2.4T to 2.4E or 2.4S "spec". Advice needed.

[M491Cabriolet]

Hello all. I am gathering parts and information before I begin the process of having my 911T 2.4 engine rebuilt. The car is a 1972 T, FYI I have some questions and hope the experts will be able to answer some or all of them and advise me if I'm on the right track. This is a car that will be driven of the street most of the time, and may be tracked at times, but rarely if ever. Here is some background and a bunch of questions. I'm beginning to become overwhelmed by all the variables and want to avoid making any costly mistakes.

1) The engine is currently stock now except for the Weber 40IDAs installed.

2) I may want to eventually reinstall the MFI (way down the road)

3) I plan to install a set of new 2.2 S Mahle 84P8 pistons and Mahle Nikasil cylinders.

4) I have a set of OEM RS camshafts with MFI drive and a set of E profile camshafts with MFI drive. Regarding the cams, I know the S cams are empty below 5000 RPMs, and the E cams are more "well-rounded". Would the E cams be preferable, or would the S cams in combination with the 2.2 pistons and 2.4 displacement make them more usable? I wonder where the torque would kick in on the S cams and E cams... Which cams should I have put in?

5) I have an RS distributor that I plan to install.

6) Regarding the heads, would I have to enlarge the ports from the stock 32mm? Should both intake and exhaust ports be the same size? What would be the optimal ports sizes for this setup? Is there any negative effect on power and/mileage in making the ports "too big" (36mm?)?

7) What is a reasonable price for a set of new Mahle pistons and cylinders, and how much can I realistically expect to spend (and should I budget)?

8) Will I have to make any changes to the piston rods and valve springs to support the extra revving and compression? If so, which rods and springs are suggested?

9) With this setup, E or S cams, how should my carbs be set up (jetting, etc.)?

10) Will the compression ratio with the 2.2 S pistons and E or S cams be too high for everyday use on normal pump gasoline? Will it be too high for the normal T starter?

11) Does this planned engine generally good? Could it be improved in terms of the equilibrium of power/usability/fun?

I know that's a whole load of questions. I hope I don't get a lot of questions instead of answers in response because I am beginning to get a headache over all the questions I already have and have no clear answers to! Thanks very much in advance for all of your help.

[daepp]

Well, I don;t have a lot of answers, but I do have a little experience/observations for you.

I had a 2.4T rebuilt with 2.2T P&C's. I never drove it before the rebuild. It ran well and had adequate power - from what I understand it was a fair HP gain, and the CR did not prove to be a problem with pump gas. Due to excessive smoke (possible due to a ring problem) I had to have the engine torn down.

Supertec used my stock case andbuilt me a 2.4 with E cams, JE pistons and used S cylinders. The power jump was awesome and it is very driveable. IIRC the CR is 9.5:1 and I run premium gas (91 in CA). I am careful not to lug it as it is not twin-plugged, but this has nto been a problem over the last 2 years. It's an early Targa so I do not track it - just spirited around town and highway driving.

While I recognize that the 2.2 route is a popular one, for me, spending just a few more dollars and accepting Henry's assertions about the quality of the used Mahle buckets, produced a much more enjoyable engine. IMHO of course.

[M491Cabriolet]

Thanks David. You say a couple of things I don't know about. First, what is IIRC? Second, you said

"While I recognize that the 2.2 route is a popular one, for me, spending just a few more dollars and accepting Henry's assertions about the quality of the used Mahle buckets, produced a much more enjoyable engine. IMHO of course."

When you say "buckets", I guess you're talking about cylinders, right? Where do I find Henry's assertions in regard?

Thanks again. I hope someone will help me out with answers and more advice on my load of questions!

[daepp]

Sorry.

IIRC - if I remember correctly

Henry and I discussed new QSC cylinders (buckets) vs. new Mahle vs. used. We had a problem with the QSC's (even though they were new), I didn;t have the dough for new Mahle's (possibly 6-8K) so we went with a good set of used S Mahle's that Henry had. He has done so much rebuilding of the early engines that I trusted him implicitly with respect to the quality of the used sets he has.

