Exhaust port, header, manifold design

[SappySE107]

This is off topic because its 3800 based, but i think it has some importance to all engines (maybe not rotary).

The Gen 2 and newer 60V6 engines all have a similar exhaust shape, with the valve seat going to the bowl, past the valve, around a slight dogleg, and finally out a D shaped runner. On the 3800 heads that I have been doing flow testing with, the exhaust port is hardly worth talking about as far as what is involved. Valve seat, past guide, done.

Bare with me on the 3800 stuff, we will get back to 60V6. With no port runner to navigate, the shape of the header primary or manifold port is critical. Very very critical. After reading before and after results from DIYers and the aftermarket, it is clear that the DIYer has no idea, and looks promising that some companies are playing games with the tube shape on the bench.

The 3800 port is oval, and points up rather than straight out from the flange mating surface. If you put a round tube on this, the flow numbers looks like this.

.200 103.5
.300 130.4
.400 143.4
.450 147.6
.500 148.9

Usually we have all the numbers (we still do) but the numbers we were comparing to were as such, so that is how they are listed here.

If you take the same 1 5/8" tube and crush it in a vice so its oval on the end, the numbers look like this

.200 108
.300 144
.400 156
.450 160
.500 162

So as to not give away everything we are doing, there was another test performed using the tube and will play a role in how we port 3800 heads for customers.

.500 numbers only, ported how we found to be the best without increasing valve size or doing a valve job to optimize the angles.

Oval port roof, round tube = 172
Oval Port roof, Oval Tube = 182
Round Port, Round Tube = 180

How does this play into the 60V6 engine? Simply put, the head has everything we need for transitions. By the time the exhaust is out of the head, its direction is set and its velocity is kept.

[robertisaar]

so..... what i'm reading out of this is that it's easier to design good 60V6 headers/manifolds than it is for the 3800s?

[SappySE107]

You won't find 12 cfm from port shapes on header design for a 3x00. You also won't find flow increases by opening up the end of the port like some companies and DIYers do. I watched a lot of 3800 head porting videos on youtube before I started my reserach. They mostly failed completely, or lacked any substance at all (just clean up casting flaws...yawn). Even that is deceiving because you don't know what a flaw is until you test it:P I just wanted to share something interesting on the 3800s but I don't post on 3800 sites...so here it is:P Its important to understand the motor you are modifying and how it may or may not respond to modifications other engines benefit from.

[ericjon262]

another win for the 60* !