Decompression plate or not?

[Bim]

Hi. As i need to put my car back to standard every MOT.
Would a decompression plate mess with the exhaust values for an MOT?

As im thinking of it wont get a good/high compression.
That could mess with it..

Or am i thinking wrong?

[axsaxoman]

there is a lot of wrong thinkng on forums,
yours is actually not wrong
the idea of dropping compression just because you are boosting is some what old thinking .
all tubo cars now made will be running 10-1 for exactly the reasons your are eluding too --low comp means poor burn
the thought that lowering comp will some how protect std pistons is just wrong
std pistons are cast and not forged so eventualy if too much boost is used ,especially if you skimp on prpper ecu adjustments. you will either squash the crown onto top ring or they will get too hot and burn

why people think that lowering the comp and then wacking in more boost is a solution is beyond me .
it makes it poor performance off boost to start with
as a rule of thumb 3.7psi is equivalent to about 1 comp ratio
the only reason why turbo pistons are made at such a low comp is a historic thing when ecu systems were not as good and also what the customers ask for
the first saxo turbo pistons were made for the european drag racing boys who also run nitrous ,and as peopel keep buying them the makers see no reason to change and would argue you can just turn up the boost to compensate for it ,
but a drag car is not a road car
I made a couple of batchs of higher comp ones for my s/c cars and never had any problems ,butthey did have some advantages .
I don,t get them made at presnt cos i can,t afford to keep 10 sets on the shelf ,and that what it needs to be to get price right .
same reason as I stopped getting batchs of omega + cosworth pistons --price seems to always be the driver
surely a better transition from no boost to spool up is worth more than just being able to say you run bigger boost number
I have run 1.2 bar with n/a lumpy 12.2 pistons but with 1,9mm gasket ,due to cams i was using with no problem .but i didn,t get any more power ,just put it up the rpm range ,so no point really ,
any engine designer will tell you that a flat top piston will always be better burn if you have the option ,most boosted cars run low duration cams ,big cut outs are rarely needed.

[Bim]

If im not wrong, old rally cars was high comp and with boost..

So, i guess i forget about the compression plate, and just adjust it to 0,5bar maximum with std compression.

[mishoka]

Originally Posted by axsaxoman

there is a lot of wrong thinkng on forums,
yours is actually not wrong
the idea of dropping compression just because you are boosting is some what old thinking .
all tubo cars now made will be running 10-1 for exactly the reasons your are eluding too --low comp means poor burn
the thought that lowering comp will some how protect std pistons is just wrong
std pistons are cast and not forged so eventualy if too much boost is used ,especially if you skimp on prpper ecu adjustments. you will either squash the crown onto top ring or they will get too hot and burn

why people think that lowering the comp and then wacking in more boost is a solution is beyond me .
it makes it poor performance off boost to start with
as a rule of thumb 3.7psi is equivalent to about 1 comp ratio
the only reason why turbo pistons are made at such a low comp is a historic thing when ecu systems were not as good and also what the customers ask for
the first saxo turbo pistons were made for the european drag racing boys who also run nitrous ,and as peopel keep buying them the makers see no reason to change and would argue you can just turn up the boost to compensate for it ,
but a drag car is not a road car
I made a couple of batchs of higher comp ones for my s/c cars and never had any problems ,butthey did have some advantages .
I don,t get them made at presnt cos i can,t afford to keep 10 sets on the shelf ,and that what it needs to be to get price right .
same reason as I stopped getting batchs of omega + cosworth pistons --price seems to always be the driver
surely a better transition from no boost to spool up is worth more than just being able to say you run bigger boost number
I have run 1.2 bar with n/a lumpy 12.2 pistons but with 1,9mm gasket ,due to cams i was using with no problem .but i didn,t get any more power ,just put it up the rpm range ,so no point really ,
any engine designer will tell you that a flat top piston will always be better burn if you have the option ,most boosted cars run low duration cams ,big cut outs are rarely needed.

So what is best way now to make a boosted car with std pistons - decompression plate, two head gasked or std compression ?

[welshpug]

Don't forget that modern cars are also on direct injection generally, and have VVT/C.

[luthor1]

Standard Compression, if you increase the distance between the piston and the flat part of the cylinder head, then you reduce the 'squish' which, ironically, increases the likelihood of detonation due to reduced gas speed as it's not squeezed back into the chamber, so I can't for the life of me work out why people lower compression anyway!

