View Full Version : Head Porting

10-23-2008, 07:18 PM
I'm getting ready to overhaul the engine of my '69 GT6 restoration project. How much gain in power will I get out of a port/polish job? Is it worth the extra cash? I wasn't planning on any internal engine mods, but since the head will be at the machine shop anyway...

Andrew Mace
10-23-2008, 08:12 PM
It might be, if done correctly. Arguably your best bet is to find one of the old Competition Preparation Manuals for the GT6 or Kas Kastner's (https://www.kaskastner.com/kasbooks.html) newer <span style="font-style: italic">Triumph Preparation Handbook</span>, which is a compilation of the old Comp. Prep. Manuals with much new related material.

10-23-2008, 08:26 PM
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]I wasn't planning on any internal engine mods[/QUOTE]

I'd invest the money in a distributor rebuild/recurve and carb rebuilding rather than the porting, if you are doing no other internal mods. Cleaning them up a bit certainly won't hurt, but there isn't much to be gained by spending machine shop money for porting and polishing a stock engine.

Oh, buy a Payen gasket set as well. How about new guides and valve seals, with a nice new valve job. All of that will help more than the P&amp;P work.


10-23-2008, 09:11 PM
BP- The internals are not as important for the effects of P&amp;P a head. For that to get the most bennies the carbs and exhaust need to be built as well. P&amp;P'ing the head won't help if it can't get the air in the first place.

10-23-2008, 10:25 PM
I'll certainly 2nd the motion on the Payen gasket, just installed one on my TR250, nicest head gasket I have ever seen, what maybe $10-15 more? definitely worth it.

10-23-2008, 10:32 PM
P&amp;P'ing is not the best bang/buck if that is all you are doing. The Kas K's book says that the best Bang/Buck is increase the compression. If the head is at the shop, spend some money to get the compression up 9.0 to 9.5. You are now into HiTest but you will notice the HP gain.

Paul is right to suggest a good valve job, 3 angle is best, I think. Then finish it off with new valve guides and seals as suggested. Check your valve spring integrity also. They maybe tired. Leave everything else as is.

10-24-2008, 01:23 AM
The Kas K's book says that the best Bang/Buck is increase the compression. If the head is at the shop, spend some money to get the compression up 9.0 to 9.5. You are now into HiTest but you will notice the HP gain.
The great thing about upping the C/R is that it boosts power (and torque) all across the range, especially the important (for the street) mid-range. Porting and polishing only helps at the high end at best; and if you don't know what you are doing, can actually hurt instead of help.

10-24-2008, 05:43 AM
As well porting and polishing must be done right to work. Frequently, it isn't. Just because a machine shop attacks your head with a grinder doesn't mean they'll make any improvements.

Be very wary of a shop that talks about the wonders of port matching. Very nominal gain in power for the price. Strong indicator of a shop that has no idea how to actually do flow work.

10-24-2008, 06:17 AM
Randall and Fox speak the truth. Spend it elsewhere.

I assume, based on your previous statements that the head is in for a shaving/compression boost already?

10-24-2008, 07:25 AM
Porting and polishing is really for high performance engines. You can smooth out the intake so much that it loses low in torque. I port matched my cylinder head and smoothed out the exhaust ports and that's about all. I wholely agree in spending the money on new valves, spirngs, guides and hardened seats. Make sure the shop uses a Serdi to do the valve job.

10-24-2008, 07:34 AM
First and foremost, read the Kastner and Dave Vizard manuals. Probably the best widely published primers on tuning these engines, bar none.

Dave Vizard indicates that porting the 2L engine head does not require a significant degree of machine work relative to other heads. Literally, he says it's basically just a "tidying up of the chamber shape". He goes on to say, "The tidying up of the chamber shape gives us improved combustion efficiency but the gains achieved are only marginal."

Most notably, Vizard indicates that porting the 2L head only results in HP gains of ". . . 1-2 percent". Not much, unless you're going racing where every bit helps.

I'd spend my bucks elsewhere.

Good luck, let us know what you do. And, PHOTOS, please! :thumbsup:

10-24-2008, 08:18 AM
I'll 2nd the suggestion to do a mild skim of the head for higher compression, shouldn't cost much at all, I don't have my itemized receipt from the machine shop handy but I am sure it was less than $100 for me,, that was a couple months ago.

10-24-2008, 11:17 AM
Here's the RTF special on the comp manuals. I'll be bringing my 70 gt6 inside this weekend for the winter restoration work and will watch your messages with interest.

10-24-2008, 01:16 PM
It cost me $200 to have my cyl head serviced. That is just the labor that included installing and reaming new guides, three angle valve job on a Serdi, skim the head 0.050" and installing the valves and springs. I took in new valves, spring and guides, so add that to the labor and it got pretty pricey.