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eNGINE REBUILD

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james ashby

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can anyone help me please, i am undertaking a full engine rebuild, ie new pistons, barrels etc, how do i get more power out of the sc engine. I have asked a few people and they say if you want more power just put a 3,2 in but i have ssi's for a 3.0 litre, and have just spent money on my webers to run on a 3.0 litre, there must be things you can do ie cam shafts, different pistons etc. I look forward to your comments.
 
James there is a lot you can do but for accurate info I need to know , are these Weber 40 IDA-3C carbs?
 
They are weber 40 ida's, but i dont know about the 3c's. i have just spent £600 having them rebushed, new spindles and modified for more power (extra 25 bhp) by Chatsworth Motors who are "TheWeber people" i have been told. I have brand new ssi heat exchangers to go on. And the rest is to be decided, i basically have a good crankcase, good crankshaft, and a pile of shit left!

 
James

With the fitting of carbs a camshaft change is made possible. The camshaft fitted to the 2.0-2.4 litre S engines the seem a popular fast road cam that would allow the SC engine to rev higher and give more power. However the SC pistons cannot be used with this cam as I believe that the valves will hit the pistons crowns. Francis Tuthill have a special piston that they use in their 3 litre rally engine presumably to get over this problem, may be worth asking if they can supply. However like all porsche modfications its easy to make expensive mistakes so I really recommed taking advice from the experts.

good luck

Bruce
 
Thanks, i have taken advice from two reputable porsche racing places, who both say stay standard, which i find hard to believe that you cant get more power reliably from these bullet proof engines. When my brother has got a (surprisingly reliable) 363 bhp out of a 1.8 Seat Ibiza Cupra R!
I will endeavour to talk to more people, however you can see from this thread that not too many people are throwing up ideas, so standard and a supercharger may be the way to go. Only time and my budget will decide!
 
I can't understand why some tuners are telling you to stay stock unless they just don't want your business due to pressure of work, there are a lot of tuning parts available for the SC talk to Martin Harvey (tunes eight cars in the club championship - 01992 462662), Tuthills, Autofarm and JZ and call Jez Parsons of Carrera performance he may be just the man you need, tell him I told you to call - 01403 891140. incidentally he runs a 135mph VW bus with a 911 engine in the back! One point to bear in mind when you have tuned the engine is the exhaust make sure you get a dyno tested device such as a Triad 2in 2 out or a factory race exhaust, most other 'performance' exhausts add noise and that's it.
A 3.2 conversion with no other mods except a tweak of the mixture will net you 220bhp combined with an early 911L type cam with carbs and the exhaust changes you will get a big horsepower gain, personally I would have fitted EFI but if you have the carbs already I guess they'll do. Mahle make wedge shaped piston sets for this conversion and you will need to gain more valve clearance or it won't even run. Mahle also make racing pistons wth a compression ratio of 10.3:1 so there is plenty of stuff out there.
Buy Bruce Anderson's 'Porsche 911 Performance Handbook' and Wayne Dempsey's engine rebuild book, both invaluable and if you don't know already go to Pelican parts forum and search for days (button top right of front page) to find the info you want.
http://forums.pelicanparts.com/forumdisplay.php?s=&daysprune=30&forumid=8
Let us all know how you get on . If you are in the London area I'd be willing to lend a hand.
 
hi, ive got both those books and have read the relevant bits, initially it was yeh i can do this but then ive bottled it. I talked to Paul this morning at Tuthills who was very positive and helpful, talking cosworth pistons and twin spark ignition, poplished heads etc, but i can kiss goodbye to £10k. So i am in a bit of a dilemma at the moment, of the best way forward, unfortunately i am not in London or anywhere near, or i would take up your generous offer. I need to work out my budget and then decide the way forward. Thanks again for your help. James
 
You already have some of the costly bits, so now it is a question of how much you want to spend - or to put it another way, how much power do you want?

I think you have a number of options and they are something like this:

1. Standard internals and bolt-ons: Use std pistons and cylinders, std cam and bolt on the SSIs and carbs. Bruce Anderson says the SSIs are good for 15hp and the carbs will certainly provide a less restrictive intake. I would guess you could get an additional 20-30hp with bolt-ons alone. The Ps & Cs, cams and heads will all limit the power in this set-up.

