Performance Boats Forum banner

1 - 16 of 16 Posts

·
Registered
Joined
·
506 Posts
Discussion Starter #1 (Edited)
So Just curios how much Hp loss do you think I could get from a TT Autronic EFI deal from changing exhaust??? 519 ci Dart pro 1 325cc heads 14 psi boost no big deal cam +/- 630 lift full roller. (Meaning from open shorty dumps to threw transom) Water exit's at the end of the tails double walled +/- 2 in from exhaust stream with threw transom exhaust as opposed to no water at all with the shorty dumps?? pics to follow. Shortys are 3 in i.d and threw transom i.d are 3 in stepped to 3-1/2 to 4 to 4-1/2 i.d. First pic shortys, second pic threw transom, (and I have already taken out the mufflers due to thinking restriction) And I've already spoke to some very knowledgeable guys so please don't call your guy to elaborate as I am not looking for their opinions, Im just looking for you guys that have knowledge on this site about these things before I have a guy come out and perform the tune. And I'm just blown away on how much change that I have noticed. Thanks.
 

Attachments

·
AAARRRRRGGGGGGG!!!!!
Joined
·
288 Posts
I would say you have lost 20% in the upper range and 40% in the lower range.

You did mean hearing loss from running the shorties In a play boat didn't you?

Matt
 

·
Registered
Joined
·
6,278 Posts
Theres a good chance that the additional back pressure caused by the through transome setup has caused more of your exhaust to exit through your waste gates, thereby reducing your boost pressure. Backpressure in the exhaust is a real hp killer. The only way to regain it is to turn the boost back up with the boost controller or return the exhaust as it was. JMO.


Nice setup :))THumbsUp
 

·
Or Seth, either one
Joined
·
3,270 Posts

·
Registered
Joined
·
506 Posts
Discussion Starter #6
Out of curiosity, what changes have you noticed?

BTW, Sweet boat. Very sano.
Noticed a big difference in mid range and top end power. Meaning while cruising at around 70mph and standing on it it just lags, does not come to life like with the shortys, also after changing the exhaust it would not break 100 then when changing back it went over with ease. I know for a fact with this new exhaust it is way fat and can tell by the soot on the transom. I guess I was just looking to see if anyone else has experianced this.
 

·
Or Seth, either one
Joined
·
3,270 Posts
Noticed a big difference in mid range and top end power. Meaning while cruising at around 70mph and standing on it it just lags, does not come to life like with the shortys, also after changing the exhaust it would not break 100 then when changing back it went over with ease. I know for a fact with this new exhaust it is way fat and can tell by the soot on the transom. I guess I was just looking to see if anyone else has experianced this.
Seems odd that the EFI didn't correct for the rich condition. Are you running closed loop?

How many RPM did you lose at WOT with the through transom exhaust?
 

·
Or Seth, either one
Joined
·
3,270 Posts
...I've already spoke to some very knowledgeable guys...
Since there doesn't seem to be too much input from the group here, do you mind sharing the input you've gathered elsewhere? What opinions have you come across so far?
 

·
Registered
Joined
·
4,318 Posts
Theres a good chance that the additional back pressure caused by the through transome setup has caused more of your exhaust to exit through your waste gates, thereby reducing your boost pressure. Backpressure in the exhaust is a real hp killer. The only way to regain it is to turn the boost back up with the boost controller or return the exhaust as it was. JMO.


Nice setup :))THumbsUp
X2 While i haven't messed with V8 turbo stuff i have done several m/c turbo deals and they all ran best with short/fat exhaust pipes. I tried a 2 bros carbon fiber exhaust can on one deal and it was the difference packing the front wheel most of the way through 3rd gear or not at all.
Bike made 290/@22 psi (74 c.i.;)) on a dyno and on a guess 230 with the can.
Same can on a n/a motor makes 1-2% less than open exhaust and jet changes didn't help.

Seems like turbos just don't like any kind of restriction.

The ignorant thing is, the can did a decent job on a n/a motor, with the turbo deal, not so much and turbo with a short pipe made about the same noise as n/a with the can.
 

·
Or Seth, either one
Joined
·
3,270 Posts
A quote from the following article.

Alameddine's attention to detail paid off when Thomson began making full dyno pulls, but there was something clearly holding back the engine. It was making more than 1,500hp, but was stymied by the mufflers on the dyno's exhaust system.

It was a simple matter of too much exhaust backpressure and once Thomson's technician's uncorked the system, the engine blew unrestricted and instantly hit the 2,000hp mark. Keep in mind that the performance-hampering backpressure wasn't anticipated because the dyno's exhaust system already measured a large five inches in diameter.
Twin Turbo LSX Engine - Super Chevy Magazine

I never would have guessed!
 

·
Registered
Joined
·
762 Posts
I spoke with someone the other day about this very thing. He said that they saw little to no difference in performance between the two.
 

·
Registered
Joined
·
6,278 Posts
X2 While i haven't messed with V8 turbo stuff i have done several m/c turbo deals and they all ran best with short/fat exhaust pipes. I tried a 2 bros carbon fiber exhaust can on one deal and it was the difference packing the front wheel most of the way through 3rd gear or not at all.
Bike made 290/@22 psi (74 c.i.;)) on a dyno and on a guess 230 with the can.
Same can on a n/a motor makes 1-2% less than open exhaust and jet changes didn't help.

Seems like turbos just don't like any kind of restriction.

The ignorant thing is, the can did a decent job on a n/a motor, with the turbo deal, not so much and turbo with a short pipe made about the same noise as n/a with the can.
A quote from the following article.



Twin Turbo LSX Engine - Super Chevy Magazine

I never would have guessed!
I spoke with someone the other day about this very thing. He said that they saw little to no difference in performance between the two.
I already posted what the problem is, now if the OP chooses to believe it is up to him. The engine certainly will need to be retuned for the new exhaust restriction but he will never regain all of the lost hp.
Mark (unchained) dynoed his engine and they put 8" pipes loosley over his dumps and the resulting backpressure caused his boost to drop from 27psi down to under 10 and the backpressure in the header went up from and even 1-1 @ 27 to up over 44psi , which cause more to go out the waste gate. He turned it up with the wastegate till he was back to 27psi in the intake manifold and made over 1800hp but in actual use out on the lake with the open exhaust and very low backpressure in the exhaust system I would bet that he's well over 2k hp. JMHO. Take it or leave it.
 

·
Platinum Member
Joined
·
2,014 Posts
I have a accurate set of gauges for testing diesel motors and hydraulic systems, motors don't like intake or exhaust restriction
You can measure the restriction in inches of water column
 
1 - 16 of 16 Posts
Top