Tuning exhaust bore size vs performance

[TJet120TJet]

Hi again im on the search for an exhaust system, not too fussed with taking out the cat as ive had a few bad experiences with lambdas etc :yuck: so im after a catback..

..so im looking for a decent custom exhaust, i know theres a few threads on this but i wanted to ask what the best bore size i should go for.. im not bothered about sound (dont mind if its a little louder) i just want it for pure performance.

so here comes the question..
my m8 said that 2.5" might be a bit too big for a small 1.4 turbo is this true??

also another question: bear in mind that its just everything after the cat im changing, would i feel a lot of difference with a 2.5 catback straight thru to an aftermarket backbox (all middle boxes out)? it wouldnt be too loud would it? i had a bit of a warning from the garage by me but you lot kno more about the tjet so im askin what you think

had a quick search but found no answer, i know ive been askin a lot lately but would appreciate some feedback on this one, thanks alot all

 

[punto_matt]

I have 2.5" cat back with no middle box its fine. 2.5 wont be too big, just means the gasses can get out quicker which is what you want with a turbo car. How loud is it will depend on how big the backbox is.

 

[TJet120TJet]

I have 2.5" cat back with no middle box its fine. 2.5 wont be too big, just means the gasses can get out quicker which is what you want with a turbo car. How loud is it will depend on how big the backbox is.

just what i wanted to hear cheers Matt
one other thing about it, i read somewhere (and i think it was you Matt..) someone said powerflow (which i was looking at to do this for me) werent very good.. also another garage by me told me they arent too good.. but how wrong can they go to just stick a straight pipe and a muffler from the cat back?? is it the quality of the materials or what that makes them not very respected

 

[trich926]

just what i wanted to hear cheers Matt
one other thing about it, i read somewhere (and i think it was you Matt..) someone said powerflow (which i was looking at to do this for me) werent very good.. also another garage by me told me they arent too good.. but how wrong can they go to just stick a straight pipe and a muffler from the cat back?? is it the quality of the materials or what that makes them not very respected

quality of steel, workmanship, welds etc.
Whereabouts do you live?

 

[TJet120TJet]

im in wolves Trich, and to be fair there are a few fitters about but they all think of themselves as the best
dont know who to ask.. part shops only recommend top brand makers who they deal with etc etc!

i just want a bit of steel tube that takes waste gasses to the rear of my car... its not rocket science lol i cant understand how anyone can muck up an exhaust fitment

about the quality of steel.. even if it isnt top grade stuff, surely any stainless steel exhaust should outlast the car its fitted on, no?

 

[Titish]

i have a t-jet Gp ..can i remove the catalyser box and the middle one and keep the original backbox with a free flow direct tubes or would i get a check engine warning because of the sensors..and what is the suitable inch to have lowest noise with good performance..thanks

 

[punto_matt]

Powerflow is just a franchise. You can get good ones and bad ones. If its a bad one then the welds will be crap, will be built badly and probably wont sit that level. I had my midbox cut out at powerflow before i got my cat back exhaust. Cant say i will ever be going back.

 

[smokeyjoe03]

Powerflow is just a franchise. You can get good ones and bad ones. If its a bad one then the welds will be crap, will be built badly and probably wont sit that level. I had my midbox cut out at powerflow before i got my cat back exhaust. Cant say i will ever be going back.

and from what I hear Mr Tyre on the Stafford road (A449) near five-ways island in Wolves are a quite reputable suppier of powerflow exhaust systems, loads of friends of mine use that garage and none have had any complaints yet.

 

[TJet120TJet]

Powerflow is just a franchise. You can get good ones and bad ones. If its a bad one then the welds will be crap, will be built badly and probably wont sit that level. I had my midbox cut out at powerflow before i got my cat back exhaust. Cant say i will ever be going back.

and from what I hear Mr Tyre on the Stafford road (A449) near five-ways island in Wolves are a quite reputable suppier of powerflow exhaust systems, loads of friends of mine use that garage and none have had any complaints yet.

cheers for that m8 its right by me, i just rang for a quote: 250 - 300 for cat-back but the bloke said it all depends on which backbox i choose.. sounded like he knew his stuff but was surprised when i asked for a 2.5 bore.. dont know whether to do what Matt did and just go for 2.5, bloke recomended 2inch .

