2.4T Engine Upgrade Options

[mattC2993]

Just bought a '70 911E project with a '73 Euro 2.4T which c/w Zeniths. I'm kinda new to early 911s but was crunching some numbers to get the 2.4T engine up to 2.4E power. I figure $20k by the time I get it fully rebuilt with E cams, distributor, PMO carbs, new P&C, exchangers and muffler. I see that people just go to a complete 3.0 or 3.2 but then they probably need rebuilding too although I could see that costing a lot less if you don't need all of those parts. Here are my choices as I see them:
- upgrade 2.4T to E specs
- get a 3.0 or 3.2 and rebuild it (or take a chance on a used one)
- look for an original 2.2E engine which might need a rebuild and pump work
- sell the car and put my money into my 356 or 993

Any suggestions? Thanks.

[procan]

In performance per dollar terms, I personally don't believe PMOs are worth the marginal cost over Zeniths. Get some 34mm venturies fab'd for the Zeniths instead. I have a 2.4T I am rebuilding with Solex cams, Zeniths, ported heads, 85mm JE 10:1 pistons, and twin plugged. No where near that $20K figure.

[copbait73]

Change to CIS then add a turbo.

[speedo]

All you have to do is swap the low C/R 2.4 T pistons for high 2.2 T pistons. Leave everything else the same...bingo 2.4 E specs. Just did it and kept the Zeniths...looks stealth. Or, you can spend big bucks on all the other upgrades

Speedo

[jstobo]

Well you can't get E-specs by changing just the pistons because you will not have E-cams. And if you put in E cams you can't use T pistons because they will hit the valves.(smaller cutout on top of T pistons) You can buy Mahle E pistons but a cheaper route is to buy a set of JE pistons. You can have them designed for any compression ratio. The 2.4E only had an 8:1 compression ratio because of emissions. Get a set of JE 9.5:1 pistons with an E cutout. Buy a set of E cams or have your T cams reground to E specs. Re venturi your Zeniths and you will have an engine that should exceed the HP rating of the 2.4E stock engine. Cost for parts should be about $2,000.

[Dodge Man]

Matt. I was in your situation in 1985. Old 911s were not worth anything close to todays prices. IMHO If it was numbers matching then putting $$ into the 2.4 would make sense. A used correct non-matching numbers 2.2 motor would give you better resale to a point if the car is factory correct otherwise. The Euro 2.4 could help to offset the cost of a period correct motor. If you go down the bigger motor route then you are open to trans upgrades, flares, etc.. to handle the increase HP. Been there, done that, and spent the $$$$. I should have saved my $$$ and kept my 73 bone stock. Used motor from a reputable parts company (search Pelican & the web) will probably make more $$$ sense than building the 2.4. You already have carbs so fuel system is pretty much set with some adaptors, jetting & tuning. However, you have to be prepared for the possible valve train work needed on higher mileage 3.0 & 3.2 motors. If the trans is stock then you have to look at the stress on the 7:31 R&P if you like to put the pedal to the metal. Big motors have the torque to break R&P teeth over time. You may want to get both the motor & trans to save yourself some grief and save the old trans for future resale. Just M2CW. Make yourself happy.

[mattC2993]

Great response guys! Can stock cylinders typically be rehoned? I didn't know that aftermarket Zenith parts were available. Who sells jets for Zeniths? I would still need $$$ for gaskets, hardware, chains, head rebuilding and exhaust. Does the distributor at least need to be recurved?

[dafischer]

What jstobo said. I did this with my stock 2.4E which needed a top end. My builder used 9.5 cr 85 mm JE pistons, which required a 1mm overbore on the cylinders. With new E cams (old were worn) and a Fidanza aluminum flywheel, it's a very happy engine.
He estimates about 185 HP, and the seat of the pants dyno seems to confirm. The whole job, including valves, guides, con rod re-bush, and new con rod bearings ran me 6K 4 yrs ago.

