HP gain expected

[Cjmartz2k]

Unless your running 32's with stock 3.07's (like me), then you'll sure as hell notice it

 

[xuv-this]

It all depends on what you want to use your engine for, and YOUR engine. For 90% of the people in this forum, having a somewhat restricted exhaust to boost the torque for low end is what is more beneficial. This bit of restriction is simply a jerry rigged way of doing it though, but it does work just fine. And some gain is better than no gain at all.

But to better answer the question. The pipe sizes are determined by the flow characteristics of your engine. Read through that article I posted links to above, buy some of Vizard's books, etc.

My guess is that most of the people here who have ran with an extremely free flow exhaust and thought there was a huge loss in low end had it predetermined in their head that the loss was going to be there. And as a result, "felt" it. Yes, if you are offroad and crawling rocks, you are indeed going to notice a loss of 10wtq below 1500k. But for those of us who run daily drivers, the 130+wtq on the ground at that point is MORE than sufficient to get you beyond 1500k before you even realize it, up to the point where you're in the 3000k range and are now gaining 2-3wtq over what a more restrictive aftermarket exhaust would be giving. I mean hell...our engines can put out more torque at idle than most daily driver engines puts out at peak...

So I really do think that people who complain about the low end power being reduced, really just have it predetermined in their head that they aren't going to like it. At the RPMs it is lost at...you simply are not going to notice the loss unless you are offroad. Butt dynos aren't that sensitive

iff you have a mostly stock 90 or up, please take your exhaust off from the header back and drive it. you can speculate all you want, but if you just do it, you will see the accelleration loss that we are talking about for yourself. it's VERY noticable.

 

[phaythe]

I have a 97 with an open exhaust. I HAVE done it. I daily drive it that way. And I notice it pulling like crazy at 4k. This isn't speculation. Yes, there is noticeable loss at low RPM. But once I hit 2k, there's a very noticeable gain in power. Around town, some people would hate that loss. But I dont' mind it. 130wtq is still PLENTY of power for cruising from a stop when you're only going to hit 35mph in traffic. But when powerbraking (yes, manual swap is in my Jeep's future) and launch at 2200...I can take damn near anything off the line...sadly, once 3rd gear comes into view...I'm done for. But that's what the tranny swap is going to fix

Like I said...you've gotta tune your exhaust for what you're using your engine for. I race mine. Backpressure is the devil for high end power. If you never take YOUR 4.0 to 5k+, then yeah, it's pointless. But I do, and I actually use the benefits of open exhaust.

 

[Cjmartz2k]

I assume you have a 97 4.0, right? I'll race you with my full exhuast and prove my point to you if you want

 

[CRASH]

I run a 2.5" on a 4.6, and it regularly sees 6k. Very pleasing.

I built a 2.5" for Jes's 4.0, and he has not complained about the low end, but he is geared even lower than I am.

We both cruise at 3,000+ at 70mph, and the gain in fuel efficiency is quite notable.

I think cam choice has WAY more to do with bottom end than the size of your exhaust.

 

[John(XJ)Jeep]

I can hit 240kph @ 6500 in 4th gear with my Jeep right now and have a dozen witnesses that say I did. Do you think your your full 2 and a quarter exhaust can help you hit even hit 200? Can you put it in 2nd @ 20kph, punch it and watch your speedo snap to 100kph? Because I've done that before too many times. I run open, no cat, straight racing muffler 3/4 length from stock with 75% of my pipe to be 2.75" dia.

I believe you when you guys say that scavenging improves your power at low but its not much and it can only take you so far. Believe what you want, do what you want, I don't care anymore. I just tired of it because you won't let go of it. It's in your head, that what was taught to you. So I have to respect your opinion.

 

[phaythe]

I think cam choice has WAY more to do with bottom end than the size of your exhaust.

VERY true. Hence why I'll soon be getting a cam that will move my powerband up...

And Cjmartz2k, saying something like "Oh, race me, I'll prove it to you" doesn't mean crap... What ELSE do you have under the hood? That's what makes the difference. Not to mention stock vs. stock, even if we had the same vehicle, subtle differences between the two would make the race uneven. Even off the factory line, camshafts off by a few degrees from each other, amount of casting flash on the intake and head, etc. can make the power output of the two vehicles vary by a LOT. Never have heard of anyone doing any testing of such things on Jeeps, but, as I am also a Neon owner, I have seen dynos of bone stock R/Ts that just rolled off the line, shipped to a dealership and sold to owners...vary by as much as 10 -wheel- horse because the camshaft tolerances were too slack off the factory line. So the only way of knowing if an exhaust system is better than another is by testing both on the same engine. And again, as I said...I'm tuning mine for all out racing. I'd like to see your exhast try to keep up with my engine's needs when I'm done with it... do I hear whispers? (...4.7 stroker.....T04 turbo...propane...5-speed autostick...)