Hope that helps.

[kucharskimb]

Weber Tuning. LM-1 and Dyno. Database, Information, Troubleshooting, Graphs.

2.2 E stroker HP output

I'm happy to give you any additional information. I know that this is a 2.4E with about 9.6:1 compression ratio, and your 2.4 pistons wouldn't be this high, but you can use it as a reference. i use a stock starter, stock springs, etc.

from the LM-1 data, i have since switched to F3 emulsion tubes with 55 and 130 jetting.

the heads flow enough volume to make close to 200hp with 32mm ports. we put the heads on a flow bench when i was trying to make the decision whether or not to enlarge port sizes. if you enlarge the ports, your bottom end will drop off. 36mm combined with the S cams is why the S motor makes more power up top... if you want it for the street/AX, then stick with the E cams and 32mm ports.

[M491Cabriolet]

Thanks. Well, I would be using new 2.2S pistons and cylinders, not 2.4, which I think would raise my compression. In fact, one of my worries is that the compression ration with thes pistons with the longer stroke would be so high I might not be able to run the engine on normal 91 octane or 93 octane pump gas. I actually have heard that it might be beneficial to increase the intake port size to 35 or 36mm and leave the exhaust port size at 32mm. What do you think of that?

How much do you think a new set of Mahle 2.2S 84P8 pistons in new Mahle cylinders will run me?

Thanks!

[Bobboloo]

Originally Posted by M491Cabriolet

Thanks. Well, I would be using new 2.2S pistons and cylinders, not 2.4, which I think would raise my compression. In fact, one of my worries is that the compression ration with thes pistons with the longer stroke would be so high I might not be able to run the engine on normal 91 octane or 93 octane pump gas. I actually have heard that it might be beneficial to increase the intake port size to 35 or 36mm and leave the exhaust port size at 32mm. What do you think of that?

How much do you think a new set of Mahle 2.2S 84P8 pistons in new Mahle cylinders will run me?

Thanks!

A new set is about $3500.

If you go with E cams then 32mm ports would be ideal. If you go with the S cam then 36mm would be ideal.

Since your motor was originally an MFI T then your intake ports are actually 29mm. Porting would be helpful with either the E or S cam. Probably not necessary with the E cam but that would leave a little peak power on the table.

The E cam is really more ideal for your application but the S cam would be a hoot when you rev it past 5.5K. For your application it would be more of a fun feature rather than part of the usual driving experience. Not saying you shouldn't do it. Just trying to put things in perspective.

Another option would be a mod-S cam or a mod-Solex.

Here's a chart to give you an idea of the torque curves of the T,E and S cams. The RS is an S cam by the way.

[kucharskimb]

i was told that stroking the 2.2 to 2.4 rods would increase the compression ratio by about .5, ie a 9.1:1 2.2E would go to 9.6:1., etc. I ran this combo for years in San Diego on 91 Octane.

Here are the numbers for a 2.2E head pulled on a flow bench. A very rudimentary but simple equation is: Airflow at 28 inches water x .257 X the number of cylinders = horsepower potential from airflow.

For this head, the intake at .450" of lift, the CFM is 207.5.

In the equation, this is 207.5*.257*6 = 320HP

for the exhaust, it is 153.4*.257*6 = 236HP

this is theoretical and does not include losses from your intake or exhaust. but either way, it should show you that the 32mm head is not the limiting factor.

it is commonly accepted that exhaust flow can be in the neighborhood of 75% of intake flow, much as you have stated above with porting the exhaust to 36mm and leaving the exhaust at 32. but look at the numbers on the chart, you are already at the 75% ratio...

if you ported the heads, would you then move to bigger venturies and manifolds or a bigger MFI system? doing one without the other is futile. the most important thing is how you want to use the car/engine, ie low/mid range power or mid/high end power...

[M491Cabriolet]

Thanks. OK, so let me get this right... If the stock 2.4 T's compression is 8.5 or lower, then the maximum compression ratio using 2.2S pistons and cylinders should be no higher than 9.0, which should be OK with normal pump gas. Is this correct? Thanks.

