I'll join in...how's this 2.4T rebuild/upgrade?
 

I've read the numerous "build me an engine" threads in the archives. I've been considering the 2.7RS upgrade, but for the sake of being unique, want to go the road less traveled.

Here's what I'm leaning toward. My 2.4L "T" engine needs a full rebuild. The #4 piston and valve became friends (possible over-rev by PO). So I need to figure out my P/C's direction.

My thought is to bore out the 84mm cylinders to 86.7, JE pistons, and build a 2.5L long stroke engine (I have a 70.4mm crank). I know I want to keep the MFI, and the existing case (unless I find issues after finishing the tear-down). Could I keep the "T" MFI calibration, and existing cams?? I plan to upgrade in the future, but wish to keep costs down now. I'd rather put money into "proper" machining and critical fasteners, to build the engine the "right" way, and do performance mods later. I figured no matter what I build, I'll want more power later on.

Should I do additional work on the heads to get better power, and prepare for future mods?? Is there work required on the heads for the larger piston bore? Also, where do I find out the cost of JE pistons? And what compression ratio should/will I have? I want to be able to run on 93 octane pump gas.

All machining work will be sent out, but assembly work will be done by myself.

Any comments are welcome.

Thanks!

I cannot help you much Jay but wondered which case came in a 2.4t engine from 1972. Any idea?

Thanks.

Jay, here's what I would do.

Bore the cylinders out like you planned.

Buy JE pistons that have enough valve clearance for S cams. (for future upgrades) You can get whatever C/R you want. 9.8/1 is my recomm.

The heads may need a little flycutting to clear the larger bore pistons.

Have the T cams reground by Elgin to E-spec.

Open the intake ports up to 32mm. (No, contrary to the factory spec book, a 2.4T intake port is actually 29mm, not 32mm. The exhaust ports are already 32mm though.) You could go a little more if you like, to 33mm or so.

Use your existing MFI pump as-is. A T pump can be adjusted to work with E cams and run just fine, assuming that it is in good condition.

This would be a nice 170-175hp motor with great streetability, and much improved top-end, and great around-town low-speed response.

Those are all great suggestions from Tyson. One question though. When I measured a T iron cylinder it didn't seem to have enough room to go out to 86.7mm without leaving enough material between the CE ring gasket and the piston. 2.15mm to be exact. Is this a large enough margin?

Did Porsche use a CE gasket on the 2.5 or not?

Any thoughts?

If your going to machine the heads (which you should) open the ports to 36mm.. (S spec) You will be charged the same by the machinist whether you specify 32mm or 36mm. With an E cam this will make a nice ballsy engine. And at a later date you could run a rad cam and have the breathing capability.

Also have the heads machined for twin plugs.. if you dont twin plug now, you may at a later date.. in the meantime put some old plugs in the lower position.

sounds like a fun project

Thanks to everyone for the info. I can see the motor taking shape in my head already. Bobboloo--I'll have to look into whether or not there's enough mat'l. This option was mentioned in an earlier thread that Tim (It9eek) talked about doing on his '72 T motor.

Any special case mods I'll have to do aside from getting it back to spec? (and the oil bypass mod. of course)

First, you have to decide what sort of motor you want -- AutoX, street hot rod, or racetracks. You shold also build the motor from the bottom end up. ie do the heads, etc. later if you dont do it all at once.

And, there are some tricks to boring out the cylinders. Get a machinist who has done this before on race engines, and talk to him.

I agree with Tim T except the 36mm port thing. It's a great idea, but wouldn't allow you to still use the stock T MFI pump, since the breathing would be quite a bit better than a stock E-spec engine.

I've seen cast iron cylinders opened up to 86mm before, and it worked just fine. The 86.7 may indeed be pushing the limit though, like Bobboloo stated.

Jay, if we can hook up, your welcome to at least a ride in my 72E with 2.7 RS pistons/cyls, E cams, and stock E mfi.

