250 bhp from CIS ? - Page 2

spuggy · 07-03-2008, 10:12 AM

Quote:

Originally Posted by Trotskyite

Hell you could get 500... for a few glorious seconds.

CIS 930's can make over 400 RWHP reliably. See no reason a forced-induction low-boost SC shouldn't make 300-350 FWHP for years if done correctly - a guy here converted his in the 80's and is still driving it. Other people have done this as well, some recently.

davidbir · 07-03-2008, 10:18 AM

Quote:

Originally Posted by Gary.H

Dyno results after my 3.0 Euro '82 SC top-end rebuild. 964 cams, race springs, TI retainers, SSIs, stock 9.8:1 cr:

Dyno plot before rebuild, stock apart from SSIs:

Lost some mid-range torque, peak power now higher up the rev range (due to not increasing the cr I suspect). Much more top end power.

That looks like a 50 bhp increase to me! The springs and retainers might be redundant though, for me anyway. The Euro cars have half a point more compression don't they? - 9.8 vs 9.3? Can I get that by shaving the heads and is it worth it?
Thanks, David B

Gary.H · 12:53 PM

Quote:

Originally Posted by davidbir

That looks like a 50 bhp increase to me! The springs and retainers might be redundant though, for me anyway. The Euro cars have half a point more compression don't they? - 9.8 vs 9.3? Can I get that by shaving the heads and is it worth it?
Thanks, David B

Strictly speaking, it's a 28bhp increase over a stock Euro '82 SC @ 204bhp. I thought the US spec SC's were a little down on the Euro models bhp-wise ? If so you're starting a little further down the power scale to start with. The race springs and retainers are also there as a little bit of insurance against the odd 915 mis-shift

Oh, forgot to say I also had the heads ported too.

The 964 cams push the power further up the rev range. Increasing the compression ratio will bring it back down again. Not sure how much half a point will lower it though ? Too high a cr will necessitate twin plugging (which I wanted to avoid for cost reasons).

Gary.H · 07-03-2008, 12:49 PM

Quote:

Originally Posted by fred cook

In a way I agree with Goran. Unless.....you are going to have to do a top end job anyway. Now all you are out is the extra cost of the cams which makes the work more justifiable. Also, I know first hand the effect of adding SSI exhausts to a 3.0 engine. That one change made my SC sooooooo much more fun to drive!

Mine needed a rebuild and as you say, seemed daft not to do the cams 'whilst you're in there'

It was more of a maintenance, reliability rebuild with some extra power thrown in for (not much more £££/$$$s). I don't think you'd go this route 'just' for the extra power.

mca · 07-03-2008, 01:06 PM

Maybe I will throw mine on a dyno.

I am putting a 1980 3.0L back together with new JE Pistons (9.5:1) and the 964 cam grind. I also have headers (which should make the same power as SSIs unless I am missing something - besides heat

) and a Bursch exhaust which the previous owner installed. All heads were completely overhauled by EBS.

Wayne's book claims a boost of up to 50HP. I hope that figure is close to being correct. Not that I would change my rebuild package ... I didn't base it on his estimate of 50HP ... I based it on my wallet.

To date I have spent about 6k and don't forsee spending more except for some fuel/vacuum lines. If I had decided to move forward with mods for more HP, that price would certainly double (maybe triple).

JV911SYDNEY · JV911SYDNEY's Garage

Quote:

Originally Posted by beepbeep

Yes, but far from worth it.

230hp 3.0 with CIS is almost in "not worth it" class. Price/performance starts increasing exponentially after 230...

yep, unless you're in a racing category that specifies the use of CIS

otto in norway · otto in norway's Garage

I think that wayne's book means a power increase of up to 50 HP, if you have 8,5:1 originally.
I had that, and I am am doing exactly what you guys have mentioned here. (9,8 pistons, 964 cams, and sporty exhaust. Rebuilding the entire engine at the same time..)

Mine had 188 HP, and I am hoping for 230HP. But this is NOT RWHP.

davidbir · 07-03-2008, 02:51 PM

Can we draw Wayne into this discussion?

911st · 07-03-2008, 03:23 PM

If 230 is doable w a 3.0, how about taking it to 3.3-3.5 for 250+ HP.

There was a 3.5 CIS built by a top notch tuner (BDR?) and reviewed in a mag in the late 80's or so. I think they got 280hp.

I like CIS, it is a good system.

hmd · 07-03-2008, 08:14 PM

Quote:

230hp 3.0 with CIS is almost in "not worth it" class. Price/performance starts increasing exponentially after 230...

Quote:

Originally Posted by JV911SYDNEY

yep, unless you're in a racing category that specifies the use of CIS

Exactly. Try Australian Historic GroupS.

