high compresion need help

Give us more to work with here. Why is it HC ? Have you bolted a tub system onto an N/A lump ? Is it the stock set-up ?
I have seen cases where people have bought a turbo car which has had a replacement engine fitted, which was the wrong variant and had a HC N/A engine fitted either out of ignorance, stupidity or lack of care or understanding.
Basically, do you definitely have the correct engine in there ? Externally many of these engines show very little difference without a knowing eye.
If all the above do not count, what have you done recently or has this been a constant problem ?
Please give more info on how you know it has HC etc etc.
 
Some turbo cars come with high compression from the factory (like the mk5 VW GTI which has a 10.5:1 CR from the factory with the 2.0L turbo.) Some cars also recommend a high CR when doing a turbo swap.

Anyways, What model of car is it? What's the engine code? Was it turbocharged from the factory or is it an aftermarket kit? More info is needed.

A good rule of thumb to lower the compression ratio is to tear the engine apart and swap for forged aftermarket pistons with a lower CR and forged connecting rods.
 
Greetings flattop and a Warm Welcome to our TorqueCars Forum my Friend!

Good to have you along with us :)
 
Hey guyz I have a 4age turbo conversion I had wiseco piston in so it detonated so I did some research and I put nissan 200sx pistons in and now I got compression problems. What do you recommend to drop compression
 
With the Wiseco pistons you were getting det/knock ? What count of knock were you getting ? Did you modify the fuel system, fit and control larger injectors, fuel pump upgrade, pressure regulator etc to feed the need for fuel ? Was the timing correct or altered by mapping ?
Are the pistons you have in now, dished top ?
What is the current compression pressure readings and what were they with the Wiseco's fitted ? Are these pressures high across all cylinders ?
 
My friend the pistons I have now is a flat top and is 83mm bore I made a 3mm copper gasket never tried it yet first need more info b4 assembling. The problem with knock I dnt know why or what went wrong the car was running nice at 0.8 boost
 
If the car was running fine then starting detonating you may have the same problem no matter what you do, if you start running too lean this may also cause detonation as far as I know[forgive me if I'm wrong] so you may have a problem in your fuelling system or boost regulating system.If the nissan pistons were suppose to work fine on your setup and now compression is a problem, sounds like your boost pressure is too high.
 
Ok, so with the Wiseco pistons and 0.8 bar boost, all was well. Then it started to produce knock. I would investigate that line. First off I would check all the boost piping for cracks, leaks or perishing etc. Then I would investigate the fuel supply, pressure and regulation side of things and of course, timing, either cam or ignition.
The reason I suggest that is that it sounds as if you may have jumped the gun and gone down another route without investigating the detonation problem fully, which if still there will cause damage to any engine or system you fit anyway.
You didn't mention if the det caused any piston damage or not. Mild det on forged pistons is mostly irrelevant regards damage and the pistons should be fine, unless the det was very high and visible damage is present. Just be aware of any det chips in the piston crown and skirts, for the purposes you require, they could be polished out anyway, if present.
As for using flat top pistons and a 3mm copper gasket, I see your aim with that but it's certainly not a route I would take.
 
The piston crown had a piece gone you could see the ring from the top. What route would you go to solve problem or do you think I must build other block?
 
Pistons for turbocharged engines are built to a better tolerance/suitability for that purpose.
Have you measured the cylinder bores ? Wiseco pistons are slightly larger than standard, even their stock size isn't a straight forward one for one replacement, measurements need to be taken and clearances need to be assessed, ring gaps always need measuring. I have not yet seen a set of Wiseco pistons that didn't require ring gapping to suit the application. That's why they give tolerance spec sheets with their piston sets.
Have you considered replacing the one damaged piston and using the forged set. I know that Wiseco do replacement ring sets, not sure if they do single piston replacements but it's worth investigating.
As already mentioned by myself and others, you really do need to find why the det was induced in the first place. Now, another thought has occured into my head with this, if you are considering putting in a stock set of pistons, I can only assume that you have stock bore sizes. The wiseco pistons expand at a different rate than normal pistons, hence the need for using their specified bore clearances too. If your cylinder bores are stock size, it is very possible that your 'det' was in fact over heating of the pistons due to expansion and not enough room for it within the cylinder bores, hence the failure.
 
The problem with detonation could also be that you're not using a high enough grade fuel. Over here in the US, we have 87, 89, 91, and 93 octane. most cars run on 87, but if you add forced induction of any kind, expect to switch to 91 or 93 octane to help keep premature detonation at bay. (insert joke about premature ejaculation here)
 
I can't use old pistons they were 82mm wiseco nissan turbo piston is 83mm the problem is I got HC from nissan piston. I know I need to sort det problem but I need to sort out HC problem also
 
I'm guessing that the Wiseco pistons were dished top of the correct application for your engine, which would give the correct compression pressure.
Regardless, you need this type [dished] of piston to run your engine with a turbo.
Flat top style of pistons will give you the higher compression pressure required to run a N/A engine.

Photo0127.jpg



This is what your standard piston should look like.
 
But why they make nissan sx turbo piston flat top I thought it would work. I'm considering putting 3mm copper gasket on tomorrow and see what happens I hope compression drops
 
Machining the head wouldn't work. Machining the surface would only increase pressure. Machining the combustion chambers would require so much work that it's totally unfeasible for this application, there's not enough material there to retain strength compared to the machining required to get the compression ratio correct. Then there's the valve and seat issue. The thicker copper gasket fitment is best used to lower compression when running a higher boost with suitable pistons and turbo upgrading. [Though personally, I'd rather use suitably made pistons with a lower C/R.]
N/A pistons are not good enough for a turbocharged set up. When used with a turbo attached they can only run such low boost that it's not worthwhile doing the project. I suspect that this is his issue with H.C.
Fit the correct pistons and do the job properly. Then find and sort your det problem which is most likely just a vac pipe issue, or as related to earlier, fuel/timing etc.
However, you really do need to get a reading on your A.F.R. to ensure that you're not running too lean or that really will kill the engine [again]. As pointed out below somewhere, the qualities of fuel do vary across the planet, poor fuel will induce det=destruction. The list is endless.
 
Last edited:
Hey guyz I'm back but I never put motor together yet will see if I get a chance this weekend. Will keep you posted
 
Similar threads

Similar threads


Please watch this on my YouTube channel & Subscribe.


Back
Top