3.2 911 engine: mods to give 7600 min red line?

[redrobin911]

I would definitely use comp valve springs Graham

Cheers

Dougherty camshafts sell their cams with the racing valve sprind and titainium hats etc

[911hillclimber]

So, does anyone make stock form pistons that will rev but not have the high peak of the crown and hence would not need twin plug change?

[Jonny Hart]

It is a 2.7RS dizzy, points and condenser with the 2.4T rotor arm, and that's it.

All set-up by Bob Watson about 9 years ago and untouched since (literally)
Carbs are too big PMO's and Bob squeezed 247 bhp from it, and about 210 lbft iirc.

No CDI? You are really missing out. I’m half tempted to lend you a box before you tear into that engine! I’ve seen 238HP from a ‘180HP’ SC with PMOs, SSIs and CDI+. That’s bog stock with no internal work whatsoever, not even rebuilt!

[911hillclimber]

That is a kind thought, but I have yet to decide what todo.
The real purpose of my thinking is not power, but to be able to run this stock engine to 7600 or more.
It is getting up the track further before I reach the red line.
More power and torque is a bonus.
If I wanted to squeeze every drop of power from his 3.2 I would be spending just too much.
I have about 2 or 3 years left to use this car, and '10k' is not a good investment.

The car weighs about 530Kg so is quite quick enough for my skill set....

[wadsworthi]

What cams are you currently running Graham?

[911hillclimber]

Stock 1986 3.2, timed to stock spec.
The long block engine is stock 3.2
50mm PMO carbs, RS 2.7 distributor, points, simple coil and condenser.
Equal length headers to open flow fibre packed silencers.
Fuel is Shell 99 octane.

[Jonny Hart]

That is a kind thought, but I have yet to decide what todo.
The real purpose of my thinking is not power, but to be able to run this stock engine to 7600 or more.
It is getting up the track further before I reach the red line.
More power and torque is a bonus.
If I wanted to squeeze every drop of power from his 3.2 I would be spending just too much.
I have about 2 or 3 years left to use this car, and '10k' is not a good investment.

The car weighs about 530Kg so is quite quick enough for my skill set....

That’s kind of my point. I reckon you could see a 10% power increase without doing anything to the internals of the engine. Inductive ignition is all wrong for that motor, there just isn’t enough dwell time to charge a coil with points at high RPM. That’s why Porsche changed to CDI in 1969!

[wadsworthi]

If you are running stock 3.2 cams and want to stretch the rev limit with plenty of lowdown torque then perhaps put in a set of 964 camshafts and you will have no issues with valve clearance. We have run at 7500 revs on 3 litre engine for 6 seasons and 2 drivers without any issues, but the 3.2 rods are not as robust as the 3 litre I understand. Therefore an aftermarket rod set should give you peace of mind for the higher revs. I am sure there are piston sets available without the high dome, but with some valve cutouts to allow for higher lift cams.

[911hillclimber]

Yes, I considered 964 cams some time ago, but it seemed a 1/2 way house and really wanted a revvy engine to run further in a gear.
The 3.2 rods are weak, the bolts are smaller than the 2.4's and so on, and I think the cast pistons will fail to.

Jonny, the ignition on the car gave 247 bhp and took Bob a long time to find as my bill showed. I was disappointed at the number and hoped for more, but it is the rpm limit that is my issue here.

I could get a long way by the 'ebay' rods, good stock shape but forged pistons and 964 cams and a trick ignition box.

7800rpm and 260 bhp could be effective at not too much money.

[Jonny Hart]

^ Sorry, maybe I need to be clearer.

There is no point looking to rev higher since a single coil ignition activated from points does not have sufficient time to charge an inductive coil much beyond 6000 RPM. When the coil is undercharged, the spark energy is severely reduced which will result in poor performance. CDI systems do not suffer from this effect which is why all high revving engines (eg motorcycles) have CDI.

The other way round it is coil on plug or an ignition amplifier. 911 engines thrive on CDI though.

[Jonny Hart]

Some maths:

Let’s say you have an inductive coil which takes 4ms to charge. This is a typical value.

With a dwell of 38 degrees on a 6 cylinder you are applying the charge for 38/120 = roughly 1/3 of the time between spark events.

At 1000 RPM the spark event is every 50ms so you have 50/3 = 17ms to charge. Plenty of time
At 2000 RPM it’s 8ms. Still ok
At 5000 RPM it’s 4ms. Still ok (just)
At 6000 RPM it’s 3.3ms. Spark output reduced
Beyond 6000, further weakening of spark.

[911hillclimber]

Thank you for that Jonny, even I understood it.
Does location of the box have a detrimental effect?
The 911 location is quite close to the engine, on this race car finding a dry(ish) place will mean the box would be around 3 times further away compared to the 911 car location.

Best place might be behind the driver's seat. Racing in the wet makes the whole engine area saturated very quickly.

[Bruce M]

Careful of eBay rods that list ARP bolts.
The often mean ARP “style” bolts that are not manufactured by ARP, are missing the correct markings and are not the same quality.
Maybe not always the case but...

[Jonny Hart]

Thank you for that Jonny, even I understood it.
Does location of the box have a detrimental effect?
The 911 location is quite close to the engine, on this race car finding a dry(ish) place will mean the box would be around 3 times further away compared to the 911 car location.

Best place might be behind the driver's seat. Racing in the wet makes the whole engine area saturated very quickly.

Not really. Standard placement for 917 was on the firewall inside the cabin. I’ve seen them under the dash on racing 911s, can’t think why...

[Yellow491]

Graham
JE pistons better than wossner,get the correct rings for your cylinders.
Big difference between 7600 and 8000 rpm engine spec,carrillos,dont skimp on these.
For high rpm,velocity of in and out is crucial over volume with modern cam grind and proper exhuast that will give you the torque.
Twin spark is not such a big deal,can be done at a sensible budget,its only good for say a extra 25/30 bhp,whats important is a efficient burn with some higher comp pistons to get the comp ratio up.
There is not a cheap way to get a 8000 rpm engine,more cubic inches ie 3.4 will give you more torque.

As forDC cams,the guy is a absolute pain to deal and tells many stories,took me nearly 9 months to get Cams from him for a 2.0 ltr engine that i have not run yet,i wont buy from him again, there are other cams available,if you are serious about some good cams i can give you a contact to a copy of a set of my cams to help.
Throttle bodies and a proper lightweight clutch willhelp with response and pick up,you have a target time of 54.05 now to get to