Compression test @ cammed engine?

[Gerben Visser]

Hello Guys,

Because next month Henk from Fastchip is going to write a custom map for my Clio, I did a compression test today (to see if my engine is healthy). I have Schrick Cams in the engine and tested all 4 cylinders @ 150/155 PSI.

They are all 4 in the same range, but they arent very high? I can imagine that it has something to do with the sport Cams? When you have more overlap and so on (because of the cams), the compression at testing is going down. Timing is good, checked them a couple of weeks ago (just to be sure).

Is there someone who knows what a compression test at a cammed car should give? Are this figures healthy? I used a proffesional gauge, not a cheap ebay one!

The most important is that they are in the same range, witch is in my case. But 150 versus the stock 190 psi is a bit low maybe?

Regards,
Gerben

 

[bashracing]

Did you remove the throttle body to allow the engine to take a breath properly?
Overlap won't affect the compression on the power stroke, only the exhaust and induction cycle.

 

[bloke]

Did you remove the throttle body to allow the engine to take a breath properly?
Overlap won't affect the compression on the power stroke, only the exhaust and induction cycle.

you'd be stuffed doing a compression test if it was still in place:wink:

 

[smith647]

you'd be stuffed doing a compression test if it was still in place:wink:

Unless he's got an RS2 :wink:

 

[Gerben Visser]

The manifold was off, otherwise I can not reach the spark plugs (stock inlet). I did the test with all te plugs out and a warm engine.

 

[bloke]

i did comp test on a phase 1 with schrick cams in, pretty much cold engine and gave 185psi per pot.

 

[Gerben Visser]

@bloke: Thats sound more like the stock value`s indeed. The strange thing is that they give exactly the same values, they were al between 150 to 155 psi. Usually when something is wrong, just 1 of 2 cylinder`s give a lower value? Possible that the gauge is giving lower value`s? Or does it happen that al the cylinders are bad?

About the cams, I googled a lot today and some people say that racing cams can affect the compression, but some say they dont. Like @bashracing already said, the compression stroke is seperate from intake/exhaust stroke. But what if you have a longer intake duration? If the intake valve closes later, there is less to build compression? Or is the intake valve always closed before BDC? In that case you always have the same compression stroke. But if the intake valve is closing after BDC it can affect compresion?

Edit: Found some more about how cams can affect compression -> http://www.crankshaftcoalition.com/wiki/Cam_and_compression_ratio_compatibility

Only thing that is a bit strange, @bloke had 185 psi with Schricks!

 

[NorthloopCup]

@Gerben Visser Technically you have changed your dynamic compression ratio. The compression ratios stated by the manufacturer are static ratios, whereas they dynamic comp ratio is never as high. My Grp n timed 172 engine had lower comp readings and went like a scalded cat. Long time ago though now so I can't remember what they were unfortunately.

 

[NorthloopCup]

Did you drop a spot of oil in the bore as well when you did the readings?

 

[Gerben Visser]

@NorthloopCup

Thats exactly what I mean. In theory nothing changed (still 1:11 dynamic), but dynamic compression can be affected by sport/race cams? So it is possible that it are healthy values? Normally a Clio 1*2 gives about 180-190 psi, but with stock cams. Also in my case all of them give the same (lower) value, when something is wrong normally 1 cylinder is off.

I did a dry test, without oil. Normally everybody do a wet test?

 

[NorthloopCup]

@NorthloopCup

Thats exactly what I mean. In theory nothing changed (still 1:11 dynamic), but dynamic compression can be affected by sport/race cams? So it is possible that it are healthy values? Normally a Clio 1*2 gives about 180-190 psi, but with stock cams. Also in my case all of them give the same (lower) value, when something is wrong normally 1 cylinder is off.

I did a dry test, without oil. Normally everybody do a wet test?

No mate you only do the oil in the cylinder test to see if it improves the reading. If it does the rings are worn basically.

