Porting

[ORFORD2004]

I just put big valves in my head and big springs. A guy chare me $400-$450 for porting my head. What do i do? Try it for one summer and see or do it now?

[baltobernie]

There's a guy in England who is reportedly the world's leading authority on the Fiat twin-cam engine. He's written two books detailing this motor and its capabilities. Basically, he says that for street use, the head flows quite well, and not to mess with it. This is in line with other remarks about similar well-designed engines. What makes a street engine perform is intake velocity, not intake volume. Bigger is slower.

So unless you've got a highly-modified motor that doesn't begin to make power until 4k, have your machine shop knock off any casting imperfections and button it up.

[maytag]

There's a guy in England who is reportedly the world's leading authority on the Fiat twin-cam engine. He's written two books detailing this motor and its capabilities. Basically, he says that for street use, the head flows quite well, and not to mess with it. This is in line with other remarks about similar well-designed engines. What makes a street engine perform is intake velocity, not intake volume. Bigger is slower.

So unless you've got a highly-modified motor that doesn't begin to make power until 4k, have your machine shop knock off any casting imperfections and button it up.

I concur completely with Baltobernie. I would make one addition only to what he said: port-matching is beneficial on nearly any motor of any build. but this is simply making the shape of the ports on the manifolds match the shape of the ports on the head, nothing more. a complete port-job is only beneficial on this motor if you've got enough cam, intake manifold, header etc to take advantage of that added volume.
pairing a ported head with unmodified intake / exhaust manifolds would be bad no matter how you look at it.

[majicwrench]

Last I heard from people in the know, port matching is not really benificial.

[maytag]

Last I heard from people in the know, port matching is not really benificial.

I don't think I've ever heard anyone "in the know" say that. I consider myself to be "in the know"..... (but I don't expect you to think of me that way.... ) having built dozens of types of motors over the years, including some that I competitively raced at national levels, and I can tell you that I never found a motor that did not benefit from port matching. The higher the required velocity in the runner, the more beneficial this becomes.

Now, I am admittedly NOT a fiat TC motor expert / guru.... but the only reason I could fathom that anyone would suggest it wouldnt benefit from port-matching would be if the head ports are already larger than the intake's ports... ???

If this is the case (and it would surprise me) then I will stand corrected.

[fiatfactory]

.

[majicwrench]

Steve certainly worded it better than I, "localised enlargement of the of the port.." which is what you end up doing with most all port matching. I'm certainly no expert, nor am I "in the know", just a guy who has been doing this for a long time.

[maytag]

Steve certainly worded it better than I, "localised enlargement of the of the port.." which is what you end up doing with most all port matching. I'm certainly no expert, nor am I "in the know", just a guy who has been doing this for a long time.

I'll buy that as the same thing I was talking about here:

...if the head ports are already larger than the intake's ports....

in essence, if you have to remove enough material on the intake (to match the head) that your runner enlarges just for that area, then certainly you've created an issue.

But this might be the first I've ever seen an issue like this in a motor. And Fiatfactory says it this way:

Port matching is always a good thing, provided you don't end up with a localised enlargement of the port at the manifold face

That's still a large "if" and "provided you don't".....

I'd say some careful attention should be paid to see if you can improve the match at the ports WITHOUT causing this enlargement. A mismatch in ports & misalignment can create some nasty turbulence, and drastically reduce velocity in that runner. Granted: so will the "localized enlargement". But I wouldn't just blanket over it and say it's not worth it.

just me. Not a GURU on the Fiat TC, like y'all.

???

[baltobernie]

Orford, if you compare the Fiat cylinder head intake ports to a new intake gasket and also to the Fiat intake manifold of your choosing, you'll find that all three have different shapes and sizes! If your machine shop traces intake gasket openings on the head and manifold, you'll end up with an embolism at the mating point, which is bad for both velocity and turbulence. If you (or anybody else) are determined to port-match anyway, make a "gasket" to fit the actual openings of both the manifold and head. Use bolts and studs for accuracy. Then swap the two "gaskets", mark the two surfaces, and remove only as much material as necessary. If you use a fresh Fiat manifold gasket, you'll remove way, way too much material, as the gasket is designed for all possible variations and manufacturing tolerances.

BTW, never port-match the exhaust side, guys. Exhaust headers/manifolds are always made a little larger than the exhaust port. The "lip" on the manifold reduces the tendency for the exhaust gasses to get sucked back into the combustion chamber.

[ORFORD2004]

My setup for this summer will be: 4mm dome pistons from vick, big valves and spring and stage 1 cam from IAP. Standard FI and headers.I'll see the improvement from the stock engine and decide if i want more power. In a month, i should have a good idea.

John

[narfire]

John, I have much the same set up but with the 84.4 Mahle pistons and Marks FI cams and adjustable cam wheels. I have a massaged 2L FI head that was "port-matched" and so far I have noticed a definate improvement compared to the 1800 head I had on last year with stock cams and wheels.. I love it....so far. The "pull" starts at around 3300 rpm and keeps going till I shift at around 5500 or so.
Chris

[Daniel]

The big valves and performance springs are a waste money you'll never get any more power out of the engine with
that setup with those Cams . I would keep the stock Valves and springs do the stage one cams, 4mm pistons and
very mild porting the Fiat FI manifolds ports are smaller then the heads intake ports and i find it hard to port match
this without removing to much material from the manifold close to the flange and mating port area to feel safe
about doing this . What i would think could or would happen is the manifold might crack or break off from a lack
of metal if you went to far .

Daniel

[ORFORD2004]

Sorry i forgot, adjustable cam gear also.

[Daniel]

if you want to save some money re drill the index pin hole on the intake cam gear/ pulley set it to
3 deg advanced, the exhaust will be fine on it's stock timing settings if you need to know more on
how to do this pm me ill share in detail .

[thechadzone]

This is a good thread with good information. What about decking the head? It's my understanding that head decking raises the CR enough to really take advantage of performance cams and dual carburetors.


TRUE or FALSE?