Engine update from '72 2.4L...suggestions?

[boyo]

Sometime in the next several years I expect my '72 2.4L engine (MFI) to reach the point where it needs an overhaul. Best guesses have it near 120,000 miles now, but it does seem to be running strong still. Just wanted to get suggestions on where to take it when it does finally need the Big Bucks put into it.

The magic number I'm thinking of is 250hp. I imagine this will lead some some auto-x track time, and having a nice "sneaker" car with classic looks that blows away the other guy at the stoplight. How would you go from what I've got to what I want?

I'd actually like to keep the MFI if at all possible!!! I bought this car as something I could work on myself, so upgrading to EFI sortof voids that point. I understand the electronics onboard the current system, and could fix them if they went awry. Not so on the later models.

It's my understanding that a 2.4L can be upgraded to a 2.7L with changes to cylinders and fuel delivery. It's also my understanding that heat and stress could be a problem with the case pulling studs. So with new studs and TimeCerts all around, will the case hold up to that level of abuse?

How about crankshaft? I presume a forged crankshaft can be substituted for the cast one. Of course new pistons, and what the heck - new rods and other gear. We'll even get the whole setup balanced. What am I missing here?

Fuel delivery - going from a 2.4L MFI to 2.7L, what does it take? New system entirely, or what?

So at best a normally aspirated 2.7L, with new cams, fuel, and air delivery systems will give you almost 200hp at best, right? What about a mild supercharger (4-6psi) to take it the rest of the way?

Is an intercooler absolutely necessary to eliminate/reduce detonation? I'm having trouble figuring out where to put that, considering I'm also not going to be adding a rear wing. Any subversive mounting points suggested?

Oil cooling up the wazoo, too.

Hmm, wondering if the original tranny can hold up to that level of power. It already needs some help, may consider replacing instead of rebuilding for the tranny only. Suggestions on replacements?


Let me know if my thinking is sound on all these changes. I'm aware the cost may be equal or greater than just getting a replacement engine - but it sounds like more of a challenge this way. Thanks!

-Boyo

[Britwrench]

Possible option;

Rebuild your engine to 2.7RS spec, re-build the MFI, use SSI exhaust, 2.7RS or web-cams, 2.7 Euro ignition distributor with MSD and new wires. Aluminum pressure plate and rebuild the trans. Front oil cooler.

Should be about 210 - 220 hp minimum.

The last 2.7RS (with carbs) conversion from a 2.7 911s was $13k
Trans rebuild is going to be around $1K depending if you want to go for a limited slip diff or not.

[zotman72]

It depends on what you have in your current 2.4L engine. Is it a T, E or S? If it is a T then, you are facing an uphill trek to get to right components of 2.7RS. An S engine is just a short hop with P/Cs, case machining and space cam change in your fi pump. I did the T--S route and am happy. Only about ~200 hp but still a hoot.

[boyo]

Good option - cost should be OK as long as the stock market picks up by then... That's more than I paid for the car!

For me it's more like...where did that bolt go that I just set down? My cousin has a dog that walks by and picks up anything greasy or otherwise tasty to a dog, and usually leaves it in the middle of the lawn...

-Boyo

[Matt Smith]

Boyo, you already have a forged crank. It's just one of the many little pleasures you will find in the 72 T.

[Matt Smith]

But you would have a far easier and cheaper time by removing but hanging on to the original engine and replacing it with a 3 or 3.2 litre mildly hopped SC/ Carrera mill for an easy-ish 230?.
Cam Baudinet is doing a mean conversion on a 69T in the near future. Wait till he chimes in.

"Crack Beauty is on its way"

[tobluforu]

Your going to spend a boat load of money trying to make a 2.7 motor make 250hp. I'm pretty sure that you might be able to upgrade to 2.8 or 2.9 motor with that block. But, if it were me, (and it's not) I would go with a used 3.2 motor. Probably cost the same as what you are planning to do. Will be much more reliable and drivable. The s cams, or rs in a 2.7 motor will give you gobs of high rpm power but, the low end will suffer. You will have to get the pump rebuilt-800 bucks. Will have to get the larger s stacks if you don't have them now-pricey. Cams aren't cheap!
There are a ot of people that will chime in on this. Some have done the 3.0. 3.2 and 3.6 conversions. Some have also done what you are thinking. I went the 2.7rs route but, w\e cams. I like this setup but, it is not fast enough for me now.
Good luck

[Bill Verburg]

Its beyond me why folks think that if they rebuild to 2.7 RS specs they expect to get more power than the factory did when building new 2.7 RS engines in '73. They were getting 210 plus or minus and that's what you should expect today.

You really need to assess your goals, are you building to a class rule? Is authenticity important for some reason? If the answer to both of the above is no then a late transplant will be far more reasonable economically and provide modern reliability and tunability to boot. The bigger displacement later engines are far better suited to the rigors of street driving where torque not hp rules.

[boyo]

So what, nobody likes superchargers?

Good suggestions from all. I'm relatively new to the 911 scene (4 months ownership now) so all input and reality checks are appreciated!

Just got the Bruce Anderson book, and it's been extremely helpful in just understanding the engine. I've rebuilt a half dozen engines in the past 2 years, but still look at the 911 engine and go "whoa....". Pretty neat beast.

