2.4T MFI - Not a complete dog?!

[Tim Walsh]

Jim
you're entirely right If I had an E instead of a T I'd definitly think twice before boring your C's just to get another 20 horses. For a T though going from 140 to 180 is a huge jump. Half of what this rebuild is for is to have a piece of mind that my longblock will be good for a decent amount of time. At least until I get out of college.

Thanks for the offer and I'll probably take you up on that but only after the engine's rebuild, which will be awhile.

[arrivederci]

Couple of things here...

Actual dyno results show a pretty signficant gain in HP on my '72 by just bumping compression. I've never cracked open my motor, and I didn't do the work on my motor...so I only think I know that I'm working with bumped compression (based on what the previous owner told me). But I have had my MFI pump rebuilt to T specs, which works very well (I assume a T pump wouldn't work well with anything but T cams). I also still use stock plastic MFI intake stacks.

Tim actually has a T motor and is looking for more power. He can have E type power with T cams...again, see my dyno chart. That's all without touching the MFI pump or cams. If there are other P&Cs that Tim can use that cost less than the 2.2S, that's great. But the point here (for Tim, I think) is to achieve as much as possible for as little $$ as possible. Once you get into cams and MFI rebuilds, you're adding to the $$ factor.

Is roughly 170 hp enough? I guess my point here is that power isn't cheap, but the first bumps up the power scale are the least expensive...and $/hp ratio will increase the higher up the power scale you go. Of course, my philosophy is that if 170 won't be enough and that's all I can afford, I'll wait until I have enough $$ to do it right the first time.

Maybe I should bring my '72 out for the next fun run instead of my '87...that way some of you can see what I'm working with.

[Halm]

Jim, here is a thought for you (because I am heading in this direction? ). As I recall the E from Hershey it very clean and oiginal. With E' s like that starting to see nice appreciation, why give it up. Instead, buy a 2.7 somewhere and build it up with carbs to what ever spec you want and KEEP the original E motor, To my way of thinking, it is the best of both worlds.

[Tim Walsh]

You're entirely right hal. Jim you really ought to use a different block for your RS motor nice E's are hard to come by. On the otherhand my car doesn't have the original engine and the interior's a mess so originality isn't a big deal at all for me.

Josh,
170 HP doesn't sound too bad at all but with the extra compression would I need to recalibrate my MFI pump? I think it might be borderline. I have a lead on a set of 2.2T pistons. I think that would bump up my compression to about a point or a point and a half. Did you do any porting or any other mods?

[arrivederci]

I don't believe my motor has any other mods (although I can't confirm that it does or doesn't because I don't have the build sheet). My MFI pump was re-built to stock T specs. From what I know, the MFI pump's space cam profile has to match your cams. I run 92-93 octane gas to deal with the added compression. Of course, to make more power, you need more gas. Not sure how that affects the in-car tuning of the MFI, though.

[Tim Walsh]

Hmm.. thinking about it now that really might be the best way to go about a power increase. It would save on MFI recalibration, S cams, JE's and boring costs. That's close to 3k right there.


The premium fuel isn't a big deal since that' what I was using til I heard that running regular is actually better for my ultra low compression engine.

[724doorE]

Another direction to go with maybe a bigger longterm topside.

Rebuild your engine with your 70.4 crank and a set of nos 2.7 RS p/c's. Leave your other stuff stock for now. Later when you have more money, do cams, heads , and mfi. Depending on a lot of variables , this should break down roughly even and net you a bigtime engine for your T, yet you might This is basically what I have done on my 72E, still have E cams, E MFI, and E ports. It runs like a striped ape ( when my ignition is right) and has some low down grunt say 2500 and up in any gear. The small ports seem to limit it at the top, but between say 40 and 100 it is pretty sweet, ahhh not that I would know that it would even reach 100 as of course that would be frowned upon

Run some numbers and see what you think.

[Tim Walsh]

Dennis,
I'd love to do that but I'm really pretty hesitant at this point to run the 90mm cylinders in my case because I don't have a very strong case. My T is running in a 3R case. I think when (not if) I do that I plan to buy a 7R case with the wide spicots and build that case up.

