Homebrew Head Porting: Attempting the dark art .....

[Gertvr]

Originally Posted by lvporschepilot

That's really wonderful power there. Congrats. PMO 50s right?

Thanks. Yes, ended up with 45mm venturis and not 41 as tested above


Cheers

Gert

[Flat6Heaven]

Amazing wealth of information, thanks for sharing!

Oh, and congratulations on the outcome.

[Flat6Heaven]

Originally Posted by Gertvr

The combination made good power, the car is very drive-able even with a very radical cam and pulls strongly from 3.5K through 8K. I am more than happy with the outcome.

Below is the result of one of the dyno pulls.

Was there a reason for the A/F discrepancies between left and right banks?

TIA,
Ben.

[MBruns]

We have 2 channels on the dyno for sensors, we used only one for this and when the other is inactive or unhooked thats the value.

Mike Bruns JBRacing.com

[Cupcar]

110 HP/liter with carbs very nice.

Question on dyno sheet: Does "JE new design forging" = their FSR or forged side relief forging?

[MBruns]

Cupcar, those were just before the production of the FSR began, these were the newest P forging with the 4 angled supports at the pin boss, we had done some testing for Je on the prototype FSR that were made from billet on our 3.8 and on a 3.0 race engine. They worked very well. I am going to dyno our 3.8 next week with the newest Xtreme heads.

Mike Bruns

[911 tweaks]

Mike...can you please post here so I don't miss the info you hopefully are wiling to post on the 3.8L w/ FSR pistons & Extreme heads you dyno...this info will help me a lot in trying to nail down an engine build...
thx in advance...Bob

[Cupcar]

Originally Posted by MBruns

Cupcar, those were just before the production of the FSR began, these were the newest P forging with the 4 angled supports at the pin boss, we had done some testing for Je on the prototype FSR that were made from billet on our 3.8 and on a 3.0 race engine. They worked very well. I am going to dyno our 3.8 next week with the newest Xtreme heads.

Mike Bruns

Thanks.
I am building a 3.8 with 130 mm GT3 Ti rods on GT3 crank and was thinking of using the JE FSR forging (-3 mm compression height) with a factory GT3 Goetz ring package and LN cylinders.

Any other experience or thoughts? Thanks again.

[Trophy]

Cupcar.....

excellent question Looking forward to the response. I haven't ordered my p&c's yet so may just wait to see what happens here.

OP: Amazing work here, very impressed with your process and willingness to jump right in. And your results are super impressive, you should be proud.....

[HKZ Bob]

Originally Posted by kenikh

Velocity of air is much more important than volume of air. Remember that before you start hogging out a head and end up with a powerless lump. Having seen good and bad port jobs at the same size, the difference is dramatic. Start by looking at these for what "good" looks like: http://www.early911sregistry.org/forum/showthread.php?t=22220

Show us some pictures of good port job.

Is this good? I have also seen pictures where the rib in front of the guide was removed completly.

[MBruns]

Here is the dyno sheet on our 3.8 with Carbs/ Dist. w MSD, we just replaced the modified OEM heads with a set from Xtreme, we picked up a little power and torque from the best numbers over the last 4 years. I suspect with the improved flow data we could use a bit more camshaft but it is so driveable that will wait for later

Mike Bruns

[MBruns]

This is what is lives in
Mike Bruns

[HawgRyder]

I found a little trick in the process of building engines for Formula Ford.
We put anti-reversion cones in the headers right at the head...and this "mellowed" out the peakyness of the torque curve slightly.
The cones were made as gasket plates (take the place of gaskets) between the head and the headers...with the "cone" part reducing the diameter of the header by about 10-15%.
The cones extend down the headers about an inch or so.
The cones stop or reduce the back pressure from re-entering the head and give you a slight suction effect to help expell the exhaust gasses.
Feel free to experiment.
Bob

[Trophy]

Interesting stuff Mike.

What sort of gain to you see going from modded heads to the Extreme heads in this case?

[MBruns]

We ran this engine in March at the 12 hr SVRA event and had it on the dyno then at 411 hp. That was the 3rd set of OEM based heads in 4 years, they make around 35 hours and split from port to port through the chamber. The Xtreme heads bare weigh 1/2 # more than the OEM due to more material where its needed. I am going to test with different cam and exhaust combinations soon, with the flow bench numbers being a good bit better than we had I bet it will respond to that.

Mike Bruns

[Walt Fricke]

Mike - these are engine dyno figures? Or chassis?

With that nice flat torque curve I can easily believe it when you say it drives like a dream.

Having heads split at 35 hours sounds discouraging, except for Extreme's business.

Bob - a header maker from Florida some years back made anti-reversion headers for 911s. I borrowed a set once, but never put anything on a dyno and didn't have any other way of comparing them with the Bursch's which took their place when he wanted them back. . A friend modified a set of Bursch headers to have these, but again I've not done back to back tests to see what the effects might be. Though I like the idea of making them as a separate piece.

[HawgRyder]

Walt...we found the things to be of benefit especially on longer tracks like Mosport.
It just sort of raised the torque level from 4500 - 6500 (seat of the pants and lap times).
The car pulled better coming out of slower turns.
The cones themselves are easy to make....just imagine a gasket (thin steel plate) with the cone extending out from it.
We whipped them up in a couple of hours...and being separate...easy to install.
BTW....we NEVER told the competition about them..and they looked very carefully to see why we were faster...even the tech inspectors missed them!
Bob

[MBruns]

Walt, that is engine dyno info, It does pull like a truck, we have been running a 6 into 2 into 1 system that is stepped on the primary's as well, power is good and we don't have to use a muffler. The 964 castings are a problem, all the earlier heads are not a problem.
When the 964/993 RSR's ran Daytona if you didn't start with new heads chances are you would not make it 24 hrs. plus the test days, BTDT
Mike Bruns

[Walt Fricke]

Mike - this makes me think we got it as close to right as could be expected for PCA Club Racing GT classification purposes. 110 hp/liter from NA 2 valve 911 engines. Same as the factory stated for its NA race motors.

Now, if I can only tweak my motor up to that level. I think it is hard for us homebrew guys to bolt together a bunch of parts and come up with that HP. Though we keep trying.

bob - the 911 anti-reversion heaers I had used had a bell where the primary attached to the flange. That allowed the anti-reversion piece to be same diameter as the port, with the gap below it, and the space above the gap in the bell, to do (supposedly) the magic.

But I may try making a slip-in cone for grins. If I can get quick on pulling headers, I could afford an hours chassis dyno time to test one with, and then without.