3.0 SC for a 650kg car

[3.0SC MUC]

Hello,

I have been reading a lot in the last days and here is my situation. I am rebuilding a 3.0 Euro SC 1981 engine which fortunatly has Mahle-Nikasils in it. This is the reason why I will not go for the Max+Moritz 3.2 option since they are as good as new. The engine shall be tuned just like many of you talked about here before. But now here is the difference: The engine is supposed to be for a very light car that only weighs 650kilogramm (about 1300pds). The car is supposed to be used 50%track and 50% on the street. I am thinking of of a car which can softly be driven in town and - when needed - can be raced on the track when you go beyond 5000rpms.

The combo I am planning to do right now is:

1. JE pistons with 10.3CR and reusing the Nikasils thus keeping 3.0l displ.
2. 906 cams
3. 46 carbs
4. weight of flywheel is 4.5 kilogramm ( about 10.5pds)
5. Port sizes are 34IN/35EX it`s a Euro 930/10
6. all the usual upgrades like stronger head bolts and rod bolts (ARP or raceware)

I am aware of that the 906 cams will be esp. suitable when using an rpm range of 5.500-8.000. But please consider that the car I will be using is much lighter than reg. 911s and only weighs 1350pds. Also, I have a 3.0litre displacement which will add torque at lower rpms when compared to a 2.0.

My questions are now:

1. When considering these goals - what do you think of this combo?
2. Would you advise to use stronger valve springs or stay with the originals?
3. Would you advise to widen the inlet ports from 34mm to 39mm and keep the exhaust ports at 39mm?
4. Would you suggest twin plug set up-we have 100octane readily available in our country?
5. What other things would you recommend ?

Thanks
Michael

[kenikh]

906 cams will run fine in a 3 liter, from what I understand. The displacement is the equalizer. That said, unless you will run the car to 8000 RPM, regardless of drivability, you will be giving up power. If the car will occasionally see 8K, go for it. Also remember, there are more modern cams that will get you 906 performance with better torque. John Dougherty will be happy to discuss this with you as long as you'd like.

[kenikh]

Oh, your questions!

My questions are now:

1. When considering these goals - what do you think of this combo? overall good, but not a fan of the cam choice
2. Would you advise to use stronger valve springs or stay with the originals? Stronger; Dougherty or Supertec springs will do the trick
3. Would you advise to widen the inlet ports from 34mm to 39mm and keep the exhaust ports at 39mm? If you plan on using anything more than an E cam, yes. 906 cams on a 3 liter will need 40 - 41mm ports.
4. Would you suggest twin plug set up-we have 100octane readily available in our country? yes; UK 100 octane is about the same as US 93 octane which means twin plugs needed at above 10:1
5. What other things would you recommend ? Search this board; these topics have been covered ad nauseum.

[Eagledriver]

With your stock rods and crankshaft you cannot rev the engine high enough to take advantage of the 906 cams. I would use 7300 RPM as a redline and port the heads to 39mm intake with the 35mm exhaust ports. A Solex or S cam would be a great choice for this engine. Stiffer springs for the valves would be a good idea. I'd lower the compression to 9.8 and keep the single plug system. You'll only give up 10 HP or so and save alot of money.

-Andy

[Flieger]

650 kilograms for a 911!!!

What kind of mods did you do?- that's an incredibly light car

[3.0SC MUC]

Flieger, the engine is not for a 911, its for a 550 that I am rebuilding rigt now.

Andy, are you sure that the regular crank plus rods can not be rewed up to 8000rpms? I believe I have heard of, that it can be done when using Raceware con-bolts. It allready has the 35/39mm ports and the higher 9.8:1 compression pistons since its a Euro SC, but these are for the CIS and the stock cams. I will prob. have to change the pistons. I agree on the solex cams that they are great cams for the engine. They would be my second choice if I decide to go the less rew. route. If I decide to do so, do you still think its necessary to use stiffer springs for an 7300rpm engine?

Kenik, I live in Germany and I am not quite sure if our 100octane fuel is the same than that in the uk. Its kind of a new fuelmixture which they call V-power for example. I am still hasseling with the dual plug if I need those or not. As far as the cams, what other cams besides the 906 do you have in mind?

Michael

[tom1394racing]

If you are planning to use the stock CIS pistons, I would check with the experts to be sure that you can use 906 cams without having piston to valve interference.

High lift cams and CIS pistons don't usually work.

[euro911sc]

Does 8000 rpm require case mods like shuffle pins, boat tailing? what about crank: like oiling mods, knife edging? Mooning the cyls?

There was an article in... Excellence or Pano about 2-3 years ago that had a guy who was pushing 8500 on his engine. Might be worth digging that up and seeing just how he did it.

Cant wait to hear it scream!

Best regards,

Michael

[Steve@Rennsport]

JMHO, but I would not use 906 cams in a 3.0 if it will see ANY street use. They do not have acceptable drivability for that type of use without a lot of difficulty.

