2.1L longstroke??

[tadd]

I've never seen this one mentioned... use a 2.4-2.7 crank with 80mm cylinders. Is would this be a bad idea? Just curious since for whatever reason I happen to have the parts. I had always assumed that is what the factory did on the 2.1 turbo, but I noticed today that it was 83 bore with 66 stroke.

I would think it would be a nice way of getting to higher compressions (~.7th more CR if I did my maths correctly - assuming a 2.0 motor at 9.8:1) with less dome. That and the longer stroke should give a torque boost.

Thoughts anyone?

tadd

[jluetjen]

A shop of somewhat ill repute has been marketing such a configuration for a while. Somehow it doesn't strike me as the best solution to a problem, but it has a few interesting things in it's favor as a compromise.

1) The only component being changed is the crankshaft and rods -- which limits the costs. Doing this does a couple of things:
a) Increase the displacement, and thus the torque
b) The Rod/Stroke ratio is reduced, which means that the piston accelerates faster off ot TDC, which tends to be more forgiving of "radical" cams and cams with overlap -- making them seem mellower.

Why I wouldn't bother...
1) If your bottom end is solid, you can upgrade a 2.0 to a 2.2 just by swapping out the pistons, cylinders and some then machining the heads. You'll never even have to touch the bottom end. Once you've opened the case -- especially a mag case, chances are that you'll need the case re-machined since it will have relaxed during dis-assembly. This is often not a trivial cost.

2) Short stroke (long-rod) cranks generate fewer stresses for a given rev range.

3) If I were going to go to the trouble of opening the case to increase the displacement, I'd most likely do the P&C's at the same time. Once you've done all of those things -- why not just buy a bigger motor to start with???

I'm aware of one person who was using a 2.1 like this in the SCCA's GT3 category which struck me as a curious choice given that GT engines (in general) are generally rev'd to 7000 - 8000 RPM. Going with a long stroke configuration (for a given capacity) for an engine destined for high-rev's is definitely going about the process of creating HP the hard way if you ask me.

[tadd]

Well, good to know my thinking is in such lofty company! MM I would assume?

I have been nickel & dime in my toy buying, so I have a pile of parts, not a complete motor. I have been out of engine building for a long while while I dealt with being dirt poor in graduate school. Of course that hole isn't filled in a day, especially when houses are being bought, remodeled, and the like. So I have been 'playing' in parts for the time being, like the 2.4T heads that got the boring bar treatment and are now 38/38 ports. Maybe this weekend I will finally sort out adding that second spark plug (I mucked it the first two - still learing how to machine things - also lucky the T heads are dirt cheap).

Anyway, I was just looking at the increasing pile of stuff (three early mag cases and couting!) and then realized that I might actually start assembling them into something. About the only thing I don't have is P&Cs.

Bottom line, I would like to keep the motor as small as possible with as high of a CR as I can mange so I can actually enjoy it on the street.

I totally missed the rod ratio aspect. Thanks! That is a nice bonus.

tadd

[BReyes]

The cases have been split on your cases. Have you had line bore checked?

Sounds you just got a new garage and are getting ready.

Good luck.

[tadd]

The case I was originally planning on building on turned out to be a 914-6, so that one never 'got checked'. Its replacement has had a 'standard drag thru' and a had a few small (dime sized) spots that didn't get hit. The operator said he would build on it as is, but that a super paranoid type would go oversize. The last case is a standard, really fresh rebuild that got stripped for parts. Since it is a 1R that got squirters, shuffle pins, case-savers one could safely assume it will be kosher. That said, I would hit it with a bore gauge before doing anything with it.

No garage, car port. Luckly I have a nice kitchen and a wife that travels alot...



tadd