I won't be in northern Chicago though anytime soon

Dennis, I'm going to take you up on that before I make an official decision on the motor rebuild. My dad lives in Michigan, so I pass thru NW Indiana from time to time. Thanks!

Jay, sounds like a plan! Just give me some notice since we seem to go back and forth to Mishawaka every few weeks. BTW I'm planning on attending Thrown Hammers Car show in Sept. if we don't meet up before then. Other wise, until I find better employment, I'll be easy to get to at Purdue U. Hammond Campus just a block north of 80 2 miles over the border.

Its nice to have a reason to go for a ride:)

I just got around to installing my MSD ignition and adjusted my throttle rods so I am now getting more than half throttle ;)

I would have replied earlier but I was on vacation.I'm looking to do the same thing. To bore out my T cylinders out and install JE's and keep my cams and MFI pump the same. Then when I get out of college swap in S
cams and recalibrate the MFI pump.

Here's what I came up with on some of my calculations:
A 2341mL 9.8:1 T engine should make about 170 and 9.8:1 2397 mL(85mm bore) 9.8:1 T engine should make about 2% above that.. about 175 or so. A T engine with an 86mm bore would displace 2454mL and probably make somewhere in the neighborhood of 178hp or so.
I'm guessing a 2397mL 9.8:1 S engine should make about 200 or 205 and a 2454 mL engine should make another 5-7HP more than that.
How close do these #'s sound?
Is there enough meat on a T cylinder to bore it out to 86mm and still be reliable enough to run for 70K-100K miles? I'm looking for an engine that I know the engine will run well for a long time and still be quite fun.

Tim, remember, I'm the pig for this situation. I'm running my stock 72 case, 3-4-or5R, Don't remember which. I'm at about 10,000 after rebuild with no case issues.

PS, you may as well put in as much displacement as you can ie,2.7 or2.9 instead of stopping at 2.5. That displacement will give you another 20-30 hp and lower your useable powerband.

Then again, my old stock 2.4E was rather stout:)

Dennis,
I'm really really hesitent to bore out my spigots to accomidate the 2.7 pistons. I just don't think they can handle the stress. I think yours is ok since it's got E cams and not RS cams but I'd like to run the S cams in my engine eventually and I'd be really worried about my case cracking.

Can you check your case for me? I know I"ve got a 3R-4R case. If I had a 5R case I'd go with the 2.7 in a heartbeat but the 3R case is a weak one.

Aye Tim, will do!

I hear you, but I have faith, and hope that all will be well!

Remember, the early 70-72 2.3, 2.4, 2.5 race engine made up to 275 hp in those early cases.....

He!!, its outside, I'll go check!

Tim, and everone else, I just looked and it is indeed a 4R case.

Tim, if you have a spare set of early S cams, I'll be happy to see how long my case lasts with them in tow :)

I do use my car every day for daily transportation and it needs many things, but the engine is sound

hmm.. You're seriously tempting me.

Dennis,
Can you check the other side this time? I've got a 3R 4R setup but dtw's actually got a 5R 4R setup so it could be either.

Took a look, its the dreaded 3R-4R. 3R on the oil cooler side. My car was 0060 of the line, so late 71 production, hence 3R-4R

I'm tempted to go the 2.7RS P/C route. I have the 4R/5R case, so I guess I'm not too worried about stressing it. I don't plan on the full RS setup...at least not for a while! My engine has a broken exhaust valve that punched a hole in the piston. If the cylinder walls are too beat up, I won't even be able to bore them out unless I find a good used replacement in the right height group.

I'm trying to get a good understanding of exactly what machining I'd have to do for the case/heads. I can't quite follow what I'd need to calculate costs of going the 2.7 route. Does anyone have a good itemized list??

Dennis, I'll be out of town tomorrow (7/2) until Mon. morning. But I do have all of next week off from work. Drop me a line how next week looks for you. I won't be able to reply until Monday, but I will get back to you!

Have a great 4th everyone!!