But with that said, if you're in an auto, and don't have a stroker, boost or N2O, I'd love to Exhaust isn't the only thing I have done anymore...that was just the start...

 

[Dr. Dyno]

I can hit 240kph @ 6500 in 4th gear with my Jeep right now and have a dozen witnesses that say I did.

I'm interested to know how your 4.0 (or stroker) managed to reach 6500rpm given that the stock rev limiter is at 5250rpm. Did you have the PCM reprogrammed? How did your engine even survive 6500rpm? What parts did you use when building it?

 

[CRASH]

Renix motors don't have a rev limiter.

 

[Cjmartz2k]

Pahythe,

I meant it in a friendly way, but since you asked:

K&N FIPK
62 mm Throttle body & matching spacer
Ported and Polished head
shaved head (9.5:1 CR)
Crane 753905 cam
borla header
mandrel bent 2.5" back to the cat
high flow cat
dynomax cat-back exhaust
MAP adjuster
Adjustable CPS
Fireposer ignition
and a about 15 dyno pulls worth of tuning.

It runs 9.8's in he 1/8 (yes I have slips if you want to see them) and all that is with stock crappy 3.07 gears and about 200 lbs worth of subs and amps in the back. BTW, if we are counting "not done yet" as wanting a 4.7L stroker in the future, I'm not done yet either, but like I said man, I wasn't trying to be a weenie to you, it was light hearted. :-D

 

[xuv-this]

I can hit 240kph @ 6500 in 4th gear with my Jeep right now and have a dozen witnesses that say I did. Do you think your your full 2 and a quarter exhaust can help you hit even hit 200? Can you put it in 2nd @ 20kph, punch it and watch your speedo snap to 100kph? Because I've done that before too many times. I run open, no cat, straight racing muffler 3/4 length from stock with 75% of my pipe to be 2.75" dia.

I believe you when you guys say that scavenging improves your power at low but its not much and it can only take you so far. Believe what you want, do what you want, I don't care anymore. I just tired of it because you won't let go of it. It's in your head, that what was taught to you. So I have to respect your opinion.

heres what is in my head:
these are JEEP motors that we are talking about. not honda. they are not made to rev high or spool up quickly. when you lose power on the low end, the motor works even harder to spool up to where the exhaust makes good power. so it spools even slower than stock for more than half of it's powerband with no exhaust. i bet your 0-60 is in the 8-9 area, too. i agree with you in that they make better high end power. that's common sense. but even in mine, i found it not worth it for a DD because that powerband does not compliment our gear ratios, and the vehicle is as a result, slower overall.

see everybody, close ratio transmissions are good for rice machines because when they shift to the next gear, the closer gearing will not allow as much of a drop in rpm, so they will stay in their powerband. the wide gearing that we have does not compliment that mod well. like if you put in a cam to smooth the flow up top, and got lower rear end gears, your shifting would be closer to(or in) your powerband, but your top speed will decrease, and kind of annull the reason that you put that on in the first place. or get a different transmission, if there even is a suitible one that will bolt up to this motor.

all this stuff, and A LOT more are considered when auto manufactures design these things. this mod just doesn't fit in the "system". this exhaust is pretty much good for circle tracks, but there are other vehicles out there that have factory trannie/diff gearing that will be way better than that.

 

[CRASH]

Your argument makes no sense. If I shift into low range, then my motor RPM's will be higher for a given speed. Meaning I would want a motor biased towards the upper end of the RPM spectrum.

Where you want your powerband has NOTHING to do with how wide your powerband is. All cams are good for about a 4,000 RPM band. That could be idle to 3,500 or it could be from 3000 - 7000. Just depends on where you want the power to come in and drop off. Close ratio trannies are always better than wide ratios for acceleration purposes, and have NOTHING to do with top speed.

Bottom line, match your axle, trans, t-case ratios to the planned use. Then build an engine to operate within the parameters dictacted by your gearing choice.

CRASH

 

[Dr. Dyno]

Close ratio trannies are always better than wide ratios for acceleration purposes...

That depends. If the engine produces most of its torque at high rpm and has a relatively narrow torque band, then a close ratio gearbox would indeed keep the engine "on the boil". If peak torque is a long way below maximum rpm, a wider ratio gearbox would work better.

