I’m installing Dutra Duals on a modified slant with 10:1 compression, a Hughes Mild Street Cam and dual 32/36 Weber carbs. My question is: using 2” exhaust pipes from the manifolds to a 2.25” outlet Y pipe, how long should the 2” pipes be, for proper scavenging, before the Y collector?
Thanks!

It is hard to say exactly with the Dutra Dual short iron manifolds. My answer for shorty headers (based on experience and testing) is to run those 2" pipes to a spot 4-12" behind the transmission crossmember, and then put them into a Y and then single 2.5" exhaust out the back. That should work well for the Dutras too. This will maintain as much low/mid range power and torque and not hurt the top end. I have never done these tests for Dutras, but this is my sense based on other experiences. However, I doubt you will lose much if you put the Y near the bottom of the engine compartment above the torsion bar. Packaging and convenient fabrication may be as much or more important than getting that last 2-4 HP?

My 2 cents...
Lou

_________________
Home of Slant6-powered fun machines since 1988

Here is something you can play around with:

_________________
Hyper_pak

My Dutra duals had about that kind of tubing. It has also 10:1 compression, 236/230 degree Hughes cam and DIY fuel injection. It was very much a low end torque engine with 5000 redline.

_________________
1966 Dart. 170 cu.in. 200 rwhp. 101.6 MPH @ 1/4 mile.

Note that Wkstiner is trying to optimize secondary pipes, not primaries (header/head) pipes.

What is the cam you are using? I assume it's the bigger one you can get from summit? Please post specs.

Lou

_________________
Home of Slant6-powered fun machines since 1988

Speaking of the creator of these manifolds and so many other things "/6".
I know that he had a horrible thing happen with one of the California wildfires a few years ago and lost a bunch of his stuff.
Is he still doing anything car or /6 related? It would be cool to see him check in here now and again

All that one N/A 225 can produce fill fit in a single 2,5" tube with no rush in it. D-duals are not the hottest exhaust a slantsix can get. Just a nice pair probably doing extra 10 hp if all other parts are good. Gill welding seem to like produce tubes which are Y-connected in the engine compartment. I got mine from local muffler shop. In the 1st setup they were true duals but I didnt like the sound at all. So the were Y-connected at the rear of transmission until I removed them before turbo installation.

_________________
1966 Dart. 170 cu.in. 200 rwhp. 101.6 MPH @ 1/4 mile.

Yep I miss having Doug on here too!

_________________
2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

I’m using a Hughes Mild Street cam

It gives me a warm feeling everytime I see 65 signet mentioned. I will have had mine for 27 years tomorrow and will never get rid of it. Bought it st pattys day in 1999, 2dr ht with 60k ish miles when I got it for $200. take care of it and make sure to enjoy driving it.