I have seen quite a few posts that mention advantages of using stock EFI split exhaust manifolds to true duals. I been searching and have seen some complaints about the quality of the Walker Y pipe.
My engine has just been rebuilt with Comp cam, H.P. roller rockers and I have a Offy "C" to bolt on, so I'd like to get the best setup with the EFI's.
Is there a "X" type crossover a few feet back?
Anyone have pictures of this setup?
I would like to see how this is done, looks like it could get tricky the way the manifolds dump out.
Thanks, Doug

 

The quality concern with the Walker Y Pipe is a small one and easily remedied. The opening where the rear tube attaches isn't always open all the way and can restrict flow. A little grinding fixes it.

The general consensus is that duals are pretty much just for looks. A single works very well. If you go with duals, keep it around 2" or so. A single about 2 1/4 or 2 1/2".

 

I'm not real impressed with the design of the walker Y pipe. While it flows better than a single, I can't help but think it would flow far better with a bit longer tubes that join at a shallower angle, like a header does at the collector.
Doesn't the factory pipe run dual into the converter, and single 2.25 or 2.5 out? If memory serves me right, that's how my 94 was, with an O2 sensor between the pipes just ahead of the converter.....

 

Increasing exhaust system flow is a good thing, but full length, long tube headers would be a GREAT thing that would significantly increase torque throughout the entire rev range.

 

The long tube headers do yield more return. And more returns under the hood to fix header leaks.
The EFI manifolds are pretty much a once and done deal.

 

I did duals and it was pretty decent, using the stock downpipe into a dual 2" system. The problem people have with duals is primarily not having a crossover, and running too big of a pipe.
The pipe between the cats on the factory system is 3", and a 3" single exhaust is a bit much for these engines, I lost a lot of lower end power with that.

 

a 3" single exhaust wont be bad, like ive read, a larger diam single exhaust helps in the low end. but yea dual you wouldnt wanna go over 2.5" for sure

 

The efi split manifolds flow just as good as headers,the ONLY time you would need to switch to headers is if the motor was fully built highperformance,other wise no difference.

 

I have a buddy who can remove the cat and put duals on my E250, you think a large single pipe would be better ?

 

Single pipe is the way to go. More room, easier, and works just as well.

2.25 and 2.50'' is all you need, as previously stated.

 

Unless the cat is failing, I'd just leave it under there. Then run a 2.25 or 2.5 single w/low restriction muffler.
I would have left the cat under mine, but it had been under it for more than 12 years without the air pump hooked up. It wasn't failing yet, but it was living on borrowed time.

Duals take up a lot of room under there, since they have to share an area that was formerly used for a single pipe and muffler. A larger single will flow just as well as smaller duals, but there's less stuff to eventually rust out.

 

Full length headers, either tri y or four tube ones, offer a SIGNIFICANT torque and economy improvement throughout the entire rev range. Shorty headers or a free flowing exhaust won't do this but headers will. They provide an individual tube for each cylinder and scavenge the exhaust. This not only helps the engine to breathe, but it doesn't have to waste energy PUSHING exhaust into a crowded manifold with pressure applied by the other cylinders.

To quantify the advantage of headers, dink around with desktop dyno. It gives a very good representation of various mods and is amazingly accurate as compared to the same testing on a real dyno.

 

Yes, full length long tube headers do offer a significant improvement in power/torque.
I'd be all over putting these on my truck, if I could find any that were built to the same specs as the headers I run on my rotaries. They're made with 7/16" flanges, and 1/8" (.125") wall tubing, then ceramic coated. No leaks, ever. Sadly, no one makes headers that are this well built for most applications, and the few that are cost a truckload of money.
Any lower quality materials, and leaks are very common.

 

Oh yea, too big and you lose low end, my E250 is just a very heavy van, thought maybe a few minor things wouldn't hurt. Plus, I've been kinda bored lately anyway.

 

Nope, small diameter helps low end, otherwise all these ricers would be able to leave a stoplight in a less than embarrassing fashion. Too big of a pipe won't scavenge, and performance and mileage will suffer. Too small of a pipe will choke your high end, it's an art to find the best size.
This all doesn't apply with forced induction, where you just want the exhaust away from the engine or turbo.