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I'm in the same camp WRT exhaust size, for a low rpm build 2.5" pipe is what you want, this will maintain exhaust gas velocity which improves cylinder scavenging and maximize low rpm torque. The stock exhaust is restrictive however, the cats probably aren't bad if they are in good shape but the head pipes compress down to close to 2" in the curves and the stock muffler is a real cork. I had a full MAC exhaust system on my '89 5.0 truck that was a 2.5" single all the way though and it produced the best throttle response and torque I have ever seen from a 5.0, I don't think it is made any more but it wouldn't be hard to replicate.
I'm in the same camp WRT exhaust size, for a low rpm build 2.5" pipe is what you want, this will maintain exhaust gas velocity which improves cylinder scavenging and maximize low rpm torque. The stock exhaust is restrictive however, the cats probably aren't bad if they are in good shape but the head pipes compress down to close to 2" in the curves and the stock muffler is a real cork. I had a full MAC exhaust system on my '89 5.0 truck that was a 2.5" single all the way though and it produced the best throttle response and torque I have ever seen from a 5.0, I don't think it is made any more but it wouldn't be hard to replicate.
So, would the cheap, bolt on shorty headers be an improvement over the stock manifolds ?
I was looking at the Summit/Pacesetter set. I would probably continue to run no muffler.
Another good thing with this setup, I can run the air pump as intended.
Years ago I went to the parts store to get a Flowmaster aluminized. The stock mufflers, with my short commute, were rotting out almost annually. I asked to order the quiter series as he only had the standard in stock. He said that with the two cats, the standard would be fine. "Hell, you don't really even need a muffler". I bought a strait piece of pipe. He was right. It's plenty quiet.
With the mods you have planned this motor is going to breath a lot better than stock so yes shorties would be an improvement as long as the factory Y pipe/cat is changed as well.
This was the system I built for my 89 Ranger: Shelby Tri-Y's into a 5"x 12" equalizer chamber (my own construction) then into dual 2.5" pipe into dual 2.5" dynomax Turbos and dual 2.5" pipes over the axle and out under the bumper. Sound was smooth with just enough noise to let you know it was there. I ran this with 5 different engine combos, from a stock 88 Crown Vic 5.0 to a 400 HP 331. Never put a cork on the 331 with it, it would pull to 6500-7000 rpms. Shorty's in my opinion are preferable to the stock iron manifolds. I went with PaceSetter coated shorty's in my 96 E150 but had to replace both when they developed cracks in the collectors. This was about 3 years ago after they were about 3 years old. I suspect the cracks were from the different expansion rate with the thermal coating. I replaced them with Summit's house brand plain steel shorty's and so far so good.
You (Conanski) told me long ago that I may be able to use such a cam with flat top, no valve relief pistons if the E6SE heads are used. (I have also recently read your sort of glowing review of the E6's benefits from back in '06) I need to mock up the heads with the cam and check that out. Also check to see if the E5 valves clear with the stock cam.
The E5s with valves at full lift.
Expounding on the matter of piston/valve clearance with flat top, no relief pistons. I just did a check of clearance with the .444" lift HO cam in a '88 Crown Vic engine with these pistons. With E5TE heads, I got good clearance.
I didn't measure the clearance with the E6SE heads. It looked like a quarter inch.
Hard to tell from the pics but was the exhaust valve the closest?
The chamber in the E6 heads is really deep so I suspect valve clearance would be even greater
If you look at the 1st photo up in the quote, it looks like the intake would be closer. I botched that measurement and didn't redo it. As mentioned, the valves on the E6 were what appeared to be a quarter inch or more.
I'm thinking about installing this well used Crown Vic engine with the HO cam and the E6 heads. It would be temporary until I get my permanent engine built. The machine shop is the hold up. I was told two weeks on June 5. Next week will be two months.