There are now far more modern cams that can deliver a higher RPM power range without all the issues that 906 ones have,...

With your existing port sizes, it would be massively overcammed anyway. Choose a profile commensurate with your engine configuration and expected power range for what you will do.

[Eagledriver]

I'm only regurgitating information from Bruce Anderson's book and from talking to other engine builders that I race with. Once you get above 7500 RPM you need titanium rods as a minimum. The valve springs required depend on the cam profile. Your 906 cam profile has very slow ramps so the stock springs may be OK. For 911S cams they maybe OK to 7300 RPM. I know with stock SC cams like on my engine the valves will float at 6900 RPM with stock springs. High performance cams like the GE series or Elgine Mod S will float the valves even sooner.

-Andy

[3.0SC MUC]

Ok, I think I am cured about the 906cam. So my setup changes to:

1. s-cam or similar
2. JE pistons 10.3:1
3. 46er carbs
4. Rev limit 7500rpm`s
5. Dual plugs for sure

When thinking it over again, more questions came up. When I will use this setup, can I:

1. keep the rods
2. keep the valve springs
3. Would I have to do anything to crank and case?
4. How high can I go with compression - will do twin plugs ?
5. What portsize would I need to use-rigt now its 34/39mm?
6. Can I regrind my 3.0SC stock cams to an S-profile?
7. anything else I might consider?

Michael

[Eagledriver]

You can keep the rods. The valve springs will be marginal at best and you'll have no excess spring rate for small over-revs. You can get the mildly stiffer Dougherty springs for something like 300 dollars and not have to worry about them. Case and crank will be fine at that rev limit. Ports are perfect. I don't know how high you can go on the compression ratio. Your SC cams would have to be welded up and then reground to S specs. I would talk to John Dougherty (camgrinder on here) about the cams and the springs. He can fix you up with everything you need in that department and it won't cost you an arm and a leg. From what you are describing you could be looking at 275 HP or so.

-Andy

[davidppp]

Hi...one question...

Have you any actual hands -on experience of driving very light cars in the wet on the road?

If not, think again..you will find a very cammy engine is extremely dangerous..ask the driver of the BMW M1 who tried to follow me around a wet roundabout in my 550 rep..he was even more scared than I..

The SC is the strongest bottom end of all the bigger motors AFAIK.no probs there.

But IMHO you should pick up thwe phone and right now talk to John Dougherty or similar..likely you will then decide to fit a modern broad powerband cam, with higher CR and twin plugs..

Kind regards
David

[JohnJL]

I don't know how that will be streetable, you must be planning on no rollcage? My 83SC has NOTHING on it that it doesnt need including zero upholstery, padding or deadening, FG 74 RS narrowbody bumpers and no spare or tools, lightweight battery, no AC or radio and no CIS. It comes in at 1040KGs with me in it. I weigh 80.

[Laneco]

Micheal,
Welcome to the "stupid-fast" replica 550 club! Please install really really good brakes....

SS 3.2
10.5 compression
Dual plug crank fire

angela

[3.0SC MUC]

Hi Laneco,

thats nice to hear from you again. You probably don`t know that you know my car quite well - just take a look at Dave A. formers 550 and you`ll know;-) Its has been sitting for a long time at my house. I decided to drop the TypeIV. I hope I`ll get the six cylinders in there - it`s a Beck... but with a more decent rear suspension. BTW nice picture of your car, I hope I will also get there some time.

I think it will be a good idea to talk to Mr. Doughtery about cams etc. Does anyone know how I can call or better skype him?

Michael

[Laneco]

Oh so YOU got Dave's car! I wondered what had become of it. Sounds like something very very wicked is planned for this...

We've rolled up close to 12,000 miles on the spyder... I even got stuck driving it with snow on the ground this last April. Not on my list of things to do ever again. Drove it five hours straight in the rain also, but it wasn't overly cold so despite sitting in standing water it was actually reasonably bearable. STeve had taken great care to seal the floor up, but he was thinking of keeping the water below OUT, not the water from above! I was looking around for a bathtub stopper to pull!

May I throw out a suggestion for street driving? The super light flywheel is a kick in the pants on a light car most of the time. With six cylinders, lots of compression, low weight and a light flywheel, the braking effect of the engine when you drop the throttle is really signficant. I suspect you are a far better driver than I am, so in your case it may only be a matter of "caution."

As for me, the heavier flywheel helps me keep my only semi-competent self pointed in the correct direction.... Another plus is it really makes it easy to drive in traffic.

Please please when you get this running post a video with AUDIO for all of us to enjoy! Oh by the way, there are a few pitfalls coming your way for fitment and cooling. If you want to give us a shout, be glad to send pictures of how we did it right (or wrong and then right as was often the case). Might save you a good bit of aggravation.

angela

[camgrinder]

Originally Posted by 3.0SC MUC

I think it will be a good idea to talk to Mr. Doughtery about cams etc. Does anyone know how I can call or better skype him?

Michael

Give me a call at 530-672-2286 during the daytime, pacific standard time (California)