[Dodge Man]

Top end on the 2.4 is a solid upgrade plan and not $$$ crazy. Splitting the mag case is where the $$$ go crazy. Just remember to have the rockers ground to match the selected cam profile at the cam shop. The Pelicans here have the P&C hardware advice. The 2.4 will be a nice fit and not tap your wallet with the flares & trans issues. My old worn out MFI 2.4 won more than a fair share of red light Grand Prixs. The car should be a fun very quick period 911 when you get the motor done. Enjoy the 70 for what it is with the 2.4 rather than long for what it is not. Please post pictures.

[procan]

These guys sell Zenith Jets:

Porsche 911 Zenith Tin Carburetor Main Jets | eBay

and

Source for new Zenith TIN Jets

[RWebb]

what is your budget for the engine work?

have you done all brake and suspension work or upgrades?

[LakeCleElum]

I had the same decision....After some careful shopping, I decided to go with a larger engine and save my 2.4 for resale purposes. I paid $4,500 and picked up 90 RWP:

FS engine and transmission.

Very happy with the outcome. I had planned to rebuild my 2.4. Had stockpiled new P/C's and heads. But, the mag case thing is pretty big money, even doing assembly yourself. Could not have touched my 2.4 for what I have in the 3.2 with high compression.

G'luck...

[procan]

Also LN Engineering will build your 85mm JE pistons to the compression you specify, and if you send them your cyls they will overbore to 85mmm and prep them for you. Pistons are like $1400 and cyl overbore is $100 per cyl. So that's $2000 for new P&Cs. Pretty good deal if you ask me.

[tobluforu]

Since these cars are increasing in value, keep it. Seems like you have two other pretty cool cars, so I would not put a 3.0, etc in it. Stick with what you have and upgrade internals. If it's drivable right now, leave it be, drive it since it's getting nice and fill your closet with parts. Then when the weather turns, bring it to shop and let them have at it.

[Roger 911]

I have owned a '72 T MFI since '98. I did not buy it as an "investment", or a show car. I bought it to be a DE car. After a couple years, I decided I wanted more top end, the motor seems pretty lifeless above 5K. After an exhaustive amount of research, I determined that I could install E cams with the 7.5:1 T pistons and still have adequate piston/valve clearance. I was right. I picked up a used Weber set up, which at the time was less than a rebuild on the MFI pump, and I ran it like this for over 10 years.

The top end was much better with the E cams, pulling strong from 3500-6200. However, the combination of the hotter E cams (more overlap) with the low compression pistons, did not provide much bottom end. At the time, it didn't really matter, since DE was my focus. However, as time went on, I started thinking about more power and especially more street drivability. Like you, I considered rebuild/upgrade, or replace. If originality and maximizing long term resale was my goal, I would have rebuilt the motor, probably a 2.7 with E cams. As you noted, this is not cheap. I would be comfortable assembling the motor myself, but parts and machining could easily run $15K. When I was done, I'd have a sweet 200-210 hp motor, that would impress the nostalgia crowd.

However, my car was already not 100 original, having been repainted a non-original color with blacked out trim, etc. Restoring back to original status would be very expensive, and personally, not very rewarding. I like driving my car, especially on the track. This really pointed towards an engine swap. I decided that a 3.2 would be best, giving me not only a lot more hp and torque, but the added drivability of a DME engine. I found a really nice motor from a well maintained and documented all original '84, with 85K miles, good leak down, etc. (purchased from Weekend Rides). It was hit in the front and totaled by State Farm. I bought the motor for $6K and sold my 2.4 for $4K (it appears I could have gotten more...oh well). I'll probably have another grand in it by the time I'm done. So, when all is said and done, I should have about 210-15 hp (w/ cat bypass) for roughly $3K. (I also wound up buying the tranny from the '84 since it had an LSD. Net cost, $1K...it looks even better than the motor!)

Could the motor blow up a week after I get it running? Sure, but not likely. Could it need a rebuild soon? Possibly, but again, not likely given the maintenance history, leak down, and the reputation for the 3.0-3.2 motors. Even if it does need a rebuild, I'm starting with a 3.2. I can perform essentially a stock rebuild and still have more power than a much more costly rebuild on my old 2.4. There is no practical downside for me.

