8000 rpm/300 bhp 3.2 rebuild

[hot66]

actually quite excited to see how it performs . Love these kind of engine builds having been through similar. It does sound good. Ironically bet it would make a lovely road engine

[gridgway]

would be mega in a road car I bet!

[911hillclimber]

Around 10 mpg.
Swallowed 2 or more gallons on the rollers


Looking at venture diameters this morning and the Anderson equation equates to 38.63mm
Engine has 38mm

[Nine One One]

If they are slide in venturi’s can you not mill them out on your lathe if there is enough metal there?

[Magnum]

Great result Graham, and surely a little more to come. Please will you answer a previous question of yours (and of course a few others, myself included)?

When next on the RR what difference does disabling one set of plugs make in outputs, as well as any difference in engine characteristics on the RR?

Let's sort this debate out?

[neilbardsley]

Doesn't the length of the distance between the top of trump and valve also affect where the torque is in the rpm range. If you want the torque to move to higher rpms doesn't this have to shorten?

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[gridgway]

I don't really know much here, but by way of a comparator, I had a mega 3.8 twin plug, high compression, G60, EFI/Canems motor built by Nick Fulljames. That had a big dip in the 3k's, but then revved liked crazy to 8k and a bit. That produced about 350bhp on the rollers which I think makes Graham as good an engine builder as Nick Fulljames

[911hillclimber]

There are a few things to consider:
This is a simple DIY build following proven changes, anyone could do this engine if they spend the enormous time as i have, and about £8K (I've lost count actually)
If it went/goes badly wrong the engine is scrap and i'm a good 14K down (think of how much 3.2's are now)
If it goes pop then it will be a Boxster engine going in, best engine for this car in hindsight.

I could pull the plugs from 12 to 6 and if/when it complained not sure what happens, but can't be good. RR rates are about £100/hour so expensive to experiment.

The venturies in the 50 mm PMO's are 38mm dia. I could machine them out to 39, but then no going back if the affect is adverse, so a new set at £120 not too back an option.

£200 to see what effect they have.

The calcs for the engine are:

Should have 46mm carbs for 3.2 litres. (ref Bruce Anderson), I have these 50mm (long story).
Bob Watson thought 38mm venturies were right and he squeezed 260 bhp from an essentially stock engine.

PMO sell a 50/39 choke combination, no 50/38. I really do not know what effect the 39mm ID would have, 5 bhp, -5 bhp, +15?

The RR guy really wanted me to get some 39's and try. The downside he felt could be a 'flat spot' at about 3500 and a better pick-up at 6K.

Hill climbing is a funny game.
You need a smooth torquey engine with no pauses, flats or delays in delivery. You cannot afford the time for such things, you have about 30 seconds to climb Shelsley Walsh, my fellow class mates will do it in 26., get 10 of these issues and 0.5 secs to get over them and it's 5 seconds lost.

Here is a picture of the final run yesterday:

[MikeB]

Graham,

When Bob set the Venturi at 38 mm, it was a very different engine. Here is the chart showing Venturi size when compared to CC and max horsepower revs. It is based on a 4 cylinder set up so your engine would be a 2.1 litre.

Looking at this, am assuming peak power at 7k, as it will rise, it looks like 40/41 mm would be the size required




This might give you the higher revs that you sought.


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[911hillclimber]

Interesting.
The Anderson book gives the calc as:

Choke dia = 20 x squ root of cylinder vol/1000 x rpm @ full power/1000
So:

dia = 20 x root of 533cc/1000 x 7000/1000
dia = 20 x root of 3.73
dia = 20 x 1.93
dia = 38.63mm
I can recall the port dias of the PMO carb manifolds.

I would be concerned about getting more at the top and less at the lower rpm.

[911hillclimber]

Just found this, pertinent to 911 flat 6's
If I interpret this correctly, 42mm?

[Gary71]

Closer to 46 from that data. It’s a bit early so my maths is probably wrong, but it’s 533cc per cylinder.

[MikeB]

Gary, it is where Max power is created, so that’s circa 7k, which is around the 42 mark. PMO lost 41 mm cents on their listings

[911hillclimber]

I think PMO have ceased trading.
Clewett ( ) are the main agents, all carb kits sold out and no PMO injection bodies either, just their own.
The Clewett site is unchanged for years, even only allows a FAX to be sent to them!

[Lightweight_911]

.

It might be worth contacting Larry Turner for his recommendation:

info@ youroil.net

- he is a main agent for PMO & has a lot of experience with Webers & PMO's on Porsche 911 engines.

I used to get any Weber 40/46 IDA jets, chokes, etc that I needed from Larry - very helpful/good price/quick shipping:

http://youroil.net/pmo_carburetors_and_kits_details.htm


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