I have a 1970 F 250, with a 400 engine, RV cam, Eldebrock aluminum manifold and and Eldelbrock 1406 600 CFM carb. (This is a used rebuilt engine that we just put in this summer - the 360 had been replaced with a 400 and C 6 tranny some years back.) There was not much left of the old exhaust system from the manifold back, and so last week I took it to a muffler shop to have new mufflers and pipes put on. Unfortunately, I neglected to tell them that the engine was not stock, (thought it would be obvious). They routed the exhaust in such a way that there are two pipes leading back from the manifold to a single muffler and tailpipe. I asked them why they did not put dual exhaust, and they asked "what size engine was that anyway" and said it was not stock to put dual exhaust on the truck. I did mention that the whole engine is not stock. I got the feeling they just did not want to be bothered. Unless it is my imgaination, I have noticed a loss of power with the new exhaust set up.

My question is, does a 400 with the cam, manifold and carb described require dual exhaust? It feels as if the engine is not able to breath correctly now, and I do not want to do damage to it.

I am going to be using the truck for hauling horses.

Thank you

 

It doesn't "require" dual exhaust but it would certainly benefit from dual exhaust, you won't do any damage by running it with single exhaust, the engine just won't perform up to its full potential, but even with dual exhaust the exhaust flow is being restricted by the stock manifolds, i would install headers if you go the dual exhaust route.

 

heres a chart thats on magnaflow website Ive seen them on alot of performance sites and there all close to each other ---http://www.magnaflow.com/07techtips/faq/question10.asp

 

go with the duals, i had a bone stock 400 an had duals on it. sounded great an gave er some more power too

 

I would have thought the exhaust system you wanted would have been dissussed before it was made.

 

I thought a properly set up single exit exhaust was best for creating maximum torque?

 

If you don't tell them what you want they will just go back to what it had stock, or what is cheapest. You can't assume they know you want performance exhaust most people would be mad if the shop put a more expensive performance exhaust on if they didn't request it. I can see them being a little ticked off if you are making requests that should have been made prior to the exhaust being made. Single exhaust would be stock for a 70 F250 and any 400, so they did what I would have done, unless I was told otherwise. I don't think you will hurt the motor at all but you very well could have lost some power.
-Johnboy

 

I live in a small town in Alaska, and they have worked on the truck before to replace the rear brakes. I should have told them that the engine was modified, but being female sometimes I hang back when it comes to talking to a mechanic. It really is amazing the things a person can be told about engines just based on gender alone. Though I guess I sort of "made it happen" in this case by not even trying. My thinking was because the truck had dual exhaust (though rusted and full of holes) when I brought it in, I thought they would just redo it and I could avoid the discomfort of having to discuss it. Realize it is my own fault though.

Thanks for your response and all the info.

 

If they put the stock big round "school bus" muffler on it you might gain something back by just replacing the muffler with something that flows better.
-Johnboy

 

The muffler is the more flat oblong type, and has two input ports and one outlet port. I think all the the pipes from the manifold back are about 2" diameter, including the tailpipe.

 

Well going back to duals would not be that hard then, on my truck I actually chose to run a dual in/dual out muffler because of the plastic gas tank and the transfer case just didn't have that much room. A single 2" outlet is pretty small for a built 400 and your muffler could be pretty restrictive too. Sucks having to tear into a brand new exhaust system, if the power loss doesn't bother you I would just leave it until the next time it needs exhaust. By the way welcome to FTE it has been a very useful site to me, I just noticed you were new.
-Johnboy

 

I agree with you , If I took it in and told them to redo it and it had duels , I would expect them to put duels on or at least ask me if I still wanted them . They fouled up not you .

 

Thanks. I have been reading this site for a while -when I have a question about something to do with my truck I can usually find an answer here. There are more than a few time when working on this "old" truck, that I hear "just get a new one". My truck has lived through quite a bit and is a part of me in a way, not about to desert it now. I consider myself lucky to have it, and like older trucks anyway.

I just measured the muffler and pipes this morning. The muffler is 22" long by 14" across by 4" in thinkness. Pipes, including tailpipe are 2.5". When it gets a bit more daylight out I will look for a brand name.

Thanks again

 

The response about creating more torque with a single exhaust has me wondering. Because I asked someone about that today and they said the same thing. Then someone else said that it should have dual exhaust.

 

You might try asking about this on the exhaust forum, it can get pretty complicated. If your exhaust is too big it hurts low end but you can also have it too small and it will hurt power down low too you have to find what is right for your engine. For a 400 you can run two pipes into a single but you would probably want at least 3"
-Johnboy