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

[911hillclimber]

Yes, that time is magic Paul.
My pb is 55.33 at Loton chasing David Seaton for a class win, just made it with a few 1/10's.
That was 2 years ago, miles off it now (age....)

There are many things to consider, the over-ruling one is 'is it worth it', Bang for the Buck etc.

All this info is good stuff and certainly allows me to look at things with my eyes wide open.

[Yellow491]

Bang for buck,a lot that ian says makes sense.
A twin spark Or single spark dizzy with a hall pick up will sort your ignition with a pair of hella or bosch ingnition modules at £20 odd each.
A 8000 rpm engine done properly gets eye watering expensive,just look at the price of motorsport rockers alone.
What can be cheaper is a pack of lead in the right boot:)

[911hillclimber]

Yes, rapidly going off the idea!
I press the right pedal as hard as I can and as long as I can, but I think after 30 years not really cut out for this motorsport lark.

I'll just make up the class numbers like I did in 2019 until I really get fed-up with bloody trailers.

[impmad2000]

Seriously, talk to Jonny about the loan. You have nothing to lose. If it doesn’t do what you expect, go back to the old system. If it’s brilliant, sing it loud and far !!

[911hillclimber]

It won't fix my problem.
I need to be able to go much further in a given gear, esp 2nd.
Changing gear ratios to do this will kill acceleration, getting the engine to rev more will do it.

Adding more power will arguably make the car run out of revs sooner forcing a gear change, just what I don't need.

My stock internally Subaru Impreza STi ran 7800 all day with zero fuss, 360 bhp, might be the answer!

[hot66]

Bit More power to compensate and then larger rear wheels / Tyres ?

[PeterK]

How about longer gears to reduce changes and bigger capacity for torque to add back acceleration ?

[911hillclimber]

Easier to change the cwp to a taller ratio, but not sure that will do the trick, would be ££££ and still have to do the engine to some degree.
The ignition from Jon sounds good, external mod so may be a good approach but @ 6K red line, will it be worth it?

[MikeB]

OK Graham, I'm finally going to give in to temptation and reply to this

So basically you want to run longer in 2nd gear.

Cheapest option is to use larger diameter rear tryes (if available). However this will raise the rear ride height slightly and potentially effect acceleration in 2nd & 3rd (I assume 1st is only a paddock gear), but this is probably cheaper than altering the gearbox gears or CWP. Bonus is a bigger rubber footprint on the ground so more grip

The second option is to increase the rev limit which will probably require a cam change so as not to lose power in the higher revs, but will give the bonus of some more power.

Maybe the best option is to do both, raise the tyre diamater and improve the engine, which with the additional power will negate the loss of acceleration of the bigger tyre. This may mean that you can reduce your max revs say to 7000 (saving a few quid) but achieve the same increased max speed in 2nd had you gone for the 7600 rev limit.

As usual you spends yer money, you makes yer choice

[911hillclimber]

You understand my options Mike!
Tyres are very limited for the rim size, I'm as tall as I can go already, no if there are some taller ones, a tyre change is £550.
I'm not messing with the box, it's taken me years to get the change/ me sorted, not going back to the start.
That brings things back to a higher red line.

Min £4000. Is it worth it when some are 4 seconds faster. 20 bhp will make little difference!

[Jonny Hart]

You’d be best getting rid of the points too. Above 7000 it can be a pain to get them to behave. Fit an SC distributor would be your best bet.

[jehintheuk]

Again, thank you all for these tech details.

Ian, you know the hills, I want torque from , say, 2500 on to a fat red line so I can avoid lumbering through a long '915' gearbox gear change wherever I can.

Thus, the purpose of this thinking is to have a simple engine that can be run to 7500 or more at minimal cost but with total reliability, I've blown this engine up once and the cost was quite tearful.

I did not think of S cams in this engine, good info James, wonder if E cams would actually be better for low down torque?

The idea of twin plug heads chill me to the bone tbh due to cost but the pistons would have a tall crown compared to the stock 3.2 pistons.
Are 'we' sure the stock rockers can cope?

I was aiming for decent low end torque from my modified SC engine and I settled on the Solex/'66 camshaft profile in my engine (the cam was from Web Cam) as a good compromise between power and driveability. The build itself is a real mismash as I had to replace my SC crank, which was damaged and I could only find a 2nd-hand longer stroke, 3.2 crank, which I used with standard 3.2 rods, arp bolts, 10.5:1 CR forged pistons, 46 PMOs, SC 3 heads (twin plugged), Nickie cylinders, SSIs and a Dansk 2:1 sport muffler (I wanted heat and relative quiet for road use). For ignition, it has a billet distributor and twin CDI+ boxes to give me a trad look. Even with the more restrictive and smaller valve SC heads (versus 3.2 heads) and the fairly restrictive road exhaust and silencer, peak torque was 262 ft-lbs at 4800 rpm but more than 200 ft-lbs from 2600 rpm on the BSM engine dyno. Peak power was 286 bhp at 6100 rpm. Obviously, it will be less at the wheels but I still think fairly strong and I really like the low and mid-range performance of the engine. The carbs still need a bit of fine tuning at the transitions but the engine is very tractable on the road. BSM did the build but the camshaft choice was the result of a long online dialogue with Steve Weiner (Rennsport Systems) in the USA.

This wouldn't allow you to run longer in second, but it might make 3rd more useable coming at it from the other direction?

[911hillclimber]

Thank you for thosedetail, very interesting.
Are those cams close to 2.4 E cams?
My hot 2.4 E engine with S Pistons was so drivable, a delight on the road and on the hills.

Would BSM run that engine to 7000 rpm even though peak power was dropping?
It would be interesting to know what max rpm the engine spec could reliably run to.

[jehintheuk]

The power doesn't actually drop off that much until about 6500, which is where we set the red line. The rockers are standard (albeit new) but the valve springs and collets have been upgraded to stop any risk of float without being too hard on the rockers. You can see from the attached table in the Bruce Anderson book that the '66 camshaft is essentially midway between the E and the S cam on the intake side but very close to the S on the exhaust.

[911hillclimber]

Thank you.
What pistons did you use please?
Did you go twin plug because of high crown Pistons?