[mishoka]

Standart compression will be fine to run with TD05 16g on 0.6bar ?

[vtr91]

why has this only just come up now.
when i done my research last year, it sounded like a decomp was the way to go. So ive sourced a decomp plate, and its fitted atm. Doh

[Bim]

If im not totally wrong..

with high comp and less boost you get a engine thats fairly strong w/o boost and when boost you get more power..
More even/smoother powerband (right word?) Driveable..

and lower comp and more boost.. opposite..

then higher comp you can get knocks easier..

[axsaxoman]

Originally Posted by Bim

If im not totally wrong..

with high comp and less boost you get a engine thats fairly strong w/o boost and when boost you get more power..
More even/smoother powerband (right word?) Driveable..

and lower comp and more boost.. opposite..

then higher comp you can get knocks easier..

yes, thats sort of correct
the key word is "excessive comp ratio+ excessive boost " coupled with bad timing control will cause det

[axsaxoman]

Originally Posted by welshpug

Don't forget that modern cars are also on direct injection generally, and have VVT/C.

not foprgatten ,but they are very few at present and they can run higher than I am suggesting ,,
its all a balancing act ,but trying to boost on an ecu that is mapped for n/a is just wrong anyway ,

[axsaxoman]

Originally Posted by vtr91

why has this only just come up now.
when i done my research last year, it sounded like a decomp was the way to go. So ive sourced a decomp plate, and its fitted atm. Doh

It hasn,t just come up , its just what forums do
its been knowledge to those who know and use good quality ecu systems for years ,

most of the posters, so called knowledgeable people ,don,t have dyno,s +don.t do real development work

EG willing to destroy engines to find out the limits and then do forensic examination to find the cause of the failure

so they just repeat as gospel what they have read on another forums.

I have been developing engines+ posting for many years and have had many heated debates and after a while I just stopped posting anything that was too controversial due to the slagging , which definately affected my buisness,
the lack of fact based responses from people didn,t seem sink in with all but a few ,the majority don,t have the knowledge to make sense of whatwas being said and I kept getting accused of long winded and superior posts just to make me sound big headed and a know it all .
the truth is simple I do have a superior depth of knowledge to most gained by 40 years of engine tuning everything from mini,s mgb,s ,mk1 escorts , ford bda engines --one of the first 15v engines .then I was first to turbo a subaru pushrod engine in 1979 ,I also turboed an RS 2000 in 1976 and a hillman imp 1977 and they were all with carbs
then I started with ecu systems in the very early 80,s and I am still learning every day .
I don,t know it all, no one will and I am always open to a reasoned argument ,backed up ny more than --"my mate did this and it goes fucking great "--
never forget every day is a school day if you want to increase your knowledge

but if you are going to believe in forums you won,t go far wrong listening + thinking carefully to what i say


some emperical evidence for you

you have a turbo car ,factory built --first thing you do is chip it to up the boost --on some engines it can be alot 100bhp on some
If you accept that 3.7psi is about 1 comp ratio you can see that the car makers design the car to give the power they want --not what it can make . plus allowing for crap fuel in some countries and not have to make dif spec engines ,and still comply wtih type approval emission regs

which just proves they could have run higher comp to start with ,and no internal engine problems

drag racing cosworth YB engine boys have taken years to realise that by running less boost + small turbo,s they can get far better response + 1/4 mile times + less engine failures

[vtr91]

ive read what you say, its just a shame i didnt find any of your posts when i done my searching on here.

im in two minds as to what to do now. :/

[Rossp]

Originally Posted by axsaxoman

Snip. In summary...

[axsaxoman]

Originally Posted by vtr91

ive read what you say, its just a shame i didnt find any of your posts when i done my searching on here.

im in two minds as to what to do now. :/

are you using std pistons ?
what boost level ?
do you have a stand alone ecu?
has engine been run with decomp plate fitted?

