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911hillclimber
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2021/09/03 17:57:50 (permalink)

8000 rpm 3.2 engine?

Hello, some reading this may well be aware of my winter project, but posting on here just in case I can find out mote info. on making my 3.2 that is stock run out to 7500 or more.
The engine is in my 550Kg  hillclimb car.
It has just been on the rollers giving 262 bhp.
I need to get this engine to run to at least 7500 rpm. It has PMO carbs, single plug heads and RS 2.7 distributor, no electronics in sight.
The engine is very fresh inside and is really good to use, long smooth power with strong torque.
So far, my plan is the following, but I will welcome any advice or opinions before I start spending money.
 
As I say, I need the engine to rev to 7500 or more, not necessarily make tons of power.
Pistons: Wossner or JE
Rods: forged steel, prob Carillo with their standard bolts or Wossner with ARP bolts
Cams: DC 60
Springs: Schrick, not sure about titanium tops
Rockers: no idea!
Ignition: possibly Clewitt, but will be machining the heads for twin plugs just in case which Clewitt and serve.
 
The engine will be a self build, this will be my 4th 911 aircooled engine.
 

 

post edited by 911hillclimber - 2021/09/03 18:00:06

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ralphmusic
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Re: 8000 rpm 3.2 engine? 2021/09/03 20:00:02 (permalink)
I’ll ping Ian our tech advisor to alert him to your question but why the higher Rev limit, power, help gearing limitations?
 
I understood when tuning a 3.2 getting much more power can be quite difficul.
 
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911hillclimber
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Re: 8000 rpm 3.2 engine? 2021/09/03 22:46:57 (permalink)
Down to reducing gear changes using the 915 box in the car. With the additional revs I can use one gear between corners instead of 2.
This is why I emphasised getting the engine to rev more than produce lots more power, although that would be useful!

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Re: 8000 rpm 3.2 engine? 2021/09/04 11:16:24 (permalink)
Just an interested observer I’m afraid Graham.
 
What’s the current max rpm? I presume you’re planning to pour in more fuel - and maybe improve the exhaust flow if possible - whilst lightening and strengthening the rotating and reciprocating parts to increase the rev limit?
 
It may be useful to contact Tuthill Porsche for some advice. They’re a very reputable established outfit for air-cooled Porsche tuning.
 
https://www.tuthillporsche.com/blog/porsche-911-engine-motec/
 
Jeff

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911hillclimber
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Re: 8000 rpm 3.2 engine? 2021/09/04 11:53:51 (permalink)
Hello Jeff, would not touch them after a poor experience several gears ago about a gearbox re-build...
 
Yes, the engine has the stock red line at 6500 where the cams drop off bit like over-revving a diesel.
There are a few hillclimbs I do where to get a better time ideally I would change from 2nd to 3rd and then back to second to take the quickly approaching corner, but the gear change is so awkward and slow I have the bad habit of revving to the limiter (rotor arm in the distributor type) in 2nd or 3rd and then dipping the cutch and essentially rolling in the gear and then easing the clutch up to get engine braking just before the corner, just simpler technique all round. The slow change accounts for maybe 1 second or even 2 and that is a country mile in hill climb terms.
Any way to save a gearchange is going to give a good payback.
Changing the box to (say) a Hewland racing box is expensive, more than doing a screamer engine!
 
I can't progress with the performance of the car as it is, so something has to be done.
 
Motorsport is a VERY bad problem to have.

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Re: 8000 rpm 3.2 engine? 2021/09/04 13:13:03 (permalink)
Disappointing to hear about your bad experience with Tuthill Graham, but I’m sure that there are other tuners out there … one of the historic Porsche race teams perhaps?
 
I can see your problem, but a delta 1,000rpm is quite a big ask in terms of improved breathing and significantly increased component loads, and if you go for higher lift cams that will give you a different torque characteristic which could be problematic. I suppose a raised final drive ratio could be an option, although that would probably introduce some downsides. I assume that you’ve looked at possible ways to improve the gearshift, or is the problem with the baulky 915 gearbox itself (I’m assuming 2nd-3rd is across the gate)?
 
How about a water-cooled engine transplant? A nice torquey 3.4L DFI engine from a 987.2 would be an ideal candidate, 320hp at 7,200rpm and 70mph in 2nd to boot! 😀
 
Good luck with your quest!
 
Jeff

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911hillclimber
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Re: 8000 rpm 3.2 engine? 2021/09/04 14:33:39 (permalink)
Yes, all very very tempting!
Looked into a Box transplant inc the slick box, but engine too wide and same for the box.
the rear chassis of the car is very narrow, it was designed for a 4 pot Pinto engine and VW based Hewland Mk7 box, all quite petite.
Box engine adds water too....
And the drive shafts won't fit....
And the gear shift is even more difficult....!
 
trying to keep it simple.
Have looked at the we've internal gate for the box. It is the poor definition of the box that is part of the problem as there is no gate on the gear lever.
changing the final drive to a taller ration will stunt acceleration, so will loose time!!
Not an easy equation I assure you.