2. Top-end plus bolt ons: As above but do cams and a light port and polish. The 964 cam will work without clearance issues and offers a better top-end and a little more midrange than the SC cam. What year SC motor do you have? Early and late SCs have different heads but all can have improved gas flow. My 3.2 has just got 993Supercup cams which run without clearance issues in a 3.2, they may be OK in an SC motor. You will need to check with someone like Dougherty cams. Check out my dyno sheet in te "Dyno Update" thread on the 3.2 board. I would think that with 964 cams you will gain 10 hp over option one and with 993Supercup cams you might get 20hp over option 1 - so maybe 240-250hp.

3. The sky is the limit: Once you decide on new Ps & Cs you can run any cam you like and you can build the engine for whatever rpm you like. I know of a 3.2 built from a 3 litre making 285hp with "S" cams and carbs running an SSI exhaust. I know of a 2.8 making 265hp on "S" cams, with RSR headers. For really big hp you would want 46mm carbs not 40s but running an S cam and SSIs, would make a very streetable motor.

It depends how deep your pockets are but if it was me, I would be thinking of a top-end with cams.

Richard

PS, you may also want to look at a lightweight flywheel, clutch, pressure plate and short gears to get a real flyer. I am running a trick lightweight aluminium pressure plate and lightweight 930 Sport clutch in my G50. The pedal weight is a little heavier but it is very livable and driveable and you can dump the clutch at 5000rpm without issue. I wish I had done the LW flywheel at the same time. The engine is very blippable as it is but I would like an even lighter flywheel effect. Somehow it just feels sportier.
 
thankyou, i do have alot to think about, my engine is a 1979 188bhp motor, and with the webers and early heat exchangers (not ssi), it was rolling roaded at 206bhp. Which i was chuffed with at the time. I would ideally like 250 bhp, and good mid range power so i will probably opt for something like your middle option. However my pistons and cylinders are knackered so i might as well go for option 3 (the sky is the limit). For christ sake don't tell the wife!!!

What i really want is someone to tell me what i want, sort it out for me, and if willing pay for it as well!!
I will endeavour to keep you informed of my decisions.
 
Tony Garcia on Pelican has an SC with a rebuilt-as-stock motor which is also fitted with 40mm carbs with 20/21 cams, SSI's and a custom silencer. There is a great thread here about a contest he ran to guess the BHP of his car on it's first dyno run.

There are always mega debates on there about how to get the most out of the 3.0 - another superb thread here about carbs versus CIS and EFI on the SC motor. Carbs/cams/pistons/SSI's definitely the way I would go as the carbs are just so wonderfully responsive. I wouldn't be overly freaked about being at 'only 240' rather than 250 if I had carb throttle response, as I think you can work wonders with 240bhp in a lighter SC. If you have changed to carbs yourself then you can certainly rebuild that motor using the experienced Pelicaners to show you the way.

'Fran's People' [8D] know the 3 litre inside out though, so Paul was a good guy to speak to - here's one they made earlier.

Tuthills033Small.jpg
 
Hi James

I've been going through this as well. The two options I got down to were
A) carbs and 6 throttle bodies which apparently will do the business with some tuning refinements - there were differing views on how much output would be added but mixed views on what it would do to driveability - I know of someone who bought a car with this conversion and hated it so much they sold the engine and replaced it with a 3.2 RS engine. JZ can do this mod, so can G Force and I'd be surprised if Jez Parsons couldn't do it the same or better.
B) Top end re-build. Capacity increase, new pistons, flowed head, new cams etc etc. Very good reports on driveability as well as output. ££ expensive. This is probably what I'll do eventually - after losing some weight (aircon for starters) and doing: wider wheels, tyres, new bilsteins, bigger torsion bars etc, strut brace, geometry and corner weighting, And then uprated brakes ..... to handle the extra power
Other options I looked at:
C) Supercharging - very mixed views. Autofarm can do it and would stand behind the work. But I have also been told that it will ruin the engine if not done right.
D) Turbo Pistons - have not got to the bottom of this one. It was a factory mod by request on run-out so I don't see why not but have been told A) it can be done and B) it can't be done Might depend on which SC engine.

Incidentally there was an SC with a 993 varioram engine and a 915 box at Brands doing the Speed Championship![:D]

Exhausts - see separate thread if you didn't already: http://www.porscheclubgbforum.com/tm.asp?m=149732 anyway Pete covered this above.

