4JB1T Performance increase with a 2.5" Exhaust

[Dayno]

Hi all Isuzu Fans,

Im just a new Bloke here but I have noticed that on the topic of new Exhaust systems for the ever popular 4JB1T, that there are mainly just alot of opiniouns being tossed around and no real hardcore FACTS. So for those that are hunting for statistics, Im going to bite the bullet and fork over close to a Grand and get a 2.5" mandrel bent exhaust straight off the face of the turbo. And too top it off afterwards its being sent off to a Dyno to get tuned and to get statistics for us all.

I booked my Rodeo to get it done next Tuesday. Currently the exact details of the setup are in its drawing board stages however ill take photos of before and after it gets done to show what it will look like. The Bloke that im getting to do it is a local in Caboolture (Brisbane) so although he is charging $622 just for the exhuast before the Dyno, You pay for convience of being close to home. So stay tuned until next week for the finnishing product.

[dasnoboarder]

Hi dayno

I've been around to see a few posts on 2.5", 3" and mixes of the two exhaust systems for the 2.8.

I'm waiting to do my body lift before I do my exhaust (4JB1T as well).

Will be interested to see your results .

Someone needs to do the same with a 3" system haha.

Cheers.
Andy.

[Jimmu]

I am not sure what statistics you are after but there is a fair few dyno sheets on here with 2.5" and 3" exhausts.

3/4 of the benefit of a bigger exhaust is only evident when the fuel and boost has been adjusted to match.

As such getting a dyno result with just the exhaust only tells 1/4 of the story.

One thing I can say is that the exhaust made f**k all difference on mine until I got the dump added.

Jimmy

[Dayno]

Its 3" coming off the face of the turbo (including the dump) then shrinks down to 2.5" after that also when it goes for a Dyno reading it is getting tuned as well which is what makes my 600$ into close to a grand depending on how much time the mechanic spends adjusting the pump.

[Jimmu]

That should put a smile on your face.

What boost you planning to run?

Jimmy

[Dayno]

I have being told by multiple people that 14 is sufficent boost for what i wish to do, which is mainly driving out the back of Mt.Mee and Glass House mountains. I also currently do a Beach run every weekend from Bribe Island upto Colundra and back and thats with everything completly stock still (except for the suspension), so ill be interested to see if i wont need to Rev the engine so hard to get through the soft patches of sand on the beach.

@ Andy -
I also got quotes on a 2" lift for my Rodeo today and the best was $2450......Leaf springs cost wayyyyyyyyyyyyyy too much to bother with for now i reakon. Is your setup Leaf Springs or Coils?

[dasnoboarder]

If thats a message for me, I've got the standard MU suspension at the moment. Rear leaf springs and front torsion bars.

When I do my suspension lift, I'll be buying a pair of Lovells (or other brand if I can't get hold of Lovells) 2" lifted leaf springs for the rear (a few hundred bucks), and then just wind up the torsion bars to match on the front.

When you wind up the torsion bars, the wheel alignment goes out and needs to be redone. If they can't get the right alignment after the lift, it's common to do a ball joint flip to help.

If you want to find out more about the ball joint flip, go to the ClubIsuzu.com homepage, click repairs & modification and theres a file there that explains it in detail.

Cheers. Andy.

[mudgrip4]

Just regarding bigbores and tuning - got into tuning my latest 2.8 this weekend. On Friday put a 2.5 bigbore from about 15" down from turbo and that helped considerably - JamesW gave me an old bigbore from a wrecked bighorn.

And today took truck over to a mate - a diesel mechanic - and in about 1 hour he advanced the injection pump timing and we tweaked up the diesel. Result a very much quicker 2.8 - not quite as quick as my last 2.8 which dynoed at 155hp, but from experience I'd say this one has gone from standard 110hp to about 140hp, with a bit more to come with addition of snorkel and K&N filter. Now very good power from 60ks on and accelerates very strongly in all gears.

Not quite as much low down torque as my earlier truck which had a 2.5 ex turbo - I've a feeling the first bit of pipe does need to be bigger bore also - as Jimmu notes above - for max grunt down low. However a huge performance gain at very little cost.

