Which is the best Thru-transom exhaust manifold

[Paul407]

I have a 1990 Carrera with a 454 that has some sort of polished thru-transom exhaust on it. I could not even begin to tell you what type it is but that the exhaust exits the rear of the header into a half moon type bend and then to my exhaust ports. I have heard of other types like Kodiak and Indmar but are they really better to the point that I am going to see a performance increase or do I already have the best free flowing one of them all. Any suggestions would be appreciated.

[Havasu Hangin']

Tough to say without more info. Sounds like they might be aftermarket manifolds already (most OEM are not polished).
As a general rule of thumb, most engine mods are designed to increase flow (blower, carb, intake manifold, heads, cam, etc.), therefore exhaust flow must also be addressed. However, on a relatively stock engine, decreasing exhaust restriction will not show significant gains. Through-transom exhaust is already fairy unrestrictive.
So, in my opinion, if your motor is pretty mild, through-transom exhaust is probably fine for now. When you bolt on that blower, Brodix heads, and Crane roller cam, then you might want to look at some new headers.
Have fun! http://www.goldenplasma.f2s.com/foru...es/happy34.gif

[spectras only]

Paul,what you have is probably log type manifolds [they almost all come polished]which is fine for moderate performance application,you could buy center riser type manifolds now polished, by Kodiak,that flows better than the log type.

[STONE]

A buddy of mine had exhaust that sounds similar to what you've described. His were made by Hardin Marine. I have a 454/425hp with indmar cast and polished aluminum center rise exhaust manifolds. I researched headers, but found that unless you're shooting for 500+horsepower, my cast indmars would work perfectly. I heard from a number of pros that the indmars flowed really well for factory manifolds.

[flat broke]

Paul,
Unless you are going to a high duration / lift cam, your logs and riser setup will work fine. As with any combustion engine, it will work better when exhaust gasses get released quicker, but there is a definite cost trade off. A decent set of center rise manifolds is going to run you at least $1600 (better stuff runs up to $2500) with risers, and that is not including the new tips and hose you will have to buy to install them. Not knowing your setup I'm guessing that kind of money could get you a nice intake, carb, ignition setup, and/or pump work that would probably do more for you than the manifold change on your current engine. If you are looking for an inexpensive alternative, depending on your logs, you can have the outlet on the end of the riser (half moon peice) cut back to where the opening is larger and then run 3.5 or 4" out to new tips for a couple hundred. One last thought, if your engine hatch is a doghouse style, you might not have room for the center-rise manifolds. Measure twice, cut once.
Chris