19 replies to this topic

[mariner]

I suppose that in principle you could reduce turbo lag if using a large turbo by injecting fuel and NOS directly into the exhaust manifold for a very brief time triggered by sensing the rate of change in the throttle pedal fly by wire system. It would be very brief just to spin up the turbo before the gas flow restarted thus using very litlle NOS.

Has this been tried anywhere to peoples knowledge?

Would the extra heat risk melting the turbine - I can see the flame front is closer to the turbine but, logically, the quantity of heat would be well below full throttle hot gas flow.

[Tony Matthews]

I think this has been/is standard practice in rallying, it may have been used in the last turbo-engined F1.

Edited by Tony Matthews, 15 March 2011 - 12:08.

[gruntguru]

I suppose that in principle you could reduce turbo lag if using a large turbo by injecting fuel and NOS directly into the exhaust manifold for a very brief time triggered by sensing the rate of change in the throttle pedal fly by wire system. It would be very brief just to spin up the turbo before the gas flow restarted thus using very litlle NOS.

I can't see the point of doing this as opposed to injecting the NOS/fuel into the intake. This has been done for decades and creates instant torque in addition to accelerating the turbo. The usual strategy is to switch off the NOS once boost has risen to a predetermined level. Even better perhaps to reduce the NOS progressively based on boost pressure.

[Kelpiecross]

I think this has been/is standard practice in rallying, it may have been used in the last turbo-engined F1.

Would this be legal under rally regulations?

[mariner]

I was not aware of rally cars using nitrous oxide systems ( NOS) but I guess it would help tehm.

The only reason to ask about injecting the nitrous and extra fuel in the exhaust manifild was to minimise the delay of the air column going through the engine and to be consistent with direct injection but I guess it would not matter much.

[Tony Matthews]

I was not aware of rally cars using nitrous oxide systems ( NOS) but I guess it would help tehm.

Sorry, my bad, I meant fuel rather than NOS, and as usual I am relying on a vague recollection rather than hard evidence.

[Kelpiecross]

Sorry, my bad, I meant fuel rather than NOS, and as usual I am relying on a vague recollection rather than hard evidence.

I think injecting even the normal fuel is banned as it amounts to having the turbo operate as a gas turbine which is akin to having another engine.

[gruntguru]

The only reason to ask about injecting the nitrous and extra fuel in the exhaust manifild was to minimise the delay of the air column going through the engine and to be consistent with direct injection but I guess it would not matter much.

Spooling the turbo with additional gas flow will still take some time to happen whereas nitrous into the engine produces an instant torque increase.

[Tony Matthews]

I think injecting even the normal fuel is banned ...

I was using the past tense - there was a time when rally cars were spitting flame and producing loud bangs all the time. I just wondered if, perhaps...

[Lee Nicolle]

I think injecting even the normal fuel is banned as it amounts to having the turbo operate as a gas turbine which is akin to having another engine.

Correct, and the same in F1, in fact all FIA type racing. In fact NOS is only legal in some clases of drag racing. And you dont need a turbo in those classes

[cheapracer]

I was using the past tense - there was a time when rally cars were spitting flame and producing loud bangs all the time. I just wondered if, perhaps...

Audi had a system which did that in principle but, and as only Audi could at the time, it was far more complicated and unreliable. I believe Blomquist won his Champ because he wouldn't use it and broke down less that the others that year.

If you look theres a guy on the net who restored a works car (or duplicated one exactly maybe, I forgot) and has a works system and goes through it with pictures in great detail.

Mariner, I am still impressed with Yamaha's answer to lag which is stupidly simple (my type of simple!) yet no one else used it - normal turbo setup but had a stupidly simple (did I mention that?) inlet bypass pipe with a reed valve in it. When idling to low revs the engine drew through the reed valve bypass that offered a path of less resistance not having that nasty turbine in the way and when the turbo boosted, which it did faster because the cylinders got more air faster via the reed vale bypass, of course it couldn't backflow through the reed valve.

Found a diagram ...

[24gerrard]

A compound turbo charger works best by keeping turbine rpm up to speed electricaly.
It also greatly improves throttle response by reducing pressure in the exhaust manifold prior to throttle on increasing scavenge.
Only works properly with a HERS with electrical storage though.

http://en.wikipedia....lls-Royce_Crecy

Of course the best and most advanced ic engines and turbo systems were done decades ago.

Edited by 24gerrard, 14 April 2011 - 13:49.

[Grumbles]

...Mariner, I am still impressed with Yamaha's answer to lag which is stupidly simple (my type of simple!) yet no one else used it - normal turbo setup but had a stupidly simple (did I mention that?) inlet bypass pipe with a reed valve in it. When idling to low revs the engine drew through the reed valve bypass that offered a path of less resistance not having that nasty turbine in the way and when the turbo boosted, which it did faster because the cylinders got more air faster via the reed vale bypass, of course it couldn't backflow through the reed valve...

