Contour Enthusiasts Group Archives Forums Modifications Duratec Maintenance Duratec engine change: Pull it or drop it?

Originally posted by DemonSVT:

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Originally posted by Stevedrivr:

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DemonSVT and I PM'd and everything's cool. And he brought up some interesting points I had not considered. We will continue to converse.

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Let's just say I was wrong on this one.

He has done his homework and shows plenty of experience.


I did bring up a few points about changing the engine from an over square to an under square (from a high rpm screamer to a stump puller IMO ) because that's what stroking a 2.5L would do.

Now a 3L starts out plenty over square and could be stroked back to a ratio around that of a 2.5L

However then custom length rods and piston to valve clearance becomes a serious issue. It would be a fair amount of design theory to work out what would work before you had a one-off set of rods & crank made. (I.E. $$$)

Still be very expensive either way and for what gains... Maybe 3 tenths of a liter tops. (raising the stroke ~10mm or an 89mm x 89mm engine = ~3.3L)
Rev ability and power band would be shortened though.

IMO that's very little bang for a lot of bucks...

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Thank you kind sir, you prove yourself to be truly both a gentleman and a scholar!

I do wish to get back to you when I get the chance with some questions/comments about the points you brought up in your PM. To be honest, I am only just beginning to research out my options on what to do about the eventual engine that will go back into this beast. As such many of the things you pointed out in your PM are things I should have considered, but most of my focus right now is on getting the Road Rat up and running again with the swapped engine. Then I'll get down to really doing my homework for the next engine.

Quick question though: Clearence/cost issues aside, wouldn't a perfectly square (89 x 89mm) engine with a longer stroke broaden the "area under the curve"? Some peak Hp/red line might be lost, but wouldn't both the Tq and HP curves flatten out, benefitting street drivability?

I very much look forward to continuing our conversation(s).

ATB,
(All The Best)
Steve