For Dayno - any diesel shop can do the injection pump timing and diesel tweak - one hour tops for very good performance gains - no need for hundreds of dollars here.

Mike

[Dayno]

Oh is that so? Ill be sure to talk to the bloke when i take the Rodeo into the shop in about an hour so it can get done in the morning while im at work, and make sure he doesnt charge the arse out of me. Its a shame when my trade of Sheetmetal Fabrication doesnt cover anything related too mechanical work. Mungrels like the first exhaust shop i went too try to pull the wool over your eyes and try to suck you into getting something done that is completly useless for your needs and then expect you too pay top dollar for it.

For Mike - Thanks for the tip, ill look into it this afternoon.

[mudgrip4]

One thing I need to add Dayno - if your truck has an electronically regulated fuel pump it is not so easy to adjust. The simple pump to tune is the mechanical system - pre about 94

[Dayno]

Have no fear Mike, I just got back from the long bike ride home -_-..... but i found out how it became close to a grand for what im getting done. heres the price list.

2.5" Exhaust from the Turbo back with a 3" Dump - $622
Dyno + Advancing the fuel and timing - $220
Boost Controller - $99
K&N Filter - $150 <--- however i already have a POD
- $150-
= $941 Total

My Rodeo is a 92 so i dont believe its Electronic however apparently the Deisel mechanic thats supposedly gonna do it does half a dozen Dyno tests after each tweak to get it done right, which in turn takes alittle longer then an hour, Thus is $220. Considering Caboolture is a relativly low tek town, if i wanted to get it cheaper id have to drive to Burpengary which would leave me no possible way to get home, so providing that the overall outcome is that i get a worthy increase in power and can utilize the Turbo better im happy to pay the near 1k total.

[mudgrip4]

Given that you've fitted a full bigbore plus dyno and filter etc, a grand is not too bad. You will find it is a different truck to drive - will pull like hell from v low revs and be quick indeed for a diesel. Let us know the results

Mike

[Dayno]

You know ive being hearing that alot lately, That it will feel like a totally diffrent truck. I just asked my father if i could borrow his car to goto work 2moro and had to explain why i couldnt take the Rodeo to work, unfortuantly he doesnt see the good side of me "Wasting money on a car thats nearly 18 years old blah blah blah" Although the Rodeo is a 92 its being reasonably well looked after, it has very few battle scars from 4x4ing by the previous owners and given how it has a new 4JB1T thats only done 50,000k's i feel that it is worth me spending some money on it to get the most out of it as i plan to keep it for quite sometime. But anyway, long story short i got the "you know what" blown out of me for not telling him i was gonna get all this done so we had a huge arguement at dinner and he aint too happy with me atm, he reakons if it comes back home 2moro and the exhaust is louder then the engine he'll rip it out. So for all this trouble im going through it better be worth it!

[Jimmu]

Sounds like you need a new crash space more than a dyno tune!

I paid pretty much the same $ for the same gear a couple of years ago so you are doing well. Just make sure the 2.5" is Mandrel bent if they can only do pipe bent get a 3" system as they are practically the same once the bend restrictions are taken into account. 2.5" pipe bent is definitely too small for this engine.

Jimmy

[mudgrip4]

Jimmu - you mentioned a 3" dump pipe made a big difference. How long was that 3" bit. Mine is still running a 2" from the bottom of the turbo to the first flange joint - about 15 inches down. Half considering making this a 2.5-3 inch dump also but wonder how much actual difference this little bit will actually make, as on closer inspection I notice also the whole 2.5" pipe from there on is actually press bent and not mandrel bent which means some bends it narrows to about 2". So may not be worth any dump pipe alteration. Still pleased with performance however and haven't fitted snorkel or filter yet which will help it breathe better again.

Dayno - good luck with the olds - can assure you the bigbore does not make for a noisy vehicle when you're not revving it hard - just a different sound. Suggest you drive it quietly up the driveway and the old man won't notice...

