Topic: Best street usage 2.5 mods.

[dudley]

My 87 Comanche 2.5 with an Aisin 4 speed, manual steering and no A/C, is a street jeep only, other than hauling stuff.  I am interested in maximizing HP without destroying gas milage, maybe even improving it (get a bit over 20mpg now). I had the engine rebuilt about 1.5 years ago and as a start installed a Delta Camshaft that has barely a bit more lift and duration.  I have a single in/dual out flowmaster.  That is all my mods so far.  I want to add headers and an electric fan. What else could I do to help make it work better, like for passing, on the highway?
Eagerly awaiting suggestions!

[bidi]

You can definately install one of those drop in K&N-style filters for cheap.  You didn't say if you transmission was manual or auto, if it's a 4-speed manual, I'd say trying finding a 5-speed.  Not sure if that 4-speed is missing the low first gear or overdrive 5th gear, but you should still see a slight increase in mileage, specially if your adding is the overdrive gear.  Besides that, it looks like you've got everything covered on the "bolt-on" front.

You're actually getting really good mileage.  If you look at the mileage thread you'll see most are getting significantly less than 20mpg.  I get exactly that most of the time.  I'm planning on getting an electric fan myself, gotta see if it helps.

[neale_rs]

A turbocharger would be the way to go.  Several threads on this can be found in the Members' Projects forum.

[Mr_Random]

Yeah, well he wanted cheaper stuff...

Go through the hassle of upgrading to MPI like me! Woo... I'm still researching, finding new problems every day, but I'll give you the whole list of everything needed when I get done (hopefully within a month)

[neale_rs]

Yeah, well he wanted cheaper stuff...

Actually, he didn't say he wanted cheeper stuff.   

[Mr_Random]

Actually, he didn't say he wanted cheeper stuff.   

Haha, I'm stupid... woo

[dudley]

You can definately install one of those drop in K&N-style filters for cheap.  You didn't say if you transmission was manual or auto, if it's a 4-speed manual, I'd say trying finding a 5-speed.  Not sure if that 4-speed is missing the low first gear or overdrive 5th gear, but you should still see a slight increase in mileage, specially if your adding is the overdrive gear.  Besides that, it looks like you've got everything covered on the "bolt-on" front.

You're actually getting really good mileage.  If you look at the mileage thread you'll see most are getting significantly less than 20mpg.  I get exactly that most of the time.  I'm planning on getting an electric fan myself, gotta see if it helps.

What difference would there be IRT a drop in K&N and an add on conical for milage?  I am getting the impression some have found the conical can give too much air that hurts low end but helps high end. As I did say, I have the Aisin 4 speed. I have given thought to a 5 speed, but this 4 speed, after almost 300.000 miles, still shifts to first while moving, and is making no noise. I'm leery of what I might find in a 5 speed.  I will do electric fan.  Has anyone used Clifford headers?  I know pacesetter's are less expensive, but Clifford has been inline engines only for a long time!

[bidi]

I have the canonical air filter, and I can't say I remember a low end power difference.  I put it in almost 7 years ago.  Since this Jeep is my DD having power between 2k-3k RPM is important to me, since this is where I spend most of the time.  It does lag between 1k-1.5k though, really bad, too.

As for the headers, I'd say stay away from anything Pacesetter.  I bought their cat-back, about the same time I got the air filter, had to get it replaced after just 50k miles because the mufler completely rusted away.  It also hit my rear shock most of the time, specially when the muffler started rotting and the tail pipe loosened.

[Mr_Random]

There probably wont be much gain from headers, and like jeffy always says, "You'll lose the scavenging effect." You may gain a ponie or two up high (4k-5k), but you'll lose low end torque (which matters more in a street application).

An electric fan would counteract the negative effects of more air flow, it significantly decreases the amount of force needed to overcome the fan's offset reciprocating inertia, freeing up a ponie or two and moving the torque curve lower on the RPM range.

If you can balance everything out, you'll get as much as 10 hp (less of a torque gain, though) at about the same curve as before.

As said before, changing air flow just moves the power around on the curve. The only TRUE gain would be from taking that extra weight off the engine and using the electric fan.

[dudley]

There probably wont be much gain from headers, and like jeffy always says, "You'll lose the scavenging effect." You may gain a ponie or two up high (4k-5k), but you'll lose low end torque (which matters more in a street application).

An electric fan would counteract the negative effects of more air flow, it significantly decreases the amount of force needed to overcome the fan's offset reciprocating inertia, freeing up a ponie or two and moving the torque curve lower on the RPM range.