 
The factory built to special order 100 (approx) 3.1 ltr SC s. They were claimed to deliver 220 bhp with changes only to the injection. I don't know if these are same engines as Bruce Anderson refers to in his book as 3.2s or if they use turbo pistons. The 3.1 ltr engine has the spec stamped on the engine casings. To make the most of his mods James should lose some weight on the SC the 911 was a fat old bugger at his point in it's long life. Fibreglass all round and a stripped out interior I think aiming for 1000kg.
 
ORIGINAL: jerry911sc

Hi James

I've been going through this as well. The two options I got down to were
A) carbs and 6 throttle bodies which apparently will do the business with some tuning refinements - there were differing views on how much output would be added but mixed views on what it would do to driveability - I know of someone who bought a car with this conversion and hated it so much they sold the engine and replaced it with a 3.2 RS engine. JZ can do this mod, so can G Force and I'd be surprised if Jez Parsons couldn't do it the same or better.
B) Top end re-build. Capacity increase, new pistons, flowed head, new cams etc etc. Very good reports on driveability as well as output. ££ expensive. This is probably what I'll do eventually - after losing some weight (aircon for starters) and doing: wider wheels, tyres, new bilsteins, bigger torsion bars etc, strut brace, geometry and corner weighting, And then uprated brakes ..... to handle the extra power
Other options I looked at:
C) Supercharging - very mixed views. Autofarm can do it and would stand behind the work. But I have also been told that it will ruin the engine if not done right.
D) Turbo Pistons - have not got to the bottom of this one. It was a factory mod by request on run-out so I don't see why not but have been told A) it can be done and B) it can't be done Might depend on which SC engine.

Incidentally there was an SC with a 993 varioram engine and a 915 box at Brands doing the Speed Championship![:D]

Exhausts - see separate thread if you didn't already: http://www.porscheclubgbforum.com/tm.asp?m=149732 anyway Pete covered this above.
Click to expand...

Just a couple of small comments.

On the Carbs/ITBs point, as you (James) have already found, cards on a std engine are not going to give you a whole lot of extra power by themselves - about 16hp, yes? Yes, they provide much better airflow than the somewhat restrictive CIS intake and CIS flapper air meter and yes, they provide much better throttle response though CIS will supply as much fuel flow as you need right up to 400hp turbo applications. Probably the greater benefit of Carbs/ITBs is that you can run any cam you like (provided you have adequate valve to piston clearance. All the common plenum induction systems - SC, 3.2, 964, 993 - cannot deal with the reversion from a cam with lots of overlap whereas MFI, Carbs, ITBs can. So the most cam a common plenum engine can run is 993 Supercup (or slight modifications on that type of cam). The second limit on cam selection is valve to piston clearance. SCs and 3.2s have a high domed piston and will in general terms have clearance issues with anything more than a 993 Supercup cam - I don't actually know if this cam even works in an SC. But I digress, a properly set up std engine on Carbs/ITBs (like James has) should be a fantastic engine to drive. It makes more hp and should have great throttle response, which feels like an extra 20hp, and should otherwise run just like normal. Only a car that is not properly set up will have drivability issues because there is no mechanical reason (unless you get the wrong size carbs/ITBs) which would cause a driveability issue - think about it [;)]

Secondly, installing Turbo pistons is a step in the wrong direction unless you are also going the forced induction route. Why, because they are low compression pistons. You would cut the horsepower by a third. If you just mean a larger diameter piston with a normal compression ratio then why not go to 3.2 capacity? Or indeed even larger? You have to replace pistons and barrels anyway so get the most capacity you can.

James, if you really need new pistons and barrels then you might think of replating your existing barrels with nicasil and buying JE pistons in whatever spec/shape/compression ratio you want. I think this will be cheaper than the Cosworth option and is more tried and tested in the 911 universe. If you pick an "S" type piston then you get deep valve pockets and can run pretty much any cam you like. I would talk to John Dougherty before picking a cam, but something like an S cam or Mod S cam is going to be drivable and give good horsepower without having to run stupid rpms. The next question once you decide to do pistons and barrels is to decide on a rev limit. This goes hand in hand with the cam selection but is also a dollar question. Building an engine for a 6500rpm rev limit means you use std valve springs, retainers, rod bolts etc. Building a 7000rpm engine means you are on the limit for std parts and have to think about upgrades. I did race valve springs, Ti retainers, rod bolts, head studs etc so I built for about 7500rpm but rev limited to 6850 as peak peak is 6300rpm with my cam and peak power drops below 250hp at about 6700rpm. A further question to think about is ignition. Do you go twin plug? A 3.0 litre with deep valve pockets and normal compression - say 10.3:1 - should be ok on Super/Optimax, but go for a much wider piston and you start to need twin plug as the deep valve pocket pistons split the combustion chamber in half and you are more likely to get pre-detonation. So this is another cost consideration.