-Boyo

[NYSCAR]

Well the way I see it, a supercharger would be much more pain than it is worth to adapt one to work for the MFI system. First of all, superchargers tend to be a bit parasitic, which might be a bit noticeable on the smaller displacement early engines (even the 2.4), as opposed to the larger and torquier versions. Then you must figure out some sort of way to pressurize the stacks, I'm not sure if the stock airbox would be up to the task (you'd have to worry about things like the oil tank ventilation). You also might run into clearance problems too (i.e. pipes feeding the system) as the engine lid doesn't leave alot of room. Lastly you'd have to have someone custom build a space cam for the MFI pump to match the fuel curve required for the car. To aquire a fuel curve for the car, you have to do dyno runs etc. Modern electronic systems allow you to custom tune this curve, but on the MFI cars this is determined by essentially a glob of steel, not very easy to tune. If you want unreal power in an early car with exotic character and race car feel and sounds, spend LOTS of money and build a 2.8RSR engine. If you want unreal power in an early car *relatively* inexpensively, you have to go to a larger displacement. If you want unreal power for cheap, buy another car

Brad

[CamB]

Chalk me up for another "no replacement for displacement" vote.

A 3.2 will be your cheapest route to 250HP - you ought to be close to that if you changed the exhaust and maybe a mass airflow conversion? Best bet is a Euro 3.2, because they have 231hp to start with... That way gives you factory reliability and there are plenty of people on the Board with 3.2s with well over 100k miles.

Randy Wells has a 3.2 in a '72 - see Excellence magazine - November. He found a way to get about 250hp too

I am going for a 3.0 that someone else has built up because:

a) it is available
b) it will rev a bit more (S cams)
c) I have the capacity to understand the (relatively simple) MFI based EFI system on this engine

But I would still prefer the same engine in 3.2 form. Or 3.4 .

You can sell the T motor, or keep it if you want to be able to sell it with the car for originality's sake. If you do achieve 250hp, remember to think about brake and suspension upgrades.

[Randy W]

I think the only way to get 250hp starting with a 2.4 MFI is to spend upwards of 20K, either going with a no holds barred 2.5 high compression dual plug slide valve or a slightly less wild 2.8/2.9 RSR high butterfly MFI. Either is pretty extreme. A stock 2.7RS MFI engine in perfect tune will give you 220HP max.

The cheapest alternative is a Euro 3.2L with race gas (about 230hp). Next cheapest is a stock 3.6L (250HP on up, depending on year). My US 3.2L is 260HP on race gas after balancing, MAF, Motec, and Flowmaster exhaust (over 20K invested). You can get the same HP out of Euro 3.2L by just adding carbs but they will stutter under high G loads and the Euro is not legal in all classes.

I think Bill's suggestion is a good one - look at what is allowed in the class you want to run in, and go from there. Each engine has its own character - there are pluses and minuses to each. If you go track racing with over 250Hp going through a 915 transmission, you will need a transmission oil cooler and are better off with a later aluminum gearbox.

Randy Wells

[911pcars]

Here's another expensive way to achieve your goal.

A 3000 lb car with 300 hp has a weight/hp ratio of 10:1
A 2500 lb car with 250 hp has a weight/hp ratio of 10:1
A 2000 lb car with 200 hp has weight/hp ratio of .... 10:1

Between the three, performance should be about the same. The lightest car though, will be the nimblest around curves.

Getting down to 2000 lbs or below is not an inexpensive task, However, it may not cost as much as 50 hp and it's been done before (see Jim Calzia's weight-reduction project on the www.Early911SRegistry.org website). It all depends on how serious you are with that 10:1 ratio.

Sherwood Lee
http://members.rennlist.org/911pcars

[dbanazek]

I agree that you will have a hard time getting a reliable and streetable 250hp out of a 2.7

I have a 2.7 RS spec with webers in a 72. It is pretty quick but not quite as fast as I would like. It is a very streetable car with plenty of power starting at about 3000 RPM

I think the 2.7 case is fine for an RS spec engine but not up to the task of supercharging. You can do several thousand dollars worth of work to an early 2.0 Aluminum case and build a stronger 2.7 but the way I see it the only reason to build a serious 2.7 or 2.8 is to meet a specific race class, ie GT 4 in PCA club racing. You can not build a streetable 2.7 without a forced induction and a 2.7 with a supercharger seems pretty fragile, and not really worth putting the extra $5000 or so for the charger.

My vote is for a 3.0 or a 3.2L with Webers. If you do the work you out to be able to buy an engine, do the basic rebuild stuff, stick some high compression JE pistons and bigger cams, maybe open the ports up a MM or two for about $10,000. This still gives you a simple engine to work on and keeps the feel of your early car. Hardly anyone would know the difference between a 3.2 with Webers and a 2.4 with Webers.

As far as weight goes my 72 with some of the insulation out and no spare tire etc weighs in at a slight 2250lbs. I built a 73 RSR look race car that weighs 1940lbs. The difference? All fiberglass body, no under coating, only 2 gauges, no interior except for an aluminum seat, cut our rear set panel, no side windows, Lexan rear window. Of course I added some weight in the form of a full roll cage, turbo brakes and trailing arms, 9 & 10" wide wheels, lots of oil lines, front mounted oil tank and a nice oil cooler (runs at an enviable 180 degrees on the track). The point is that losing the first 200 lbs makes your car uncomfortable and the next 100 lbs is about $2500 in fiberglass. The next 100lbs is going to be very expensive.

Dave @ Dart