If you can balance everything out, you'll get as much as 10 hp (less of a torque gain, though) at about the same curve as before.

As said before, changing air flow just moves the power around on the curve. The only TRUE gain would be from taking that extra weight off the engine and using the electric fan.

Agreed on the electric fan.  Freeing up the engine is always the best.  When it comes to headers, Clifford claims theirs will gain you a decent percentage of hp increase.  I know those are only figures they put out, but given they are seriously into inline engines, I might believe them.  As far as I learned, giving an engine the ability to better breath in, as did fuel injection over carburation, and breath out, like allowing for more even back pressure in the exhaust, does increase hp, torque, and milage.  What am I missing here IRT scavanging in all this?

[Mr_Random]

Agreed on the electric fan.  Freeing up the engine is always the best.  When it comes to headers, Clifford claims theirs will gain you a decent percentage of hp increase.  I know those are only figures they put out, but given they are seriously into inline engines, I might believe them.  As far as I learned, giving an engine the ability to better breath in, as did fuel injection over carburation, and breath out, like allowing for more even back pressure in the exhaust, does increase hp, torque, and milage.  What am I missing here IRT scavanging in all this?

your comment on even back pressure has to do with scavenging. IIRC, having the correct amount of back pressure can create a vaccuum in the combustion chamber that more efficiently pulls intake air in, and everyone should know that more air means more power!

Thinking about it more, a higher flowing header with the stock 2.25" pipe would probably be very beneficial. I THINK it's mainly the diameter of the straight pipe that determines the scavenging on the port end, and if the Y connector on the header is slender/long enough, it can add it's own scavenging effect to the mix.

Okay... all this talk is hurting my brain... Good luck anyways!

[dudley]

your comment on even back pressure has to do with scavenging. IIRC, having the correct amount of back pressure can create a vaccuum in the combustion chamber that more efficiently pulls intake air in, and everyone should know that more air means more power!

Thinking about it more, a higher flowing header with the stock 2.25" pipe would probably be very beneficial. I THINK it's mainly the diameter of the straight pipe that determines the scavenging on the port end, and if the Y connector on the header is slender/long enough, it can add it's own scavenging effect to the mix.

Okay... all this talk is hurting my brain... Good luck anyways!

That's what I was thinking IRT scavenging.  The idea of headers is to create a fast, but not too fast, escape of exhaust .  I talked my family into helping me get the header Clifford sells for the 2.5 for my birthday.  They feel sorry for me since I am turning 60.  Clifford deals with inline engines only. Jack Clifford was the driver of a stock Hudson in the 1950's that was cleaning up on even the early hemi's at drag races. After then working in Aerospace for a while, Ford hired him to beat the chevy team.
The tech guy swears it will gain a minimum of an 18% hp increase over stock.  He says they developed them when the 2.5 came out, so the dyno info is gone, but he said this header, when bolted on to a stock engine, cut 2 seconds off the quarter mile time in their tests. But, he say you have to go with 2 inch all the way back.  I will ask him about the stock 2.25 head pipe, if that would hurt the scavenging.
So, after I get this header paid for, and can get a hiflow catalytic converter since mine is older than the hills, I will bolt them on and do a "seat of the pants" dyno test.

[Mr_Random]

That's odd?? 2" instead of stock 2.25"? I bet the stock will be fine... but might as well ask him!

Haha... I'm turning 18 in... 40 days, but any presents there will be for upcoming college!

[dudley]

That's odd?? 2" instead of stock 2.25"? I bet the stock will be fine... but might as well ask him!

Haha... I'm turning 18 in... 40 days, but any presents there will be for upcoming college!

Only soon to be 18? You pretty smart for a young-un! At your age I was working on a 55 chevy station wagon that by the time I was 21 had a 327 in it with 525hp.  Now, since I will be 60 next month, it's probably not good for me to have that kind of HP.  Thus, my working on "hot rodding" a 4 popper!   

[GeorgiaYJguy]

Dudley, Since you did some old school working I'm sure you know a simple tune-up and properly gaped plugs will make a big difference. There aint much you can do to the 4popper to get some real power. Having a slight vacume leak will reduce your power. Just give it a good look over and check it out. If you want to go big you can cut the cylinder .010, .020, or .030 over and add some bigger pistons. Not much for a cam that I have found unless you spend a million bucks and custom cut one. As your fuel intake you can get creative with a dremmel tool and clean out the casting scabs. A header is never a bad idea neather is a Aftermarket air intake!