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Discussion Starter #1
Not to start a war but what, if any, are the drawbacks to running Bassett through transom headers versus Bassett O/T headers?

I'm currently running Bassett O/T twisties, with baffles and water. I would like to run some Bassett T/T headers. Is there going to be a noticeable difference other than the volume?

Thanks in advance
Skip
 

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Not to start a war but what, if any, are the drawbacks to running Bassett through transom headers versus Bassett O/T headers?

I'm currently running Bassett O/T twisties, with baffles and water. I would like to run some Bassett T/T headers. Is there going to be a noticeable difference other than the volume?

Thanks in advance
Skip
IMHO, just a couple more bends in all the pipes, I doubt my Ass-O-Nometer would be able to tell the difference..;)
 

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I ran a set on a blown motor in a 19ft cruiser and was more than pleased, Out of the way, seemed to flow as well as ot bassetts and sounded awsome.
 

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I have the TT's on my heap. I also put 4" tips in. I believe it flows just as well as OT's. Granted there is a little more water in the TT's due to the engine water dumps at the hoses. And yes, it it quieter too.
 

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The extra bends will impose more restriction. The extra length will rob a little top end hp, but favor mid range torque. Like everyone else is saying, you probably won't be able to feel the difference. If you ran them back to back at the track you would probably see a very minor loss, just guessing, but maybe 1/2 a tenth or something in that ballpark......
 

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The Possibility/probability of marine wet exaust water reversion is greatly increased with any thru hull exaust applications of nearly any type (logs or headers) and because reversion is Camshaft related thus limits Cam selection choices
just my 02 Tom

We even use a "positive water shut off" even on over transom applications regardless of cam size , doing this on thru hulls will reuslt in burned thru exaust hoses ;)
 

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The Possibility/probability of marine wet exaust water reversion is greatly increased with any thru hull exaust applications of nearly any type (logs or headers) and because reversion is Camshaft related thus limits Cam selection choices
just my 02 Tom

We even use a "positive water shut off" even on over transom applications regardless of cam size , doing this on thru hulls will reuslt in burned thru exaust hoses ;)
Very true Tom and if you are building a motor for a customer that wants to idle around for extended amounts of time cause it sounds cool, and even better if I turn the idle down to 800rpm, then the problem multiplies. If you are building a motor for someone that understands the idea behind over-lap and lobe separation then they will understand that a clean out rap will eliminate alot of issues. But this won't happen. Hell bolt on a blower and problem solved!
 

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Discussion Starter #9
I don't now, and won't when the T/T headers go on, have a problem with reversion. I'm still going to use my water control valve to control the injection. The hose section will be cooled regardless of the injector water being on or off.
 

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Constant water flow to tailpipes is standard for the thru hull set ups (to keep the hoses cool ) The "reversion issue" for thru hull headers isn't so much with the injection water (shutting off and on) as it can be by having the constant water dumping into the tailpipes (not present in over transom headers) Tom
 

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Discussion Starter #11 (Edited)
Constant water flow to tailpipes is standard for the thru hull set ups (to keep the hoses cool ) The "reversion issue" for thru hull headers isn't so much with the injection water (shutting off and on) as it can be by having the constant water dumping into the tailpipes (not present in over transom headers) Tom
Tom, with the constant water being so far from the exhaust ports, not to mention the fact that the water would have to go uphill to get there, how can you say this would be an issue? I may not know everything, but I know that water will always take the path of least resistance, in this case the 3.5" tube right through the transom.

If I'm wrong, or missing something, please enlighten me. Knowledge is a good thing.

Skip

PS- After having spoken with Tom Bandy about his setup, I will be adjusting the constant flow to just enough to keep the hoses cool.

