Compression & leakdown test numbers
Discussion
Numbers look ok to my eyes but welcome expert opinion.
1998 450. Engine was hot and with throttle wide open and did dry and wet compression test then a leakdown test.
Compression Leakdown
Psi Air reg around 8 psi
Cyl Dry Wet % drop
1 125 140 18%
3 122 138 14%
5 122 139 15%
7 122 145 15%
2 131 145 11%
4 130 142 14%
6 122 143 9%
8 n/a n/a 17%
Can't get compression body in #8.
The cold tests with closed throttle were too varied wild so to help others test on a warm engine. You can remove plugs using socket and the angle adapter without burning yourself plus the manifolds cool down quickly but engine will remain warm. Didn't think it would matter but hold open the throttle, place a spanner on throttle body to lock it open.
PS - Wasn't happy with yesterdays numbers as engine was cold and throttle closed so instead of editing it all again it's just easier to start a new topic. It may help others in the future.
1998 450. Engine was hot and with throttle wide open and did dry and wet compression test then a leakdown test.
Compression Leakdown
Psi Air reg around 8 psi
Cyl Dry Wet % drop
1 125 140 18%
3 122 138 14%
5 122 139 15%
7 122 145 15%
2 131 145 11%
4 130 142 14%
6 122 143 9%
8 n/a n/a 17%
Can't get compression body in #8.
The cold tests with closed throttle were too varied wild so to help others test on a warm engine. You can remove plugs using socket and the angle adapter without burning yourself plus the manifolds cool down quickly but engine will remain warm. Didn't think it would matter but hold open the throttle, place a spanner on throttle body to lock it open.
PS - Wasn't happy with yesterdays numbers as engine was cold and throttle closed so instead of editing it all again it's just easier to start a new topic. It may help others in the future.
DangerousDerek said:
? Any insight to go with the link ?
. Is it possible to have low compression and a strong rolling road result. 282 bhp on a 450 seems healthy enough! No?
Chimp871 said:
DangerousDerek said:
? Any insight to go with the link ?Phazed - its about the numbers on the 1 st post and the RR chart. It looks like compression numbers are weak but its bhp is about right for a 450.
The leakdown for other engines is ok-ish 15% is acceptable but not sure what is good/bad for a 450.
If my engine is stuffed, fine I'll rebuild it but before I start om that I'd like some feedback on if it is knacked, worn or acceptable.
The leakdown for other engines is ok-ish 15% is acceptable but not sure what is good/bad for a 450.
If my engine is stuffed, fine I'll rebuild it but before I start om that I'd like some feedback on if it is knacked, worn or acceptable.
I understood that this type of test was just a guide. As long as the cylinders are within 10% of each other generally every thing is ok.
In my opinion I wouldn't focus too much on it as long as the car starts and runs ok, there is no smoke and your getting good power and if your that concerned take it to a professional for a check up.
In my opinion I wouldn't focus too much on it as long as the car starts and runs ok, there is no smoke and your getting good power and if your that concerned take it to a professional for a check up.
ClassicChimaera said:
Why have you pulled the heads off, that dyno graph shows a very healthy engine for a standard lump it seems to me!
Hi CC. The heads were pulled befire the RR after a water leak where water temp rose to 120oC and oil pressure dropped to zero. I'd owned the car a year at this point and didn't trust the seals, or the work done by previous owners so it was easier for me to change all the main seals on the engine, I'm glad I did.Whilst in pieces I changed the cam to stealth version as the original was excessively worn. Took the opportunity to clean the heads, valves etc.
It then went to Jools for a RR session in case new cam needed ecu tweaking. So the chart was the final chapter of the completed work.
But the compression test was done after I scraped by on mot emissions through either over fuelling or oil.
Sometimes you can get distracted to and mislead down wrong paths and was curious to know others opinions. The engine feels healthy enough but I'll have to come a meet and see what another 450 goes like.
Ps - the dark side of me fancies puling the engine out, but I'm resisting.....
ClassicChimaera said:
New cam so I understand the figures more now. Correctly gapped new rings might help for a while but I'm no engine builder.
What do the pistons look like below the rings?
Well, when the heads were off I only remember checking the cylinder lining walls and could see cross-hatching, assumed ok and so moved on to the heads as warping was my #1 concern (they were fine). With hindsight I'd have done more. Will dig out and post some of the pictures of pistons to see if anything stands out.What do the pistons look like below the rings?
I've searched quite a bit for comparative compression numbers (wet & dry) for a 450 but no luck. A little surprising as it's a common test but hope mine could assist others.
I'd quite happily do another RR to check engine health over rabbit hole searches. RR was the best £150 I spent.
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