destroking and boosting for mpg

[Duffman]

Originally Posted by metromizer

I have a few comments for the original poster:

Crankshaft- when destroking an engine, you usually purchase a destroked crankshaft, or modify the one you already have by a couple of methods.
a) no one makes aftermarket crankshafts for Geo engines
b) the traditional offset grinding you read about requires a different, smaller journal rod and some research.More than a couple mm is not usually possible without grinding into the oil passeges. Finding a rod with a smaller journal than a Geo my be tough, they are already tiny. Research, research, trail and error.
c) Weld offset grinding, by a process called submerged arc welding, can only be done on a steel crankshaft, and the first several cranks are research projects. The 4cyl metro crank on my bench is cast iron, I'd guess the 3 cyl crank is too. so weld stroking is out.
d) custom cranshaft machined from billet. I've personally ordered semi-custom cranks (custom stroke, different main journal and rod journal sizes, etc) for commonly modified engines. It's expensive and often takes months. But their isn't much call for semi-custom Geo cranks. Fully custom odd-ball engine custom cranks have been built, but it's painful, $$$, time, begging and pleading to stay on schedule...

Rods -you never modify rods to make them shorter, or longer. For commonly modified engines, different length rod options are available. The metro engine does not fall into that category. However, with a big budget, semi-custom connecting rods can be ordered for just about any project from places like Pauter Machine in Chula Vista, CA, Cunningham in Denver, Crower, etc. for about $250-$500/rod. The last semi-custom set I bought from Pauter, 2" chevy journal, 356 Porsche length, 22mm wrist pins, light weight chromoly race rods cost ~$800/4 rods

-pistons with custom placed wrist pins, higher for larger stroke, lower in the bore for a shorter stroke, is a common way to account for changed stroke and not modifying the block. The dimension you'd change is called 'compression height' of the piston.

So in a nut shell, you might be able to shorten the stroke by a few mm's, if you can find the right rod journal diameter, rod, and custom pistons.

I hope that is helpful.

This sums it up nicely and agrees with my knowledge of what is required. With no significant aftermarket support for this engine you need to have your own machine shop or just start looking for a different project because the costs are going to get ridiculous. High performance engine builds can run $10K, 20K or $stupid, due to the custom nature you will fall in that range somewhere.

[Frank Lee]

Originally Posted by ecomodded

What part of theory on paper do you not understand.
You are grand standing , being a fool on purpose.
It was a idea , that was there to think about not for you to shove back down my throat.
You know what ? your being a jackass. Plain and simple.

You've never had much of quality to say. And now there are two on ignore. Bye bye.

[mechman600]

Frank is right. This thread started off as a "what if" question. But it soon became a "this is how it can be done" answer. This is the point where those with experience/knowledge on the subject piped in to set things straight. And all those answers, as far as I can tell, were pretty much right on the money.

Let's lay this one to rest please.

[ecomodded]

Originally Posted by Frank Lee

You've never had much of quality to say. And now there are two on ignore. Bye bye.

Thank God, you are a pest.
(EDITED to remove high emotion)
Good riddens

[baldlobo]

ecomodded; don't be pointing fingers at anyone, because 3 of them are pointing back at you.

by the way it's "your imagination" vs. reality

reality normally wins(generally it's by darwin; where angels fear to tread)

[ecomodded]

I had to give him a rebuttal , for he has time and time again harassed me. the fig newton is a pest plain and simple. read his last 45000 posts. He is a broken record, i do not have too nor will i take his garbage.
Thanks for your interest..

[ecomodded]

Originally Posted by Frank Lee

I got the impression OP was talking about a real, live project; not a sky-high "what if". So throwing out a bunch of uninformed speculation really doesn't fit in that well there (but by all means, throw just about anything out there if it is clearly labelled as such).

You are ridiculous, maybe you should reread the op first post,it is as pie in the sky as my first post.
Your are a pest plain and simple.

[mechman600]

Originally Posted by baldlobo

reality normally wins(generally it's by darwin; where angels fear to tread)

Really? Darwin was a man with a new idea. He still had to meet his maker.