Reducing lag?

[u63af]

I fitted a tial dpw, chips and uprated fuel pressure reg along with a greddy profec. The car feels quicker onece spooled in but still fells pretty laggy. Could this be due to my car having a cat? Or is there anything else I can do to reduce the lag?

Cheers
Sandy

 

[944 man]

You could lag the manifold and the up-pipe (along with the turbocharger its self). The hotter the exhaust gasses are the better. Short of moving the turbo closer to the exhaust ports or using a small (or hybrid) turbocharger there isnt a deal that you can do. The position, although poor, cant easily be improved; so Id suggest lagging first and maybe a hybrid turbo second. The trick is to get as small a turbocharger as possible, thatll still pump sufficient air.....

 

[944 man]

You could also have the manifold/up-pipe matched to the cylinder head ports. This wont alter the boost characteristics, but it will move everything down the rev range by a reasonable amount (perhaps over 500rpm!).

Simon

 

[sawood12]

Lag characteristics are mostly due to the turbo itself. The turbo turbines don't act like windmills they work by expansion of gasses through the turbine blades i.e. the pressure drop accross the turbine, therefore modern turbo's with better turbine vane profiles and ball bearings to reduce resistance help. You can't get away from the fact our old KKK turbo's are laggy and there isn't much you can do with them. Measures such as lagging the exhaust manifold and better ECU mapping help, but wont significantly eliminate lag.

The most significant technology to combat lag is the variable vane's you get on the 997 turbo. These close up the gaps between the turbine inlet vane when off boost to allow expansion of the exhaust gasses at low RPM and open up as the revs rise. This is very expensive though due to the exotic material requried to withstand the high temps. The turbo's for a 997 turbo come in at around £6k each. Would be a great mod for a 944 turbo though.

However even modern turbo's don't elminate lag. Modern cars (i.e. hot hatches) simply install smaller turbo's, but if you look at something like the Evo's with large turbo's you still get horrendous turbo lag.

You could always master left foot breaking which allows you to maintain boost pressure while braking!

 

[944 man]

Turbo technology has moved on a good deal from when the 944 engine was developed (1980-1981) and Im confident that Porsche would site the turbocharger in a different location now. The primitive engine management doesnt help either, but as Scott has implied: the real culprit is the agricultural turbocharger. Im not sure that Id agree that a 944T needs a large turbo and that that makes lag mandatory. A tiny Mitsubishi TD04 turbocharger is good for about 280bhp, with a decent and very reasonably priced hybrid pumping enough air to make 320bhp (pretty much vmax for most 951s...). A little turbo like this will spool up at low revs with virtually no perceptible lag on a two litre engine, making full boost by 2,500rpm and a good deal less on a 2,500cc engine. A TD05 20G would be able to generate over 1 bar or boost at the same revs on a 2,500cc engine (full boost by 3,000rpm) and pump enough air to produce 450bhp! The turbocharger is the vehicles achilles heel (along with the DME) and unfortunately, people always seem to look towards terrible Lindsey Racing kit when they decide to change. A 450bhp turbo doesnt have to equate to lag.....

 

[u63af]

Its funny you mention a td04 as one of the cars I am comparing mine to as being laggy is my friends lancer gsr (1.8 turbo). It comes on boost almost instantly but starts to slow off towards the top end. He is just about to put on a td05 on it.

If I were to send my turbo to turbo technics, get 360 deg bearings, and different profiled blades on the turbine then I was hoping that it would reduce lag a bit. Also the cat on my car must be slowing down spool up aswell. Would the current ecu cope with a lightly modified turbo?

I think one of the main problems is that my last car was a 5 litre tvr and it had a lot of power from about 1500 rpm.

 

[944 man]

Mitsubishi makes many, many TD04 & TD05 turbochargers and TDO4 applications vary greatly. I was talking about a non-Mitsubishi fitment because Im particularly familiar with it.

944 Turbos are well and truly out of my system; but if I was looking to improve one then Id do the following:
* Improved turbocharger and up-pipe
* Manifold and up-pipe ported and lagged
* Replace the DME and AFM with a MAP based ECU

That done you can address other issues, such as charge temperature... It wont cost a deal more than people are commonly spending but the difference will be substantial I think. Im definitely not going to do it though; and if someone offered me a cheap 951 then I wouldnt look twice at it.....

 

[944Turbo]

ensure you have no boost / vacuum leaks as these will require the turbo to work harder to attain the pre-set level of boost. The small bore pipes are a source of leaks and I also had quite a large leak from the ISV. the short rubber pipes to/from the IC are also potential leak points.
Tony

 

[944 man]

The wastegate leaks too of course. Even when they were only a couple of years old, there were plenty of cars that couldnt achieve full boost, let alone sustain it. Even when everythings perfect though, its all very old tech with an archaic turbocharger that has the delivery characteristics of a time-delayed safe...[]

 

[edh]

I think your main problem is that TVR [] - particularly in low gears, you really miss the low rev torque that large capacity engines give you. To be honest, it's a characteristic of the car you can drive around relatively easily.

I'd have a chat to Jon Mitchell about your requirements - my bet is that a Garret BB hybrid will be a good option for you. It's a lot cheaper than fitting a 3l engine or an LSx (which would probably be exactly what you want).

