'Fast Road' Tuning a 911 3.0

[MikeH]

While I've got no complaints about the performance of my 911, more mundane cars are definitely a lot quicker than they used to be. I'm starting to think it might need an engine rebuild in the next couple of years (after 30 years on the original lump, it probably wouldn't hurt) and maybe I should squeeze some more power out of it while I'm in there...

I'm not about to rush into this, so I thought I'd start this off as a chatty thread, and see where it goes....

It's a 3.0 Carrera (I think it's basically the same as an early SC apart from cam timing), so I'd be very interested to hear others' experiences... it strikes me that there's potential for more power, largely due to the very low compression ratio, and I notice that Newman Cams list a set of cams which might help, for fairly sensible money.

I'm also involved in messing with KJet VWs, which benefit from tweaking the Warm Up / Fuel Pressure regulator to increase the fuelling a bit. Worth about 10 bhp on a standard Golf Mk2 1.8 16v


I see the obvious pitfalls as

1. The ability of KJet to release any much more power from the engine, and the possible 'metering flap flutter' problems associated with Kjet and hairy cams. Although some Ferraris run KJet I think, so maybe the power output isn't an absolute constraint?

2. Keeping the mixture rich enough, and the engine cool enough to avoid pinking at higher compression (richer mixture, bigger injectors, extra oil coolers?).


So what's been done? What information resources are out there to help? Are there 'standard' components to swap over, which can help to release more power - e.g. higher compression pistons?

The only constraint I'd place on this is I want to stay at 3 litres, rather than going for bigger barrels and pistons...

 

[pncarrerars]

I fitted SSI heat exchangers to my '78 SC. A very noticable improvement in performance & 21 years later they still look as good as new!

 

[bones]

If I was to rebuild my SC now I'd replace the CIS with EFI from bitz racing and maybe fit 3.2 P&Cs. That combined with my early HEs and Triad exhaust should make in the region of 240bhp.

 

[MikeH]

Thanks for the replies so far... please keep it coming

@ Bones: P&C's = pistons and cylinders, or did you mean crank? I notice on Carfolio that 3.2 and 3.0 engines seem to have the same bore (different stroke) so is that the most practical way of increasing compression (rather than skimming the head, or decking the existing block) and . Carfolio lists the 3.2 compression as 10.3:1 vs 8.5 for the 3.0 engines. Is there any reason why the 3.2 pistons can't be used with the 3.0 barrels for the same effect (e.g. cooling?)


I've already got SSI heat exchangers... Is the exhaust a way of improving power then, rather than just adding noise? Any views on modifying the induction side on a kjet engine? What are the early/later differences?

I know a man who builds Megasquirt ECUs, but to be honest I was after 'invisible' mods rather than visible.

 

[bones]

I mean cylinders.
'Is there any reason why the 3.2 pistons can't be used with the 3.0 barrels for the same effect....'
Yes you can build a 3.2 short stroke engine with JE pistons from the U.S. Compression ratio is 9:8.1, combine with a 964 cam, uses CIS injection. The early HEs and a dyno proven Triad exhaust such as I have will give between 10-15 bhp, so it is not about noise.
Dynoed results for such an engine are between 30-50 bhp gain.
By Wayne Dempsey's book 'How to rebuild and modify 911 engines'.
I haven't heard of successful modification of the CIS apart from increasing the amount of fuel flowed.

 

[bones]

Hi Phil buy Wayne Dempsey's book 'How to rebuild and modify 911 engines', there is a proven chart of successful mods in there with massive bhp increases for the SC, costly yes but it can be done. If rebuilding don't expect any increase in performance if using stock parts, why should you? The SC engines that make the most bhp are modified. My 180bhp SC was dynoed at just over 200bhp after fitting '73 HEs and a triad exhaust. If I was rebuilding, a Bitz racing EFI kit would net another 25bhp straightaway, couple that with cams and pistons, compression etc and for the cost of the parts for a stock rebuild you can put together a fast SC engine for little more money than rebuilding with stock parts.

 

[MikeH]

Getting some good stuff here...

Bones, are 964 cams better than carrera 3.0 ones? I'd have thought the stock ones weren't bad considering they produce about 16bhp more than an otherwise very similar early SC engine. Or were horses just smaller pre '78 []

I'm yet to investigate with the 911 version of K-Jet (CIS), but the trick with the VW version is to modify the warm up regulator (WUR) by drilling a hole in the plate at the back to expose the 'factory sealed' allen screw. By reducing the control pressure you up the fuel pressure at the injectors, and effectively increase the flow rate of the injectors. K-jet golfs (especially the 16v ones) tend to run lean at the top end, and this helps a great deal on a modded 2.0 16v, with 200bhp being just about achievable on the otherwise standard Kjet setup, with head-work, cams, and a decent exhaust. Stealth Racing (Nr Banbury) are the acknowledged experts in this WUR mod, but anyone could do it with a rolling rode and lambda probe up the exhaust to measure the AFR. I'd have thought that on the 6-pot Kjet setup, then 250 horses should be possible via Kjet, depending on the how conservative the ignition map is.

