High revving 3.2: what is needed?

[911hillclimber]

My 3.2 in the race car has coil/condenser/points ignition and big carbs.
The engine is a stock 1986 3.2 with custom exhaust manifolds.

I'm expecting a re-build to arrive soon and if so will want to open the spec up from stock.

To this end the highest revving rotor arm I can get is 7300rpm, is this true?
So, lets assume the red line to be 7500 to safely run the engine to.
In hillclimbing, bouncing off the rev limit is a common affaire.

Questions:
Will the stock 3.2 rods take 7500?
As above with stock cap bolts?
ARP hardware on the rods, stock rods ok to 7500?

Stock 3.2 pistons
Will these take 7500?
If not, what pistons can be used with S spec cams?
I'll never find good S cams, so what is the spec etc and supplier for such cams?

Crank:
I am assuming the crank is ok at 7500, true?

Ignition:
I have an RS spec distributor with T rotor arm at the moment. I am assuming this dist is good for 7500.
I don't want to fit an ECU etc. just to drive the ignition, I like things simple.

Finally:
Will a stock 3.2 rev to 7500 ???

Hope some can help answer all or some of these questions or I'll have to fit a 3.2 Boxster and box!

[Ashley James]

To get higher revs with power you’ll need new camshafts and fitting will require skill because you must make sure the valve springs don’t coil bind and that the valves don’t touch the pistons. You’ll also lose some bottom end that’ll make the car more difficult to drive.

Camshafts alone control the amount a car will rev and produce power.

[neilbardsley]

Can the bouncing off the delimiter cause damaged from the de acceleration?

Sent from my HTC One M9 using Tapatalk

[andytat]

Graham.
First you need to look at what prevents a 3.2 from reving to 7,500.

The std cams are not designed to make power that high up the rev range.
Schrick make good cams for 911 engines and so do DC in the USA.

Once you have a means to make the engine rev there are other factors
to think of.
The pistons have to be changed otherwise the valves will hit them due to the
higher valve lift. JE make good pistons for 911 engines.
The valve springs will not take 7500 rpm with higher lift cams so they need to
be changed along with the retaining caps.

Changing the above will give you an engine that will rev to 7,500 rpm, but
not for long as the rods, or rod bolts will probably break!

Carrillo or Pauter are a couple of favorites for 911 con rods.
Doing the above will give you a good strong high reving 911 engine.
What is the minimum rpm you would use, with the gearing that you have?
That will be a factor when deciding which camshafts you fit.
I hope that helps.

Andy

[911hillclimber]

Thank you all.
The reasoning behind this is to up grade the existing 3.2 whichalways seems to come to 5k or more, or to change the whole drive train, selling the 3.2 and its custom parts to fund it all.
A Boxster is to my mind the only realistic option but will be a bitch to fit, not sure I want to fight that one.
Last option is to leave well alone and enjoy the ride for the next few years until the car gets too much.
Not ready to throw the towel in yet!

[andytat]

Have you thought about a light pressure turbo Graham?

[911hillclimber]

First thing Bob Watson said to me after he stopped laughing when he saw the car!
He suggested twin turbos...
Even harder to do than to change it all I think?

The swop to a Boxster might be a bit more 'mecano' to do.
Remember it will be diy all the way with me.

[mycar]

Can the bouncing off the delimiter cause damaged from the de acceleration?

I too would like to know the answer to this.

[Lightweight_911]

Thank you all.
Last option is to leave well alone and enjoy the ride for the next few years until the car gets too much.

/\ /\ /\ - this option

Find something else/another mini-project to while away your spare time ...

[911hillclimber]

Did Mrs Hillclimber tell you to type that?
That is my wife's opinion and the only permission I have so far.

Just have a bit of an itch for what to get stuck into next Xmas.

[Nine One One]

Building Santa a new sleigh??

[Ashley James]

Can the bouncing off the delimiter cause damaged from the de acceleration?

I too would like to know the answer to this.

If you’re exceeding the rev limit, you risk damage.

[keith fellowes]

I heard of a bloke with a French bike that he can't get running.
Maybe you could take it off his hands and complete the project for him?

Mrs 911H would know where you were then!

[911hillclimber]

Ha!
I have over-revved this engine mechanically at Prescott and it cost me a 4K DIY rebuild, so I know how fragile these can be over 6500 red explosive line.
What a mess it was.
That French Follie is banished to the shed.
Until I can find another original carb, that is where it will stay. My crumpled knee injury has it's root kicking that thing over and over and ove and ov…..
I'd forgotten about it until someone just reminded me!

So, not much progress on this question except the 3.2 probably is not right for any advancing on the hill climb front.
I have 2 very difficult cars arriving in my Class this season and I like winning the Championship Class.

Will be v difficult at the moment.

Here is the lost #6 cylinder, about 1 second after snatching 1st from 2nd when I was going for a 3rd gear slot.

[fetuhoe]

Rev limits and modifying 3.2 Carrera Engines raises several interesting questions.

It seems commonly accepted that the rods used in these engines are rev limiting and that the M9 x 1.25 bolts fail on a regular basis and that replacing them with ARP Bolts will result in a substantial improvement in reliability.

In reality broken bolts are relatively rare but the 3.2 engine does suffer from 'spun' rod bearings which can result in broken rods.

The Factory Workshop Manual for the 3.2 Carrera describes the M9 Rod Bolt as a 'stretch' bolt which must be replaced at each re-build and recommend tightening using 20m torque + 90 degree rotation.

This is equivalent to stretch of around 0.3mm compared to the 0.25mm recommended by ARP. This would suggest that the factory bolt has a higher preload than the ARP bolt.

It is possible that the factory bolt has a lower tensile strength than the ARP Bolt and the load reversal at the end of exhaust stroke may cause an over-tightend bolt to plastically deform causing a loss in preload which could allow the bearing to spin.

I would like to make some detailed measurements of the M9 bolts to try to understand why they are descrided as stretch bolts and to see when they did plastically deform.

The early Turbo engine also used M9 rod bolts but these engines don't appear to suffer from the same rod bolt problems and the recommended tightening is to use 50-55Nm which could result in a lower preload than the Torque + angle method.

I think that the best way to make high revving 3.2 engines is to grind the rod journals on the crank to a nominal 56mm diameter and then use a 3.0SC rod with M10 bolts and this configuration would easily allow 7500 rpm and substituting a Carillo or similar rod would alloy 8000rpm +.

The extra rod length would mean using a custom Piston with a modified compression height and a 22mm pin.

Both JE and CP have manufactured this design of piston.

A GE62 profile cam would suit this type of engine and give a wide power band.

I would also use a 98mm dia piston and have the cylinders bored/re-plated.

If you also Twin plugged it should make around 320BHP.