230bhp (at the engine) is easily achievable considering a Carrera 3 with 8.5 C/R is 210bhp out of the factory. Putting milder cam and 9.8 pistons headers and exhaust = 230bhp +++

911st · 07-03-2008, 08:43 PM

It takes a lot of work and knowledge to get carbs to work right from what I understand. Also, the cost of converting is almost in the $4k range w PMO's and everything needed.

CIS dose not have any flooding issues in high G corners, dose not have the A/F transition problems , they run a more consistent A/Fs, and they compensate pretty well with altitude and temp change.

Carbs are little more responsive and add about 10hp, but then MFI is more responsive and makes more HP than carbs.

I like CIS and it is a great system and I lot of clubies race with them. Of coarse, a state of the art EFI is best but...

I suspect spending some money on a having a nice professional porting job on a small port system might out do a stock large port head.

With CIS you do not want your ports to big or it slows down port velocity which is important at slower speeds to insure proper Air Fuel mixing.

Gary.H · 07-03-2008, 10:45 PM

Quote:

Originally Posted by 911st

If 230 is doable w a 3.0, how about taking it to 3.3-3.5 for 250+ HP.

There was a 3.5 CIS built by a top notch tuner (BDR?) and reviewed in a mag in the late 80's or so. I think they got 280hp.

I think you need a 3.2 crank for that - which is $$$s

afterburn 549 · 07-04-2008, 03:24 AM

I do not what you know..we all are here for the school of Borg. The quicker you you tumble to the fact Hp is hard to bolt on.
The best advice is to think in long term where you want it to be so as not to have to redo your redos....
Looking at crank Hp is ..one thing, in real life its power to the wheels is the issue and most important.
Your power all comes from how much air you can get into the Cyl, and then how far it can be compressed (big domes on pistons )
There is nothing wrong with CIS....and a proven fact that a turbo and related parts my be more up your tail pipe.
Your static C/R is there
you might review this idea b4 jumping to to carbs ....
To get the most out of carbs, You need cams, higher C/R......pretty spendy no matter which way you go.
If you look in Tech articles "Noah" states 964 cams , bump the pistons up 9.5 and he got 230 / 240 RWH
That would be the cheapest $$ ever spent per HP

safe · safe's Garage

One thing to remember is that the 964 made 250 hp with 3.6 liter, 964 cams (obviously) and twinplugs.
With a proper exhaust it made 272 in the 993.

Now I know for a fact that the stated 250 hp is a somewhat modest figure, most cars makes a lot more.

afterburn 549 · 07-04-2008, 08:40 AM

Maybe I read wrong..but I think Noah has / had a smaller eng then that..you guys go read under " Tech" articles in the running header at the top near sighn in part here

davidbir · 07-04-2008, 09:09 AM

Quote:

Originally Posted by afterburn 549

I do not what you know..we all are here for the school of Borg. The quicker you you tumble to the fact Hp is hard to bolt on.
The best advice is to think in long term where you want it to be so as not to have to redo your redos....
Looking at crank Hp is ..one thing, in real life its power to the wheels is the issue and most important.
Your power all comes from how much air you can get into the Cyl, and then how far it can be compressed (big domes on pistons )
There is nothing wrong with CIS....and a proven fact that a turbo and related parts my be more up your tail pipe.
Your static C/R is there
you might review this idea b4 jumping to to carbs ....
To get the most out of carbs, You need cams, higher C/R......pretty spendy no matter which way you go.
If you look in Tech articles "Noah" states 964 cams , bump the pistons up 9.5 and he got 230 / 240 RWH
That would be the cheapest $$ ever spent per HP

Afterburn, many thanks for the info, esp re the "Noah" article.
I may be new to Porsche but I didn't just fall out of the crib

911st · 07-04-2008, 10:21 AM

Quote:

Originally Posted by Gary.H

I think you need a 3.2 crank for that - which is $$$s

Yes, but the 3.0 crank is valuable and that will defray some of the cost. Need the crank and rods. Better yet, a 964 crank for a torque monster. If you juse the 3.0 pistons, you end up w a higher compression but best to get J&E's made for the application.

911st · 07-04-2008, 10:29 AM

Somone just built a 3.8 on a Carrera motor. Had the crank stroked w a regrind to smaller bearings and went w a very big P&C. How about a 300hp CIS. It is possable.

davidbir · 07-04-2008, 11:47 AM

I saw in Wayne's book that he mentions an engine built by Andial that had CIS but was out to 3.7 with a 3.2 crank and special P&Cs. Apparently it ended up with someone on this board?

davidbir · 07-04-2008, 03:20 PM

One point I would like cleared up; what is the difference between the US and Euro SCs apart from the half point of compression? There is no way that the 20 bhp difference comes from that alone is there?
Also, can the heads be shaved enough to make up the half point on a US 82 SC? What do you experts think?
This seems to be a popular thread so we have to assume a lot of people are interested in boosting an SC.