FWIW, I found that the vitesse MAF improved the spooling of the turbo by a few hundred rpm, nothing particularly significant.

 

[u63af]

I ahve replaced all of the vacuum pipes with silicon. What is the ISV ? I have disabled the cycling valve. #

Took the car out today. With the boost controller off, it boosts to 11 psi and holds it to the red line. When I put my ebc on, it boosts to 16 psi as I set it but something doies not feel right. It feels like it is being limited. It will reach 16 psi and hold it but just does not pull right. I have chips so it is not reaching fuel cut. I used an old 3 bar FPR which I suspect may not be up to the job. Does anyone think that a dodgy FPR may cause this to happen? My thoughts on it may be that it is not getting enough fuel at 16 psi and was concerned I may melt my engine.

 

[Neil Haughey]

Pretty much any modern turbo engine will have the turbo mounted as close as possible to the exhaust ports. With such a long path round the engine I think you will always have slow boosting, a smaller turbine will just shift things lower down in the rev range. Personally I don't mind the characteristics of the 951 motor, modern turbo cars can feel like a bad diesel sometimes giving nothing below 1500 rpm and then pulling hard from 2k rpm.

 

[944Turbo]

Idle stabiliser valve under the inlet manifold. Also dump valve and heater valve diaphragms can fail and leak,
Tony

 

[sawood12]

Not sure I agree about the location of the turbo. I really don't think it has a significant effect on lag. It is exhaust manifold pressure that drives the turbo and not velocity of the gas flow, in fact the slower the velocity of the gas flow the better the turbo spools. The only benefit you get by positioning the turbo closer to the exhaust side of the block is less heat loss in the gas flow. Moving the turbo closer to the exhaust ports can cause problems due to pulsing of the exhaust gas also the higher temps reduce turbine life. You need a bit of manifold length to act as a plenum and settle the gas flow. 951's are laggy because of the old turbo's and large turbo's. You'll find that modern cars have much smaller turbo's and run lower boost levels hence less lag. If you were happy with 0.5 bar of boost as a suitably small turbo you could easily get modern day car levels of lag - but you wouldn't make much power.

 

[Neil Haughey]

Actually the inverse is exactly what you want.

Page 324 of Advanced Engine Technology by Heinz Heisler says this "It is important for effective cylinder scavenging that pulsed exhaust gas energy is introduced to the turbine wheel in contrast to a damped steady flow of gas" or thereabouts. He also says enough to fill a whole chapter on turbocharging/supercharging.

 

[appletonn]

I replaced the standard blow off valve with a Bailey BV30 one about a month ago (much to some people's disgust!), mainly in the name of research!

After covering around 300 miles since fitting it, my backside dyno would indicate that the boost does come in slightly sooner (about 200-300 revs lower down) and it feels smoother as the hurricane gathers pace.

Could be all psychological of course or my old one was kaputt....[8|]

 

[sawood12]

ORIGINAL: Neil Haughey

Actually the inverse is exactly what you want.

Page 324 of Advanced Engine Technology by Heinz Heisler says this "It is important for effective cylinder scavenging that pulsed exhaust gas energy is introduced to the turbine wheel in contrast to a damped steady flow of gas" or thereabouts. He also says enough to fill a whole chapter on turbocharging/supercharging.

Not read that book but from other material I have read I think this is more about harnessing the energy of the pulses in the exhaust gas flow i.e. improving turbo efficiency, which no current turbo can do, rather than combating lag. You also need a continuously active variable geometry turbo to change the turbine inlet area's to match the pressure pulses in the gas flow. This sort of turbo is the technology that will supercede VGT turbo's - if they can get it to work - and even then it will likely be horrendously expensive. With our cars we simply have to learn to deal with lag the old fashioned way.

 

[Peter Empson]

Add a supercharger? It worked on the Lancia Delta S4...

I'm not being very helpful am I []

 

[944 man]

The best benefit from exhaust pulses comes when fitting a twin scroll turbo. You need a speacial manifold/up-pipe for this though, and its a job that needs a manufacturers resources and level of development: you cant just bolt one on... Im not sure that its correct to state that modern vehicles dont suffer lag because they have small turbos and low boost levels either. The 951 is laggy because it is old and road turbocharger technology was relatively new and undeveloped. The DME is primitive and this exagerates the principal problem which is an agricultural turbocharger (which is large and inneficient, hence the lag) and its location doesnt help. A smaller modern turbo will be able to pump more than enough air to exceed the output of high-end 944 turbos and still be considerably less laggy (see my earlier post). Most modern performance cars seem to use a higher boost pressure than a 951: Im saying that off the top of my head though as its a long while since Ive owned one. As a comparitive example my Impreza achieves a peak bost level of approximately 16psi, which is roughly 1.1 bar. Of course; boost pressure doesnt directly affect spool up.....

 

[nags]

In terms of replacement/reconditioned turbos, what are the options?

I'm aware that Lindsay Racing offer a reconditioned (exchange) turbo for what seems to be reasonable money, but they do come in for a bit of criticism. Is there something similar out of the UK or europe? Are there any ball bearing bolt-in replacement options?

Thanks