[BK911]

2.4 crank and rods with:
2.4T pistons 7.5:1
2.4E pistons 8.0:1
2.4S pistons 8.5:1
2.2T pistons 8.6:1
2.2E pistons 9.1:1
2.2S pistons 9.6:1

Actual results may vary slightly.

A high compression 2.4E engine is an awesome engine. Several members have a similar engine. I had one in several early cars and was my alltime favorite.

[M491Cabriolet]

Thanks for that. So, from what you say, the 2.4 engine with E cams and 2.2S pistons is the best way to go. But you also got me wondering... Would this engine with E cams and 2.4S pistons be interesting? Keep in mind, I want a hot engine, but most driving is very "spirited" around town. A set of 2.4S pistons would probably be much cheaper I think. Any feedback re would be greatly appreciated.

[BK911]

I had a bone stock 2.4E with MFI. I added 2.4S pistons for the slight increase in CR. That was the best engine I ever had. In fact, I still regret replacing it with a 3.0. It pulled like stink from idle to redline and sounded awesome the entire way.

2.2T pistons will give a very slight bump in CR over the 2.4S pistons and can be found MUCH cheaper. But they are also a bit heavier.

[dafischer]

Another possibility to save some $$ and still have a nice runner is to do what I did with my 2.4E. It was torn down for a top end job, and was found to need new pistons due to ring lands being out of spec. The guy (Fred Apgar) that did the engine for me recommended boring the cylinders out to 85mm, and going with 9.5:1 JE pistons.

The pistons and boring cost a little over $1,000, and I have to say the results are fantastic. It pulls like a freight train off idle to redline, and sounds marvelous. The downside? I had to switch to premium gas. Oh well, it costs $$ to go fast.

Oh, by the way, I'm running MFI.

Just something else to consider.

[kucharskimb]

you want a hot engine.
you want to use E85 octane.
you want it for free.

pick one.

as with life, everything is a compromise. we all seem to agree that a compression ratio of about 9-9.5:1 and E cams is the way to go. now go do it.

FYI, the HP graphs I linked to in the above post were at the wheels. that's damn near 200hp at the crank assuming 15% losses. that's more than the 2.4S made. what more do you want?

i guess the big decision is with your 2.4T heads, which pistons will give you 9-9.5:1. double check the numbers above and go for it.

[M491Cabriolet]

'Zat right? Who's we?

Of course I want the best of all worlds. I like the idea of a higher compression ratio, but there is one person who said the 2.2S pistons on the 2.4T crank would give a compression ratio of 10.something, and not work with pump gas. So I'm a bit confused by this rocket science. That's why I asked about the 2.4 S pistons. Does anyone know if this is a good idea? Thanks.

[barney911rs]

1) The engine is currently stock now except for the Weber 40IDAs installed.
2) I may want to eventually reinstall the MFI (way down the road)

The Webers should be fine, unless you want to put the MFI back on for originality.

3) I plan to install a set of new 2.2 S Mahle 84P8 pistons and Mahle Nikasil cylinders.

Before I made a 2.7 out of my 2.4, these are the P&C's I had, it only raises the compression about a half point is what I recall from Bruce Anderson's book. Good upgrade for a 2.4 motor.

4) I have a set of OEM RS camshafts with MFI drive and a set of E profile camshafts with MFI drive. Regarding the cams, I know the S cams are empty below 5000 RPMs, and the E cams are more "well-rounded". Would the E cams be preferable, or would the S cams in combination with the 2.2 pistons and 2.4 displacement make them more usable? I wonder where the torque would kick in on the S cams and E cams... Which cams should I have put in?

For a street car, I would use the E cams. I had S cams, but my car was mostly for track use. The few times it was driven around town, it was happy up in the revs 4000 and up. It was somewhat sluggish in traffic.

5) I have an RS distributor that I plan to install.

Not sure, but you should be able to simply re-curve the distributer you have to work just fine.

