EGT's and Piston failiures....

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EGT's and Piston failiures.... #65923 06/03/2006 16:58 06/03/2006 16:58
A Anonymous Unregistered
Anonymous Unregistered A	‘e.g. a car fitted with a 2.25 catback exhaust would have a higher exhaust gas temperature and therefore cylinder temperature at 1.2 bar than a car fitted with a 3 inch turbo back exhaust at 1.4 bar so the car running 1.2 bar would do less miles considering both cars get drove equally as hard, the lower the backpressure the lower the cylinder temperature under load = the longer your engine will last.’ A recent quote from turboDan on the PTS unichip thread….. If this is the case then why do the pistons on the coupe 20VT normally go on the inlet side? On a separate note – isn’t there a tendency to loose torque if you open up the exhaust side up too much with headwork? Would this not also be true of opening up the exhaust itself?

Re: EGT's and Piston failiures.... #65924 06/03/2006 17:09 06/03/2006 17:09
A Anonymous Unregistered
Anonymous Unregistered A	I think you only lose torque on an NA or when the turbo is picking up at the lower end of the rev range. Like anythng you will trade the low down power and torque for the top end when you flow it all.

Re: EGT's and Piston failiures.... #65925 06/03/2006 17:42 06/03/2006 17:42
A Anonymous Unregistered
Anonymous Unregistered A	I think its more complicated than that. The better the exhaust system (and efficiency of removing gases) will then have an affect on the cylinders burning. This also applies to the efficieny of valves/cam setup & design. If not all the gases are expelled from the cylinder then the following inlet stroke will include some heated air. No doubt this will then affect combustion.

Re: EGT's and Piston failiures.... #65926 06/03/2006 17:47 06/03/2006 17:47
A Anonymous Unregistered
Anonymous Unregistered A	The best way to make sure the exhaust flows well is by keeping the temps hot so the exhaust wrap stuff helps keep your bay cooler and the temps in the pipes hotter as hotter gas moves quicker than colder gas

Re: EGT's and Piston failiures.... #65927 06/03/2006 17:49 06/03/2006 17:49
Joined: Dec 2005 Posts: 12,302 Sandhurst Begbie ex El Presidente
Begbie ex El Presidente I AM a Coop Joined: Dec 2005 Posts: 12,302 Sandhurst	but you also have to remember you have a turbo which is causing most of the back pressure, which can be anything up to 2 times the pressure you putting into the cylinders in the first place Originally Posted by Jonny - After being taken out at Spa Your car is Usain Bolt with wellies

Re: EGT's and Piston failiures.... #65928 06/03/2006 18:06 06/03/2006 18:06
A Anonymous Unregistered
Anonymous Unregistered A	makes me want to install an EGT probe and gauge....

Re: EGT's and Piston failiures.... #65929 06/03/2006 18:56 06/03/2006 18:56
A Anonymous Unregistered
Anonymous Unregistered A	Is this probe installed just on the downpipe also? Who makes these gauges? This post adds to the paranoia

Re: EGT's and Piston failiures.... #65930 06/03/2006 19:07 06/03/2006 19:07
Joined: Dec 2005 Posts: 1,092 Drakelow Jamiepm Club member 1989
Jamiepm Club member 1989 Enjoying the ride Joined: Dec 2005 Posts: 1,092 Drakelow	I use an EGT probe which is directly mounted into the collector plate of the manifold which is meant to be the place for mounting this type of probe. In terms of you backpressure theory, then at prolonged periods of boost the smaller more restrictive exhaust would probably be more suseptable to piston failure due to DET.Johns is probably better to comment than me as he has explored the mechanical limits in detail ( 1.7 bar!) on his 'old' engine and he felt that gas buildback led to the demise of that engine partly due to crappy OE manifold design. Regards jamie She's alive!

