HI all,

Just a quick question.

I have fitted a decomp plate back in August last year to my RST with a STG 2 Turbo (Sierra Cos Housing) and found that my car is really laggy due to the bigger turbo and decomp plate. I've done a compression test and the compression is 120psi. My question is should I take the decomp plate off to give me the extra bottom end I want. I've run the car up to about 18psi with a chipped ecu but I want the bottom pickup aswell. I am now running the car on a standard ECU due to my chipped one being faulty.

Cheers
Dave

 

Anyone?

 

take the sierra cos housing off, and run a normal housing to reduce your lag

 

If I can avoid that I wouldn't mind. Just had the Turbo rebuilt and sold my standard one.

Cheers
Dave

 

I am facing a similar dilemma on my engine (although different, priciples the same)

120psi per pot, whats that going to be, at a rough guess 7.5-1 CR, or even lower?

If your going to be running up to 18psi, i see no reason why you couldnt use a higher octane fuel if you feel your going to get detonation by reverting back to standard compresion. 97-98 octane readily available and Millers Octane Plus also useful to get it to close to 100 octane at minimal cost.

I assume the stock CR is something like 8.5-1? This is the same as mine. It will obviously limit you to future boost increases though but if you want driveability (like myself) then you have to make a compromise and find the power elsewhere than just increasing the boost, like ported head with bigger valves, different cam, getting the inlet temps down as low as possible etc. I realise that different engines will behave differently with regards resistance to detonation, my engine doesnt even have 'squish' to worry about because its a flat top heron head, the CVH will of course be much better in this department with a well designed combustion chamber in comparison but not being an expert with this particular engine i could say, only going by common sense.

I have a Cossie 4x4 turbo on mine, when the engine was wire rung with the intention to run high boost, the block was skimmed Anyway, this raised the compression 0.2 over stock leaving me at 8.7-1. When i first got the engine back on the road i was getting det problems at a mere 13psi, occuring at peak torque. I put this down to the slight compression increase but it actually turned out to be a dodgy gone off batch of super unleaded!

I have now gone up to 17psi without detonation problems but as a knee jerk reaction i had Mike at Ferriday make me a de-comp plate, sufficent to lower it to 7.9-1, as this would make a noticeable different to off boost response i wanted to avoid this at all costs but had it done anyway.

Now, knowing i dont have det problems and limiting myself to no more than 18-20psi boost (my turbo only has a 270 bearing) i dont want to compromise any of the driveability and will be quite happy at 250-260bhp . So for this reason i wont be lowering the compression now.

Others will say keep the compression low but i would say no if you want a fast road car, lowering compression these days is the wrong route for extra power, it's all very well for a drag strip car but how often do you drive at part throttle on the strip , modern day turbocharged cars run 9.5-1CR without problems because they are mapped to do so and this is the key.. there are other factors aswell

 

i have to say it all sounds intresting that,cos ive noticed the difference in throttle response on a low comp to a standard comp but im not to sure about these decomp plates,surely they must cause problems
also what does "wire rung" mean??

 

Depends on the quality of the decomp plate. Ferriday has an excellent reputation and i had no problems with the fitting technique which was to place it on top of my original gasket and Elring sealer between the head and decomp plate itself. It would just become an extension of the head in effect. But it was recommended that i should re-torque the head bolts after a few miles which i'm not keen on.

Wire ringing is a process where a groove is cut into the block face (or sometimes cylinder head) for a piece of wire to be inserted, in my case, 0.6mm welding wire. The protrusion of the wire isnt very much, but what it does is dig into the fire ring of the headgasket and once fully clamped down means virtually no risk of the head gasket blowing due to higher boost. For me i had no choice as an uprated gasket such as a tri-metal layer item is not available. Ford boys will have a better choice however so unless your going for really silly boost its not needed.

Here is a picture of my block showing the wire rings installed to give you a better idea.



hope this helps

Gareth[/img]

 

standard comp and 18psi should be fine...i know a few people running this and so far their car has been reliable...just make sure it is setup RIGHT!!

some guy from Performance Ford is running 17-18psi on a stock bottom end and his has been ok so far (i think lol)

bassboy

 

What boost can a standard bottom end take without any mods. Also what boost can a low comp bottom end take on standard rods. The car at the minute is running spot on but is just a laggy would an uprated cam be the way to go to help that as I am on a new standard cam which is what I was advised to get due to the bigger turbo. To be honest I don't know what to do for the best as I've had alot of hassle getting this car right since the conversion and now its right do I want to start messing with it again.

Cheers
Dave

 

Not speaking from personal experience again but i have seen evidence of people running up to 18psi on a standard bottom end as mentioned above.

A different cam is likely to make it more laggy, combine it with the bigger turbo like you've got and you lose whatever driveabilty you had with the engine as standard, you need to ensure that the engine is set up right to make the most of it though, there is no reason why a mild upgrade on the cam would be noticeably different off boost if for example, your cam timing is out now, and when a different one is fitted the new one is timed in accurately with a vernier pulley.

 

With the compression plate being on would this put the cam timing out by enough to make a difference as the head now sits 1mm further up than it would as standard? If this makes sense.

Cheers
Dave

 

It shouldnt affect the cam timing as much as it would if you machined off 1mm from the head or block face. Usuaully the best you can line up the timing is half a tooth out, this does have a small affect on performance.

In effect the belt will become tighter and the tensioner wont need to have as much movement as before, the difference is going to be slight though. Belt could also be harder to put on.