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Re: 8000 rpm 3.2 engine? 2021/09/04 18:36:47 (permalink)
Ha! Much as I expected Graham, and the engine transplant suggestion was very much tongue-in-cheek.  Too much extra weight and complication with a water-cooled engine, although a Hyabusa engine with a sequential ‘box might do the trick! 😀
 
Power/Torque/Gearing/Weight/Simplicity … too many complications, especially when you’re on a limited budget. 
 
I know very little about these things but would a Hewland ‘box give you more flexibility with gearing in terms of being able to swap cogs for different hillclimbs? As you’ve indicated, I presume that the potentially high cost involved rules this out?
 
Jeff
 
 

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911hillclimber
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Re: 8000 rpm 3.2 engine? 2021/09/04 19:22:24 (permalink)
In many ways yes.
The engine delivers a very gutsy torque, about 240 lbft, and that is the gearbox killer.
The Mk7 will take 1/2 that, the FT200 about 200lbft, and then there is a BIG jump to near F5000 levels of torque and cost, and space needed.
The 915 in the car is good, just the gearchange awkward or very wrong.
I once changed from 2nd to 3rd but got 1st and zinged the engine big time, the internal carnage had to be seen to be believed.
It has happened since too but I'm so careful the change is so very slow, or a change from 4th to 3rd, 3rd to 2nd = 3rd to 4th not 2nd.
Awkward into a bend at 85 mph.
I'm considering fitting a WEVO internal gate kit tot he 915, about £1500, instead of the engine mod.
This might remove or reduce the surety issue of the gear change.
 
The current engine is very strong, and fitting 964 cams might allow a few more rpm to 6900 ish.
 
I'm finding it hard to make my mind up.

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Re: 8000 rpm 3.2 engine? 2021/09/04 21:03:59 (permalink)
This ... https://youtu.be/Wwb8cj-5x1s?t=1334 ... your rev. limiter ?
 
Is it worth replacing with a `simple` electronic unit ? ... I used a basic OMEX unit on my Mk1 Golf GTI that had the rotor arm type. Has both a soft and hard limit, simple to adjust / set up. It attaches to the coil posts, I still have it somewhere if you`d like to try it ? 
 
Liking the WEVO + cams option ... 

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Re: 8000 rpm 3.2 engine? 2021/09/04 21:41:49 (permalink)
As an affordable (?) starting point, the WEVO shift kit and the 964 cam option has its merits Graham … a half-way house on revs and an improved shift action may be sufficient to gain a few seconds?
 
Jeff

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911hillclimber
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Re: 8000 rpm 3.2 engine? 2021/09/04 22:43:52 (permalink) ☄ Helpfulby AndrewCS 2021/09/04 22:57:12
Andrew:
The engine has that very same rotor arm design, just set by Bosch at 6500.
The stock 3.2 is 6500 red line. Going further bothers me as the thing is written up as being fragile with smaller con rod bolts and cast pistons etc.
I really don't like the idea of going further than the 3.2 CS @ 6900.
 
To go over 7 you need a comprehensive re-working, about £6K, but you can run 8K rpm.
 
As to the 964 cams and WEVO in the box:
Just been quoted £500 to fit the WEVO shift parts in labour so with the parts, about £1500.
946 cams are about £850 if I'm lucky, labour to fit them is free as it is DIY.
Such a 3.2 would still be 6900 max, some bhp and a positive shift that would give me confidence.
 
Last time I over revved it:
 
 
https://impactbumpers.com...745c4774f9cf6d0d08.jpg
 
 
 
 
post edited by 911hillclimber - 2021/09/04 22:48:37

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AndrewCS
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Re: 8000 rpm 3.2 engine? 2021/09/04 23:02:56 (permalink)
Ouch ... 
 
Wish you well with it all 

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Re: 8000 rpm 3.2 engine? 2021/09/05 09:09:16 (permalink)
Ouch indeed! An expensive collection of scrap metal there Graham. Obviously not something you’d wish to repeat, and hopefully the damage was confined to a single cylinder making the engine recoverable?
 
£7k for the beefed-up reciprocating parts you outline in your first post is a very significant investment, and only you can decide if it’s worthwhile for future peace of mind. How marginal is the 6,900rpm rev limit with the current engine?
 
Jeff

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911hillclimber
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Re: 8000 rpm 3.2 engine? 2021/09/05 09:36:15 (permalink)
The Big Bang at Prescott hillclimb was about 5 years ago, maybe 6 and the failure was obviously the piston, the lower skirt had 'vanished' or rather totally shreadded buy the engine on it's way our of the pot to the crankcase. The conrod and bolts did not fail just met their death on the way.
The barrel was cracked from top to bottom as the piston top wedged across.
All valves were bent, 6 rockers broke and aluminium was everywhere, in the oil pump in the gallaries and the oil cooler, dry sump tank etc.
It cost £4K in bits, s second-hand but correct height piston and barrel and a lot of cleaning, and then some more cleaning.
This is why I'm sensitive to revs and missed gear shifts. It was changing from 2nd to 3rd but hit 1st instead which over revved the engine, about 10K rpm for an instant.
 
