Short motor differences VCT - non VCT?

spope · 17-10-2005, 11:34 PM

Hello all - thought i'd pop into your forum for a moment as hopefully I will be fortunate enough to have an au motor to install in my car soon.
I was wondering if anyone knows the exact differences in short motors between the VCT and non VCT AU motors.
Ie, bore, stroke, compression, etc...
Have heard that VCT had higher compression - was this due to different pistons or was it in the head?
Any info appreciated.

HLC · 18-10-2005, 03:00 PM

all i know is that the VCT has variable cam timing and its more powerful the the other OHC motor.

and that probably didnt help at all.

**DJM83** · 18-10-2005, 05:02 PM

Quote:

Originally Posted by HLC

all i know is that the VCT has variable cam timing and its more powerful the the other OHC motor.

and that probably didnt help at all.

yeah the VCT is a tad more powerfull but that advantage is cancelled via IRS

jonbays · 18-10-2005, 07:56 PM

VCT engine has a different head and different cam. Bottom end is the same.

Head inlet and exhaust valve sizes the same and i doubt the compression is any different.

loxxr6 · 18-10-2005, 08:26 PM

Quote:

Head inlet and exhaust valve sizes the same and i doubt the compression is any different.

I'm sure there was something mentioned about the compression ratio being different between the s1 and s2-3. One of the other members way back scored a higher dyno reading that Casper was investigating. I'm damn sure it was a VCT too.

JC · 18-10-2005, 08:37 PM

I'd PM Casper - he is likely to have the info somewhere. The info, or some if it, should also be in the owners manual.

TCK-098 · 18-10-2005, 09:06 PM

well i think with the normal AU 4.0 they had 157kw and the VCT in the Fairmont ghia had 168kw and the XR6 had 172kw.

hope that answesr the question.

buickman · 18-10-2005, 09:49 PM

Quote:

Originally Posted by jonbays

VCT engine has a different head and different cam. Bottom end is the same.

Head inlet and exhaust valve sizes the same and i doubt the compression is any different.

They run the same compression ratio of 9.65.1.
Its only the head & cam that different. Plus the exhaust on the XR6 gave it the extra KW's over the ghia VCT mtr.

buickman

Casper · 22-10-2005, 07:58 AM

Quote:

Originally Posted by loxxr6

I'm sure there was something mentioned about the compression ratio being different between the s1 and s2-3. One of the other members way back scored a higher dyno reading that Casper was investigating. I'm damn sure it was a VCT too.

OK, for the record.
ALL AU I6 bottom ends are the same.. end of story.
The VCT Head is the only difference from the HP or Intec engines.

As for compression, there is a slight issue with the S1 VCT heads. They seemed to have a manufacturing fault that left them mith margianly less compression than the later VCT's. Same head but there appears to be a "fix" (possibly a slight shave) that upped the compression. Nothing official from Ford and it was never listed anywhere. This was found by JMM after they noticed something odd and started testing. We are only talking minimal difference here but it could account for 3-5rwkw missing in the earlier VCT's. Not that that seems to be a great big issue..not on mine anyhow

buickman · 22-10-2005, 02:43 PM

Quote:

Originally Posted by Casper

OK, for the record.
As for compression, there is a slight issue with the S1 VCT heads. They seemed to have a manufacturing fault that left them mith margianly less compression than the later VCT's. Same head but there appears to be a "fix" (possibly a slight shave) that upped the compression. Nothing official from Ford and it was never listed anywhere. This was found by JMM after they noticed something odd and started testing. We are only talking minimal difference here but it could account for 3-5rwkw missing in the earlier VCT's. Not that that seems to be a great big issue..not on mine anyhow

First I heard of it all documents & figures I've read has all the AU six mtrs compression from factory at 9.65.1. Nothing that a good exhuast system would'nt fix

buickman

Casper · 22-10-2005, 02:44 PM

Quote:

Originally Posted by buickman

First I heard of it all documents & figures I've read has all the AU six mtrs compression from factory at 9.65.1.

buickman

yep, but then again we all believe everything that Ford tell us dont we? Riiiight. From all I've seen the original VCT heads had slightly less compression than the HP or Intech heads... which were closer to 9.3:1 than 9.65:1 anyhow.