Maxbore does dis/reassemble the parts, so best to let him do this piece as well.

Here are 2 pictures which I hope will help again, this is from an AJ26 unit like you have, and the butterfly is fully opened in this case (which is the relax state).

 

Sending off my TB to maxbore. I measured the interior diameter was 78mm. I will remeasure once I get it back.

 

Maxbored AJ26 TB. Before 75mm - after 81mm.

 

Sweet, I am excited!

 

The price is more than reasonable for the amount of work performed. Question regarding additional services: are there any apparent benefits of TB shaft machining? Would that affect fatiguing over a period of time with a larger butterfly installed? What sorts of power gains can we expect from TB boring of the existing TB?

 

I thought about the getting the shaft machined, but unless you are going full race it most likely wouldn't be noticed. Plus I worry that it might break. From looking at dynos on various forums, anywhere from 2-6 across the range. More if you have other mods, but for the price point and the fact the STR is currently in pieces, I figured why not.

 

+1

You can't beat the price. Plus I'd think the real benefit would be in the throttle response.

 

Ok got it back today. I was off on the starting size as it was 75mm. Per the tag it was bored out to 78.5mm. Not as big as I would have hoped, but at least it is cleaner than before.

Before:




After:

 

It does look as if he bored it as much as he safely could, but yeah...3mm is not that much. Better than nothing, but not that much better.

The XJs must have a much thicker wall as mine went from 75 to 82.5 mm

It is good that you posted, even with less than ideal results, because at least now everyone knows what to expect when thinking about doing this. So it does help the board community.

 

Ya I think that the later cars went with a thinner casting. If I do the math right, I should have an increase of about 5% in flow. Plus now I have a shiny new butterfly.

 

You have 9.55% more surface area with a 78.5mm vs 75mm


AND...You have a shiny new butterfly!



It was a bottleneck, so +9.5% will help some.

 

Lol I am bad at math which is why I took economics!

 

EuroToys have confirmed in the last week they can supply a 90mm TB for a XKR 1999. $850 not including shipping. apparently they bore out the housing to 93mm and then insert a new Core, 90mm, make and fit new butterfly etc.

 

Good that ET is trying this, when I checked with Maxbore for doing it that way, he said he didn't want to do this as the bearings would become to short in his opinion.

Imho its overkill as well for an eaton setup, a 82.5mm for a AJ26 engine (which you refer to), will already flow enough, and that's only $100 or so with Maxbore, you can better spend the other $750 on other items.

 

Do not pay attention to the man behind the curtain.

Oh look, over there, something shiny!

Gonna get one.

 

Proof me wrong if you can, ET certainly isn't able to, are you?

 

Is it even possible to prove you wrong?

 

Well if you don't try, we may never know.

 

Ya $850 is a lot to spend. What about the other bottlenecks? Intake tube and maf tube?

 

A few fun facts for comparison of my current system:

ORIGINAL & -----> NOW
75mm/2.95" ------> 92 mm MAF is 3.6"
75mm -------> intake tube is 4" then down to 3.5"
75mm -------> 82.5mm TB is 3.25"
75mm -------> port matched elbow is the equivalent of 3.25" as is the entrance to my Gen V Eaton.