Suggest also your development work is no bad investment in the rodeo, as these trucks - unlike alot of other vehicles - are very long lasting if looked after. There is one 4JB1 here in Chch with over 1,000,000ks on it and going well, and know of another with 500,000ks plus which is also fine - unlike most cars etc which your old man may be comparing it to. The 4JB1T is one of the best small diesels to come from japan and if you've got one done 50k, you're a lucky man.

Mike

[Dayno]

Ahhh yes, the long awaited and highly anticipated day "TUESDAY" , Today i got the Rodeo back and after forking over $1035 (which made me cry alittle inside) Immediatly apon starting it up there was a completly diffrent sound which shocked me considering its on idle. Taking it for its maiden drive home, I fed it off the mark at lights and through various gears and i was definantly impressed, i have alot more pick up at low end and is slightly more responsive too boot. The new 2.5" exhaust as mike said does not make for a noisy system however it has a much deeper and more truck like note to it, which im not complaining in the least bit about.

The second item on the agenda id like to point out is the Dump pipe. Unfortuantly or Luckily (depends which way you look at it) The boys down at the shop couldnt remove the stock pipe and the boss said he'd rather not cut it off and cost me more money for a custom connection. So inclosing although im losing possibly 3 - 5kw? at top end. I was told today that in its current state putting a 3" would do 1 of 2 things for me. either do very minimal in the way of power increase, or it would probly blow up the Turbo. Which now btw whistles off its head. I never used to be able to hear it spooling up until 3 grand inside the cabin over the engine sound however now its definantly hearable probly from 2500 - 3200 (although it starts outside at around 2100).

So unfortauntly the Dump pipe seems to be a topic of much personal prefrence as i can't disprove it in anyway, however i can say that even though i still have the original im in no way dissapointed that i couldnt get a 3". In all honesty if anyone feels that the dump pipe is a must then i say "Be my guest and get it done" however with my results without getting it done i dont see a point really.

I have a dyno graph for the results however i personally do not own a Scanner, so please bear with me, while i text a few mates and see if any of them have a scanner i can use to post the results for you all too see. I do however have the pictures of the before and after work, so tonight ill post them after dinner.

[geeves]

While a larger dump pipe does make a big difference a large gain can be go from just improving everything behind the dump pipe like you have done. I believe the rodeo is pretty much the same as the bighorn and a 2.5 inch dump pipe is a pain to get round the oil filter housing A 3 inch would be near impossible and would probably need removing to change the oil filter. One way round this is to use an oil filter/cooler from a 3.1 engine as it sits on an angle.
A turbo that squeals is not good. It is either surface cracks in the impeller housing which although noisy is harmless or something bad about to happen

[Jimmu]

Mike: The one on mine is 2.5" and goes to the flexi joint.

I have run the Mandrel 2.5" with both the standard dump and custom dump and can assure you it makes a very big difference. I would say it made more of a difference than all the other mods I had done to date combined. If you want a drive sometime Dayno just let me know

Jimmy

[Dayno]

Sorry for the delay guys, Iv'e had a very busy week so far so havnt had the time to post the results so here they are now.

Remeber this is just from tuning the pump and an exhaust nothing else, The exhaust is 2.5" mandrel bent from dump pipe back, as a 3" would not fit with the current oil filter i need to look into the 3.1L filter as has being recommended in other threds as it sits on an angle which allows room for a 3", so when i get that done later down the track we can finnally test the dump pipe theory.





Heres the before shots............................













As you can see in some of the pictures, 16 years of beach runs of occasional 4x4 use, rusted the hell out of the flanges on the exhaust and along the bottom of the pipe too. also the muffler was starting to get pretty old so was time for a new one anyway.

[Dayno]

And this is the After job pictures =D














Im not too sure about why the muffler had to be put on.... i was sure i asked for straigh through without one, but meh, whats done is done i guess. Well there you have it folks, just from a tune and 2.5" mandrel bent exhaust i gained a very noticeable power increase without a dump pipe change. Now if the dump pipe really makes a large diffrence ill be getting it done next probly towards the end of the year september/november.

@ Jimmy - Id love to take you up on your offer for a drive sometime just to see the diffrence in power. What are you doing this ANZAC long weekend? maybe we could plan a trip somewhere or something.