[yr51ocw]

Originally Posted by axsaxoman

there is a lot of wrong thinkng on forums,
yours is actually not wrong
the idea of dropping compression just because you are boosting is some what old thinking .
all tubo cars now made will be running 10-1 for exactly the reasons your are eluding too --low comp means poor burn
the thought that lowering comp will some how protect std pistons is just wrong

As mentioned, modern cars run very high CR (Volvo's new range of engines is running 10.8:1 @ 23bar BMEP) is to gain part load fuel economy, in the quest for lower CO2 figures to meet EU legislation. You will notice that Volvos same family of engines has a higher output variant (25bar BMEP) with a 0.5 CR lower. Having such a high CR with low duration cams leads to poor combustion phasing at full load and can increase the tenancy for Pre-Ignition. Something that is becoming more and more of a problem with highly boosted downsized engines. So even OEMs have a limit on how much compression they can get away with even with DI which raises the knock limit compared to PFI.

Look at AMG's A45 engine, 340bhp from a 2.0ltr but it only uses a 8.8:1 CR, I assume because that is as much as they could use while still maintaining sensible full load combustion phasing, which will also have a huge influence on pre-turbine temps, to the lower compression ratio actually improves the fuel economy at higher loads.

In a few years, I would expect to see external cooled EGR making its way into gasoline production engines due to its tenancy to mitigate knock, meaning similar performance levels can be achieved, but with even higher CR, meaning improved part load efficiency.

[axsaxoman]

I think we are getting to far into modern car technology ,as I have yet to see a saxo with a MODERN type turbo or anything like real boost control or motorised throttle and as far as emission regs --well that just doesn,t compute with after market tuning .

I am guessing the reason for the lower comp ratio with the AMG is the 340 bhp ,so they needed more volume to fill with micture to get the extra power .
.another one of these compromises --bugger cv volume means more burnable mxture so should give more power for same boost level and- keeping ex gas temp down to stay awya from the det on modern low octane bio fuel
-but its all a compromise.
I quite sure if they could run less emmison friendly fuelling then they could also run higher comp ratio ,as the extra richness would cool the burn .
as for EGr ,that just buggers up everything as far as power goes .
a compromise

its all these sort of things that makes believe that after market engine tuning is very close to dissappearing -due to costs involved in doing anything major to the latest era of engines .
which is also why i think the saxo will become a classic as it was probably the last car that can be tuned simply .
I would love to develop the DS3 engine ,but i don,t see the market for it .
even the non turboed ,non direct injection engine has a lot of advantages over the tu 5 ,but needs alot of things changing to make it release the extra potential it has over the tu5 .

[vtr91]

Originally Posted by axsaxoman

are you using std pistons ?
what boost level ?
do you have a stand alone ecu?
has engine been run with decomp plate fitted?

yes, im using standard pistons.
im unsure as to what boost level im going to be running it at, was thinking around 8psi wich is fairly low. but i really dont know what boost level to set it at to be safe for a daily on standard internals (any suggestion welcome )
The turbo im going to be using will be a gt17.

i do have a standalone ECU, ive got a predator.
And i havent run the engine with the decomp plate yet, ive literally just built it up and fitted it all.
(fitted new rings end shells, gaskets ect + the decomp plate)
But so far, the engine hasnt been fitted yet, i still need to sort a few things out.

[welshpug]

is the Mini variant of the EP6DTH that much different to make it not worthwhile venturing into offering Mini tuning which would apply to the DS3 as well?

the R3T spec DS3's seem to be pretty quick

[yr51ocw]

Originally Posted by axsaxoman

as for EGr ,that just buggers up everything as far as power goes

II would love to develop the DS3 engine ,but i don,t see the market for it .
even the non turboed ,non direct injection engine has a lot of advantages over the tu 5 ,but needs alot of things changing to make it release the extra potential it has over the tu5 .

Cooled external EGR definitely has the potential to increase peak power due to increasing the knock threshold, but I am yet to see it enter a production gasoline engine, due to the higher EGTs than what is seen on a diesel engine and thus the materials required for the cooler make it un-economical (for now, but I still see it being an option). Plenty of research has been done to prove its potential. EGR is used on diesels for a long time to reduce NOx output, but has little to do with performance increase on diesels.

I definitely agree with you on the BMW/PSA princess engine. I think it has plenty of potential, but as you say it is going to be very complicated and expensive to develop further. You are talking approx £2000 for an aftermarket ECU that is capable of CVVT, closed loop boost control, DI injector drivers etc.... then there is the dyno time to set the thing up.

I personally would at turbo charger spec, as I feel they have not fully utilized the scavenging effect on the torque knee point due to emissions regs. If you were able to take advantage of the scavenging effect you could increase the compressor size to maintain low speed torque and also increase peak power.