[724doorE]

Oh, I forgot to mention that part, I am running my stock 72 3R or 4R case. No problems so far maybe 10,000 miles in the last 12 years. I'm much more worried about the dilivar studs I put on the bottom half than anything else. I figure when I pull the heads and port them, I'll change the studs or at least examine them closely.

Just had the case halves surfaced and then line bored for std bearings and of course time certed as was the norm at that time. I do wish I had popped for the dowel pin mod even though I don't really need it.

Does that ease your mind???

[Tim Walsh]

That does ease my mind a fair amount about the case although the second reason for second case is that way I could drive the car and build up my dream engine at the same time. Sure it's probably a little more expensive in the long run but this way I can also sell my existing engine when I'm done or I can tear it all the way down and build up my other dream, a 2.5MFI engine with 9.9:1 JE's and S cams.

[724doorE]

Tim, now your thinkin!!

You can still get factory 89 mm 2.5 short stroke pistons/cylinders from Andial for the princely sum of about $3200 I checked myself last fall. Would be about twice as much as the JE set up after you factor in getting the cylinders redone to match the pistons.

Oh and I don't remember if you were talking about racing afterword, but 89X66 is 2466cc and 90X66 is 2513 or some such and the latter would screw you out of the 2.5 L class if there is such a thing where you might plan to play.

Just something else to think about

I got a buddie up here who is planning on useing the newer JE pistons in a 2.7 hotrod that will go into an autocross 914/6. I am curious to find out wether he is happy with them or not. I say that because there have been a few that were not overall satisfied with the "older" JE pistons and their wear characteristics. But I personally have no useful input on them. I will say this, At the present time, I would consider using a "good" set of used mahle pistons of the RS variety before I spent 1K on JE's, but thts just my opinion and results may vary!

PS, I spent about 6500 to get where I am now on my engine 12 years ago... new RS p/c's new oil pump, bypass mod, case work, head work, new valves springs and retainers, new tensioners chains and wheels and my own assembly plus whatever other parts I may have forgot. It don't come cheap, but then you also will have an immense satisfaction when you are through!

You wouldn't by chance studing engineering would you?

[Tim Walsh]

As a student the risks of full out racing are too much for me right now but I do plan to autocross my car. Someday I'd love to track my/a 911 but not anytime in the near future so class restrictions dont' mean anything to me.

I haven't heard about quality problems with JE's but I'm a relative newbie. It's looking more and more like I'll be doing a stock rebuild with 2.2 pistons or the 85mm S engine depending on how the money comes together.

[jluetjen]

Hi Again.
I'm going back to the question of..Can you use a 2.2E 3D MFI cam in a 2.4E, or maybe a 2.5E?

At the bottom of the following HP chart is Porsche's Specific Fuel Consumption graph for the 2.2E. I've also added on the consumption graph for the 2.0E and 2.4E. Note that I fear that the 2.2 data (which I got from the factory shop manual) might be wrong since it so completely different from the other two.



Looking at just the 2.0 and 2.4, it looks like you could take an MFI pump from a 2.0 and (assuming that there is enough travel) just adjust the part-throttle adjustment to move the fuel curve up/down until it matches a 2.4, and vice versa. I think that this should work since the part throttle adjustment moves the entire adjustment rack richer/leaner, which should be up/down on this chart.

For comparison, here is the MFI'd S fuel consumption graph. Unfortunately I don't have a graph for the 2.0S. For some reason it is not in the factory shop manuals.



Surprisingly, the curve for the 2.2 S engine appears to be pretty close to the curve for the E engines. Just look at the points at 2000, 4000 and 7000 RPM and you'll see that if you move the an E curve up/down to match the S curve at 2000 RPM, that the other 2 points seem to match also. Hmmmm

This would suggest that you could use an E 3D-cam in an S engine after you adjust the part-throttle adjustment. Anyone else have data that could support/refute this theory?

[Tim Walsh]

I'm not sure I fully understand that but I think that you're right as long as the cams stay the same. When you throw the timing of the cams off in relation to the injectors is when you really get problems.