951Dreams

I have posted this up before in 944 land, out on another (not as popular but still great) forum. But I didn't get a whole lot info. Mainly because no one really knew the answers. I have researched this till I have dreams about CR's. The main problem is Clarks, LR, Pelican, Wikipedia and the 944 FAQ all have slightly differing info on this. But I have some empirical evidence now, see below.



The bottom ones are the stock 87's in my...well 87. The top piston is some 88's I picked up. The reason I bring this up is I spent weeks researching if the 87's had the higher CR like the 88's. Many sources said the 88 only did. But several reliable sources said it was for the 87 AND 88. (Like Lindsey Racing).

Now, Dave at Lindsey has had more than a few of these apart. So how could LR be off? I'm thinking MAYBE there is a 87 and 87.5??? Or something along those lines, where maybe later 87's got the pistons we see on all the 88's????? That would explain some of the confusion.

Here is my current thinking of how things worked for the 2.5L, euro cars aside. US only:

83-85 9.5:1 CR for around 143 HP

85.5-87 9.7:1 CR for around 147 HP (**Maybe** not pistons, but Heads???? See below)

88 CR 10.2:1 for around 158 HP

So what does RL think??? What's your real world experiences (please just add what you've seen with your own eyes, not anything from any of the online sources). I will add my 87 owners manual list the CR as 9.7:1.

I've also ran across some info in the last few days (from PCA's PANORAMA magazine) that the 85.5+ heads may be different as well, and may add to a slightly higher CR, but that's the first I had ever heard of it, so I'm putting that investigation on the back burner for now. I'm just going to address pistons till I get this figured out. I want to put this to bed!

H.F.B.

The pic below shows the different castings.




The different CR are more or less down to the piston dishes.

V2Rocket

There never was a 9.7cr engine.
That was a typo in a sales brochure or something.
They were all 9.5 until 1988.

82-85 and 85.5-87 us engines are 100% identical in function and internal parts, as much as it matters.

The 85.5+ 4hp bump is entirely due to the revised camshaft.

951Dreams

And my owners manual!

On the heads, what changed with the different castings, if the chambers CC the same, if there a flow improvement?

I didn't know there was any difference in the cams between the years. That's great info!!! I hadn't heard that before either!

So I'm guessing the 88's had the best of it all?

V2Rocket

Not sure but I think the .xR number is the model year...86, 87, 88...maybe.

Late NA cam had 1mm more lift and 8 degrees more duration on the exhaust side, relative to the early NA cam (which was also used in the 951).

H.F.B.

6R is the "early" (machined/milled)
7R is the first "late" generation (85-86) (cast)
8R is the second "late" >86 (cast)

Porsche tried to improve the 944 NA 8V over the years. The late is around 200 lb (powersteering, AC, ABS, power windows, side impact protection, etc.) havier than the early, so Porsche tried to compensate that with a slightly improved cylinder head, which should help the power output. But acutally the late was a bit slower than the early.

H.F.B.

according to the 924S-944 tech.-specs, there was a 9.7 CR engine. I hope it wasn't a typo.
As far as I know the 924S had an engine with 9.7 CR.

V2Rocket

the 944 SPEC guys have gone to the ends of the earth to find any such pistons or parts combo that would make that CR - none have been found.

951Dreams

Was probably just one of those marketing things, or maybe they changed the way they did the math? Who knows. My manual shows the 9.7:1, and that started my journey to find out how and why. I've spent HOURS researching, and like you side V2, nada.... there is nothing out there except random hints from Porsche about "upgrades" to performance in 85.5. But you have found that's the cam, so who knows!

For years American car companies UNDERRATED their HP figures. Look at cars like the BOSS 302, or Corvettes during the 60's-70's. It wasn't uncommon for their numbers to be 100 HP low from what people would find on dyno's. Who knows why really, someone had some reason, somewhere. Maybe to meet some weird government rules (I'm thinking I've heard that has something to do with it). So maybe Porsche did the same thing over here?? Used imaginative math to get numbers to meet some weird requirement? You would think the Euro cars would have gotten bumps too... but didn't they stay flat till 89?

EDIT: I see in the listing above, they in fact did, and got a 2 HP increase in 89..... now THAT's weird. Gained a 1/2 liter and higher compression for 2 HP?????? How does THAT work?!?!?!? (I'm guessing, not sure if the M44.11/12 is US or EURO......)

V2Rocket

supposedly the 89 has a milder camshaft that is more torque oriented than pure power.
havent ever found lift/duration figures though.

Van

Remember, the earlier cars also have a different style DME - the tune could be a little different, too.

Ish_944

I think a cat was added...

FRporscheman

The 1989 8v n/a was not 3.0L, but 2.7L. An increase of 0.2L, higher compression, different injectors, DME, head, intake valves, etc, netted a 5hp increase (158 of 1988 to 163 of 1989).

951Dreams

Also of interest, Jon Milledge told me you could gain a good amount of low end torque using a 2.7L cam in the 2.5L. At the cost of about 16 HP up top.

If it did something similar in the 2.7L (and I'm sure it did) then that would explain it! The extra displacement and CR, but only 5 HP gained, makes perfect sense when you factor in the cam being torque oriented. I guess on the flip side, you could throw a 2.5L cam in a 2.7 and make around 180 HP!

Thanks for clearing that up FRporscheman, I was forgetting that 89 was the one year for the 2.7. I knew it, but wasn't thinking it.

Humboldtgrin

I need to get a magnetic base dial gauge tool. I have an 89 cam in its tower just sitting here ready to be installed in my 89 944. I have a cam degree wheel already. Had I not bought all those cool parts for my 951 that I wanted out of a growing habit, or addiction, I would have $ left over for that tool. I'll put it on my growing want list. Oh dang it needs a cut in line on that list if that camshaft is to be measured this year. Let's put it past those other projects. I'll just start a new list, one with tools wanted and one with parts wanted. Problem solved. It's now at the top of the new tools wanted list.