Porting the 348

randyleepublic · Sep 18, 2008

I ran across this in the 308 forum. For those of you who are unfamiliar with Mark, he is the wizard of Pennsylvania who is taking a 400i engine, putting Testa Rosa heads on it, and doing such a good job that he expects, and I believe he will be successful, to get about 750 hp from the finished product. BTW, did I tell you that engine is going in his 308?

Anyway, a fascinating thread - like going to school at a machine shop - so I wanted to share his analysis of current thinking on porting:

mk e said: ↑

I hear port volume a lot from the US car guys but it really doesn’t actually mean anything to performance. I guess the thought is measuring port volume is an easy way to tell if the ports are all the same but in true there are an infinite number or port variations that will yield identical volumes so the number is nearly useless for comparing ports as far as I can tell….but the US car guys always want to tell me about their port volume.

What actually works is knowing the flow velocity at the valve seat. The higher the velocity for any given flow, the better the cylinder will fill, the better the fuel will atomize, the more turbulence in the combustion chamber and the more hp you make. Velocity helps everything. At 10in H2O pressure on the flow bench 195-200 fpm is possible at the seat when everything is right and when you are in that range the torque curve will be wide and flat and volumetric efficiency will be up in the 120% range meaning gobs of both torque and hp. So, the velocity is in my opinion the most important number, it tells you if you are building a good engine or not.

The second number is the actual flow. You can’t make hp without air and the peak flow number tells you how much hp is possible. A lot of guys get focused on this number and forget the velocity number which is what leads to horror stories of “over-ported” or “peaky” engines. Making flow with a small efficient port is good, making flow by just hogging out the port and stuffing in big valves is bad.

All the general stuff said, lets talk specifics. Ferrari in the 70s and 80s did what a lot of people did at that time and made “high velocity ports”. The port/runner is kind of hour glass shaped area wise with the smallest and highest velocity part right about in the middle then the port area increases all the way to the valves. It works, but understanding has changed and we now know it is not an optimum design because diffusing (going from small to big) is always inefficient and causes you to really just hit a hp wall that you simply can’t get past. The 2 valve head has a valve and seat ID big enough for 400+ hp of air but is only flowing 240hp or air and the QV and TR heads are similar.

There are 2 ways to fix the ports. The first is to weld in the port up by the valve and fit smaller valves. This will let you make maybe 10% more hp while fattening up the torque curve. The second option is to open up the other end of the port and the whole manifold enough to match the valve seat area or better yet taper larger at about 4 degrees from the seat all the way out. This will let you make 30+% more hp with a fatter torque curve and is basically what I was doing with the TR heads and had the flow up just about 30% with the stock valves…..before I realized I need to buy cams anyway and decided to make the engine spin another couple thousand rpm which meant I needed even more air and required opening up the port until I found water jacket and still wishing they were bigger.

A 308 engine with stock cams (early carb or QV….2vi cams s*ck) the heads done right and EFI should make 320+ hp without any problem and the one engine I know was done right and dyno’d does and does it with more low end power and better driveability than a stock engine. The numbers always work out, there may very well be a way to do it that is better yet, but you can get 30+% more power today going to the numbers the way we understand them today vs what was the hot ticket in the 70s.
Click to expand...

Does this ring any bells? Has anyone tried this approach or something similar on a 348?

ferrari.ace · Sep 18, 2008

randyleepublic said: ↑

I ran across this in the 308 forum. For those of you who are unfamiliar with Mark, he is the wizard of Pennsylvania who is taking a 400i engine, putting Testa Rosa heads on it, and doing such a good job that he expects, and I believe he will be successful, to get about 750 hp from the finished product. BTW, did I tell you that engine is going in his 308?

Anyway, a fascinating thread - like going to school at a machine shop - so I wanted to share his analysis of current thinking on porting:

Does this ring any bells? Has anyone tried this approach or something similar on a 348?
Click to expand...

Just the tip of the iceburg.

There is allot more that has and can be done with these heads.

randyleepublic · Sep 18, 2008

Can you point me to the most successful experiments? Who has gotten real improvement?

ferrari.ace · Sep 18, 2008

randyleepublic said: ↑

Can you point me to the most successful experiments? Who has gotten real improvement?
Click to expand...

Competition Cyliner Heads (CCH) in VA. does interesting work with heads. I'm not sure if Jim is still making heads flow or retired???

Great guy with tons of R&D experience.

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