Adding GE80 cams to 2.0 litre engines

[obrut]

Doing a little project musing...

1. Can GE80 cams be added to a stock 69E engine without issue? (eg. will valve to piston clearance be ok?) Any idea of the hp increase?

2. Can GE80 cams be added to a stock 69S engine without issue? Any idea of the hp increase?

[jluetjen]

I would expect to find valve-piston clearance issues with both. Especially with the E pistons. But then again, once the valve hits the piston -- it's dead. The degree of interference really doesn't matter.

Then you get into CR issues. The GE80's have significant overlap, and the intake valve on the GE80 will close about 20 degrees later then on the E cam. This will reduce the static CR of the engine significantly. The result will be that the engine will be weaker off-cam. This is less of an issue comparing the GE80 with the S cam, but it will still exagerate the peakyness of the engine compared to a stock S or an as with a GE40 or GE60 cam.

With no other modificiations I would expect the HP increase to be 0 or even negative in so much as the engine won't run with a bent valve.

Now if you were to change the pistons and the camshaft, that would be something else again...

[obrut]

john

thanks for the info. i run GE80's in my 2.7 MFI and really like them.

i'm looking at a 69E as a potential historic race car - your info was just added to some basic research.

[kenikh]

Interesting. Has anyone run GE80s in a higher compression, S piston motor? Higher comp than S 2.0 motor?

[obrut]

yep, i run them in my 2.7 which has 10.5:1 pistons. love 'em

[jluetjen]

I'll say again, I doubt that the stock S pistons have enough valve clearance for a cam which is similar to a 906 cam. If you don't have clearance, the rest doesn't matter. Is there enough meat to cut additional clearance on S pistons for 906 cams. I don't know.

[Mark McClure]

Obrut,

Are the GE80's peaky in your engine? what sort of bottom end torque do you get or is it all way up high, how high?

I am about to finish my 3.0 with 10.5 and GE80's I thought that I might have overcammed it!

Cheers

Mark...

[obrut]

mark

i don't find it too peaky at all. there is a definite 'on cam' feeling from about 4500rpm but the car has a strong punch from about 2000-2500 ish rpms

[kenikh]

I think this a little off topic; weren't we talking about 2 liter motors?

[obrut]

yes, but we were kinda done with that so i just went with the flow

i wonder if i could add GE80's to my 930... (just kidding)

[kenikh]

Originally posted by obrut
yes, but we were kinda done with that so i just went with the flow

i wonder if i could add GE80's to my 930... (just kidding)

LOL!

[obrut]

back on topic we go:

"I would expect to find valve-piston clearance issues with both. Especially with the E pistons"

john - could you explain this a little further? in a simple sense i thought that the E pistons (being relatively low compression) would, at TDC, be relatively further away from the valves than say a higher compression piston (like an S) how do you then go about simultaneously running high lift cams and high compression? does this require piston that a relatively 'high' (for want of a better word) in all regions other than those adjacent the valve - where they are more recessed?

[davidppp]

Hello there.

If you Have any ix of the 906 pistons (BA's book etc) youll see that the crown is almost like a high wedge..what is harder to see is that there are deep valve pockets.

FWIW, there is some margin of safety to be had by cutting the ex pocket even deeper than stock on the late 2L (1969 model) 2L pistons...they are an affordable alternative to the 906 piston.

However, the details of timing are as important as measured clearances, and lift, and I have never used the G80...

Camgrinder will be along soon, and I'm sure he will know all you need to know..

Kind regards
David

[camgrinder]

I agree with John (jluetjen) with the c/r the engine will have lousy low speed power.
The best choice is a set of my DC40 cams (Mod-s, GE40 all the same) these give a nice 3500 to 7500 rpm band with an otherwise stock 911 S. If you need more than 7500 rpms, go with the DC60 profile.
As with any performance engine build, valve to piston clearance has to be checked. The DC40 are a bolt in swap, and the others mentioned might have V to P issues.

[jluetjen]

Looking at this in a different light, here's some food for thought. What you're really talking about is a "radical cam with small port" situation if you put GE80's (or 906's) in a 2.0E engine.

First off, what do the torque curves look like for the different engines if you have assume adequate porting and CR? Here's a comparison chart from the Porsche factory graphs for different variant 2.0 engines.



Now in general, 911 engines don't seem to make much HP when the intake gas speed gets much above 100 meters/second. In the case of the 2.0E, this occurs at about 7200 RPM -- which is just above the speed when 906's develop peak torque. Being a newer design, I expect GE80's to develop a broader torque curve, but you're still faced with a situation where the HP will drop soon after the engine comes on cam.

Now Porsche did run 906 cams in a modified T engine in some of their rally cars in the late 60's. There isn't a lot of data on the performance, but I would estimate based on this chart and other data that I have that those engines would have outpulled a standard 2.0S engine from 5000 RPM through the redline. This may not be a bad compromise for a purpose built rally car, but it can be murder to drive around town while trying to observe speed limits and noise levels.

Using a full-race cam with S heads on a 2.0 liter engine would most likely be an acceptable compromise for a DE car or regional level race car -- assuming that the engine's bottom end is prepared appropriately.

[Walko]

John

what does BMEP in the graph mean

Michael

[jluetjen]

Break mean effective pressure. This is basically torque normalized by engine size. So you can compare the BMEP of a 1 liter engine with the BMEP of a 3 liter engine (both will be in PSI or similar units) and see which engine is most effective at generating torque per liter -- and not get confused by the fact that the 3 liter will create more torque (about 3x as much) just because it is 3 times larger.

Looking at the above chart, you can see that properly made engines with 906 cams can make about 29% more torque then then "torquey" T spec engines. But they do it at significantly higher engine speeds. In this case I was comparing only 2.0 liter engines, so I could have just as well labeled the chart using lb-feet or Mkp of torque. It's a straight conversion from one to the other if the engine size is the same.

[kenikh]

A question: why are the curves for the higher strung motors non-existent at low revs? I could see there being a dramatic fall off, but to be non-existent strikes me as odd.

[jluetjen]

I don't have my 906 charts in front of me, but I believe that they only started to graph the data at 4500 or 5000 RPM. This leads me to believe that the torque dropped off pretty significantly as low rev's, especially in the case of the carb'd 906 spec engine which would have some reversion issues around 4000 RPM.

[kenikh]

Originally posted by jluetjen
I don't have my 906 charts in front of me, but I believe that they only started to graph the data at 4500 or 5000 RPM. This leads me to believe that the torque dropped off pretty significantly as low rev's, especially in the case of the carb'd 906 spec engine which would have some reversion issues around 4000 RPM.

This is what I assumed. All I can think is that reversion leads to such an unsteady idle that mapping power at this rev range would be difficult. So am I to assume that the idle on these cars is set between 2000 and 4000 RPM?