ALFAGTV6.COM

[bcal]

Hi, I want to clean up the ports on my 2.5L heads and was wondering how far you could go before catastrophe.

I don't want to open the ports all that much but I do want to remove some of the lumps and bumps especially on the outlet ports in the area around the valve guides. There seems to be quite a lot of restriction in that area.

Also, for a mildly tuned engine (stock cams etc), how much should you shave off the heads to give a reasonable boost in compression. I'm guessing around 30 thou.

[GarthW]

Lumps and bumps are good, they create turbulance which is what you want, never go too smooth, then your going backwards.

[bcal]

Is it really worth porting if the cams, valves etc are stock?
Maybe just a tidy up of the rough factory effort. It does look like a bit of a bat cave in there.

At only 2000lb and 4.1 final drive I don't really need to make a lot of horses.
In theory it should perform better than a GTV6 with stock 3.0L.
In theory.

[MD]

bcal
Mild porting and polishing of the exhaust ports will result in better flow in theory but in reality unless its all part of a comprehensive plan to modify the head as a "package" for some specific CR ,cams, valve revision, modified spring rates, etc, etc in which case you will get almost as much performance gain as you would blackening the tyres.

..of course it can be a feel good thing if you just want to tinker..otherwise lots of work for pretty much sweet F.A.

[bcal]

Cheers mate.
I've ported a 2L head and that was PITA and of dubious results.
Just the megasquirt alone made the single biggest and most noticable change in performance. The rest was just marginal.

I like your tyre black idea though, I'll give that a go instead.

[Greg Gordon]

I may have already said this, but I will say it again. I strongly suggest anyone considering porting their heads wait for Jim K.'s new book. It has a lot of clear and proven information on this subject.

Greg Gordon,
www.hiperformancestore.com

[mjr]

it's close to release then?.... jim K.?

[Greg Gordon]

I hope it will be out soon. However, I am quite sure that if you port the heads without this book, once you read it you will go out, get another set of heads, port them out to Jim K's specs and be quite happy.

Greg

[Jim K]

A long overdue update: after solving the vibration problem with the big-bore headers, I put in a WBO2 sensor to help me see why I get misfiring at ~6900 in 2nd and severe cutout at ~6700 in 3rd. With ~full load it read 12.7afr but the cutout is still there. I'm now baffled, as I was really hoping to see a very lean condition (causing the misfire). In the interim everything was changed, from wiring to ecu's to coils, injectors etc. My next test will be backpressure check this weekend. If this also gets me nowhere, I'm putting back the CSC so that I can finish testing with 2 types of cams, fast road and ~1/2 race. That will conclude the darn book. Re. the 24v, as I've said before, I'll only describe head mods and some cam proposals (block work being common with the 12v).

Now for the headwork at hand, 'port cleanup' is just a cleanup, no caliper measurements or substantial grinding. As MD says, its always better to combine this work with a number of things to have a worthwhile gain.
Jim K.

[kevin]

Hi Jim, welcome back. on the subject of porting and shaving to increase velocity i have noticed further down the chain that only my collector box(the 3 primaries join) on my exhaust glows deep red at 6000-7000rpm on dyno. Is that a form of restriction or just bad design.
Cheers
Kevin

[Jim K]

Hi Kevin, if primary/secondary pipe sizes are properly calculated and laid out, there shouldn't be any restriction. On the other hand, the collector pipe receives 3 times the quantity of hot gases each of the primaries handle. Further down, gases cool off -no more red color. I would check fuel mixture to make sure there is no overheat coming from weakness.
Jim K.

[Zamani]

JimK,

Glad to see you're back. Do you think backpressure can cause severe misfiring? I know that I got severe misfiring at high rpms due to bad coil and bad distributor cap.

Are the headers really going to make it to production? With the euro being where it is now, I wouldn't mind getting a set .

Back to the head, for the 2.5 I would suggest getting it shaved. I had a 2.5 with QV cams and I thought it could have used a bit more compression. Something like 10:1 with cams should be nice.

[Jim K]

Hi Z, I'm only back because someone asked about the book.
Re. the misfire, a friend had the same problem with another (non-Alfa) and after trying everything (...like I have) he unbolted the headers from the rest of the system so there was ~1" of very-very noisy gap! He then tried a full power run and the misfire disappeared. Going up from 50mm OD exhaust pipe to 63mm solved the problem! However, in my case, I already have the large pipe and all relevant calcs point to that. I can't see a na 3liter with ~225-230hp needing 70mm !! (thats the next size up). Besides, there's no way I'll be able to run anywhere with an open exhaust! I don't think I would get away with it and they won't have that at the dyno shops (they're all in populated areas).
2.5/3.0 heads can be easily milled even more than 1.6mm (~0.064") without concern. Afterwards, just check and adjust belt timing by elongating cam pulley holes and also test for piston/valve clearance -depending on cams. The biggest problem in this is making sure you end up with identical size chambers in both heads...it takes some doing at the machine shop, as these heads are wedge shaped and need special fixing arrangements on the mill. Do not discount this and cc the chambers after the fact! Chances are you'll have to redo them once or twice again before they're identical!
Jim K.

[Zamani]

Hi JK,

OK then we'll frequently ask about your book

What are the chances your muffler is clogged? On some bad installs, it rubs against the 1/2 shaft.'s hub close to the disc and actually causes restriction.

About the heads most places won't bother to CC them. I think the owner will have to do it himself. Don't forget cams. I never liked the stock cams. QV cams are super expensive these days, 2X the price of GTA cams, at least over here in the US.

BTW if you want to dispose of the new headers or CSC headers, please PM me . I need a little bit more power before I finish up the 24V

[Jim K]

QV cams expensive?? Just for info, how much do they sell for? I have 2 extra pairs laying around here (plus one more pair in the car now). I'm not saying I'm selling them now, so don't ask (and yes, they are 10.4mm intake lift, not 10.1)
Re. the exhaust, I can only suspect the final y joint; its poorly made imo, so it'll have to be changed before the headers come off. The rest of the system is just perfect. Last week I 'sold' the second set of CSC's I had, however, these were cut ~6" after the 3-1 joints (no flex pipes). The guy who got them will consider actually buying them if his mechanic agrees (!!) If not, he'll bring them back.
Maybe when I buy the 2010 Mustang , I'll have a general Alfa sale here...bring a truck along!
Jim K.