1980 SC CIS - Upgrade to 1978 CIS ?

[Dave Kost]

I have an 1980 SC that the PO rebuilt the motor to the following specs-

98mm Mahle Cylinders
JE 9.5 compression pistons
964 cams
B and B 2 in 1 out exhaust

PO retained the 1980 CIS system. The engine runs very strong to 6000 rpm but seems to cut out there.

My question is would a 1978 CIS system increase the HP and would the 78 CIS bolt up to the 1980 heads?

Thanks

[mpetry]

The CIS will not bolt up to the early heads, which are have larger valves. My opinion - this is not a worthwhile upgrade path. If you want more ponies out of your 3.0, I'd suggest looking at the Bitz or Megasquirt EFI systems replacing the CIS, and some kind of twin plug setup after that, to allow more advance with modern (crappy) gas.

/markp

[Josh D]

'78-'79 US SC 3.0 had 39mm intake ports
'78-'83 RoW SC 3.0 had 39 mm intake ports
'80-'83 US SC 3.0 had 34mm intake ports

If the CIS on your '80 SC is stock, it would be for the small port head. To go to the large port CIS you would need to either:

1. Change to large port heads
2. Have your '80 small port heads intake port opened up to 39mm to match the intake runners of the large port CIS

[kerthunk]

I doubt that you would get any additional power from switching to the 78 CIS. The 78+79 CIS have the potential to create more power, but it is also due to the fact that the 78+79 heads had larger ports. The 78 CIS will bolt onto the 80 heads, but there would be a step in the airflow due to the smaller port diameter on the heads. You will also need to rewire a bit to eliminate the O2 system.

I think that you would be better off figuring out what is going on in your CIS at high RPMs.

[Josh D]

Originally Posted by mpetry

The CIS will not bolt up to the early heads, which are have larger valves. /markp

Valve sizes are the same. It's the port sizes that are different.

[timmy2]

Originally Posted by kerthunk

I think that you would be better off figuring out what is going on in your CIS at high RPMs.

This...
And the Bitz kit is a great option in my very biased opinion..
Or, going to the next level....
PMO High Performance Porsche 911 Carburetion

[Dave Kost]

Thanks for all the quick replies.

A very reasonable 78 CIS became available, so I was thinking about going that direction. In dead, my plan is to put it on a dyno to see what is happening and to tune it in. The engine pulls very good to to 6k but seems it just runs out of air or fuel.

Very fun car to drive - a lot of torque up to 6K then it like hits a wall.

But always looking for a little bit more.....

I never had any luck with carbs- they always seemed to vapor lock in the summer.

I will report back when I get it on a dyno. Im curious about the hp.

[timmy2]

Maybe the rev limiter is cutting out a little early at 6K instead of 6.5K?

I was suggesting the throttle body EFI's in the middle of the page at PMO, on my wish list...

[Dodge Man]

Both have their strengths but flow diameters need to be matched on intake & exhaust ports. Big valve heads(78-79 & ROW) need big runner CIS, etc.... My US SC had nice low end and my euro "big valve" SC has better mid to top end. Carbs will give you more HP but you have the get them thru SMOG for a street car. Pay your money and make your choice.

[Dave Kost]

No need to fret emissions, I'm on Pa. Those throttle bodies look interesting. I really like the sound of my MFI 1970e.

My concern is that now the idle hunts (hunts -set up rich), so it doesn't go lean up top- a no no. I don't think the stock CIS can handle higher hp builds, so you must compromise somewhere. That is why I was thinking the big runner CIS would cover the build I inherited.

[timmy2]

The beauty of a programmable EFI system is the ability to map the fuel delivery the way you want for different engine load conditions and driving styles.
I have a few maps for my Bitz EFI running Megasquirt for both mileage and performance as well as one for in between. (my favorite)
I just hook up my laptop and after a couple of clicks I'm running a new map and the car responds differently.
It takes a while to learn, but once you figure it out, it gets easy.

[Josh D]

By the time you did everything to get the big port CIS to work, you'd be getting close to having EFI with ITB's (well, at least partially there).

EFI (Tbitz) with the mods you have would be a solution, but would limit potential due to the long small port intake runners of your CIS.

[G450X]

I have an '82 that I plan to backdate to an early U.S. SC set-up, but I am swapping the heads to the early large port ones. I also have Max Moritz P&C's to use along with 964 cams, an early 3.0 distributor, and SSI's.

Quite a few Pelicans have used this "backdated" set-up with good results, they were my inspiration. I will trust JW in Seattle to sort out the wiring, which is one of my concerns.

From what I've read the only downside seems to be a slight drop in fuel economy and a little low end torque, but I would prefer a bit more mid and top end power myself. It will be faster which justifies the slight increase in fuel consumption (logical) - it's not like going to carbs and getting 12 m.p.g. like my V-8 Scout! When I'm in a slow "torque" driving mood I drive my old IH Scout or VW TDI...

I plan to use this set-up for a few years while I save up for a better injection system.

[timmy2]

G450X,
Sounds like a good plan.
Your mileage will drop quite a bit, my CIS in my '78 was giving me about 15 mpg combined! (I have a heavy foot!)

I looked at the road and track write up from 1978 and the car was rated at 18 mpg.

I'm getting 18 combined with my Bitz EFI.

[Flat6pac]

Either way with the CIS youre limited with fuel flow to feed the system that you built because of the fuel distributor. If you could find a 82/83 euro fuel distributor might answer the question.
Bruce

[Dave Kost]

Bruce

AHA! A fairly cheap quick upgrade based on the Dyno and AF results

[Mothy]

Dave - your problems at 6k revs are consistent with my US spec '83 engine. Small port heads and smaller intake runners give good torque down low but the engine just plain runs out of puff at 6k - my dyno results shows sharp drop off round about there.

With small port heads combined with the bigger capacity at 3.2 over the 3.0 standard and the different CAM, it would just highlight the issue.

Tim

[Dave Kost]

Tim,

So I need more air. Could you hear a squeal at 6K? i can. As though it is trying to breath but cant. Sounds like a squealing pig! Could you PM your dyno results so I can compare to mine?

Dont get me wrong it is a really fun car to drive but it feels the engine can and wants to do more.

So, EFI or ITB won't do it with out bigger heads? Maybe I should leave well enough alone for now.

[Mothy]

No squeal.

Mine just feels like it stops accelerating at that point. Shows up more in 4th or 5th gear on long straights at track days (close ratio gears) - in the lower gears I just grab the next gear and keep going using the torque.

As background, it's a US Spec '83 which has SSI's, 2in/2out exhaust, manual advance dizzy and Euro Spec fuel distributor. Still 3.0 capacity and standard cams. Done almost 300,000km's so due for full rebuild some time soon.

The Maha dyno measures gearbox drag to determine flywheel HP (red curve)




Tim

[Dave Kost]

Thanks for sharing Tim.

My 1980 sc feels stronger that my 1989 3.2 Carrera ~ 217HP. Much more torque too. It is about a 3.4 Liter with 964 cams. Cant wait to get it on a dyno to see what I got. I will post the numbers when i get it done.

Thanks again.