RV8 Compression Test

[rabowman]

Sorry to kind of hijack this forum but when I had my 400SE and Chim 450 the advise on RV8s was amazing.

I bought a Cobra replica recently with a std 3.5 v8. I am just about to have some pricey upgrades carried out but before I do, I decided to check compression.

This was done COLD with throttle fully open and results were from 1 to 8 (psi) 149..142..158..134..138..142..138..148

Before I spend any money I would be grateful for views on the above

Thanks
Rob

[Number 7]

You need to do the test with a hot engine. There's a very good "how to" from Dave Baker somewhere online. Let me see if I can find it..

[Number 7]

Here you go:

http://www.max-boost.co.uk/max-boost/internet_arti...

[rabowman]

Thanks, It is not possible to test hot as the 'Banana Bunch' manifolds are not wrapped and I value my hands!! However it is not the values that worry me but the variation.
Rob

[Julesprivate]

rabowman said:

Sorry to kind of hijack this forum but when I had my 400SE and Chim 450 the advise on RV8s was amazing.

I bought a Cobra replica recently with a std 3.5 v8. I am just about to have some pricey upgrades carried out but before I do, I decided to check compression.

This was done COLD with throttle fully open and results were from 1 to 8 (psi) 149..142..158..134..138..142..138..148

Before I spend any money I would be grateful for views on the above

Thanks
Rob

When you say a std 3.5, any idea what from and what year? It'll make a fairly big difference as the type of cam you're running will have a big impact (bigger overlap will lower the reading). Normally if they are within 10% of each other you're over the first hurdle... I'd do a quick leakdown test on number 4 just to be happy..

ETA
Compressions tests on a cold engine give lower readings, so the 10% rule is your best sign if you can't do it hot...

Edited by Julesprivate on Tuesday 30th July 18:05

[rabowman]

RPI unit fully rebuilt ex SD1 only 11k miles since rebuild in 1996. (full s/h since)
Piper270/2 cam and stage 1 heads

[v8 racing]

To be fair all fairly meaningless depends on what upgrades you have planed, the difference in c/r is fairly high, this could be down to a shot cam, but like I say if you are upgrading the cam these figures wont matter.
Just out of interest, you really cant do a compression test on an engine like the rover that has hydraulic tappets, the more you crank the engine over without it actually firing, the more the lifters will bleed down and reduce lift and opening times on the camshaft, which will screw the figures, better off doing a leak down test.

[rabowman]

Thanks V8 racing.
upgrades are 123 ignition instead of Mallory dual point and Offy manifold plus 500 Edelbrook instead of SUs

[v8 racing]

rabowman said:

Thanks V8 racing.
upgrades are 123 ignition instead of Mallory dual point and Offy manifold plus 500 Edelbrook instead of SUs

Certainly worth upgrading from points, for the life of me I just don't understand why people are still using these, the 123 I can't really comment on, I have never used one, but the big downside on a v8 is only using 1 coil, in essence it is the same as a 4 cylinder reving to 12000rpm as a v8 revving to 6000rpm, maybe worth looking at going coilpacks and a budget ignition system, as for the offy manifold, if you have bonnet clearance issues then you may be stuck with the offy, but the edelbrock is a far better manifold and worth a good 20bhp over the offy

[rabowman]

Thanks, will check clearance