newly rebuilt engine - poor compression figures

[trotter]

Sorry, but I have to ask...

Is it high knock itself, or INDICATED high knock via the knock sensor?

If it\'s the later there\'s a better than evens chance that it\'s the sensor thats rubber ducked!

graeme

[Prof]

Sorry, but I have to ask...
 
Is it high knock itself, or INDICATED high knock via the knock sensor?
 
If it\'s the later there\'s a better than evens chance that it\'s the sensor thats rubber ducked!
 
graeme

^^ What he said ^^
 
My knock sensor wiring at the little plug where the single wire becomes shileded was very badly corroded.  Also, since the knock sensor is just a *sensitive* tuned microphone and required a good ground contact also to operate properly - what about engine earthing...
 
An oscilliscope reveals many sins in the loom....

[steve garbutt]

I dont thinks its the pts seals for the poor compression, I ran 3 years of hard driving on PTS seals on the street and drag strip with plenty of power.

Havent you just stripped your engine and found that your rear PTS seals have uneven wear and are mullerd and the fronts are ok ?

Just trying to get a picture as im trying to decide what to use in my project.

[steve garbutt]

Also as other have echoed here, iv found that if its knock via the sensor then it can also be a faulty sensor or even faulty power steering producing a noise that a temperamental sensor detects.

[suba]

Mark - the 1600cc secondary injectors are only a year old, but in answer to your question they have not been flow tested to my knowledge.  the external swirl pot was also recently installed.

The loom was cut back for the single turbo, and I asked that if anything looked \'iffy\' that it was to be replaced.

I believe that the knock was detected via the PFC commander, and I can accept that this reading might have been incorrect - though this would not account for the low compression figures from the engine, which is the issue that I want to be investigated and sorted out.

[BlitzBoy]

Havent you just stripped your engine and found that your rear PTS seals have uneven wear and are mullerd and the fronts are ok ?

Just trying to get a picture as im trying to decide what to use in my project.

The fronts showed uneven wear, but had I had full even compression on both rotors, the uneven wear was due to apex seal jumping before the exhaust port, needs more of a bevel to prevent this.

Im not going PTS seals in future as they will not work with the full bridge port Im looking at.

The main reason why people go PTS seals on race type engines so if you do get det they will bend and not break therefore not taking out your housings and plates and turbo, and to be honest I am quite pleased how they performed, still running a 10 second quarter on its last run in anger before the winter.

[BlitzBoy]

Mark - the 1600cc secondary injectors are only a year old, but in answer to your question they have not been flow tested to my knowledge.  the external swirl pot was also recently installed.

.

So you didnt ask for your primary injectors to get flow tested and cleaned, these are the injectors that get used the most when cruising and running in.
I would defo get this done now whilst the engine is out, get all four done.

[JayDee]

At a recent mapping session on a new engine my car was having issues with knock over 6,800 rpm - 13b single turbo fd3.

As a result of this the engine was then compression tested with the following results:

front - 7.1 8.0 7.4
rear - 6.2 6.5 6.5

Obviously these are way off what they should be, and there is a big discrepancy between the two rotors, which would indicate the issues when mapping.

I have never seen those compression figures cause a car to knock, it would be interesting to know if your idle vacuum post tuning is the same as before at the same rpm and AF.
A standard knock sensor is not worth talking about and should not be used for tuning, you say issues at high revs do you mean det and then the knock sensor was looked at?

[Ed_RX7]

just reading through this ...if the tuner noticed high knock why would they comp test the car unless they knew it had det......

hmmmmm sounds like they reliased and then thought oh fduk.....better check.

Just stating what i think it looks like...if i\'m wrong then apologies to all.

[PGiljevic]

On the topic of knock and Shell V-Power.

I do not use this fuel anymore, I had a situation about 6 months or more ago now where I was doing heat soak testing and the V-Power had caused pinging. I found out through much research later that V-Power is one of the more rubbish fuels around (no guarantee of octane) and also it degrades very quickly. Depending on local markets too it is "cut" with a raft of other things to make up the estimated 98 oct rating too...... After finding all this out I switched to BP Ultimate, the BP while not making the same power as the Shell (marginally less) has not had any problems in any conditions I subjected to in trials

FWIW something to consider.

