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I've got hours worth of BBC exhaust reading material here in quite a few books. I'd rather not regurgitate any of that info, I'm already known as the regurgitating googler. :party-smiley-004:

But hey, check out this exhaust test from 1964 from Chevrolet Engineering Dept. Wonder if that had anything to do with the 427 Corvette exhaust setups.

Crap, here we go with the sideways pics again

Quote:

Originally Posted by getrdunn (Post 4480798)

Helps scavenging big time. We use to mess around with that back in the drag strip days when dynos were far and few in between. Results would always very but knowledge was always gained regardless.

Here's the thing.....reversion too.

So, even though max peak power doesn't change much, most of the curve can shift power upwards big time. One of the CMI's in Mild Thunder's pdf shows a lot more middle power than the others....I'm willing to bet this had a better sized 'collector.'

Now, staying on this, PapaSmurf had Diamond Performance's KE exhaust, and he was able to get his collector length to within a smidge of a best length and it fixed his reversion. KE's use a relatively short pipe connected to the manifold compared to many others,

I'll try to find the page,

He was killing 02's due to water..ie: reversion.

Okay,here:
http://www.offshoreonly.com/forums/f...epowering.html

and will quote it below:

Quote:

Originally Posted by Papasmurf (Post 4471708)

Greetings Formula Brothers !

One quick lesson I learned about repowering my Formula, that I wanted to share.

If you are installing a "performance engine with O2 sensor " in a Formula with a swim platform, make sure your exhaust tails are 4 to 6" out past the transom. Myself, and a few others I know have had a unexplained vortex backdraft when using the short 2" tails we like to run sometime

Just food for thought

Quote:

Originally Posted by SB (Post 4471724)

What is the length of your 4" exhaust from where it bolts to the header to the end of your 2" tailpipe and then to end of your new tailpipe ?

I may / may not have answers for you on why this is happening.

Quote:

Originally Posted by Papasmurf (Post 4471978)

Old pipes where 16" total length from header
New pipes are right at 20" total length from header

Quote:

Originally Posted by SB (Post 4472080)

3rd Harmonic = 38.8 inches long ... more bottom-end Torque
4th Harmonic = 19.4 inches long ... highly recommended , best Torque Curve
5th Harmonic = 9.7 inches long ... reduced Torque , more top-end HP sometimes
6th Harmonic = 4.9 inches long ... reduced Torque , not recommended

Tuned Lengths= 19.4 best and also 9.7 or 38.8

Look like you are good now !

Good find SB. I hope endeavor32 is reading this thread and or knows about the formula swim platform. He's been battling some brother sister issues with the engines in his formula. I would imagine he's read the thread but I've been wanting him to yank his swim platform off and leave it off for two years now so I can get a grin while he leaves dock and I'm working. What can I say it's much more entertaining than dealing with the public.

Quote:

Originally Posted by getrdunn (Post 4480837)

HA- It's in the overall plan. Once I find a nice aluminum swim platform the Silent Thunder is gone. That thing is heavy and really quiets the boat to much, even with 4 4" holes drilled into it. Also once I get the boat budget built back up, 2 sets of Eickerts are being ordered. I'll never be running a blower so for me they are perfect.

You know what is better than hearing me at the golf course? Doing circles around me with your boat! Getrdunn!

With dry tails on any of these setups should I concern myself with reversion???

I am definitely going dry tails...

Quote:

Originally Posted by G-NOTE (Post 4480949)

With dry tails on any of these setups should I concern myself with reversion???

I am definitely going dry tails...

Yes especially if you have a bravo drive and it gets stuck in reverse on a windy day it can and will revert. There is a cure for that as well... Tractor stocks or put your tails out the side of the boat.

I saw IMCO power flow have a pretty good power curve based on that chart, they are a little more cost effective then the KE stuff. Any thoughts?

I am assuming that they are testing the powerflow plus model ? which is right there with the KE price wise. Imco offers three different risers for these

http://www.imcomarine.com/cal_store/...-polished.html

It would be nice to see a updated test of exhaust manifolds with the newer models thrown in including the risers/ tails that are used

I'm curious why you want dry tails? Dry to the tip is loud, dry is stupid loud. If I ever pull the silent thunder off my boat I'll be running mufflers!