HP increase in a 2.4

[cmcfaul]

I have my 2.4 E striped down to the case. I have to replace a piston and may need to buy 6. Current config is stock but with 9.5 / 1 CR via JE pistons in Nickicell jugs with single plug ignition on a 7R case.

I am having the heads rebuilt but am not sure exactly what that entails except for new valve guides. I guess it comes down to what's in and out of spec. budgeted about a grand for the heads.

I feel like I need to do something to it "while you are in there" to justify the cost and effort. The only options I am aware of are to twin plug it and up the CR or up the displacement to 2.7.

I don't want to dump a whole lot of extra money into it in the form of "upgrades". I want to keep the existing MFI setup. I don't want to split the case (for fear of not being able to put Humpty Dumpty back together again).

Use of car is to have fun and a couple DE's per year.

So what are the recommendations?

Many Thanks,

Chris

73 911 E

[Tyson Schmidt]

Twin plug it, port the heads to S-spec, and get some S cams. The JE pistons you have should work with the S cams.

I wouldn't recommend going to 2.7 unless it's a 7R case.

[cmcfaul]

It is a 7R case

[RSTarga]

If you have to get new pistons you might as well go to 2.7 . From my experience going from 2.4S spec motor to 2.7 RS spec motor was a HUGE difference. And I have 8.5 compression. I wouldn't twin plug it unless I was going above 10 compression. The expense of twin plugging is not worth it if you only plan 8.5 or 9.5 . The torque difference is outstanding. Is your case shuffle pinned? I wouldn't put it back together without having this done, those magnesium blocks are getting fragile as they age. You should also go for the Raceware hardware, studs etc. for reliability. I've got 50,000miles on my upgrade and it is still rock solid.

[cmcfaul]

to go to 2.7 do I need new jugs or have the existing Nickacells bored?

[RSTarga]

You can't bore a Nikasil, in fact even honing is a delicate procedure the Nikasil is a very thin finish in the cylinders. You need pistons and cylinders. You also need a different space cam on your MFI. I think Mahle makes both a 2.7 9.5 conversion and a 2.8 9.5 conversion. I don't know the cost difference between the 2. As I said I have the original 2.7 8.5 Pistons and cylinders.

[cmcfaul]

this is where it starts getting expensive. I could probably get some money from my existing jugs as they look perfect....still have all the original honing patters inside. But doing the space cams in the MFI is another grand. My car runs so rich right now. Could the existing MFI provide enough fuel for a 2.7. It has many clicks left on the enrichment screw to up the fuel flow.

[rsscotty]

We have our Nikasil cylinders bored with no problem for custom piston applications. We send them to US Chrome for new Nikasil plating. Never had any issues.

Your MFI pump should be redone to 2.7RS specs. by Gus @ Pacific Fuel Injection.

[RSTarga]

if your pump is off now you need a rebuild anyway, fiddling with the enrichment screw won't solve your problem. Send your injectors along with the pump.

[cmcfaul]

Gus rebuilt and recalibrated my MFI about 5 years ago and I have not touched it since. Sent the injectors with it as well.

[Tyson Schmidt]

Originally Posted by cmcfaul

It is a 7R case

Well that changes everything.

Properly going to 2.7 RS specs but with high compression pistons and twin plug would be my recommendation.

Unfortunately to do it right requires about $2000 in machine work on the case, and proper head studs.

Case savers, bore the cylinder spigots, shuffle pin, and align bore of needed, plus ARP or Supertec head studs. Oh, and the bypass mod to the pressure relief system and going to a later oil pump.

[Tyson Schmidt]

Originally Posted by cmcfaul

this is where it starts getting expensive. I could probably get some money from my existing jugs as they look perfect....still have all the original honing patters inside. But doing the space cams in the MFI is another grand. My car runs so rich right now. Could the existing MFI provide enough fuel for a 2.7. It has many clicks left on the enrichment screw to up the fuel flow.

No, it won't work. It will end up being WAY too rich at low rpm in order to get enough fuel at high rpm. The curve is just all wrong.

[BK911]

Originally Posted by cmcfaul

I don't want to split the case (for fear of not being able to put Humpty Dumpty back together again).

Sorry, no 2.7.

A 2.4E is an awesome engine. A hi compression 2.4E is even more awesome'er.

You could port the heads at expense to bottom end. If it were me, I would build it back as it is. Balance everything so it is PERFECT. Get the heads port matched.

