Porting the Pontiac head and measuring swirl
 

Hi everybody. Has anyone measured swirl when it comes to porting d ports and at what point is too much swirl? Following Mr Hand’s book doing his combustion chamber mods I’ve picked up 1000 rpm swirl. So we’re at 4000 rpm swirl with a modified 4x chamber. We also flowed a set of 906 vortec sbc heads which I thought were supposed to be big swirl and only saw 2500 rpm. ( we flowed the sbc head to reverse engineer it). So I have a limited understanding of swirl that it’s good and too much can be bad. If anybody can shed more light on it I’d appreciate it. Have a great weekend.

Key Point you want to be careful of is if the swirl is too high then the air and fuel mixture entering the chamber will separate out with the fuel impacting on the combustion chamber walls and a lean "hole in the fuel/air mixture.

You want a clean continuous flame front across the chamber from the spark plug ignition point. The combustion process IS NOT one event there are several stages to the combustion event. This is a pretty good video that explains this combustion process.

https://www.youtube.com/watch?v=xL6x3sqH9QU

That being said, the link also has other videos that explain other engine processes happening.
The MIT Guys who taught at my employer's company (for the research guys mostly) had a similar
presentation but not a video at that time. This was years and years ago. I retired 5 years ago.

So Pay attention to what the engine is trying to tell you. Jim Hand did a fine job with his book and SF 110 small flow bench.
There is a lot more to the combustion event subject though. And there ARE some fine videos out there today.

Tom V.

ps I measured Swirl & Tumble and a lot of other things in my Research job.

Swirl, being a form of turbulence, is not in and of itself, a measurable way to make power. Best to focus on actual key areas that would need to be addressed for a given combination that do make a difference. Just my $.02.

Has it been that long?...!!!

Let's assume PMD totally researched Intake/Runner/valve/chamber/piston Shapes and got the IDEAL design in the EARLY 60s. Just assume. Balanced mixture distro/HP/ acceleration/ and winning. Lets assume the optimal total Advance was 34 Degrees.

Later on, Closed Chamber went to open chamber, and boom: 34 degrees Total ADV was re-attained.

Fuels have changed, yet the optimal kernel chemisry remains a aero-mechanical effort.

Then any MIXTURE improvements (shapes/swirl/atomizations) would yield a leaner carb JET for best performance. Also the Total Advance would go down due to optimixed kernel chemistry.

I run 32 degrees for best results. Wonder if anybody has best results <32*.

Ken Sperry could give you real dates.
He sent me a GM Air Flow Manual many years ago and we discussed when GM
first started using flow benches.

He is involved with a company that puts on presentations.
https://www.technical-insights.com/E...VDs-EADVD1.htm

If you have a spare $300 maybe he can help you out HIS, on how airflow actually works and when GM Engineering had their first Flow Bench.

Tom V.

Pontiac heads were ahead of their time in some ways. Fully machined chambers with all the little cuts in them were all about swirl and working well with low lift cam shafts as they were designed to have "right now" power in heavy cars.

Pontiac was able to run the chamber shape that was first used in the D port heads in 68 right on up to 79 and yet meet emission standards while other car makers where having a hard time doing that!

That in itself says a lot!

Pontiacs leg up so to speak on everyone else is due to in no peticular order 1) big Intake valve to provide fat flow numbers at lifts under .400" due to the big curtain area and the 30 degree seat.

2) 14 degree valve inclination angle that keeps the fuel that does get in from slamming onto the cylinder walls and not getting burnt which lowers fuel mileage, increases emissions and less causing ware!

3) the chamber shape and the high level of low lift swirl it produces.

4) even though the 68 cast number 16 D port heads where still cast with the air injection bosses in the exh ports like the 67 heads, engineering found out by mid production that they where not needed to meet emissions in CAvand where happily deleted from the late year casting 16s!

This is yet another thumbs up to the 68 and up chamber shape.

I have yet to investigate if the changes they made so darn late in the game to the Intake port shape of the 5 series and 6 series heads was done for greater power level, or better emissions, or maybe some of both.

One things for sure this change did not hurt power levels!

The width and shape / arc of the short turn has a effect on the swirl rate as valve lifts rise from .400" on up, this is for certain!