 

[Percyhahn]

im sure that anything bigger than 3inches is to big, and the power starts to drain a little.

 

[George ncl]

I had the opportunity to test out dozens of different exhaust setups on Tjets (mine and friends cars) running mapped and on VL36 turbo.All I can say is that suprisingly enough the stock backbox even if it reduces the noice by far much, it wont be that restrictive as most people believe.The best performance I have seen on a VL36 tjet engine was the following: stock middlebox,stock cat removed and inox staight pipes replaced these parts.The rest of the exhaust was completely stock.The engine was running suprizingly high boost on high rpm range without sacrifying the overboost (low rpm range power).

P.S.All road tests were performed with the usual OBD2 data logging procedure on the same road place and on quite similar weather conditions in order to have as accurate results as possible..

P.S2 Dont go with anything bigger than 2.5'' catback.Even 2.5'' is quite big to be honest..2.5''downpipe and 2'' would be ideal imo unless you are after a big turbo setup and your power target is 230+bhp..

 

[TJet120TJet]

im sure that anything bigger than 3inches is to big, and the power starts to drain a little.

yeah thats what my missus always says

I had the opportunity to test out dozens of different exhaust setups on Tjets (mine and friends cars) running mapped and on VL36 turbo.All I can say is that suprisingly enough the stock backbox even if it reduces the noice by far much, it wont be that restrictive as most people believe.The best performance I have seen on a VL36 tjet engine was the following: stock middlebox,stock cat removed and inox staight pipes replaced these parts.The rest of the exhaust was completely stock.The engine was running suprizingly high boost on high rpm range without sacrifying the overboost (low rpm range power).

P.S.All road tests were performed with the usual OBD2 data logging procedure on the same road place and on quite similar weather conditions in order to have as accurate results as possible..

P.S2 Dont go with anything bigger than 2.5'' catback.Even 2.5'' is quite big to be honest..2.5''downpipe and 2'' would be ideal imo unless you are after a big turbo setup and your power target is 230+bhp..

right thats a good bit of knowledge there thanks George, i will be getting the VL36 in the future, but not just yet.. that was why im thinking if i get the 2.5 now with a new map, then when i get the new turbo i dont have to do too much with the exhaust (as u say, bored out downpipe) and high flow cat.

you think there would be a power loss if i were to remap with a 2.5 rather then 2"? or just unnecessary? if its mapped to incorporate the exhaust then i wouldnt have thought thered be a problem?

thanks for the informative reply again

p.s it wont let me thank you.. think ive run out of thanks's
ill have 2 try again 2morro lol

 

[howsaboutno]

A bit off topic but will an Abarth Backbox fit onto a tjet mid pipe without a collar etc?

 

[nickkk]

Powerflow in kford Tyres are good, been there a few times my self and know people had full systems made up and all are happy!

 

[George ncl]

right thats a good bit of knowledge there thanks George, i will be getting the VL36 in the future, but not just yet.. that was why im thinking if i get the 2.5 now with a new map, then when i get the new turbo i dont have to do too much with the exhaust (as u say, bored out downpipe) and high flow cat.

you think there would be a power loss if i were to remap with a 2.5 rather then 2"? or just unnecessary? if its mapped to incorporate the exhaust then i wouldnt have thought thered be a problem?

thanks for the informative reply again

There is another concept that you might not have thought of. You could bolt on a VL36 turbocharger and get the engine mapped, running on completely oem exhaust.That would save you some quid while at the same time the engine will produce more bhp, hence more smiles per money spend ratio!
150bhp Bravo's are running on VL36 turbos and when running with oem exhaust system can easily see 170bhp while whatever you do with VL37 turbocharger(intercooler,cams,actuators,etc - you name it) you will not gonna see more than 165bhp and your turbo unit will be running well beyond its limits(exceeding compressor map choke limit).

If you insist on having an aftermarket catback though asap, it would be unnecessary to swap catbacks for every single part that you add on(unless you add a T3 Garrett turbo :devil: ). Power wise the difference wont be that massive and definately not easily noticeable.Go for 2.25'' or 2.5'' catback so you have some good foundation when you will add more parts - in order to gain more bhp - in the future..