 

[phaythe]

Pahythe,

I meant it in a friendly way, but since you asked:

K&N FIPK
62 mm Throttle body & matching spacer
Ported and Polished head
shaved head (9.5:1 CR)
Crane 753905 cam
borla header
mandrel bent 2.5" back to the cat
high flow cat
dynomax cat-back exhaust
MAP adjuster
Adjustable CPS
Fireposer ignition
and a about 15 dyno pulls worth of tuning.

It runs 9.8's in he 1/8 (yes I have slips if you want to see them) and all that is with stock crappy 3.07 gears and about 200 lbs worth of subs and amps in the back. BTW, if we are counting "not done yet" as wanting a 4.7L stroker in the future, I'm not done yet either, but like I said man, I wasn't trying to be a weenie to you, it was light hearted. :-D

hehe, I meant to be light hearted as well, but suppose it didn't come off too much that way always glad to see someone that actually tunes their Jeep, wether for low end grunt, or high end power.

And yeah, you've got me there Did you pull off that time on your 32"s? That's impressive...hopefully I'll have my cams in by summer's end...gonna use the same cam. If I had a manual like you do though, I'd be doin' better

 

[xuv-this]

Your argument makes no sense. If I shift into low range, then my motor RPM's will be higher for a given speed. Meaning I would want a motor biased towards the upper end of the RPM spectrum.

yes, you would - if you intended only on drag racing for 60 ft times.

Where you want your powerband has NOTHING to do with how wide your powerband is. All cams are good for about a 4,000 RPM band. That could be idle to 3,500 or it could be from 3000 - 7000. Just depends on where you want the power to come in and drop off. Close ratio trannies are always better than wide ratios for acceleration purposes, and have NOTHING to do with top speed.

sorry; i'm not the best at explaining stuff. you don't buy a cam for power. more power here or there from a cam is a product of matching it to the mods to the motor and what you want out of it. the cam just helps the motor run better for it's intended purpose. and no, close ratio trannies are not always better. a honda 6 speed close ratio on a jeep w/o high gearing would result in shifting out of the last gear at 5k and into the next gear hittin' at like 4k. you would shift like at least once every second. but that honda redlines at 7k, giving him 3x the rpm's to go through. which is right in the intended powerband for it. long story short, close ratio trannies are better for cars that live in the high rpm band. but the diff. gears are totally different ratios than jeeps. lower diff gears in a jeep would put the shifting more into the higher powerband, so you wouldn't have to go through the lower rpm's as much and cancel out the advantage of the mod(s).<dammit i need to stop tryin' to do this because this is gonna take forever for me to explain>

Bottom line, match your axle, trans, t-case ratios to the planned use. Then build an engine to operate within the parameters dictacted by your gearing choice.

likewise, but my point was that if you start with tryin' to mod a jeep motor just for high rpm's, then you will have to redo everything else for it to be worth a damn.

 

[John(XJ)Jeep]

I'm interested to know how your 4.0 (or stroker) managed to reach 6500rpm given that the stock rev limiter is at 5250rpm. Did you have the PCM reprogrammed? How did your engine even survive 6500rpm? What parts did you use when building it?

First theres no rev limiter or anything like that. Second if I told you what I did to it I'd have to kill you, even my buddies don't know what I did to it. Its' not a stroker and on top of that I can rev and hold 6500 rpm any higher and it starts to vibrate if under load, idle is different story but I can hold it longer but I don't like to do just because. I would never hold it at that rpm for more than a few seconds or so under load. Heres a hint though on what could have been done, it is a special built show model or should I say once was. Its power output is higher than factory roll-off Jeeps, considerably. I got lucky I guess. :laugh3:

 

[Cjmartz2k]

6500 rpm on a stock motor? ummmmmmmmm......

Paythe,
no, I've got a set of 30's that I drive on long trips that I did that on. I'll be with the traction my swampers get me, a 4k rpm clutch drop would result in one of two things---the front tires coming off the ground (this is a TJ) or a blown up tranny/transfer case/rearend/or something like that--and I got my money on the later ;-)

 

[John(XJ)Jeep]

If you can't pull a wheelie on a stock TJ you shouldn't be driving, That's easy to do. A buddy from school bought a TJ (about 5 years ago) and used to do wheelies in the parking lot. Wasn't even hard for him to do. Just even taking off slightly hard you can see the front end almost lifting off the ground.

6500 RPM is unbelievable to some of you folk eh? Its nothing for me. I can blip the gas and it reaches 4000. It sounds like you haven't seen that high in a Jeep engine. I bet most of you are scared of even thinking going 4500 RPM.
Look, you just got regular factory engines that you have to deal with... I don't. Simple as that. Deal with it. :wave:

 

[Cjmartz2k]

OK, I'm gonna have to call BS now.

 

[Purple]

bullshit, canadian bullshit