PSS- Here's a pic of the headers I have:
 

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Constant water flow to tailpipes is standard for the thru hull set ups (to keep the hoses cool ) The "reversion issue" for thru hull headers isn't so much with the injection water (shutting off and on) as it can be by having the constant water dumping into the tailpipes (not present in over transom headers) Tom
The constant water thru is not only for the hoses that exit thru the transom but I am sure you can imagine the damage to the transom with fiberglass and paint using a dry set-up would be Very Ugly. The T/T headers I have used have a standard injection to the tubes at the lowest point before the "up sweep" and far enough away from the port to eliminate the reversion issue if the water is not like a garden hose, and a secondary "wet" system at the collector and thru the transom. Regulating the flow for both is the main issue. Just what I do to keep the chrome and look pretty plus get the same performance as you would if they go over the transom. FWIW. M
 

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Skip You may get lucky and have it work well for you its not "flow" , backflow or backwash, thats at issue , For me it was not wanting to take a chance ,I spent well over a grand on stainless jacketed tailpipes to make sure the tailpipe water enters as far from the heads as possible and my manifold center line is well above the water line , my cam is 240 @ 50 , just following the recommendations of Eddie, Dana ,Rewarder etc. Best of luck Tom

heres some good reading from Rewarder :
Water Reversion/Ingestion
VERY IMPORTANT NOTICE, PLEASE READ CAREFULLY!!!

Reversion, what is it? It is simply the exhaust pulse flowing backwards momentarily during the overlap phase of the camshaft at low cycling rates. During the overlap phase the piston is pushing out the last of the exhaust gases and prior to reaching top dead center (T.D.C) the intake valve and the exhaust valve is still closing. At this point in the engine cycle both valves are in the open position. At high cycling rates the inertia of the incoming intake charge and the outgoing exhaust pulses keep the exhaust flowing in the proper direction. But at low cycling rates, as the piston is pushing out the last of the exhaust gases the intake valve opens and some of the spent exhaust charge is pushed into the intake manifold. As the piston reaches T.D.C. and begins the intake stroke the exhaust valve is still not completely closed. As a result, the piston pulls from the intake and exhaust valves simultaneously causing the exhaust gases to flow in a reverse direction. This is normally not a problem until you add water into the exhaust stream. Reversion can be severe enough to stall the engine, add water to the oil, rust the exhaust seats, etc. This effect only happens at idle speeds, but remember that during shut down the engine encounters the greatest reversion.

For these reasons Rewarder Custom Headers has guidelines for camshaft selection. Our guidelines are based on 454 c.i. with a 285 degree camshaft (242 at .050), on a 114 degree lobe center. Larger cams may cause reversion. These figures are just guidelines. Cubic inches, valve size, exhaust valve timing, etc., all will have an effect on reversion. The only true test is to run the engine with the headers attached, shut it down, remove the headers and check for water residue in the header ports to check for an occurrence of water reversion.

Your Options are:

Install extended dry pipes This option substantially reduces if not eliminates water reversion. With this option you can adjust where water is introduced into the exhaust stream. Remember the longer you extend the dry pipe the louder the system becomes.
 

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Discussion Starter #14 (Edited)
Tom,

I think we're on two pages of the same book. If you look in the pic I posted of the Bassetts, the exit water bung is nearly 30" TDL from the closest exhaust port, that includes a 12" rise in the header.
Maybe I'm missing something but I can't for the life of me see that water is going to be introduced to my cylinder via the exhaust port from this bung. Am I just dumb and I'm missing something? I get
that reversion can be an issue, but I gotta ask, if it was going to happen, wouldn't it be just as likely with O/T headers? Maybe even more likely due to the way the O/T headers are built, with the flow
going up from the exhaust ports versus going down as they do on the T/T style.



Enlighten me please.

Here are my cam specs:

Solid Lifter
108* Lobe Separation
294 INT duration
304 EXH duration
343/358 lift
256/266 duration @ .050" lift
 

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Skip I'm sure you'll probably be fine , the rule of thumb has been 235 to maybe 240 @50 on all thru hull apps for as long as I can remember , the information is just that I followed the recommendations because I just prefered to err on the side of caution. Truth be know if I thought I could have I would have put a lot more cam in Rhondas boat,
Good luck good to chat Tom
 

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Lucky, I am on the same page as you. I can't see the water backing up the pipes from the engine dumps either. I have the exact TT's you have and am running the ball and spring bassett "T" valve with a hydrolic roller cam:
242-254 @ 50 575 lift w/113. I have zero reversion issues. I can idle all day. Granted my idle is at 1200rpm and injection turns on at 1800rpm. I also have 4inch rubber exhaust hose and 4inch exhaust tips. Very easy for the water to get out of the pipes and hose.

Mike
 
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