[Prof]

On the topic of knock and Shell V-Power.
 
I do not use this fuel anymore, I had a situation about 6 months or more ago now where I was doing heat soak testing and the V-Power had caused pinging. I found out through much research later that V-Power is one of the more rubbish fuels around (no guarantee of octane) and also it degrades very quickly. Depending on local markets too it is "cut" with a raft of other things to make up the estimated 98 oct rating too...... After finding all this out I switched to BP Ultimate, the BP while not making the same power as the Shell (marginally less) has not had any problems in any conditions I subjected to in trials
 
FWIW something to consider.

For me the experience has been the reverse.  I use a mixture of Tesco Momentum (99 RON) or Shell V Power.  Both fuels seem fine with the current tune, but the BP fuel is noticeably \'rougher\' - I don\'t push the car if I ever have to put that stuff in the tank.
 
Agree with what you say about the fuel\'s \'going off\' - I think a lot of the higher octane fuels have very volatile additives in them, and if left sat for any time they will degrade and lower the octane.  Mine never gets the chance - I\'d empty a tank in a week no problem. :Giggle

[PGiljevic]

For me the experience has been the reverse.  I use a mixture of Tesco Momentum (99 RON) or Shell V Power.  Both fuels seem fine with the current tune, but the BP fuel is noticeably \'rougher\' - I don\'t push the car if I ever have to put that stuff in the tank.
 
Agree with what you say about the fuel\'s \'going off\' - I think a lot of the higher octane fuels have very volatile additives in them, and if left sat for any time they will degrade and lower the octane.  Mine never gets the chance - I\'d empty a tank in a week no problem. :Giggle

Yeah fuel variability is just a total arse, regardless of what type/brand you gag over...... this is why I water inject all turbo cars @ the end of the day.

Chasing power n .... like a homo on a dyno on X boost etc is gayer than Elton John in assless chaps waving a dildo in the air. It\'s far better to run WI and more boost and ironically a metric dic load more safety :2Confused but you learn this as you get older.

[gazzgazz]

Sorry buts that\'s not true about compression. Even bridgeports and Peripheral Ports still give good compression figures as do major extend ports also. Having 6 bar is really poor you must admit!!!???
 
It is true that high knock can come from other issues including an old knock sensor that is more sensitive to knock, or ancillaries such as the power steering pump.
 
What is interesting is that the engine should have the same porting front and rear and clearly compression is capable of being 8 bar as there is one reading that is that high, but having so much disparity either denotes a poor engine build or a problem has occured after the build during run in or tuning.
 
Does your engine builder warranty his engines? If so what kind of warranty?
 
Regards
Carl

Carl, i looked at a car that had been bridgeported and built by you, blue fd in Oxorfd, cat c damaged, the chaps name escapes me atm
compression test after 1600 miles was low 7\'s to mid 6\'s on 1 rotor and low 6\'s to high 5\'s on the other,

i remember the diff being a maximum of 1.3 bar, from front to back rotor.
 we called you up there and then and you said it was what you expected and not too worry, you\'d still be willing to warrant the motor but wouldnt tear it down because of those figures.

so i dont understand how you can say having 6bar in really poor here when you told me high 5\'s where fine,

[Prof]

Carl, i looked at a car that had been bridgeported and built by you, blue fd in Oxorfd, cat c damaged, the chaps name escapes me atm
compression test after 1600 miles was low 7\'s to mid 6\'s on 1 rotor and low 6\'s to high 5\'s on the other,
 
i remember the diff being a maximum of 1.3 bar, from front to back rotor.
we called you up there and then and you said it was what you expected and not too worry, you\'d still be willing to warrant the motor but wouldnt tear it down because of those figures.
 
so i dont understand how you can say having 6bar in really poor here when you told me high 5\'s where fine,

Maybe it was based on mileage on the engine - this engine has only done about a 1000 - so the figures aren\'t good - after a run in the compression will be as good as it\'s going to get.  What mileage was on the engine you were looking at ?

[Rzla]

Maybe it was based on mileage on the engine - this engine has only done about a 1000 - so the figures aren\'t good - after a run in the compression will be as good as it\'s going to get.  What mileage was on the engine you were looking at ?

I belive his post says 1600 miles which is more or less the same?