Exhaust / Turbo Problem

[Dave Whitt]

Hi folks, Last friday I had a custom made free flow stainless steel exhaust fitted to my 30Td (KZN130) Looked great, Sounded great untill I put my foot down, in 1st & 2nd gear as the revs go up engine seems to struggle, in 3rd gear it wont go over 3000 rpm I took it straingt back to the garage who said "it`s not got enough resistance" and has booked it in Monday. It seems to me the exhaust is causing too much resistance.
I have noticed on some threads free flow exhausts are reccomended has anyone else encountered this problem ?, Is there garage telling me a load of crap about not enough resistance for a diesel engine ?

Dave

[stormforce]

when i had my powerflow exhaust fitted my truck went into safe mode and i had no power at all.Once i got the truck home i disconnected the batteries over night to reset the ecu and then fitted them back the following day and no trouble since so its worth doing that before taking it back

[TonyN]

They are saying you need more back pressure and the exhaust is to big/freeflowing to provide any, which is a little odd as Turbo motors generally don't need much backpressure because of the turbo, especailly diesels.

I know of a 3.0 Surf with 2 3/4" pipe all the way from the turbo the back, then T's in to twin 2 1/2" pipes with no silencers at all, and it runs stunningly, if a little loud.

Our 3.0 has 3" pipe from the crossover bit, and then just a silencer and exits under the back passenger door, just in front of the wheel and has very little back pressure and runs great.

Some custom exhaust places stuff silencers on diesel motors with wire/glass wool, to cut down the sooty smoke they make under load, if they've rammed to much in, it could be blocked and not flowing enough.

[Dave Whitt]

Thanks mine is powerflow as well so I will try that tonight.

Dave

[Dave Whitt]

They are saying you need more back pressure and the exhaust is to big/freeflowing to provide any, which is a little odd as Turbo motors generally don't need much backpressure because of the turbo, especailly diesels.

I know of a 3.0 Surf with 2 3/4" pipe all the way from the turbo the back, then T's in to twin 2 1/2" pipes with no silencers at all, and it runs stunningly, if a little loud.

Our 3.0 has 3" pipe from the crossover bit, and then just a silencer and exits under the back passenger door, just in front of the wheel and has very little back pressure and runs great.

Some custom exhaust places stuff silencers on diesel motors with wire/glass wool, to cut down the sooty smoke they make under load, if they've rammed to much in, it could be blocked and not flowing enough.

Thanks, This is 2 3/4" from the downpipe, into Midbox, then splits into two 2 1/2" to twin exits at the back.

I think its not running free, My wife works for Honda and I have spoke to a couple of the tech guys and they are in the same opinion that very little back pressure is required and if there was not enough I would probabally get a managment light, they think they have probabally used a box that is causing a restriction.

Dave

[soramad]

regardless of turbo or not all engines need back pressure for the engine to work correctly, if you get the the combination wrong then instead of an increase in power you can get a decrease which is pretty disapointing usually due to the boost going through the roof due to no restriction , which will in turn eventually cause your turbo to self destuct and vanish down your exhaust pipe.

[uk_vette]

regardless of turbo or not all engines need back pressure for the engine to work correctly, if you get the the combination wrong then instead of an increase in power you can get a decrease which is pretty disapointing usually due to the boost going through the roof due to no restriction , which will in turn eventually cause your turbo to self destuct and vanish down your exhaust pipe.

,
,
Agree, most engines require some back pressure.
Back pressure is an aid so scavageing, witch actually helps draw out the exhaust.
EG. the exhaust from cyl 1 gets pushed down the exh. then the exiting gas charge, assists in drawing out the exhaust gasses from cyl. 3, then that in turn assists drawing out the gasses from cyl 4, and so on.

If you simply run your engine with the exhaust manifold off, then the truck will have no power at all, full stop.

So having a free flow exhaust, is not always the what it means, there is a difference between free flow, and no back pressure.

[TonyN]

,

.......So having a free flow exhaust, is not always the what it means, there is a difference between free flow, and no back pressure.

Agreed, but with a Turbo Diesel, it's nowhere near as important as on petrol motor, especially for most people here who arn't building a Dyno queen, and just want the truck to sound better and are replacing a rusty stock system.

[Gamedawn]

Can't quite see how you can have no back pressure in an engine that has a turbo impeller blocking the exhaust system

[Dave Whitt]

Took it back to powerflow yesturday, first off they gave the exhaust more resistance /more back pressure, no differance then even more back pressure still no differance. Then they tried several different combinations ie sing outlet at rear, different mid box but nothing made any differance. So I now think it is nothing to do with the exhaust the reason I think this is it only lacks "go" in 3rd and 4th gear 1st and 2nd are fine is goes really well, if it was a restriction in the pipe it would struggle in every gear not just the top 2 as the volume of gas being expelled from the engine is the same reguardless of which gear the car is in. So does anyone have any ideas what may cause the problem.

Also thanks to the lads at powerflow they worked ther nuts off for 4 hours trying to solve the problem, I would recomend them to anyone thinking of having a custom system.

Dave

[stormforce]

Dave have you tried dis-connecting the batteries for a while and see if that helps at all.It cured mine as i said earlier in the thread so may work on yours

[surfenstein]

i will put my five pence worth in also.having spent most of my life dyno testing various engines from little diesels to out and out performance diesel race engines.turbo diesel engines require very little back pressure, if any due to the turbo forcing air into the cylinder under pressure.they do not require the scavenging effect of a na diesel engine for obvious reasons. have you checked to make sure the fitters have not knocked something off like a vac pipe whilst they removed battery terminals,its quite possible they have .have a look around the engine compartment for loose vac pipes or electrical connectors.

[Dave Whitt]

Dave have you tried dis-connecting the batteries for a while and see if that helps at all.It cured mine as i said earlier in the thread so may work on yours

Tried I left them disconnected all night on saturday.

[Dave Whitt]

i will put my five pence worth in also.having spent most of my life dyno testing various engines from little diesels to out and out performance diesel race engines.turbo diesel engines require very little back pressure, if any due to the turbo forcing air into the cylinder under pressure.they do not require the scavenging effect of a na diesel engine for obvious reasons. have you checked to make sure the fitters have not knocked something off like a vac pipe whilst they removed battery terminals,its quite possible they have .have a look around the engine compartment for loose vac pipes or electrical connectors.

Cheers, I have had a good look round but cant find anything. Just seen the engine spec of your surf are there are ther any full size pics on the forum ?

[surfenstein]

Cheers, I have had a good look round but cant find anything. Just seen the engine spec of your surf are there are ther any full size pics on the forum ?

yes.