It's effectively the same as putting an adjustable, or higher rated fuel pressure regulator on an EFI car (e.g. a Porsche 944 regulator works well on a Bosch L-Jet (Digifant in VW speak) golf, to get the best from a modified engine.)

Anyway, I digress, but I'd hypothesise that upping the fuel pressure on a KJet 911 must be helpful if you go for a higher CR, to avoid pinking, melted pistons, etc.

I'll have a look for that book. As I said earlier, I'm in no rush to do this, as I'm concentrating on tweaking my trackday prepped golf at the minute.

I notice there's no mention of head work - are the 911 heads properly hand finished from the factory then?

 

[MikeH]

ORIGINAL: phillipps44

Mike,

I was recently at RSR Engineering for a tune up and had a long conversation with Russ Lewis about this subject.
He told me (and he is regarded as top 3 or 4 best in country) that even with a rebuild to late SC spec (all standard bits) and with an SSI exhaust he had never been able to squeeze more than 212 bhp out of the SC engine. This would all
come out at a cost of over £5000. It doesn't seem worth it for that engine especially when, in the end all you will get is half a second off the 0-60.
I personally feel the way to go if your'e going to spend loads of money is a 993 engine transplant. By the time youv'e sold your SC engine you will probably have not spent much more and you have an almost stock 100bhp extra on tap.
Good thread, lots of ideas, much to be learn't.      

Hi

Thanks for the reply, but I'm definitely not after a capacity increase, as I want to keep the car outwardly standard, including the engine bay. I'm also working from a very original matching numbers car, so I don't want to change from the 'spirit' of the original car.

 

[MikeH]

ORIGINAL: bones

Hi Phil buy Wayne Dempsey's book 'How to rebuild and modify 911 engines', there is a proven chart of successful mods in there with massive bhp increases for the SC, costly yes but it can be done. If rebuilding don't expect any increase in performance if using stock parts, why should you? The SC engines that make the most bhp are modified. My 180bhp SC was dynoed at just over 200bhp after fitting '73 HEs and a triad exhaust. If I was rebuilding, a Bitz racing EFI kit would net another 25bhp straightaway, couple that with cams and pistons, compression etc and for the cost of the parts for a stock rebuild you can put together a fast SC engine for little more money than rebuilding with stock parts.

Just ordered it on ebay []

 

[bones]

The 964 cams seem to be a favourite if you want a higher revving engine, just keep researching on the net and a consensus will emerge on their value. I think the way to go is with higher compression, a larger displacement and EFI. I don't know if the WUR on 911SCs has the adjuster you speak of but you could tap the body and fit your own if not.
The early SC heads have the bigger inlet valves.

 

[MikeH]

Thanks again. I'll have to have a look at a head the next time I'm at an autojumble, to see if there's much scope for improvement. It would probably cost me about £200-250 + VAT per head (EDIT: Should have read per SIDE) to have them ported by my cylinder head contact (see the "3 Angle valve job" thread), so well worth investigating, compared to the prices of other 911 items.

Sounds like high comp pistons are definitely the way to go, either from a 3.2 or a 204 bhp SC I guess if I take Porsche items. Although it wouldn't be a huge surprise if the aftermarket 'racing' pistons are cheaper!

Any idea on the relative valve sizes? I'll check out the manuals to see if they mention it, but if you happen to know then feel free. I wonder if the early SC and Carrera 3.0 have the same head and valves?

 

[Guest]

Hi Mike,
Have been following this thread with much interest.
I have been reading my copy of
911SC" The esential companion by Adrian Streather"
I bought my copy from the club shop, the book is not cheep but you would find it most informative with regard to extracting more power from a 3ltr SC.

There are options for more power all the way up to engine transplants which I know is not where you are coming from.
I will type the first paragraph which will give you the flavour of the information.

"A potentially serious problem facing Porsche owners in thier insufficient research before embarking on performance modifications. Failure to do this research can lead to expensive failures or modifications which do not perform to expectations."

Good luck
John

 

[bones]

Sorry Mike I fed you a bit of incorrect info there, valve sizes are the same for all SCs but the ports differ. 78/79 SCs have ports
int'39-out 35 and for 1980 on
int'34-out 35. and valve spec. is
int'49-out 41.5 all models
Carrera 3.0 engines have the same valves and port sizes as early SCs but the camshafts are timed differently. There are lots of charts and specs in the Wayne Dempsey book.

 

[bones]

John's right this is an essential book for the 911 owner, it puts things in perspective and helps you understand just how good the original is without messing with it and how good it can be with a little informed tweaking.

