3.5 goodness - 1988 build article - 7 pages...
 

Thought this would interest the 3.5 crowd. Taken from VW & Porsche Magazine / April 1988:

Quality was tough to keep intact at this size.....

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Thanks Rick!

Your welcome Soukster.
Took a couple of hours foolin with the damned images.

Does anyone know if Greg Brown and BRD/Precision Porsche are still around?

What ever happened to BRD? Name change? out of business? They always used to have neat projects going.

Good article, thanks for scanning it in.

Helmet Bott (head of Porsche R&D) build a similar engine for his personal car in the mid '70s and used it for many years

My 3.4 CIS is close to what was being done here.

The sub 5 second 0-60 times are easy enough. The reason Porsche didn't market these big bore engines (besides smog) was the big bore NA engines would trash a Turbo pretty easily up to the mid 80s.

It was decided that was bad for business ;)

I would think that would give you better throttle response but not more horsepower, motors are air pumps, more air = more horsepower. But I do know that head porting modifications can be fairly counterintuitive, bigger does not always flow better. I have a 3.5 L engine and it is really a great motor tons of torque great horsepower.
Phil

Greg Brown runs Precision Motorwerks here in SoCal. They are a fixture at local POC races. I think BRD was just what they were trying to market their performance parts under.

Ralph

I guess back then nobody was concerned about giving away a few secrets about the build up of an engine?

That was a good magazine. I used to buy it when I first got my GTI

The article mentions PMO. I never knew PMO stood for Porsche Mail Order.
-Chris

That car looks pretty slick as well. Appears to be a widebody with the stone guards removed and have 9 and 11 inch wide 15" Fuchs.

Dyno results would be nice. Very interesting!

Nothing really new here. Tom Tweed's 3.4 is a good example of what this engine can dyno with carbs and a hot cam.

A well done CIS 3.4 does indeed have a good deal of torgue on the low end. Mine is 224 rear wheel hp and 215 rw torque on the most recent dyno. 9.8:1 compression on street gas with 20/21 cams and SSIs.

I know this has been probably gone over hundreds of times, but it looks like a stock 3.6 is just about as fast. That wasn't available in 1988 but lucky for us it is now (and a fairly simple conversion with a kit).

For comparable power none of them are cheap or simple.

I'd hesitate to use simple, and it's definetly not cheap. It's just getting done more often.

Maybe relatively simple would be a better expression. I may be wrong, but from my inexperienced point of view it seems easier to swap in a complete engine than to build one from scratch.

Noah,

I saw your comment about the valve size and had to read the article. I saved the article, but didn’t have time to read it ‘til now. It’s especially interesting to me as I have the 78 SC engine in my Bastard. One interesting note in the article is the mention of “backcut intakes.” In conjunction with that, the picture of the BRD heads sandwiching the stock head makes me think that the increased flow is not in the port port size solely. The valve to valve seat opening )flow area when at full lift) is important right? I assume that is what the “backcut” allows for.

I’ve performed numerous calculations of pipeline valves of various types, and approach area is rarely as important as the final restriction. Approach area is important to me as erosion at 100 feet per second or greater become a problem inside pipes. Some obvious things to notice with valve design, a “full port” ball valve versus a plug valve which has a more tortuous flow path is that the full port can flow a lot better, even when the port velocity through a plug valve is 2 times greater.

The discharge coefficient for valves in engines is closer to the plug valve if you consider just the ball valve and the plug valve. Lift is measured at the cam right? So let’s discount that as the lift is the same for the small port heads and the large port heads. There are folks out there and on this BBS that have more valve and head flow experience than I will have when I die, so perhaps they will chime in. My take on the flow advantage of the BRD heads is in the shaping of the valve to valve seat area when the valve is at full open. Obviously approach velocity and the momentum in that flow is a great factor, and removing any momentum robbing features of the intake is important to right?

Shaping the final restriction such that there is more flow area seems to be a key advantage of the BRD heads.

There was an interesting discussion on a Pantera BBS about lift and duration which referenced some practices of Dema Elgin. My vague recollection of that discussion leads me to put two and two together making the above somewhat valid. (I'll have to find that discussion)

I hope that makes some sense, and at the very least it leads to some good discussion.

Yes, a smaller approach pipe for the same volume will definitely provide higher upstream velocity, but if the flow area at the valve is the same, there will be marginal gains. I'm not saying that BRD did it wrong, just that flow from the air filter to the top of the piston is not just intake pipe size and port size. When I design flow facilities, I take into consideration the pipe hundereds of feet away upstream and downstream...and anything in between that will make things less efficient.

I wonder what the flow numbers would be with just the BRD valve treatment. If they had performed a before and after comparison of just the valve work, it would have been very interesting. I would love to see the flow numbers at each step of the modification and head assembly...

From my understanding, one should expect approx 100HP per Liter. That's 350HP out of a 3.5L. I saw this on the Engine rebuilding board.

I would also think a conversion would be used as a last result. The engine would fit but then the trickle down effect starts:

Engine then DME unit then G50 trans (early Carreras) then new clutch system then new shifter... It can get expensive real fast even before you start making any modes.

What kits are you talking about? Could you (or should I say Would you) install a 3.6L behind a 915 trans?