Re: EGT's and Piston failiures.... #65931 06/03/2006 19:20 06/03/2006 19:20
A Anonymous Unregistered
Anonymous Unregistered A	the loss of torque on an NA engine is often down to the velocity of incoming air, a larger port has a lower velocity thus cylinder filling is reduced. Long duration cams with greater overlap increase problems by creating a period of rpm where useful charge air is sucked out the exhaust. But te problem with larger exhaust ports relates to a lower gas velocity out of the cylinder, the pressure drop this causes in the cylinder is monumental in cylinder filling especially on the overlap past tdc, if the velocity is lower then the pressure drop is less - reducing VE. But of course this situation cahnges at higher rpms where the gas volume is greater being expelled as as inlet velocity picks up so does VE, and the need for larger exhaust flow. Its useful to remember an exhaust port and valve need only flow 65% of max inlet, this is for a number of reasons the main one being the fact that gases go in the reverse direction ot the inlet and valve head does not present the same knid of obstruction. In the turbo car there is large back pressure, hence the avoidance of large overlap or identiacl cam profiles in turbo applications. Only a small amount of exhaust gas is needed in the cylinders to raise its temperatures significantly. An external waste gate can help in higher boost applications as a dedicated valve and exhuast route can serve to flow excess gases no required to drive the turbine more effectively then its internal cousin, thus controlling pre turbine exhaust pressure. rich

Re: EGT's and Piston failiures.... #65932 06/03/2006 19:27 06/03/2006 19:27
A Anonymous Unregistered
Anonymous Unregistered A	thanks Rich - top post. Anyone know why coops tend to blow/melt pistons on the inlet side? I would have thought the exhaust side would be hotter...

Re: EGT's and Piston failiures.... #65933 06/03/2006 20:02 06/03/2006 20:02
A Anonymous Unregistered
Anonymous Unregistered A	Simon, I think you'll soon be getting an EGT gauge As regards to your question, I have noticed this also, it might be the inlet side is the place to suffer DET? Joe

Re: EGT's and Piston failiures.... #65934 06/03/2006 20:15 06/03/2006 20:15
A Anonymous Unregistered
Anonymous Unregistered A	Joe, No more guages - I've got enough! I'd assumed that the inlet side was the one to go from DET and poor fuelling too - anyone know different?

Re: EGT's and Piston failiures.... #65935 06/03/2006 20:28 06/03/2006 20:28
Joined: Dec 2005 Posts: 9,706 Gone J Jimbo Je suis un Coupé
Jimbo Je suis un Coupé J Joined: Dec 2005 Posts: 9,706 Gone	No point in fitting an EGT probe in the downpipe because the turbine on the turbo will have shed lots of heat from the clyinders, the manifold is the only real place to fit an EGT probe, its also the manifold that needs to be worked on if you want to lower EGT temps through escaping gas.

Re: EGT's and Piston failiures.... #65936 06/03/2006 20:46 06/03/2006 20:46
A Anonymous Unregistered
Anonymous Unregistered A	Its important to note the differences between pre-ignition and detonation Pre-ignition - is self igniting of the fuel/air mix caused by hot spots within the cylinder, or excessive pressure. This will cause the top of a piston to melt and sometime puncture a holes. Will have a melted look also. This is usually down to blocked coolant lines, deposits around the crown/valves, spark plugs 'glowing' because they are too hot, plus some others. Detonation - violent combustion of gases, basically a double ignition (1 from spark, 1 from elsewhere) which once meet create an even bigger explosion. This could cause a hole in the crown but will have the cracked appearance. This is usually down to excessive boost and high intake temperatures, very lean mixture and too much advance. Are the inlet and exhaust valves the same diameter? I'm guessing the inlet are slightly larger and will mean the piston crown could be slightly thinner that side?.. i.e the piston is not a complete mirror each side. Chris

Re: EGT's and Piston failiures.... #65937 06/03/2006 23:42 06/03/2006 23:42
A Anonymous Unregistered
Anonymous Unregistered A	I'll have a look at my shagged piston + let you know...

Re: EGT's and Piston failiures.... #65938 07/03/2006 05:53 07/03/2006 05:53
A Anonymous Unregistered
Anonymous Unregistered A	Quote: A recent quote from turboDan on the PTS unichip thread….. If this is the case then why do the pistons on the coupe 20VT normally go on the inlet side? On a separate note – isn’t there a tendency to loose torque if you open up the exhaust side up too much with headwork? Would this not also be true of opening up the exhaust itself? a smaller bore exhaust system creates more backpressure than a larger bore one higher backpressure creates more heat so you will reach higher temps quicker and with a exhaust which is too small it would be allot easier to reach sky high cylinder temps causing pre-ignition and if your unlucky damage to your engine, with an egt gauge you have less chance of damaging your engine, you have more of a warning anything above 920c means time to back off(this is the peak egt a standard 20vt runs)so keeping below this should keep you in the safety zone, a good investment IMHO especially if your running 300 bhp + more important than a air fuel gauge, although if you have both you can detect a lean condition and and get the fault fixed/turn boost down, last year a friend of mine had is car mapped for the gt2871r turbo running 396 bhp, he mentioned in a email to me that when tuning his car he replaced his old exhaust for a blue flame 2.75 turbo back and that he saw a drop in his peak egt’s by 100c he put this drop in temperature down to lower backpressure, on a turbo car the backpressure after the turbo can never be too low from my experience, I know from a experiment I did last year me and a friend completely removed my exhaust and drove with just a 3 inch down pipe my car was the fastest it’s ever been with 600 rpm better spool than with a 3 inch exhaust fitted.

