Cooler Engine through loud Exhaust

This forum is specifically for engine and gearbox posts, please try to keep on topic in any thread to make things easy to find

Moderator: Board Moderators

Post Reply
Oldtimer_Basis
Junior Poster
Posts: 58
Joined: Wed Sep 01, 2021 18:14

Cooler Engine through loud Exhaust

Post by Oldtimer_Basis »

Hi again.
I just want to inform you about an Observation I´ve made:
After replacing the original rear Mufflers by a pair of 2.5" Cherry Bombs, the engine not only sounds cooler, but runs cooler as well. The Temp-Gauge hasn´t risen past 92°C yet (haven´t had any traffic-jams so far) and the Fans were off all the time.
I still haven´t dynoed the Performance, but it also feels like the Engine revs up a bit faster above 3krpm.
Not sure, if this will generally be the Case, because the Rest of the Exhaust is also heavily modified, but the Engine Temperature was normal througout all Modifications and only went down after the rear Muffler Change.
As for the Sound:
Now it sounds like it should - I love it. It´s a 7.5 on the Barry-White-Scale, with a good Portion of Joe Cocker mixed in above 3.5krpm. It is not screaming loud, but loud... and quiet beneath 2krpm. So you still can come home late at night without your Neighbors pointing their Shotguns at you :lol:
To get this sound I used: A d-i-y large primary Header with a 1-4 / 2-3 Setup, 2.5" Exhaust Pipe, a 20" Cherry-Bomb-Style Middle-Muffler, but with Louvers inside (Louvers facing backwards), continuing with 2" Pipe, going into the original, tiny Y-Pipe and original left/right Pipes and then into the 2.5" Cherries (18" Length, Flanges needed to be shortened to fit space) and ending in the original Tips, but without Inlay.
Greetz,
Raf

Oldtimer_Basis
Junior Poster
Posts: 58
Joined: Wed Sep 01, 2021 18:14

Re: Cooler Engine through loud Exhaust

Post by Oldtimer_Basis »

Aaah, I meant: The Primaries on the Header are connected 1-2 and 3-4, not 1-4 and 2-3...

User avatar
Lotus-e-Clan
Senior Poster
Posts: 4295
Joined: Thu Nov 30, 2006 13:25
Model: Excel SE - EWP/Waterless!
Colour: Not Blue or Green
Year: 1989
Location: Swaledale

Re: Cooler Engine through loud Exhaust

Post by Lotus-e-Clan »

Interesting findings. :)

So I guess the system has less back pressure than std?

Any pictures of the system?
Peter K

Pete Boole
Senior Poster
Posts: 3243
Joined: Tue Apr 04, 2006 21:28
Model: Elite
Colour: Monaco White
Year: 1974
Location: Nottingham

Re: Cooler Engine through loud Exhaust

Post by Pete Boole »

Love your music-based exhaust comparison scale! :D I can't explain the drop in engine temp either. It is interesting though!

Pete

TAR
Regular Poster
Posts: 101
Joined: Thu Apr 28, 2016 22:21
Model: Elite Type 75
Colour: blue
Location: Buckinghamshire

Re: Cooler Engine through loud Exhaust

Post by TAR »

Back pressure in the exhaust is a really important concept for a normally aspirated engine; it can be used to help scavenge the gasses from the combustion chamber. The exhaust can be tuned to create pressure pulses which are timed with the exhaust valve opening so it sucks the gasses out.

This is a very simple outline of a very complex process. I guess if it's optimised, it could allow the engine to run a bit cooler but I'm not totally sure on that specific point :)

Oldtimer_Basis
Junior Poster
Posts: 58
Joined: Wed Sep 01, 2021 18:14

Re: Cooler Engine through loud Exhaust

Post by Oldtimer_Basis »

I haven´t made Pictures of the Exhaust, yet, but we´ll be making some Car-Videos, soon, and we will lift them up and plan to talk tech a lot... in german, but I doubt that I can tell you something new, anyway, so in case of the Excel that wouldn´t matter much.

As for the cooler Engine: The Effect is noticeable from 2krpm upwards. I´ve had some smaller Traffic Jams, meanwhile, and there the Temperature acts as usual (climbing slowly until the Fans turn on and then dropping quickly).
I guess the Backpressure, that generates the Heat, originates from the two 180° Turns in the Mufflers. They reduce Loudness very efficiently, but apparently at the Cost of generating a lot of Pressure.
The Cherry Bombs I used have a much larger Bore than the Pipes before them, so they only slow Flow down a bit and dampen down high pitch Noise.
I would be interesting, if only changing the rear Mufflers and leaving the Rest of the Exhaust stock causes the same Effect...

Post Reply