Piston & Cylinder ID

[JH282]

Still trying to figure out why my 3.0 runs like crap, ran a bore scope down the plug hole, didn't look like CIS pistons, so the heads came off. Found these.




Previous owner passed away so I don't have any idea how the engine was built. Can't find my micrometer, but vernier calipers say inside of bore is just under 95mm. No markings on topside or bottom of cylinder. I really don't want to pull cylinders off, hoping someone can ID these.

Are these the Mahle Racing 3.0 P&C set?

[Bob Kontak]

Did the engine (ever) run well since you have owned it?

[JH282]

I had it running, but it didn't idle right and had low vac. Compression and leak down tests were good. Found out it had aftermarket pistons and a cam, so I pulled the engine to figure out what was inside.

[juanbenae]

is it still running the CIS? those do appear to be J&E or the like, but are not CIS pistons as you are likely aware. could have been a motor built specifically for carbs or some other injection system and cams and when the car was sold they slapped the CIS back on. those pistons and the wrong cams, if still present with any overlap at all would cause a CIS equipped motor to run like crap I would think.

different example, but in the same vein when I bought my new to me 75 a couple years ago it had stock bumpers on it that you could tell were patched together. all the parts were there including new bumper shocks, but the only parts not rattle canned were a different shade of white very obviously. ive long believed that a set of IROC or other fiberglass bumpers were poached from the thing and the included bumpers were cobbled together for a complete sale.

[JH282]

Juan,
The car came with carbs, but I pulled them off. I put the CIS intake back on and run EFI

[juanbenae]

does the EFI provide data and the ability to adjust based on that info? a motor with good leakdown, pretty low carbon count on those pistons indicating a motor that is not tired id be looking to see if your EFI system is the problem. did it run good with the carbs?

if your not collecting data, or have an 02 sensor not adjusting the mixture accurately in real time all bets are off. what are your air/fuel numbers looking like?

[jamesjedi]

If the motor had carbs, it would be interesting to check what your cams are. If this is a 1978 or 1979 motor it would have been an upgrade to change the Pistons and Cams. The motor was rated at 180 hp, but with these changes you could possibly get 30 to 50 hp.

[JH282]

Juan,
I'm running a Bitz Racing EFI kit, so Megasquirt basically. I assumed the engine was stock, so I set cam timing to spec and the Megasquirt was configured to run a stock 3.0. Found out the thing wasn't stock. A cam had to come out to ID the profile, so I'd know where to set timing. Pulled the heads to see what kind of pistons were in it. I can collect data, adjust/monitor fuel and all that with my EFI, but I have to figure out how this thing was built before I set up the EFI again.

[JH282]

James,
It's a 79 3.0. The pistons look like the 98MM Mahle pistons folks use on the 3.2SS conversion, but the bore on my engine seems to be 95mm

[Trackrash]

Don't look like JEs. They look like the Mahles I had in my 2,5SS. I wonder what the CR is.

How did it run with the carbs?

For comparison these are JE 95 bore with 9.5 to 1 CR.

[JH282]

Maybe Mahle RSR pistons? Anyone know?

[lvporschepilot]

Any idea what cam? Could be just a high overlap cam which just won't idle that great, period.

[Trackrash]

With no documentation, looks like you need to start from scratch.

I would measure the deck height and piston dome volume to figure your compression ratio as a start.

You might want to ask this question in the Rebuild forum. I'm no expert, but they look like some Mahle turbo pistons I saw a picture of posted recently.

There is no stamp on the end of the cams? Most cam grinders will stamp the end of cams with their no.

[JH282]

There are no markings on the front of the cam, other than the factory numbers. I'm in the process of removing the rockers so I can pull the cam. The bolts that run through the rocker arm shafts are on there ridiculously tight. I've been heating them and soaking them in PB Blaster for 3 days. 3 came out, 2 got stripped.

I'll try posting in the engine build thread. Thanks guys.

[pampadori]

the dome doesn't appear to come above the deck very high at all. If you look at the JEs pcitured, they look like they would protrude quite a bit above the deck. So all of that is to say, low compression turbo pistons maybe?

When life hands you lemons, buy a turbo manifold and a Precision T&E snail and boost that motor!

[Trackrash]

FWIW my JE 9.5 - 1 pistons have a dome height of 10.16mm.

[Flat6pac]

Pull off a cylinder then remove the piston
There is usually identification numbers inside and product producer name
A friend just did installing into a 3.0 using the old cylinders and new JE PISTONS
Bruce

[JH282]

Pampadori, it comes out quite a bit, here's a better pic. Still have to get measurements.



Got the stripped rocker bolts off, pulled the cam. It says WEBCAM B 9 93 134 135.
Web says to set it at 6.8mm. When I first checked my timing it was at about 2.4mm. That might be the cause of my idling issue?

[Henry Schmidt]

My guess 3.0 RSR Mahle 95mm.

If the cams are carburetor or MFI spec, the wide lobe center will create issues for the CIS or EFI injection.
The piston below is from an RSR 3.0. Claimed 10.4:1 with an RSR head. The chamber size on a 3.0 RSR is much smaller than an SC head (77 vs 90 cc) IMSM.
The RSR compression was overestimated @ 10.4:1 so in an SC chamber the RSR piston would be under 8.0:!.

The 134/135 is a 906 cam. 96 degree lobe center. Even with carbs it will not run well with low compression.

[JH282]

Pulled a cylinder. Cosworth PM1152. Anyone have any info on these?