For those who have the HRC log style mani. Have you ever had to have it decked due to be warped? If so...after getting it decked did you notice that your turbo spooled faster?

Also has anyone cut notches where the bolts go in to allow for better expansion when heating up and cooling down so less stress on the mani and less warpage over time?

I've noticed other companies using this notching technique on their manifolds and I was wondering if anyone has done that to their HRC log style mani, and if so what have been the overall results?

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- 05 Subaru STi
- 97 eclipse gs (289whp w/ 276tq)

lol...guess not!

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- 05 Subaru STi
- 97 eclipse gs (289whp w/ 276tq)

I know I've read here that someone had their HRC manifold un-warped at a machine shop uding a fly cutter. I had mine done at a local shop using a large belt sander and stopping very often to cool the piece so it would not affect the flatness as they worked. I have seen the manifold-to-head bolt holes enlarged in Corky Bell's turbocharging book to allow for expansion. I have not done that and have not seen it mentioned here by anyone running HRC logs but I have not searched that fact fully.

I had to have mine unwarped as well. Must be a common thing.

1996 eclipse GS-T
1968 Ford Mustang
2004 Suzuki GSXR600
2006 Honda CBR1000RR
Decisions Decisions

Mine has been decked twice. After the second time I got a set of 4G63 exhaust studs and nuts, haven't had a problem since.

Of course it will spool up better after you deck it, it's no longer leaking!

2016 WRX STi Limited (current)
2001 A4 1.8tqms (donated)
1991 GVR4 #1933 (sold)
old.dsmregistry.com/detail.php?carid=218 (dismantled)

Hmmm, I've had mine for about 4 years and I do not notice any leak or warping

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Kon C

"Sometimes, a man has to do what a man has to do."

Seems to be hit and miss in regards to the manifolds "flatness" out of the box. If it's suspect then get it decked and just go with the 8mm 4G63 nuts and studs as Nate mentioned. You'll never have a problem after that.

Here are the part numbers if you plan on getting them:

Exhaust man. stud to head 8mm MD005317
Exhaust man. nut 8mm MD092806
Exhaust washer 8mm MD041192

RRE sells them if you can't find them locally:

http://www.roadraceengineering.com/2g16ginstallkit.htm

As far as cutting between the runners... I'll leave that one up to you. If I were building a manifold myself I would opt to build it that way but work with what you got IMO.

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BPU'd skittle

the relief cuts you are seeing in other manifolds may be because these other manifolds are stainless steel. Expansion rates of the two materials are very different.