EGT Probe and Gauge. #65939 07/03/2006 06:15 07/03/2006 06:15
A Anonymous Unregistered
Anonymous Unregistered A	Quote: a smaller bore exhaust system creates more backpressure than a larger bore one higher backpressure creates more heat so you will reach higher temps quicker and with a exhaust which is too small it would be allot easier to reach sky high cylinder temps causing pre-ignition and if your unlucky damage to your engine, with an egt gauge you have less chance of damaging your engine, you have more of a warning anything above 920c means time to back off(this is the peak egt a standard 20vt runs)so keeping below this should keep you in the safety zone, a good investment IMHO especially if your running 300 bhp + more important than a air fuel gauge, although if you have both you can detect a lean condition and and get the fault fixed/turn boost down, last year a friend of mine had is car mapped for the gt2871r turbo running 396 bhp, he mentioned in a email to me that when tuning his car he replaced his old exhaust for a blue flame 2.75 turbo back and that he saw a drop in his peak egt’s by 100c he put this drop in temperature down to lower backpressure, on a turbo car the backpressure after the turbo can never be too low from my experience, I know from a experiment I did last year me and a friend completely removed my exhaust and drove with just a 3 inch down pipe my car was the fastest it’s ever been with 600 rpm better spool than with a 3 inch exhaust fitted. thanks for that heads up on the EGT gauge and backpressure. will note these during my turbo swap. BTW , where would be the best location to tap in the EGT gauge probe ? cheers.

Re: EGT Probe and Gauge. #65940 07/03/2006 07:15 07/03/2006 07:15
A Anonymous Unregistered
Anonymous Unregistered A	Good post by Nobby. Other main failure on big boost / power 20vts is the ringlands cracking.

Re: EGT Probe and Gauge. #65941 07/03/2006 15:19 07/03/2006 15:19
A Anonymous Unregistered
Anonymous Unregistered A	dan whats the general tuning phrase - the best turbo exhaust is no exhuast!! I think there must be rare examples where more is less but in general I think big bore get rid of the hot gases is the way to go, I would only estimate that further down the system a mild reduction in diameter would speed the gases out. High manifold pressure and low exhust pressure is a turbo's friend, but its neighbour the engine does not share the enthusiasm for high back pressure!! EGT and wide band lambda are real useful tuning tools for turbos. EGT can hint at a lean condition, and warning of trouble, the wide band gives feed back to conditions that can account for the EGT change hand in hand I think any failure would be easily diagnosed or avoided - shame niether are cheap, but then niether are engines. rich

Re: EGT Probe and Gauge. #65942 07/03/2006 15:37 07/03/2006 15:37
A Anonymous Unregistered
Anonymous Unregistered A	Quote: EGT and wide band lambda are real useful tuning tools for turbos. EGT can hint at a lean condition, and warning of trouble, the wide band gives feed back to conditions that can account for the EGT change hand in hand I think any failure would be easily diagnosed or avoided - shame niether are cheap, but then niether are engines. good points. . .

Re: EGT Probe and Gauge. #65943 07/03/2006 16:02 07/03/2006 16:02
A Anonymous Unregistered
Anonymous Unregistered A	I've been told that EGT is also related to ignition advance, but that's about as much as I know about it. Someone care to explain their relation, or perhaps a link?

Re: EGT Probe and Gauge. #65944 07/03/2006 16:06 07/03/2006 16:06
A Anonymous Unregistered
Anonymous Unregistered A	well , if the ignition timing is too advanced , you'll effectively get pre-ignition. and this will raise exhaust temps. . .

