much, you´ll get residue gases and less efficiency and worse smog, one of the reasons why the new engines have the rings that high, to avoid dead space.

Seems like squish areas create a flat plate effect, like water over a wide spillway, as soon as the compressed gasses creep out as the cylinder begins to drop.

*)
Not if you have angled squish areas that change the dirdection vector of the gases. Also if you have two or more gasclouds you can basically steer them, and bring the resultant cloud closer to or from the spark in the direction of the exhaust port in order to accomodate for short blowby period during exhaustduration.

The groove making a jet of motion towards the cylinder wall seems like a sure way to get more burn going on, sooner, and in a more turbulent fashion.

*)
Not if one takes into consideration the way big factories can predict flame propagation, through rapid cycle analysis or true visualisation. Also as said threedimensional asymetric squishes might produce a resulting flame propagation vector.

swirl from the port and assymetrical chambers have an established benefit to a point. Doesn't the groove act in those moments between the end and restart of the chamber's influence on combustion?

*)
Yes it most likely will but not in such a manner like a good scientific squish area.The swirl or tumble during duration is mostly to fill the chamber efficiently and make the fuel droplets smaller and more homogenous in size. Sort of like small area crossections.

I'm trying to figure it out too, so thanks for the input Ape.

You´re more than welcome, gladly gaven my input, i wish i could find those dam... bmw chamber pictures.

If you´re really interested in modern squish technique that might me somewhat comvertable try to catch a glimpse into the newer single cylinder 4Strokes, they have the squish desinged in a way that it gets propagated towards the exhaust port and biased upwards in order to get faster reached by the sparkplug flame nucleus.

kind regards

[liquigas]

Do they look like 'cat whiskers'?

There is a lot of interesting newer cylinder designs, that I found thanks to your tip, but what about quantifying existing design changes?

Endyn is tantalizing info to say the least. Seems like we could all be driving 70mpg biodiesels by now.

Humph.

[Silverback]

-I'm not an expert on fast burn heads but I experimented with a set of the early 1987 vortec heads that had the corkscrew intake ports….

Sounds like you’re talking about swirl ports heads, they used a normal, “slow burn” wedge chamber but had the swirl ramps in the ports. Totally different deal.

I’d say that fast burn heads are characterized by heart shaped or similar chambers that use quench pads to force swirl into the mixture.

GM didn’t officially make fast burn heads till ’95 on the V8’s, though there were a few 305 heads in the early 80’s that had chambers that looked very much like fast burn chambers.

What are some other heads besides the vortech heads that are faster burn?

The stock Dodge Magnum heads have the same "fast burn" ideas built into them, small double quench chambers, and a swirl inducing intake port. The intake port is interesting, right past the pushrod pinch the port is narrow on the top 1/3 or so and wide on the bottom 2/3rds. Many people look into a Magnum intake port and think that the narrower upper half of the port is that way for rocker pad support. I don't think that is the reason. In theory there would be a flow to the narrow higher velocity (lower pressure) part of the port thus inducing swirl in the port.

This port design is a major difference between the Dodge 4448308 casting which is sometimes called "high swirl".

Yea, a bunch of the late 80’s/early 90’s mopar 318 heads had a very distinct, fast burn style chamber on them, the weird thing was that Chrysler didn’t make any serious attempt at using it and instead most of those engines ran such extreme quench distances that the superior chamber design did virtually nothing…