Is there a resident cooling/exhaust expert in the house? I made some changes that I’m regretting.

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Afternoon Chris, I’ll try to give you an accurate and consise description; I’ll be a bit long but I’ll attach some pics for visual cues. I have a couple 580/775hp tall decks in my Cafe, the exhaust consists of Hardin Cyclone headers and gil full length through transom tails with 3/4” dumps coming off each tail to a through hull fitting. Right now my risers are running much warmer than last year, I can keep my hand on them but its pretty hot. Last year I ran a crossover with bypass/no T-stat and a “wet” exhaust I had no problems with tails being too warm. When I say wet I mean my inner pipes werent tightly swaged to my outter pipes, so water came out between them at the tip; also of note the through hull dumps flowed just a little water at idle. This year my engine builder took off the by pass setup because he said I dont need it w/out a t-stat which was fine with me; and added just a std crossover system, still with no t-stat. I also reswaged my tails affecticely making them a dry type setup with a retangular shaped drain hole at the bottom of the inner pipe at each tip for water to drain from, approx 1/8” High X 5/8” long. Also of note the dumps are now flowing a lot more at idle naturally because I swaged the tips of the tails; although I did try to make the new drain holes equal to the size of what would have been the cumulative of the entire space that they had last year if that makes sense. I only have about 45 minutes on the power as I’m still breaking them in so my running data is from the lake w 70 degree ambient water temps and from idle up to varying RPMs around 3500. @ 3500 I saw about 14 psi water pressure so I’m ok there so far. I’m trying to target mid to high teens to a max of low 20s @ WOT. So, the real problem I’m thinking about is the heat in the risers and how to cool them better and or If I should be worried about it at all at this point. Secondly I’m focused on water psi naturally. Anyway that about sums it up in a round about way.

The previous owner had butchered the tail tips so I recut them to even them up, then reswaged them. Admittedly my die grinding work doesnt represent my best efforts so give me a pass on that hacky attempt. I have bolt on Harden tips on them now.

Yeah, thats one of the stronger possibilities BUT, I’m having a hard time believing the new retangular holes I made on the inner pipes is bigger cumulatively than last year with the seperation of the pipes and the holes drilled at that point. I was kinda hoping there was an exhaust guru lurking around somewhere here.

Very good point. Although its not. There needs to be a drain at the bottom. I suppose it could have smaller and I could have drilled a few holes at the top. Hindsight is 20/20... Hoping I can do something with my current architecture .

thanks Tim. Well, I suppose I could Tig them back up and give it a shot...