Re: EGT Probe and Gauge. #65945 07/03/2006 16:10 07/03/2006 16:10
Joined: Dec 2005 Posts: 3,158 Near Reading JohnS I need some sleep
JohnS I need some sleep Joined: Dec 2005 Posts: 3,158 Near Reading	One word of caution on the EGT probes. I had one snap off in my exhaust manifold. By pure luck it didn't damage my turbo but it could've very easily destroyed it. Best place is in the collector. The inlet valves are indeed bigger than the exhaust valves and that is reflected on the piston face with different depth cut-outs. Don't forget that the turbo itself has backpressure as well as the exhaust and the T/GT25 turbine housings (GT28R & GT28RS included) are particularly bad for it. So if you up your boost and get a disproportianately lower increase in power chances are most of the extra potential is lost through heat and backpressure. That's why you should tune a turbocharged road car to the point where the power is starting to tail off and not the point where you can make as much power as possible. Otherwise you leave no ceiling for extreme weather or low quality fuels etc. The 20VT has shorter exhaust ports in the head than most heads which is one of the reasons why we get melted pistons sooner than most engines (as well as the cr*ppy manifold design). Former low boost hero - 616BHP@1.5 bar. 2.4 20VT RIP

Re: EGT Probe and Gauge. #65946 07/03/2006 16:12 07/03/2006 16:12
A Anonymous Unregistered
Anonymous Unregistered A	Quote: One word of caution on the EGT probes. I had one snap off in my exhaust manifold. By pure luck it didn't damage my turbo but it could've very easily destroyed it. Best place is in the collector. that would be immediately after the turbo ? . .

Re: EGT's and Piston failiures.... #65947 07/03/2006 16:18 07/03/2006 16:18
A Anonymous Unregistered
Anonymous Unregistered A	Quote: a friend completely removed my exhaust and drove with just a 3 inch down pipe my car was the fastest it’s ever been with 600 rpm better spool than with a 3 inch exhaust fitted. I also heard ,that your car could be heard from 3 miles away! Yes, the best exhaust is no exhuast as the turbo needs to work on a pressure differential, so max pressure in and no pressure out. My EGT probe is in the downpipe,.. wrong place,.. so this weekend we're mounting it in the manifold Joe

Re: EGT's and Piston failiures.... #65948 07/03/2006 16:30 07/03/2006 16:30
A Anonymous Unregistered
Anonymous Unregistered A	Quote: My EGT probe is in the downpipe,.. wrong place,.. so this weekend we're mounting it in the manifold hi. where exactly on the manifold would it need to be mounted ? Ie , drill and tap in the probe ? cheers. . .

Re: EGT's and Piston failiures.... #65949 07/03/2006 16:33 07/03/2006 16:33
A Anonymous Unregistered
Anonymous Unregistered A	The ideal place for a EGT probe will be inthe cylinder!, but as you can't do this practically, then as close as . However, different clyinders mayhave different EGT's, so you could mount it at the exit of the hottest one (cylinder 5 springs to mind), but general consensus is that at the colelcting point of all the manifold primaries i.e near the turbo wwill give you the most reliable reading, but it will still eb a bit less than in cylinder temperatures of course Joe

Re: EGT's and Piston failiures.... #65950 07/03/2006 16:39 07/03/2006 16:39
A Anonymous Unregistered
Anonymous Unregistered A	Sorry to be a pain but which one is 5 as im guessing we could outward from the flywheel it would be the one at the cambelt end??? Which cylinders run the coldest on the 20vt as i may just mount my differnt plug in those to combat the problems im having with my running on gas which could be down to plugs being too cold although they are only the bkur7et ones at min

Re: EGT's and Piston failiures.... #65951 07/03/2006 16:59 07/03/2006 16:59
Joined: Dec 2005 Posts: 3,158 Near Reading JohnS I need some sleep
JohnS I need some sleep Joined: Dec 2005 Posts: 3,158 Near Reading	no 5 is the one at the other end to the timing belt. 7 heat plugs are OE actually - the OE Bosch plugs are closer to 7 than 6 AFAIK. John

Re: EGT's and Piston failiures.... #65952 07/03/2006 17:01 07/03/2006 17:01
A Anonymous Unregistered
Anonymous Unregistered A	Kingpleb, cylinder 5 is at the opposite end to the cambelt ,so lookign at the front of the engine, on the right. I don't know about which other ones run cooler, we only say cylinder 5 as this is the one where the pistons fail the most ,followed by cylinder 3?, maybe Rog can share his expereinces with us? joe

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