mark kibort

After doing some 60-100mph tests and the ole holbert car seems to be feeling a little tired. my race times are still within 1 second of my best, but the last one was on a 100degree F day, and the tires sure felt a little slippery. However, ive posted my fastest times on days like this so i was beginning to wonder whether something is getting a little soft on the holbert engine.

so, i did a compression test.

185 186 187 185psi on the passeger side
195 190 191 191 190 on the driver side

I never before noticed this kind of variance, but i did take the compression tests to 7 -9 full hits. first to second hit usualy is near 150psi.

Im wondering if the cam timing could have slipped on the passenger side. or if this is normal variance.

Ill probably hit the dyno this next week just to see whats happening.

Plugs all look pretty white, but they always have this "white "appearnce". From what ive been told, this can be normal if, the inside of the plug looks grey down the electrode. mixture last time was 12:5 to 13:1 ish.

Has anyone seen the new plugs for the S4 from bosch now? they are called "super" bosch. they have black writing on the plug and still have the part number WR7DC. the electrode tip is a little pointed compared to the squared off prior version. thoughts here??

mk



mk

Charley B

Very Common. Caused by spending too much time on clock-wise running tracks.

AO

Were you running Mobil 1?

Big Dave

dr bob

Just on the driver's side.

AO

Seriously though... did you do the Compression test with the engine warm?

SwayBar

Man, those are some good looking consistent numbers; I wouldn't worry about them at all. I'm speculating that all that knockin' on wood really helps.

Whatever plug you get, make sure it's the plain ol' copper version.

mark kibort

But i spend much more time on the counter clockwise tracks though!!


mk

mark kibort

pretty amazing, considering how much this engine has been through.
i was just thinking the 5psi shift from side to side could be a slight difference in cam timing. (you know how the pulleys really dont line up right, and can be near 1 tooth off pretty easily) if one tooth off, would the compression vary this much or much more?? Im trying to remember if i had done a water pump after my cam timing effort while putting the new 85 cams on. If i did the timing belt afterwards, maybe its possible that im off partially.

so, why the plain ole copper versions???? as far as i know, thats what i got. the spec bosch, but for some reason they are new and improved! (i guess)

mk

PorKen

In theory, with a cold engine, the right side would show a little less compression. Properly adjusted, the 1-4 cam timing is retarded until the engine is warm. (Easy enough to check. )

You are racing on stock plugs? I would think that 6 or even 5 would be safer and make for less knock retard.

I run WR5DC on my '86 (5 is the coldest I could find), and they are always clean.

IcemanG17

MK
Those numbers seem just fine considering the history on that motor.....a low of 185psi on a 10.0 compression engine is still just fine....the variance of 10 psi is also quite good......

A quick way to check if the cam timing betweens banks is wrong is the temp differential between banks...if one is substantially hotter than the other....there it is...like what happened to edcos 928

mark kibort

Thanks! i guess im still thinking of fine tuning getting the next 5-10hp.
the engine was warm (sat for 2 hours before i checked the compression)

remember, i did set the cams where the holbert car originally had them set.
i started out stock at 1.7 and 2mm for the cam settings and then ended up moving the driver side to 2mm to match the driver side. somehow this got my hp and audible sounds of the engine under max revs and power, to how it used to be before the 85 cam swap.

mk

mark kibort

I have alwasy run stock plugs, and they are very clean, but a little on the white side, but look great for a full season of racing.

maybe thats why i felt like i was down in power, some knocking going on and some retarding happening because of it?

Mk

Daniel Dudley

Aside from your compression variance, how old is the MAF ? Has it ever gotten oiled ?

bdstott

So now we know why that engine runs so well... It has an extra cylinder on the drivers side!!