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Discussion Starter · #1 ·
What is the diameter of the exhaust pipe on the coupe? Is it 3 inch, 4 inch? I am sure a larger diameter will help to relieve back pressure so I am wondering what it already has versus what it should have... Or a better question is what is the optimal size? Is the Larini a different size from stock?


Anyone here know?
 

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2.5" on the Maserati. Larini is the same size. The Maserati does not have much back pressure once the mufflers and X-pipe have been installed. The only remaining restriction is under the steering rack. We'll have something for that soon.

Once we go with forced induction this may be a problem, however we'll cross that bridge soon enough.
 

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What is the diameter of the exhaust pipe on the coupe? Is it 3 inch, 4 inch? I am sure a larger diameter will help to relieve back pressure so I am wondering what it already has versus what it should have... Or a better question is what is the optimal size? Is the Larini a different size from stock?

Anyone here know?
Exhaust pipe diameters are not guessed but determined. Piping of too large a diameter can cause gasses to exit too quickly and it was found to warp exhaust valves in some instances!

The rule of thumb was that the ID of the pipe never exceeded the OD of the largest valve in the cylinder head.

You are not going to relieve pressure just by going to larger diameter pipe. You have to look at the internal construction of the resonators and mufflers in the system, and then you have to balance the system collectively.

I have never designed a system with tubing larger than @ 50 mm which is right around 2" and that included systems with large 12 cylinder engines.

Look at race car photos from the 60's and 70's and see the tuned exhausts with tubing about 1.5" diameter!
 

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Discussion Starter · #4 ·
Steering Rack...

Jeff's Quote:

"2.5" on the Maserati. Larini is the same size. The Maserati does not have much back pressure once the mufflers and X-pipe have been installed. The only remaining restriction is under the steering rack. We'll have something for that soon.

Once we go with forced induction this may be a problem, however we'll cross that bridge soon enough."


Reponse: I was wondering about that as well, it's a nice kink in there and has to restrict exhause flow. Let me know when you have this done, I need to up the exhaust system next, it's way to restrictive with the new ECU and the DBW, the cats are getting hot with the extra fuel, etc.

Response to GCalo: So the rule of thumb is same diameter as the largest exhaust value diameter... Now I do remember starting the engine in a drag car, getting it hot and then spraying paint on the exhaust pipe until it quit burning and then cutting off the pipe at that point to keep it from burning the exhaust valves. So you do need some back pressure, but really the optimum amount?
 

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The drag race paint trick has to do with temperature so that you don't crack your valves. The idea is that if the pipe is too short ( always use a min length of at least 18" ) then you can crack your valves by letting outside air ( which is much colder ) into the engine between pulses which will cause a crack due to expansion. By lengthening the pipe to the point where the paint no longer boils, you've allowed enough of a temperature buffer to be safe.

Backpressure can aide or restrict an engine. Basically it's all got to do with the design of the engine. The Maserati isn't the best, but certainly is not the worst. You'll improve quite a bit with good mufflers and an X-pipe. For further performance HP Cats and the compression underneath the steering rack fix will help as well.

Best Regards,
-- Jeff
 
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