 

[NorthloopCup]

@Gerben Visser yeah sport/race cams will affect the dynamic compression ratio. It's all down to the overlap.
That's how mine gave a lower reading on Grp n cam timing compared to when it was standard timing. Nothing changed - just the timing.

 

[NorthloopCup]

More overlap = lower cylinder pressures mate FYI. :up:

 

[Gerben Visser]

@NorthloopCup

Thats what I thought as well, like I posted in my first post! Properly nothing to worry about then, also because they are all in the same range. I read about doing a wet test to check if the rings are worn, but because mine all give the same pressure I thought they were okay. Afterwards I began to worry, because of the low values and thats why I wanted to ask you guys. My dad is a car mechanic and told me it was because of the overlap, but afterwards I was a bit concerned.

Thanks again, I am a litte bit more confidence now! 21 of May I have a appointment with Henk form fastchip and the car gets a custom map at the rolling road. I will tell you how it ended and make a page of my car, so you guys can see some more.

Regards,
Gerben

 

[bloke]

will dig my schrick cams out for you and see what ones they are so you hopefully have a comparison.

 

[SharkyUK]

I ran Schrick cams on my high comp ITB build. I don't have the exact figures to hand any more but I'm pretty confident the readings across the 4 cylinders were in the 175-185 psi range.

 

[Gerben Visser]

will dig my schrick cams out for you and see what ones they are so you hopefully have a comparison.

Schrick made only 1 set for the Clio 172/182, so I think they must be the same!

I ran Schrick cams on my high comp ITB build. I don't have the exact figures to hand any more but I'm pretty confident the readings across the 4 cylinders were in the 175-185 psi range.

So that was with high compression pistons? Then it is possible that the psi value`s are lower on my stock pistons! If a healthy engine has 180-190 psi with stock pistons, you should score higher with high compression pistons, but you had Schricks cams as well.

Anyway, next month we will find out (mapping @ rolling road)! It is also possible that my compression tester gives lower value`s. They were all in the same range en it would be very strange if all 4 of my pistons, rings, valves, seals etc. are bad!

But, I stick with my first opinion and that was that sport cams give lower compression because of durations and overlap. Does it means a 30 to 40 psi drop? I don’t know, but we shall see next month! I hope that my engine is healthy, but I have good hope because they are all 4 the same.

 

[bloke]

Schrick made only 1 set for the Clio 172/182, so I think they must be the same!

am sure they make two different profiles? or was it that they list them individually? will have to check...

 

[Gerben Visser]

For a Clio 172/182 there is only 1 profile!

 

[bloke]

yeah, looked before and they list the two cams separately as opposed to in pairs.

 

[Gerben Visser]

Thats correct indeed, intake and exhaust are separated at the list.

 

[SharkyUK]

So that was with high compression pistons? Then it is possible that the psi value`s are lower on my stock pistons! If a healthy engine has 180-190 psi with stock pistons, you should score higher with high compression pistons, but you had Schricks cams as well.

Yes - with high compression pistons. In hindsight I'm beginning to think something was wrong with my engine in the first place as I know of other folks running similar high compression builds who were seeing 205-215 psi across cylinders... I was expecting to be around the 200 psi mark. Given the spec of my build I was expecting slightly higher performance figures than I actually got hence why I think something was wrong somewhere in my build.

 

[T.Trophy]

When you increase your exhaust cam duration unless it's profiled so the centre point moves towards TDC you will start opening your exhaust vales earlier and this will bleed off CR.

For example on my old turbo build with oe 182 cams I was at 145psi. I've now got a 197 ex cam in there and I'm around 130psi, admittedly I do have the exhaust cam advanced a little to avoid mega overlap but it gives you an idea on the CR difference a few more degrees can make.

 

[Gerben Visser]

The results from mapping @ the dyno, engine seems to be very healthy:

http://www.cliosport.net/threads/clio-172-ph2-flamer-from-the-netherlands.795412/