Building on a 2.4 questions

stratoblaster · 01-08-2007, 08:17 AM

This weekend I got a good deal on a 2.4 7R MFI longblock. I am considering building a motor with this to E or S specs with carbs. The car will be a steel flared 914. I want a motor good for the street first, fun for DE/AX second. Also, runs on pump gas.

As with most people $ is a concern so the sky is not the limit.

Are 2.2E pistons the same as 2.4E pistons? If I find some E pistons without cylinders will they work with my T cylinders? What would I have to do to the heads to make them compatible?

What combos of pistons and cams would you suggest?

Bobboloo · Bobboloo's Garage

I'll assume you have a 2.4T motor since you say you have T cylinders.

First off 2.4E and 2.2E pistons have different compression ratios. The 2.2E pistons have higher CR and when they are combined with the 2.4 crank have an even higher ratio than when used with a 2.2 crank. They will make a nice upgrade to the 2.4T motor and will still allow you to use pump gas with no worries of detonation. They will work with your T heads with no problem.

When you break the motor down inspect the cylinders for ovality. I've rebuilt a couple T motors and the cylinders were out of spec. The iron cylinders tend to were out. I've heard this is possibly due to there lack of heat dissipation when compared to aluminum and iron isn't as hard as say a nickel coating. If they are out of spec you can bore them out and install JEs' for a slight displacement increase.

For a street motor I would stick with the T cams and ports if you keep the 2.4L displacement. Ideally though, if it were me, I would prefer to bump the displacement up to 2.7 and build a 2.7 mod S or Solex cam motor. The larger displacement lowers the torque curve to give you better street manners when using an S, E or Solex cam.

Building a 2.7 mod S motor is more expensive than just a CR bump but if your cylinders are past the wear limit then you have to buy a P+C set and as far as P+Cs go the 2.7RS set is about the cheapest and will give you long term reliability that you don't get with other alternatives.

stratoblaster · 01-08-2007, 02:16 PM

Quote:

Originally posted by Bobboloo
I'll assume you have a 2.4T motor since you say you have T cylinders.

Yes, but that was more a curiousity question than anything else. I would like to get some good-used E Pistons with Cylinders.

Quote:

Originally posted by Bobboloo
First off 2.4E and 2.2E pistons have different compression ratios. The 2.2E pistons have higher CR and when they are combined with the 2.4 crank have an even higher ratio than when used with a 2.2 crank.

Thats what I thought, thanks for the confirmation.

Quote:

Originally posted by Bobboloo
They will make a nice upgrade to the 2.4T motor and will still allow you to use pump gas with no worries of detonation. They will work with your T heads with no problem.

-Snip

For a street motor I would stick with the T cams and ports if you keep the 2.4L displacement.

$1000000 question, what are talking here, maybe 150hp? I would like to get close to 170 if possible.

Quote:

Originally posted by Bobboloo
Ideally though, if it were me, I would prefer to bump the displacement up to 2.7 and build a 2.7 mod S or Solex cam motor. The larger displacement lowers the torque curve to give you better street manners when using an S, E or Solex cam.

Building a 2.7 mod S motor is more expensive than just a CR bump but if your cylinders are past the wear limit then you have to buy a P+C set and as far as P+Cs go the 2.7RS set is about the cheapest and will give you long term reliability that you don't get with other alternatives.

I'm trying to be reasonable with what I might be able to spend and not cutting too many corners. I know these motors are a slippery slope and snowball fast. BTDT on many projects. Actually, a 2.4 kind of intrigues me for some reason.

Lukesportsman · 01-08-2007, 03:43 PM

Look at Waynes book, he has some nice combos. Do you have Anderson's performance book? He has some nice build ups with quoted hp.

2.4 with 2.7 RS cylinders, worked heads or better heads, E cams, good exhaust, bumped compression and MFI should yield you close to 190hp. If you had S cams, heads and correct MFI cams you'd have essentially a RS engine at 210hp. I think they figure the cam loss to a more tractable E cam looses you 20hp or so. You also can not fit S cams with other pistons.

This is essentially what I have and from memory so don't flame me too hard on details but correct as needed. It will run fairly strong in a light car esp. if you have 7/31 transmission.

T heads are likely to be your bottle neck. T pistons your limit on cams.

Brant · 01-08-2007, 04:17 PM

Jason,
I think that your heads might actually be CIS heads and not MFI heads.

check on that first
brant

BK911 · BK911's Garage

Quote:

Originally posted by Brant
Jason,
I think that your heads might actually be CIS heads and not MFI heads.

check on that first
brant

That's what I was thinking. I've never seen a 7R T case with MFI, they've all been CIS.

I'll recommend what I always recommend when people ask this question:

E cams, 2.2 p/c's and a set of zeniths. You'll have your 170hp and it will be a lot of fun to drive anywhere. Plus it's a relatively cheap engine to build since you can use all your old parts (if within spec). I drove an engine like this for about 5 years and regret selling it and not putting it in my 914.

stratoblaster · 01-08-2007, 05:27 PM

Quote:

Originally posted by BK911
That's what I was thinking. I've never seen a 7R T case with MFI, they've all been CIS.

I'll recommend what I always recommend when people ask this question:

E cams, 2.2 p/c's and a set of zeniths. You'll have your 170hp and it will be a lot of fun to drive anywhere. Plus it's a relatively cheap engine to build since you can use all your old parts (if within spec). I drove an engine like this for about 5 years and regret selling it and not putting it in my 914.

Which ones have the injector ports in the heads? This has the ports in the heads and they are plugged.

I know the CIS is way more common. The case has a 911/61 number which I think is MFI Sporto. Also the serial number is 61391XX. Checkout the little image I included. Its from some reference manual I found somewhere. If I understand it correctly, its telling me this is MFI.

BK, thats pretty much the engine I'm thinking. Didn't you just sell one like that?

Brant · 01-09-2007, 08:08 AM

Jason,

cool.
I didn't realize that was an option with the MFI

it wouldn't be cheap, but you ought to consider putting it back to MFI?

cool
brant

stratoblaster · 01-09-2007, 08:33 AM

MFI would be cool, but I'm sure its out of my budget. I think its pretty rare to find an MFI T with a 7R case. At least thats what I've gathered. I've done a ton of homework since I first found this thing. I honestly knew jack about 911 motors 2 weeks ago.

BTW, I measured the intake ports and I they are 29mm or 30mm? I was hoping for 32's.