Jay i'll pm you my work phone and if you want you can come by during the day and we'll check it out. I can show you my receipts for the work I had done (machining) and the parts I purchased.See Ya and Have a great holiday!!

Jay I've got 12 of those cylinders. Chances are I have one you could use. No charge.

The machining cost can get pretty steep. Upwards to $1200. However since this is a T case motor your probably in pretty good shape. The T cases don't seem to get as warped as the 75' on 2.7S motors. i've got two 2.4T cases and both had line bores that checked out.

The work you should consider though...

1.verify the line bore
2.casesavers
3.deck the spigots
4.timesert the layshaft case studs

About $600 for the above work.

To go to 2.7 you'll need.

1.cut the spigots
2.oil bypass mod

About another $350

So your close to a grand for the case and you still need to address the heads.

I'll second what Bobboloo said: I've got a 3R/4R case on my '72T, and the line bore checked out ok. I'm was going to go with 85mm JE pistons in my stock cast iron cylinders (bored out, of course) but all this talk about using 86mm pistons has me thinking: I like the idea of 86mm pistons simply because I could then mount one of my 2.5 badges on the grille! 85mm pistons don't get me over 2.4L, so the 2.5 badge would be cheating. :D Are there head mods that need to be done? My heads were rebuilt a year ago so I don't want to disturb them if I don't have to. I'm going to use E cams and (hopefully) my T MFI, at least for a while.

BTW, small towns have their perks: My machine shop is only charging me $90 to do the case savers. I thought that was far too cheap, but after talking to my machinist (I'm a machinist as well, just not a Porsche machinist), I came away very confidant in his abilities, and he's done a ton of Porsches, especially small displacement engines.

Good Luck,
Jim
'72T

Jim,

$90 for casesavers is a good deal. The cheapest I've had it done it for is $175. That's almost a 50% discount compared to what you would pay at Otto's or Ollies here in L.A.

So I guess Jay could figure the cost of doing the case for a 2.5 rebuild would be from $500 to $1000 depending on where he goes.

As far as the heads go, I guess it depends on the pistons. If you go for higher C/R with deep pockets and an 86mm bore you might have to fly cut the heads. I guess it comes down to how JE makes the crown of the piston. I would think if the piston crown is flat for the 1st mm going inward from the outer edge, before it starts to crown, then I guess you would be alright.

I've never done this conversion so I don't know. Maybe one of the knowledgeable people here can chime in.

Can you actually go as big as 86mm? I wouldn't think there would be enough meat in the cylinders for that and to still be reliable.

86mm has been done. (see Tysons post) 86mm will leave you a 2.5mm wall between the piston and the CE ring gasket cutout.

86.7 might even be doable but you'd be covering new ground. You'd have a 2.15 mm wall and remember, the point where the cylinder meets the head is where the highest compression pressures occur . Obviously you'd have less room for error so your machining tolerances become more critical.

Too bad someone doesn't have a set of the factory 86.7 P+C's so we could see what they did.

One other consideration is the bottom of the T cylinder is only 89mm on it's outer dimension so if you bored out to 86.7 you'd be left with a skirt that is only 1.15mm thick. That's pretty thin.

So 86mm would be feasible and still be reliable? I'd love to have the extra little bit to make a 2.5 instead of a 2.4 but I'd be worried that the cylinders won't last for 70K-100K

Tim,

You are going to be making so much money after you graduate - don't worry about longevity. You can buy another engine in a few years if this one doesn't last. Same applies to the case. My impression from my reading, which may not be as extensive as yours, is that the weaker case is an issue on engines that will be raced and abused. For the street car that you want to build, I'll bet that any case will do. Use your case and parts and do a budget rebuild the first time around. The next time you will be ready for more exotic work. In my view, you worked too hard to get your car to where it is to delay getting it back on the road for 6 months due to machining and budgetary delays. I also think really think you should consider using my engine. I imagine we can have it up and running for peanuts (one or two bent valves). You can use it while you build something else.