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[T.m.f]

He is on once the engine gives up on the 0-60 tests 

[Sir Tigger KC]

He might not be able to resist the cash on offer!   

[Broomies Mate]

Engine at running temperature for the compression test Webster. 

[Webby the Bear]

Engine at running temperature for the compression test Webster. 

lol thanks broomie for the only sensible reply! 

presumably if I was to do it from cold it may give a lower reading??? thinking heat expansion closing rings up, valves expanding etc.?

[henryd]

Engine at running temperature for the compression test Webster. 

lol thanks broomie for the only sensible reply! 

presumably if I was to do it from cold it may give a lower reading??? thinking heat expansion closing rings up, valves expanding etc.?

Not neccesarily.cold engine has thicker oil which could improve piston ring sealing

[Webby the Bear]

Engine at running temperature for the compression test Webster. 

lol thanks broomie for the only sensible reply! 

presumably if I was to do it from cold it may give a lower reading??? thinking heat expansion closing rings up, valves expanding etc.?

Not neccesarily.cold engine has thicker oil which could improve piston ring sealing

Good point mate 

[biggriffin]

Page 25, and still going

[Webby the Bear]

Page 25, and still going

I know! 

one other thing id mention....

the vauxhal chap said that the track for testing would be perfectly level and using ''high grip tarmac''. would this tarmac have a real impact on times?

[biggriffin]

Page 25, and still going

I know! 

one other thing id mention....

the vauxhal chap said that the track for testing would be perfectly level and using ''high grip tarmac''. would this tarmac have a real impact on times?

They were tested at Millbrook. High grip tarmac means skid resistance coating.
25 and counting.

[Sir Tigger KC]

Shit! Where are you going to find some 'high grip tarmac' for your test?   

[biggriffin]

Shit! Where are you going to find some 'high grip tarmac' for your test?   

Its used on approach's to roundabouts and zebra crossing,
 so the bear be doing 0-60 starts on the crossing.

[Andy H]

Guys not bumping this thread but I'm going to get the car weighed on Monday but in the mean time I feel another compression test is in order to see if I have a slight drop (perhaos due to rings) just to ensure theres not a problem there and I haven't got anything better to do

one quick question....should the engine be hot or cold for compression testing?

 

You need to be able to work comfortably on the engine so compression tests are usually done with a cold engine. The final readings are very dependent on cranking speed (which is itself dependent on battery state and oil viscosity) therefore it is very difficult to predict what pressures you will get - variation between cylinders is more significant than the actual numbers.

[Rods2]

A hot engine will also heat the intake air making it less dense, which reduces power. I'm sure there must be available charts for this along with engine oil viscosity and ring sealing. Please put these up on the website, so we can all inspect and take the p comment accordingly!

Engineering is all about compromise as a god squad lecturer used to tell me, the lord giveth, which we engineers take advantage of, but then with further order effects the lord taketh away. Nothing is free in life!!!

Control theory is a classic for this and multiple partial differential equations and their standard solutions to model this are just wonderful, or so I had to do at collage and hated I've heard.

[Webby the Bear]

Some say with engine warmed up. Some say from cold. That leaves me no choice but to do both and see if the results vary 

Re the Tarmac. I was merely wondering if this would make up a big percentage of time.  . . Ie half a second or so?

[Diamond Black Geezer]

I forget the percentages, but I did read somewhere that the road surface accounts for a far larger percentage of your total grip than the choice of tyre does. Of course this isnt the same me saying  'I recommend you just fit cheap ditchfinder tyres, then' - the better tyres still increases grip of course, but compare your grip levels on Pingpong XL crossplys on hot, dry tarmac, vs Goodyear Eagles on wet, oily uneven roads as you'll take my point.

Anyway, point being, that yes, the road surface affect grip in a large way. However that's surely in cornering, however, in a straight line I'm not so sure what affect that will have... negligable, or less? Unless you're actually wheelspinning when you set of, and a grippier surface would let the wheels literally grip quicker, as I say, not sure that the road surface isn't only a tiny amount.


Also I'm well aware that I have used the 'I did read somewhere' line, so please take my opinion with the same pinch of salt that you would with the bloke in the pub who has a mate who knows a guy that definitely knows about cars