6) Regarding the heads, would I have to enlarge the ports from the stock 32mm? Should both intake and exhaust ports be the same size? What would be the optimal ports sizes for this setup? Is there any negative effect on power and/mileage in making the ports "too big" (36mm?)?

Don't have any specs handy, but I would not go any larger then what the stock E heads used. The motor I have now suffers because the ports are too big. You need compression and RPM to really make use of the larger ports.

7) What is a reasonable price for a set of new Mahle pistons and cylinders, and how much can I realistically expect to spend (and should I budget)?

no clue, have not checked pricing in a long time. You can check with LN Engineering unless you have another source already.

8) Will I have to make any changes to the piston rods and valve springs to support the extra revving and compression? If so, which rods and springs are suggested?

I'm still using stock rods, valve springs etc. I have my rev limiter at 7200. There should not be any need to go higher then that on a street car. If you want 8000, you will need better rods, rod bolts, etc.

9) With this setup, E or S cams, how should my carbs be set up (jetting, etc.)?

The fine tuning will have to take into account, the elevation, typical temps ranges. Someone else should have more info on this.

10) Will the compression ratio with the 2.2 S pistons and E or S cams be too high for everyday use on normal pump gasoline? Will it be too high for the normal T starter?

You should use the highest regular octane available on your area. I don't think there is any difference in the starters so that should be fine.

11) Does this planned engine generally good? Could it be improved in terms of the equilibrium of power/usability/fun?

It can always be better, it just depends on how much you want to spend on it and how long you want it to last. For a street car you don't need every last bit of HP you can wring out of it. It;s better to have something that will run trouble free for years. You may want to post this in the engine building forum as well.

[911pcars]

Displacement. There is no substitute ..... unless it's force fed with air.

Sherwood

[kucharskimb]

http://www.supertecperformance.com/

call henry at supertec and he will give you the scoop about the correct pistons to use. report back so's the rest of us can get it straight.

[jluetjen]

Originally Posted by kucharskimb

i was told that stroking the 2.2 to 2.4 rods would increase the compression ratio by about .5, ie a 9.1:1 2.2E would go to 9.6:1., etc. I ran this combo for years in San Diego on 91 Octane.

Here are the numbers for a 2.2E head pulled on a flow bench. A very rudimentary but simple equation is: Airflow at 28 inches water x .257 X the number of cylinders = horsepower potential from airflow.

For this head, the intake at .450" of lift, the CFM is 207.5.

In the equation, this is 207.5*.257*6 = 320HP

for the exhaust, it is 153.4*.257*6 = 236HP

this is theoretical and does not include losses from your intake or exhaust. but either way, it should show you that the 32mm head is not the limiting factor.

it is commonly accepted that exhaust flow can be in the neighborhood of 75% of intake flow, much as you have stated above with porting the exhaust to 36mm and leaving the exhaust at 32. but look at the numbers on the chart, you are already at the 75% ratio...

if you ported the heads, would you then move to bigger venturies and manifolds or a bigger MFI system? doing one without the other is futile. the most important thing is how you want to use the car/engine, ie low/mid range power or mid/high end power...

I would tend to dis-agree with that rule of thumb that says that 200 HP is possible from 32 mm intake ports for 911 engines. I have yet to find a 911 engine with 32 mm intake ports that makes more then 160 HP. This applies to 2.0's through 2.7's. As far as M491's questions in general, I've pretty well summed up my thoughts on this thread.

[Bobboloo]

Originally Posted by 911pcars

Displacement. There is no substitute ..... unless it's force fed with air.

Sherwood

Sherwood makes a good point. Considering that you can get a new set of 90mm Mahle 2.7RS P+C's for $1950. The lower cost of the set will pay for the additional machine work needed for them compared to a new set of 2.2S P+C's.

If you look at the chart I posted above you'll notice that the torque curve of the RS motor is similar to the 2.4E. That's because the increase in displacement moves the peak torque of the S cam down to 5000 RPM but it has more power across the whole band.

An added plus is that you can run the car on regular and it'll still be faster than any of the 2.4 motors on premium.