Anybody use RS pistons with CIS in a 2.7?
 

Has anybody used Mahle RS 8:5.1 pistons in a 2.7 with CIS fuel injection? If yes how does it run?

Thanks
Eric

great..

I run a little rich, so I don't know what happens on a lean fuel adjustment.. stock pistons is supposed to swirl the mix.

and I had a lousy running engine with Indianapolis summer gas with alcohol in it.. not sure if stock pistons would have helped.

Thanks Roon,

Yes the cis pistons are supposed to swirl the fuel to the plugs. Did you do any other mods?

I just had my engine completely rebuilt (1975 2.7L). I used RS pistons, SC cam grind from Webcam, SSI's and sport muffler, and a few other mods. I am getting a stumble between 3000 - 4500 rpm and we are trying to find the problem. The car is leaning out on at high rpm's on the analyzer and has low vacum around 13.

Eric

. I think your going to have a Great 2.7 street engine.
assuming a good rebuild,
If my situation I would eyeball dizzy advance curves for your style of use.. sometimes it can be a simple tweak instead of a custom curve. I would follow the cam torque curves for info.
best kind of 911 entertainment IMO.......... Ron

Ronin,

Sorry for my ignorance but when you say dizzy are you refering to the distributor? I also just had a crane ignition installed.
Yes, it was a quality rebuild. I spared no expense and it was completed by the best in south Florida and the case was sent to competition engineering to be redone, nice work. The street performance is real nice and once I get the bugs out it will be awsome.


http://forums.pelicanparts.com/uploa...1073533207.jpg

I know you can't run a "hot" cam with CIS injection due to pulsing created in the airbox from overlap in the cams. I've no experience with RS pistons in a CIS engine but all I've ever read said it's a potential problem just like the hot cams with CIS.
MFI will work with anything you throw at it as will carburettors, however, CIS is a completely different animal.

good luck,

Tom

I'm not a pro on this. marcesq has more experience than me..
so yes, the distributor curve may have to be dialed in if I assume everything else is OK. I've slightly noticed that the RS pistons are a bit more sensitive to ignition advance than stock pistons with my stock 2.7 cam/ no big deal.

there may be another answer.. so it's only a guess

Competition Engineering does great work.. your gonna have a nice one.

absolutely, but

an SC cam doesn't have any overlap to be a problem.
E-cams would create a sloppy engine w/CIS, but I think it would start and run..
I don't think early S-cams would allow the engine to run.
I don't have any experience trying it..

Ronin you are absolutely correct the SC cam is not agressive and no overlap. It was a highly recommended profile by webcam if I stayed with the CIS. Also I understand it was a popular upgrade for 2.7 's in the late 70's when the SC came out. I have to say I have great pull in my car straight up to redline.

What timing specs are you using, and is the vacuum advance hose connected to the distributor under normal driving??

Marc, I believe the timing is set around 35 degrees. Yes, the vacum hose is connected. The vacum is about 13 and the co 3.5 .. When the car is reved up the co drops to .60 and the car is leaned out. The sensor plate does is not raising because it doesnt have enough vacum.

Just taking a wild guess here, and since you had guys that know there stuff do the assembly probably not worth mentioning.

What causes vacuum? Something with the cams right? Shouldnt a zero over lap cam like the SC produce tons of vacuum? Could it be the cams are not timed quite right causing a loss of vacuum? Or maybe just one if off just a hair?

How do you spell vacume?

1] great question.. a hard answer would be book stuff for me now, but.. I figure everything in the whole package affects vacuum. I took off on dialing the ignition into the SC cams in a 2.7 .. and I assumed the rebuild was AOK.. so the cams are in spec. and cam timing could be used to fine tune the vac for the most rewarding rpm action/ only an opnion.
So if I had the tuning problem I would vary the dizzy timing 5deg it both directions without the dizzy vacuum attached.. run the dizzy WithOut the dizzy vac attached, start at 0deg at Z1 then read the difference at idle.. drive it, , then +- 5deg.. no dizzy vac would kinda symplyfy the curve and remove it from the early smog crap curve. hopefully.. maybe even running a vac hose and ga inside the cabin to monitor things.. carbs would be cool to have for dialing this in.. sometimes dialingin a mechanical secondary Holly double pumper can definately be helped by a vac ga in the cabin. So the CIS is a kinda fixed system.. and I don't think it's a problem anyway/figuring a good install.
But I would like to find a meter to varry the timing at specific rpms. I'd pay $200 to have a toy like that around to use on different engines as a shop tool.

then if the new ignition curve without the vac hose cleared things up and I still wanted to tweak I'd probably look at the cam install timing spec.. and figure the book info would say which direction assists the fuel mix vac. If I was bored

2] SC cam = tons of vac..
Exactly.. so I'd really have to be bored to play with cam timing. an early S-cam would require an "while your in there" situation..

3] "vacume"
I'm no prize either.. on 25cent words I spell like it sounds also.

As I understand the SC's had two different factory settings fot cam timming. 1978 & 1979 - .9mm-1.1mm, 1980-1983 - 1.4mm-1.7mm. May car wa set at the later 1.4-1.7mm. My mechanic is about to retard the timming to the earlier setting. But I don't see how this can create more vacum. FYI cam timing for 2.7L is .4-.54mm.

I would disconnect the dizzy vac hose before tearing into the engine.. The stock smog dizzy curve is screwed up for a clean running engine.

Thanks Ronin. Should I cut the hose short and plug it up?

I'll throw something in.

Have you checked your CIS control and system pressures? Its easy to get 3.5% co at idle by adjusting the 3mm allen screw (which manually raises the plunger in the fuel distrib). If its leaning out more than .6, its going too lean. .6 is about a 14.5 a/f ratio which is a bit too lean for max performance. Try dialing in an AFR between 12.5-13.5 at WOT. Check your control and system pressures and make sure they are in spec. as too high a pressure will hinder sensor plate movement.