Extrude Honing

[Paul SM]

Can anyone offer a "before" and "after" testimonial on the effectiveness of Extrude Honing a cast iron stock exhaust manifold?

I have found two places on the net which do extrude honing (abrasive polishing of the inside of the manifold to improve gas flow), one is in Sydney (Abrasive Flow Industries) the other in Victoria (Specialised Power Porting). Has anyone used either of them?

[N1GTR]

Have you called to get prices?

[wolverine]

I have an extrude honed HKS manifold.

It flows more evenly pre to post but unless they create a new decimal scale of increments along a bees dick I don't think it will prove to be great value versus other modifications for a light to moderately modified car.

[WARLORD]

listen to wolverine,ive been down that road and it has little gains,for big $$$$$$

[Paul SM]

Thanks for the comments. My stainless steel "high flow" manifold has once again developed a couple of cracks (nothing too noticeable as yet but it sure won't get better..) and before facing down the changeover job back to the stock manifold I thought perhaps extrude honing it might minimise the loss of response while achieving reliability.

As for prices, the place in Vic quoted me $550 last February but is now $660. The place in Sydney quoted $1500! Are there really that many people wanting this mod that they can demand these bucks? A guy at Just Jap told me the process cost him just $200 a couple of years ago.

[wolverine]

Don't get me wrong extrude honing is very cool, it feels like oily glass when it is finished but trying to measure a substantial difference is next to impossible for most of us. Perhaps on a race team budget it would be worthwhile to sneak any incremental gain but on a heavy car like the stagea it would be money better put towards an RB30.

What turbo are you running?

$500 sounds about the money that was paid by Legend01 when he owned the manifold.

[Dale FZ1]

In building my RB30, I checked out extrude honing and spoke to one company that provides this sort of service.

Found out that they commenced the job with a fair bit of die grinder work and then pump the abrasive medium through the gas passages to finish off.

I looked at the stock manifold and then took to it with my porting tools and abrasives. The biggest two areas needing attention were the sharp shoulders inside each primary runner, and then a pretty ugly looking collector area.

Spent probably a few hours from start to finish, lots of looking and planning, with pretty satisfactory looking results and much reduced turbulance inducing edges + a fair go at port matching to the head. I followed the same principle in doing a basic porting job on the head. Bugger all material removed, but a decent amount of time spent smoothing sharp edges and blending curves.

I'll have no idea if it improved things because no direct before/after tests were possible and I didn't put it on a flow bench. But I know my approach wasn't that far from the job being enquired about, and the job didn't look or feel much different from a few heads I've seen done by reputable porting services.

I'd agree with Wolverine about the manifold unless you have the time, inclination and gear to do it yourself. And even at $500 you're a good way towards paying for a 6boost or ETM.

[R31Nismoid]

Paul - what is the current setup?

That might help us a bit, need a tad more info

[Paul SM]

I guess what I was asking was whether anyone actually felt an appreciable difference in the performance of the car after extrude honing the manifold.

I have noticed the sharp edges on the shoulders of the bends inside the manifold and that's what made me wonder if extrude honing might make a significant difference. Rather than paying at least $700 (incl freight) for extrude honing though, I might invest in a flexible drive and have a go at smoothing those edges myself before re-installing the stock manifold.

The engine is in a fairly mild state of modification: big exhaust and s.s. manifold (which cracked, was repaired, straightened and has now cracked again after a supersprint at EC) big Blitz front intercooler, HKS turbo (but don't know what kind as it came with the car) but it's in the standard position and set for a maximum 1 bar of boost, Splitfires and a Nistune board in the ECU. Tuning the ECU on the dyno only showed 182 rwkw but the workshop reckon it could be 10% conservative, so 200 at best.

You're right about the weight, of course, which is why spending heaps on power mods to overcome that disadvantage is pretty questionable. Having said that I really enjoy the feel of the car on the track - it will never be seriously competitive, however, and always a compromise vehicle in which I can also take my mal and my dog to the beach!

[R31Nismoid]

Honestly for those mods and power i don't really think there is much point in spending $700.

I mean you have free power - boost. Another 2psi would give you more gains the porting a stocker manifold. I think stock manifold wise you'll be quite fine.

Also the time/labour to fit/refit etc.

[KiwiRS4T]

^^^ as above -turn up the boost. Actually maybe you need to take a trip up to Sydney and get someone like Yavuz at Unigroup to do a proper tune. My S1 Stagea with a GCG highflowed R33 turbo was making 245awkw at 1 bar so yours sounds a bit low. Try to find out what kind of turbo you have - maybe you need bigger injectors, a Z32afm and maybe a better fuel pump if that hasn't already been upgraded. As has been said before the stock exhaust manifold is good for 300kw, stainless high rises are good for nothing except cracking. Your stock manifod will be fine although you may need some kind of spacer depending on the turbo.

[Paul SM]

I very much appreciate all the thoughts and advice provided on the extrude honing option. Certainly the boost is still modest and I'm running a stock airflow meter, so some opportunities there but I'm amazed at some of the rkw figures you are all quoting - clearly I have a lot to learn about the mod's available.

Before removing the cracked s.s. manifold and refitting the stock one I will now have a go at porting it, with the help of pics taken of a similar exercise by Dale.

[R31Nismoid]

Don't take too much material off if you do mate - otherwise you'll weaken even the cast one also

I think someone here removed too much and had a factory one fail.

[STATUS]

Thanks for the comments. My stainless steel "high flow" manifold has once again developed a couple of cracks (nothing too noticeable as yet but it sure won't get better..) and before facing down the changeover job back to the stock manifold I thought perhaps extrude honing it might minimise the loss of response while achieving reliability.

As for prices, the place in Vic quoted me $550 last February but is now $660. The place in Sydney quoted $1500! Are there really that many people wanting this mod that they can demand these bucks? A guy at Just Jap told me the process cost him just $200 a couple of years ago.

i would not play with the std manifold much they are prone to cracking as it is... could end up with a real expensive paperweight.

[Paul SM]

I wasn't planning to take out metal like you would in a porting job, just to smooth the rough finish inside the runners, but thanks for the advice...