The stock 3.2 is red lined at 6500. The 3.2 CS was allowed 6.9K but they were nice engines and sodium valves, but the rest was as per ordinary 3.2.
It will probably take 6.9K for the instants I hit the rev limiter stretching between corners, but 6.9 v 6.5 is not that much.
 
Oddly, the wife said this morning that she thought this engine with 964 cams was not what I wanted, the screamer is.
She also thought the WEVO shift kit a good idea!
 
I suppose in all this these early aircooled engines are getting valuable, so such a engine when doe will keep it's value.
 
I see on ebay a 3.4 Boxster engine complete is around 6K

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Re: 8000 rpm 3.2 engine? 2021/09/05 13:07:28 (permalink)
At 10,000rpm I can see how the engine self-destructed Graham, but if the 3.2 CS was good for 6,900rpm - which presumably would still have headroom for safety (?) - then 6,500rpm would seem very conservative. With a better defined gearshift gate I’m sure you’ll be more confident pushing to the higher value. And 6,900rpm is a long way off 10,000rpm! 😀
 
Given that good air-cooled engines and transmissions are becoming scarce, I would imagine that any money spent could be considered an “investment”.
 
Jeff
 
 

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911hillclimber
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Re: 8000 rpm 3.2 engine? 2021/09/05 16:33:39 (permalink)
I see what you mean of course, and the next rotor arm with a higher limit is 7100 rpm.
However, with the last Big Bang still in my head where I very nearly lost the engine, I'm apprehensive to push my luck.
Not sure where the final limit is, 7, 7.1, 7.6?
Engine parts list is firming up and the cost is escalating.
Wossner pistons
Carillo rods with WMC bolts, good for 8K
DC60 cams, DC rockers and springs.
Scared to think ignition yet, but keeping the carbs.
WEVO shift internal gate in the box by MB Engineering who rebuilt this box twice already.
 
I will have to sell some 2 wheel toys to ease my conscience.
Need this picture to Keep the Faith.
 


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Re: 8000 rpm 3.2 engine? 2021/09/05 18:43:01 (permalink)
Those components no doubt represent a significant beefing-up of the system in your quest to extend the rev range Graham … £££! 😲
 
Maybe I’ve got this wrong but I presume you have non-electronic ignition ATM and are looking to use Clewett electronic components? In addition to giving more precise control of the spark would that also give you the opportunity for a “softer” rev-limiter rather than the sharp cut-off from a mechanical limiter, which might give you a bit more confidence for exploring the top end of the rev range?
 
One other thing that occurred to me which I’m sure you’ve considered. I don’t know if you use 1st gear other than to get off the line but if so, would it be possible to devise a spring-loaded gate on the gear lever to block any 1st to 2nd changes once you’re under way? At least it would overcome the fear-factor of buzzing the engine on the critical 2nd - 3rd change as I’m sure that most of your driving is in 2nd, 3rd and 4th.
 
That’s a great pic Graham. It’s a very neat little car … a Lola I think you said? Would be good to see it in action sometime, never having been to a hillclimb myself for some unknown reason.
 
Jeff
 
 

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Re: 8000 rpm 3.2 engine? 2021/09/05 19:54:48 (permalink)
Tried many lock-outs Jeff and all are tricky to attain a reliable movement that will take the thump of hillclimb gearchanges which are not gentle...
But, always worth the revisit to see if my poor imagination can conjure up such a clip.
The gear lever is the original 1978 Lola linkage which is very u-guided, hence the thought of the WEVO device.
 
Up to £6K so far for the engine bits and box mods.
No cam shafts available until Dec 2021 which makes me a bit nervous. They run out of blanks in 2 weeks time so may have to take the plunge early.
Discussion with the Boss tomorrow at a nice National Trust.
Been married to her for 42 years, so she will see this coming a universe away.
 
The car is a dainty light Lola T492 Sports Racer with a stupidly heavy Porsche flat 6 and box in the middle and an even more stupid pilot.

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Re: 8000 rpm 3.2 engine? 2021/09/06 10:10:12 (permalink)
I found a photo from the seat of a T492 showing the gear-shift … looks like the usual magic wand on a stick Graham, so I see your problem! I’m surprised that you can find any gears without a clearly-defined gate in the ‘box itself, so I would think that the WEVO shift kit is a no-brainer even if you don’t do anything else.
 
You’re not alone in putting a big lump in the back. There’s what looks to be a Cosworth-Ford DFV squeezed in on one car for sale (POA!).
 
Hope the discussion with Mrs. H. Goes well. 
 
Jeff
 

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