When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Hello Rennlisters,
I’m in the midst of building a stroker engine; 102mm X 80.4mm.
Had Steve Weiner rework my heads with the 993 RS valves and his valves guides, but now I’m giving serious thought to having my heads reworked by Xtreme. Highlights of the Xtreme rework seem to be:
- porting intake to 44mm
- 8mm valve stems
- intake valve size increased to 53mm
Price appears to be a little less than half that of full custom/new heads.
So the question is; are these reworked stock heads worth paying for? Or are full custom heads worth twice the money?
We don't port 993 heads due to their propensity for cracking and all that does is accelerate the process.
Stock Varioram heads support up to about 350 BHP with a proper valve job, however if more power is anticipated or desired, the Extreme heads are the only way to go.
Nice to see this thread pick up some steam. I ended up sending my 964 heads to Xtreme for rework. They came back looking great and Bill’s customer service was second to none. I’ve included some detail shots below. And speaking of the Xtreme rework; that means I’ve got all the 993RS valves and Aasco springs & retainers Steve installed previously if anybody’s interested.
Originally Posted by -nick
I always wonder what these head modifiers do with the ceramic exhaust ports? Used heads with good ceramic are getting rare.
Regarding the ceramic on the exhaust port, I think that everybody just leaves those ports alone in order to preserve the ceramic. That said, if the ceramic does deteriorate, it might be a good excuse to buy some of these fancy new heads...
Originally Posted by Steve Weiner-Rennsport Systems
We don't port 993 heads due to their propensity for cracking and all that does is accelerate the process.
Stock Varioram heads support up to about 350 BHP with a proper valve job, however if more power is anticipated or desired, the Extreme heads are the only way to go.
Steve, when ported, are 964 heads just as prone to cracking as 993 heads? Should this cracking be a concern with the reworking of stock heads that Xtreme does?
Steve, when ported, are 964 heads just as prone to cracking as 993 heads? Should this cracking be a concern with the reworking of stock heads that Xtreme does?
Nossir, not to the same degree. One needs to leave sufficient material to accommodate expansion and contraction whenever any factory heads are modified.
964 heads do not flow the same volumes as 993 heads do, however a relatively cheap improvement is to install the 51mm 993 intake valves which are not only larger, they have 8mm stems which improves airflow at all valve lifts.This simply requires a different guide and seat dimensions which is not a problem. 993 RS valves are 52mm and require the RS seats.
Bill at Xtreme is the best person I have ever dealt with. Quality of work, expertise and his customer service are like no other. I actually have a set of 964 heads that Bill just did the works to that I did no end up using as I did not complete my 964 project and sold the car.
08-31-2018, 02:40 AM
Advice on heads? 4L stroker build