Accel used to sell a kit with a bypass valve (they called it a priority valve) back in the 80's. It was designed for carbed draw through setups and sandwiched between the carb and manifold. Under no boost conditions the intake charge would bypass the compressor and drop straight into the manifold. Never used one but they supposedly worked well.

[gruntguru]

Mariner, I am still impressed with Yamaha's answer to lag which is stupidly simple (my type of simple!) yet no one else used it - normal turbo setup but had a stupidly simple (did I mention that?) inlet bypass pipe with a reed valve in it. When idling to low revs the engine drew through the reed valve bypass that offered a path of less resistance not having that nasty turbine in the way and when the turbo boosted, which it did faster because the cylinders got more air faster via the reed vale bypass, of course it couldn't backflow through the reed valve.

There is a reason no one else used it - it does bugger all! Espicially with oversized turbo's - the ones that suffer most from lag - the compressor presents very little restriction to flow so doesn't need bypassing.

[Magoo]

Accel used to sell a kit with a bypass valve (they called it a priority valve) back in the 80's. It was designed for carbed draw through setups and sandwiched between the carb and manifold. Under no boost conditions the intake charge would bypass the compressor and drop straight into the manifold. Never used one but they supposedly worked well.

Bob Keller.

[gruntguru]

Probably had just as much to do with handling air/fuel mix at low boost (low flow). Keeping fuel droplets suspended is difficult and bypassing the turbo would help.

[cheapracer]

the compressor presents very little restriction to flow so doesn't need bypassing.

I would like to see actual flow figures supporting that statement for a turbo in a dynamic state against a static state that you are probably analyzing from.

As I have previously mentioned my Mate used to turbo cars in the mid 80's, external bolt on kits - they went on to stock standard untouched engines and gave about 4 or 5 psi boost and they had noticable lag down low - this could only be from the turbo restricting flow because compression ratio was untouched.

BTW - Those kits had an awful setup for the turbo oil drainback, was like a big self tapping screw that you tapped into the side of the sump!

Edited by cheapracer, 15 April 2011 - 03:04.

[gruntguru]

I would like to see actual flow figures supporting that statement for a turbo in a dynamic state against a static state that you are probably analyzing from.

Don't need flow figures - just look at a boost/vacuum gauge when you nail the throttle off-boost. Any vacuum indicates restriction through the compressor. (Done it many times)

As I have previously mentioned my Mate used to turbo cars in the mid 80's, external bolt on kits - they went on to stock standard untouched engines and gave about 4 or 5 psi boost and they had noticable lag down low - this could only be from the turbo restricting flow because compression ratio was untouched.

"Noticeable lag" arises from a lot of sources:
1. Boost lag - even at 4 psi - results in a major difference in grunt/feel when you are off-boost and waiting for the turbo to spool up.
2. The off- boost performance of the converted car will be worse than the original NA for a number of reasons - ******** timing, turbine restriction, inferior exhaust manifold etc

BTW - Those kits had an awful setup for the turbo oil drainback, was like a big self tapping screw that you tapped into the side of the sump!

Also seen plenty that had a 3 "bolt" flange with 3 self tappers holding it onto the sump - plus silicone sealant. Hole in sump created with a sharp punch rather than a hole-saw (to avoid filings in oil). Yuk!

[Lee Nicolle]

And it is the old story, Turbo. Why? Yes it makes power but with all the whistles and bells and plumbers nightmare and you still have something with less driveability down low than a standard type engine. And on boost a means of making ash trays from pistons!! Totally bog standard modern turbo cars are generally ok, provided the maintenance is kept right up, provided you do not get s**t fuel etc etc etc.
But as soon as you chase power, hoo boy. I have a business around the corner who make a very good living fixing these things, mostly Lancers and WRXs. Lots of broken engines, and if not drivelines.
Went to a hillclimb 2 weeks ago,a Turbo 4wd won, but several broke and blew up too [and crashed]

A straight supercharge is more reliable, more driveable but still needs all the plumbing to make the engine live. And the engines still wear out quite quickly.

Yes I am old fashioned, give me a carby V8 !!!

[Grumbles]

...Yes I am old fashioned, give me a carby V8 !!!

I'm hearing you.. I don't for a second pretend that modern cars aren't far superior to the old ones in nearly every way, especially handling. But for driving pleasure I just love a nice old 400+ inch V8 with a TH400. I find turbocharged petrol engines in street cars quite irritating, so much so that they've been added to my ignore list..
Diesels are a different kettle of fish - turbocharging improves the diesels dramatically in nearly every way.