If it was me, I would check whether your Ps & Cs are in spec or really need replacing and then make a decision after that. If you can reuse them, then you are limited on cam choice to 964 or 993 Supercup - like I was. If you have to replace them then the only limitation is what you want to spend. I think a 3 litre - less than 200cc smaller than a 3.2 - with 40mm carbs, SSIs, and 993 Supercup cams is potentially a 250-260hp motor, maybe more. Your 188hp engine has the good heads so its a good place to start. If you do Ps & Cs and S or better cams you are certainly building 250+hp engine - all IMHO.

HTH
Richard
 
Just remembered seeing this on Pelican, which may be of use:

3.0L - stock of course (95mm bore x 70.4mm stroke)

3.2L - 98mm bore x 70.4mm stroke (no case machining required) AKA short-stroke

3.3L - 100mm bore x 70.4mm stroke (case opened to 105mm)

3.4L - 98mm bore x 74.4mm stroke (no case machining but also need 3.2L Carrera crank & rods)

3.5L - 100mm bore x 74.4mm stroke (case opened to 105mm and need 3.2L Carrera crank & rods)

3.6L - 100mm bore x 76.4mm stroke (case opened to 105mm, pistons need addl. machining, 964 crank w/ 3.2L Carrera rods)
 
James is that 206bhp result at the crank or the wheels I hope at the wheels if not then you already have a problem somewhere as that set up providing you have decent fuel, engine in a good state of tune and a clean air filter and not to restrictive a rear silencer should yield at least 210bhp. 250 bhp is achieveable I recently had the pleasure of being a passenger in a Tuthill rally 911 and it was an absolute animal, it was on carbs and producing about 240 bhp. Revved higher than stock though, extremely responsive and quick, also very light I think that is essential when tuning these car you lose some weight and get more from the brakes and suspension you already have because that is the next area that will need improving. In the past I have considered putting on 3.5 litre barrels I saw a 911SC in the 80s with such a mod and with no other mods apart from the exhaust and HEs it was producing 235bhp! I haven't seen the owner in years and I don't know what pistons and cylinders he used but it was massively torquey . Talk to Jez Parsons and Martin Harvey as well as Tuthill.
 
James
At the Brands festival Porscheshop had a 911 race car with a 3.0 SC engine on carbs so they might be worth a call as well for some advice, the engine bay and install looked very nice and minimalist. Your point about the " experts" not being very forth coming is quite common.
Baz
 
Yes that was 206 bhp at the wheels, i will have to confess at this point i am running the sc engine in a 73 car, so weight issues are not as bad as the sc. I believe my barrels now have 6 thou clearance and have a step in them. My porsche bloke says they are scrap, but your comments would be appreciated.
Today i have just been offered a 1982 204 bhp sc engine and gearbox (100k miles) out of a crashed car for £2800. which i thought was not a bad deal.
Someone might know the car it was a full insurance payout of £14k, is dark metallic green and had a massive front end shunt. If anyone can enlighten me on this car and its history, i may go down this cheaper route, now and modify it a t a later date.
 
That's sounds like a good deal on the engine and gearbox providing they are in good shape but that is pretty hard to check unless they let you strip it (doubt it) and as your current cylinders are well outside spec. you want to be buying good cylinders. If you are going the upgrade route why are you interested in another engine just rebuild yours with new pistons and cylinders, it's unusual for Nikasil cylinders to have that much wear on them at that mileage.
 
Well there you go then, marry the two engines together and you are good to go. Use the early heads with 964 cams on the 204hp engine with SSIs and your carbs. If you are 204 rwhp, then you already have 225-230fwhp and the high compression SC motor with the better early heads will - with carbs and exhaust - give you 240fwhp. Job done.
 
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