 

[TJet120TJet]

There is another concept that you might not have thought of. You could bolt on a VL36 turbocharger and get the engine mapped, running on completely oem exhaust.That would save you some quid while at the same time the engine will produce more bhp, hence more smiles per money spend ratio!
150bhp Bravo's are running on VL36 turbos and when running with oem exhaust system can easily see 170bhp while whatever you do with VL37 turbocharger(intercooler,cams,actuators,etc - you name it) you will not gonna see more than 165bhp and your turbo unit will be running well beyond its limits(exceeding compressor map choke limit).

If you insist on having an aftermarket catback though asap, it would be unnecessary to swap catbacks for every single part that you add on(unless you add a T3 Garrett turbo :devil: ). Power wise the difference wont be that massive and definately not easily noticeable.Go for 2.25'' or 2.5'' catback so you have some good foundation when you will add more parts - in order to gain more bhp - in the future..

again.. another great reply George, the reason i didnt want to get the VL36 with a map yet is cause ill have to get the new FMIC as well, id want to do that in one go.. and being as im a touch of death to all cars i tinker with myself, id have to get a garage to do the work
so id have to pay for turbo, FMIC, LABOUR and map on top..
im a procrastinator so i couldnt just fit the turbo while were in the cold weather and do the FMIC later on as id never get round to it :bang:

anyway i wasnt thinking about changing the catback after i got the system, i was just going to work further up the pipe, so change the cat, downpipe and mani, as you say, make a good foundation for future messin..

but you make a good point.. you say it wont take much to push the '37 to its limits.. well if i do go ahead with my plan and do the catback and remap first, (its only to get a bit more whoosh for the time being) then i wont bother with any other things, (IC, cams, etc) until i get the '36 and then ive only lost out on the cost of one map..

anyway cheers for checking out the thread and sharing your experience, your a proper credit to this site m8

 

[George ncl]

again.. another great reply George, the reason i didnt want to get the VL36 with a map yet is cause ill have to get the new FMIC as well, id want to do that in one go.. and being as im a touch of death to all cars i tinker with myself, id have to get a garage to do the work
so id have to pay for turbo, FMIC, LABOUR and map on top..
im a procrastinator so i couldnt just fit the turbo while were in the cold weather and do the FMIC later on as id never get round to it :bang:

anyway i wasnt thinking about changing the catback after i got the system, i was just going to work further up the pipe, so change the cat, downpipe and mani, as you say, make a good foundation for future messin..

but you make a good point.. you say it wont take much to push the '37 to its limits.. well if i do go ahead with my plan and do the catback and remap first, (its only to get a bit more whoosh for the time being) then i wont bother with any other things, (IC, cams, etc) until i get the '36 and then ive only lost out on the cost of one map..

anyway cheers for checking out the thread and sharing your experience, your a proper credit to this site m8

You are living in UK, dont you?If yes, I wouldnt bother fitting a larger intercooler at that stage.OEM intercooler does perfectly the job since the ambient temperature is lower than 25degC..Mine is running more than 195bhp and IC is not neccessary at all unless I am attending autoruns or push the car on its limits for more than 5-10mins on B-roads(which I dont anyway ).A friend of mine is running on 250bhp and the ic is still not that neccessary when ambient temp is below 15-20degC.You will be suprised if I tell you that a stock 207 1.6 Turbo or a VW TSI engine will raise its Intake Air Temperature more than the 250bhp Tjet(running on OEM ic) does, during an identical run.hope I have convinced you now If you are attending track days, its a definately yeah from me.If not, there is not reason to bother.

Losing out on the cost of one map??Well, in that case, I would think of the concept that I proposed, twice..

 

[punto_matt]

What has he done to get it to 250bhp? Pics and graphs please? And the Tjet suffers from heat soak terribly IME.

 

[George ncl]

What has he done to get it to 250bhp? Pics and graphs please? And the Tjet suffers from heat soak terribly IME.

2560R turbo,custom cams, BMC intake, 386cc injectors, 4bar fpr, custom exhaust, walbro intank fuel pump and probably some more bits that I cant think of at the moment..Cant upload pictures without getting his permision 1st Im afraid..

As I say, if you believe that Tjet suffers from heat soak you havent seen log files from cars like VW 1.4 Twincharged engine, Pug 207 1.6Turbo engine etc running both stock and maped..

 

[punto_matt]

No your right i havent, but i have driven a Tjet with a standard intercooler and an uprated one so i dont need to see what a bit of paper tells me about other cars.