 

[MikeH]

I think I'll read one book before deciding whether to buy the next one... but I'll bear it in mind.

@ bones - I'd heard/read about the cam timing. As far as I'm aware that's the main (or only?) diff between the Carrera 3.0 and the early SC.

Looking through the Bentley I see diagrams which suggest the valve seats are already 3-angled from the factory, so there may be limited scope for head mods. At a later date I'll do more research on the cams to see if 964 or C3 items provide more lift, but more 'squeeze' seems to be the obvious opportunity for more power, with some of the other items already mentioned like exhaust and heat exchangers.

 

[bones]

I haven't heard of many people changing valves to bigger sizes for fast road cars but the early heads with the larger ports give more scope for tuned engines. I'd keep it simple if I rebuilt, go for higher compression, bigger displacement and chuck the CIS.

 

[Guest]

Mike

You may like to check out this article
http://forums.pelicanparts.com/showthread.php?s=&threadid=147128&perpage=20&pagenumber=1

Cheers

 

[MikeH]

Stunning info! Looks like exactly what I need to know. I'm going to the US with work soon, so might see about a little personal importing while I'm there. []

 

[Guest]

Congrats Mike on owning a proper car. I also own a C3 and they are the bees knees - you can see mine at www.continentalorange.com.

You have quite a few options open to you even staying with the 3.0 displacement.

Cheapest option to increase performance is to lose weight. My car is down around 965 kilos now on a dry fuel tank but all else full, this is with stock glass and the ally bumpers and an ally Heigo cage. You can feel the weight loss as soon as the car turns a wheel. A lighter car is an all-round performance gain - motor/suspension/brakes all have less to do and the car is a hoot to drive. Mine also runs LSD with a 7:31 diff in a mag box, so is shorter geared than stock. It tops out at under 140 but gets there a bit faster. A stock C3 is faster than a 930 to 60 so this is a little sharper still, but 60-90 is where the fun really starts.

Your motor is rather different to the early SC unit. You have a different ignition setup, diff injection components and the same 6-bolt crank as the '73 RS, so a revvier engine. The 930/02 motors are rated at 200bhp, but even stock they should be more than that. Last time mine was dynoed (stock) it made a flywheel extrapolated 202 with a high-end fuel pressure problem, this is now sorted so the curve suggests it should be doing 210, maybe even slightly more. Not unheard of - I know stock SCs making way more than their 204bhp and my own SC makes 208 stock.

I have the MS/Bitz racing setup to go in my C3, and some 964 cams also. This will be twinned with SSIs and a custom 2in/3out M&K muffler, and uncapped I am aiming at 230 (flywheel) on stock pistons. I am chasing a set of 98mm P&Cs to give me a displacement increase and allow me to build a 3.2 short stroke motor, but that will require a diferent intake also to get the best out of it. You can fit the Bitz kit and keep it all looking stock.

You should dyno the car and weigh it also. Older cars can have fuel pressure probs at revs that may not manifest themselves until it's too late, so a dyno run is handy for measuring the AFRs at the top end. Knowing where you are on the scales is a great idea for early 911 drivers - if there is stuff in the car that you are not using then think about getting rid ot it - every kilo is noticeable and weight loss is easily reversible.

If you've not dyno'd yours before, then I highly recommend Bob Watson. He is a great guy on C3s, and all the impact bumper cars, a CIS/K-Jet afficionado and knows what to look out for on the dyno - his is working non-stop.

Hope this is useful. If there's anything else I can help you with, give me a shout via my site. Guy is the C3 club register by the way, make sure he has your details on file.

 

[MikeH]

Thanks John... good food for thought there.

I did some fiddling with the car at the weekend.

....before I do anything else, I need to replace the injector seals (and replacing the injectors might not be a bad idea either, but I'll have a look in the service history to see if they've been done before.), as the injectors feel a bit loose, so are probably drawing extra, un-metered air.

I was also surprised to notice that the air intake draws hot air from on top of the engine. Surely this isn't doing any good in terms of the density of charge getting to the engine. Is there any gain to be had from moving the intake pipe? Maybe I'm missing a part?

the Warm Up Regulator looks very similar to VW Golf 16v ones, so needs pulling off to see if it can be tweaked in the same way (drill through the brass plug on the back and adjust allen screw to reduce control pressure - helps the car run richer) If anyone's got an old scrap WUR I can play with I'd be happy to hear from them.

What are the main ways of reducing weight on these cars? I'm not too keen on taking any weight off the front end, as I notice a difference in the handling with a full tank, and tend to run it as full as I can.

Where's Bob Watson based? I live in Windsor, although the car is stored out in the sticks nr. Oxford. If he's reasonably local I might get him to look it over. The car needs a service anyway.