Then go vroom vroom.

[TimT]

You can't bore a Nikasil

That is a myth.

We rebore Nikasil barrels, as mentioned above US Chrome does a nice job of it..

[Grady Clay]

Chris,

Let’s figure out exactly where you are at now before we then get carried away spending your money.


First, exactly what is wrong that you took it apart and want to replace one piston – at least?

You have JE pistons and Nikasil cylinders? I wasn’t aware there were aluminum cylinders available (other than Nikies?) that were 84 mm and could be Nikasil plated. Are they Biral? Something else? Is it possible those cylinders are 90 mm Mahle Nikasil or 90 mm Kobenschmidt Alusil that were Nikasil plated?

Did you measure the CR with these JEs? How do you know it is 9.5:1 CR? Are there any non-standard shims (or none) under the cylinders?

What is the current condition of each of your piston-cylinder pairs? What is the piston-to-cylinder clearance? Are the ring lands in spec? Any other problems?


Exactly what is the condition of the heads? What guide-to-valve clearance? What condition are the valve seats and valve head sealing surfaces? Is there any sign of head gasket leaks? Are they virgin or has someone machined on them? Any other problems?

What condition are the cams, rocker arms, rocker shafts and cam housings?

Do you need chains, sprockets, tensioners, tensioner arm update? How are the chain housings - tensioner pin loose?

You have a 7R case – good. What is the history of the bottom end? Does it have ‘case savers’ installed? What cylinder head studs? If it has been apart, was anything else done; oil mod, etc.? If apart, what bearings were used? New rod bolts and nuts?

What else are you going to need to get it running? Clutch? Exhaust? How are the syncros?

What is the overall condition of the car?


I agree with the above, a 2341 cc 911E MFI with slightly higher compression is an awesome 911. I have one with 2808 cc and 10.5:1 CR. It is just awesomer.

I recommend you stick with an ‘E’ unless you are ready to modify the MFI pump to RS specs, mod the stacks and throttle bodies to S/RS specs, port the heads and replace or regrind the cams. If you want to do all this then go for the 90 mm or 92 mm Mahle P&Cs, high compression and twin ignition.


Here is a tip for Tyson: You can shim the aneroid to gain the fuel delivery needed and retain the ‘E’ characteristics of the space cam. Works great after dozens of 2.7 & 2.8 E and S MFI engines. The MFI pump just thinks it is below sea level. I have an MFI 2808S (started as a virgin ’73, 2.4S) in my 914-6 right now.

It is good to see Tyson here more.

Best,
Grady

[tobluforu]

You can always go to a solex cam as well, sure it's almost an E cam, but not quite. Just a thought.

[Bobboloo]

If your budget is $5000 or less then you can only afford to replace what is broken or out of spec.

If your budget is more like $7500 then you could get a nice used, but in spec, set of 2.7RS pistons and make a 2.7E.

If your budget is closer to $12,000 then you can build a real 2.7RS motor.

"Use of car is to have fun and a couple DE's per year."

Any of the above motors fits that description but the 2.7RS would be by far the most fun in my opinion. It just matches the early 911 chassis in a way that is as close to perfect as you can get.

[MFAFF]

A 2.7E is a fantastic engine...I love mine.
The cost difference between a simple 2.4 rebuild and one to 2.7 was limited to teh case work for me.. (needed 6 new pistons and cylinders anyway.. the MFI pump needed a complete rebuild regardless...plus splitting the case etc etc....head work...)

Having driven it a bit now and a gen 2.7RS then its a very subjective call as to which is 'better'.. they both dyno'd out at the same power range (219 for the E 221 for the RS) and subjectively the E felt better/ stronger lower down... with the RS being more active at teh upper end...

On the road the E felt more responsive and useful.

I think if you do need a decent amount of work on the engine anyway (replacing the P+Cs all round) plus case work you 'may' end up wondering why didn't I.....the additional power on an E cam is all very handy....

Just my view of it....

[Jim Richards]

Chris, I've been down this path and IMO, a swap to a 3.2 (or maybe a 3.6) would be more bang for the buck.

[Bobboloo]

Jim is right. A 3.2 swap is the best bang for the buck. A 3.6 swap is not cheap though and I prefer the 3.2 in the early car anyway. I've driven both and the 3.2 matches the chassis better IMO.