If you like the "period correctness" of a smaller displacement motor with carbs, it should be pretty easy to swap in some E cams (assuming you have 7.5:1 pistons in there). It will be a nice boost on the top end. If you want a lot more power, and you don't care about nostalgia, I'd strongly consider a swap to a bigger motor. You're starting with a non-original motor already, so I wouldn't be too concerned about "investment value", IMHO.

Have fun!

Roger

[speedo]

My suggestion to keep everything else and use the higher compression 2.2 T pistons was so you could keep the T cams you have. Not only do you get a compression bump because of the higher CR, but with the stroke of the 70.4 crank vs the 66mm crank, you get a compression boost. Correct...you won't get the top end bonus you would pick up from the E cam profile, but you will get better low end from the T profile. And, the car will be happier on the street. All depends what the objective is here...best bang for the buck, or how to pour money into the hole. Street car that is a definite improvement, or a track day car for which money is not an issue. Before I stroked my 2.2, I did a lot of research. I found that the more things I changed out...the greater the ripple effect. The factory numbers for the 72-73 2.4 T were CR of 7.5 and 140 hp, the E was a CR of 8.0 and hp of 165. The original factory numbers for the lowly 2.2 T engine were 125 hp but a CR of 8.6 The hp estimates for using the 2.2 T pistons with the 70.4 crank were in the 165 range...with a CR near 9.2:1. To me...these numbers look somewhat 2.4 E-ish.

Rebuilt Zeniths

End of the day it is your $$ and time. If you ever do sell the car, it will still be pretty close to original...just hand the buyer the box of old 2.4 T pistons.

Speedo

[copbait73]

Ok, here is my experence and experiment.
Start early spring in the midwest with a stock 1973.5 2.4L cis T. Drove for a couple of months, pulled the cis and added new PMOs with modified distributor. Ran it on the street for about one month. Friend offered a 2.4E long block so I pulled the 2.4T, installed the 2.4E with my new PMOs. It ran a little better but not strikingly so. Called the same friend up and found he just got a '84 3.2 from a wreck. Out came the 2.4E with PMOs and in went the stock 3.2L. Wow, now this is what I'm after, racer performance without the cost and hassle........ "no one is talking me out of this combo".
My son shows up one weekend and we talk about his vision of a 2.4S with PMOs to replace the stock 2.2T in his '71. He drives the 3.2L and there is no more talk about an expensive 2.4S build. He talks me out of my 3.2L. I sell the 2.4S stuff and new PMOs. My '73.5T gets it's motor 3.2l stripped out and placed in my son's '71 with a 915 trans also.
Later I find a sweet driver '73.5 cis T. With original becoming the thing for longhoods I opt to install a DIY TURBO on this stock engine. Turbo'd this motor now runs at modest 6PSI and I'll put it up against any stock 3.2L swap.
For you, I go for finding a 3.0 or better yet a 3.2L swap. Store the original engine if you must. I have two longhood motors sitting on the shelves for this "possible" future.

[copbait73]

BTW, I have a 2.2E disassembled.

[mattC2993]

Thanks for the great advice! I wish I could reply to each post (is there a multiquote?) . Yes I will certainly get the mechanicals in good working order before spending $$$ on the engine. Do you all recommend brake upgrades when going to the 3 .0 or larger? It is just a street car. Max power isn't my objective. I drive a 356 after all I'll just try and get the car running and sorted first and get an idea of how far I want to take the power. If it doesn't run well I'll just have to figure it out sooner. For a budget build I see 9.9:1 AA cylinder and piston sets for around $1k. It seems that a simple rebuild with these pistons would be okay. I'll have to keep my eye out for a 3.2 but they will be hard to find up here and it seems that a used one is only a good solution if it runs well enough to not warrant more money spent.

[copbait73]

I happen to believe the stock brakes are adequate for street driving as long as they are properly maintained. "S" got premium to pull down from high speeds you will not see.
Modern Porsches get gonzo brakes because they are HEAVY.....and have high speed potential.