Crazy Cheap*ss idea!!

[Bobboloo]

Here's the deal. I have a 2.4T MFI motor. It came with my 72' Coupe. Anyway, the motor had had a top end rebuild and ran great but lacked any real balls. Of course it was a T so what do you expect but it was worse than that. A compression check revealed all was not well. So I tore down the motor and found the culprit. Worn out pistons. The top ring land was .09 I think .04 is the limit. Luckily I opened it up before a ring broke.

The heads are great. The case checked out. The crank polished up fine. The rods have all been resized. The MFI performs flawless.

So what to do. I want to put the motor back in and sell the car so I can devote all my time to restoring my Targa.

I don't want to throw money at a motor that is going to drive up the resale price of the car.

This means no RS conversion etc.

What I have sitting around available though.

2.4T P+C's used in spec
2.7 CIS Alusil P+C's in spec
T MFI setup (ready to rock)
E MFI setup pump needs a rebuild (have plenty of spare parts.)

My crazy cheap idea is to use the 2.7 CIS P+C's with either the T and or E MFI setup.

Going to a full E setup will diffenently cost more in the way of rebuilding and cams so...

What about a 2.7T motor.

2.7 CIS P+C's
T cams
T MFI pump
E MFI stacks
port the heads to 32mm on intake

Basically this would be a MFI version of the 74'/75' 911 normal motor.

Type 911/41
90x70.4 2687cc
I32 E32
150HP@5700rpm 173lb/ft @ 3800 (not bad!!)

The cam in the 911/41 motor has basically the same specs as T cams.

911/41 (2.7 normal) cam

intake 216 deg 9.6mm lift
exhaust 202 deg 8.8mm lift

911/51 (2.4T ) cam

intake 216 deg 9.7mm lift
exhaust 207 deg 8.9mm lift

Should make for a quick car up to 4kRPM's after that fuggetabout it your at the next light.

I mean wouldn't a 2.7T be preferable over a 2.4T? For the extra cost of cutting the spigots.

I am in a quandary over what would be the best settings to time the cams at. MFI motors in general are timed more advanced than CIS motors. This could cause a clearance problem with CIS pistons.

Being that the pistons are CIS however means you don't need as much advance since the gas mixture is pocketed by the plug. So maybe it would be best to time it like the CIS motor and copy over that to the MFI pump as well as the distributor.

Is this crazy or should I just play it safe and put in the T P+C's?

I almost want to do it to see if it will work.

Flamesuit On.

[Bobboloo]

Anyone have an opinion on this?

[dtw]

I actually had pretty much the same parts lying around and asked the same questions a while back. The responses briefly summarized were:

-The CIS pistons don't like any kind of injection other than CIS

-While the CIS pistons be made to run with cams other than CIS cams, it will be a dog.

Also, the conversion is not cheap. You have to have a fair amount of machining done to the case and heads to adapt them to the larger bore.

Back to the drawing board with you

[Wayne 962]

Not completely true - the CIS pistons are fine to run with carbs and will probably run fine with MFI. The domes are not that big of an issue. I'm 99% sure you can't run CIS pistons with T/E/S cams without machining the piston. Although the T cam is considered a mild cam, it's still way more agressive than the CIS cams. See the specs in Appendix A of the Engine Book.

-Wayne

[jluetjen]

The other thing is that the MFI pump will need to be set-up for cylinders that are 12.5% larger. I don't know if the rack adjustment on the pump can accomdate that much of a change. Unless someone has tried, someone like Gus at Pacific would be the only guy who could answer that.

[Bobboloo]

Thanks for the replies.
The cams are very close in lift and duration as you can see above but the timing issue could cause clearance problems. The pumps ability to supply enough fuel is also an issue.

As much as I would love to try this so I could report back I've decided to just rebuild as a 2.4T since the car in question will be sold. To make any mods would be trying to guess what the next buyer is looking for. So abort,abort.

Thanks