as a preliminary step in my persuit of increased power for the orange car i have now had a leakdown test with the following result:
1) 13%
2) 18%
3) 14%
4) 12%

5) 18%
6) 7%
7) 8%
8) 20%

its all going past the rings according to the mechanic, with the test performed on the engine when warm ie less than operating temp.

im quite pleased at the result in light of the cars 170k miles and the fact that it still goes very well but im not sure of the practicality in adding forced induction. anyone care to comment?

 

What would be the downside of worn rings on a forced induction car?
Is the only concern additional crankcase pressures?
If so, a good vent setup should handle it.
Obviously, a worn engine may not hanfle the boost as well as a young, strong one.
But does that really mean that the rods or pistons are actually worn, or weak?
Or is a poor leakdown test just a sign of age in the rings?

I haven't done a leakdown yet on my car, but it is pretty strong.
But it does have a lot of blowby, which makes me think that
perhaps the rings may be showing signs of age. But it is
still strong, and I am guessing it should take boost without
too much of a problem...

 

yeah bc,

i hope so too and im waiting for someone to definitely talk me into it! the reason i ask is because others have suggested compression and leakdown testing prior to boosting, i presume for a reason??

 

A car as pretty as that needs boost. Eh, go for it!!!
My car has nearly 155K miles. Im going to do a leak down on it but, honeslty, whatever the results, it will get a blower either way.

 

yeah tony!

im going to paint the little scuffed bits under the mouth blood red i think.. after ive chewed on some ferrari!!

but honestly, what is important to verify prior to boosting?

 

Leak down testing is typically done by applying air at 100 PSI and measuring how much the cylinder can retain letting 18 to 20 % of that escape is a pretty big percentage . The pressures with the engine running are very much higher . Add boost and the blowby into the crankcase is going to be a lot to deal with . One negative to blow by is that the oil mist / vapors may cause detonation since it burns much different than gasoline if you allow it to be dumped in to the intake . Vent it to atmosphere catch can and you may have other problems . An engine that is that tired is not ideal for supercharging . On the other hand , not much to risk ; the engine needs to be rebuilt anyway !

 

> Vent it to atmosphere catch can and you may have other problems...

Such as?

 

If under the hood the fumes vapors may get into the heating A/C system making it smell like an oil leak ,, the catch can will require service or dumping , plumb it into the exhaust and you get clouds of smoke . Any such venting is strickly cut and try until it works .

 

granted, this tired old engine isnt 'ideal' to be supercharged and as pointed out it needs rebuilding anyway. maybe it wont be so bad??

 

I'll let you guys know soon if my catch can vented to the exhaust works or not.
My idea is to separate the oil mist, prior to venting to the exhaust.
And yes, an under-hood breather smells bad and looks bad.

What do you guys think of Quick Carl's breather kit?

http://www.928motorsports.com/parts/oilcontrol.html

 

drnick,

I would echo Jim's statement - most of the guys I've talked to who design supercharger systems for a living will tell you that anything over 10-12% leakdown means it's time for a rebuild before it's time for a blower. I would also add it would suck to frag the motor bad because of a broken ring or some such.

I am a little surprised (not terribly, but a little) at a couple of the numbers you posted, if in fact, it is all going past the rings. I would not be shocked at those numbers if the majority were blowing by the valves - the valves/guides seem to follow the 'normal' rates of wear for most engines. The Alusil block though, tends to mitigate a lot of the normal wear, I have seen more than a few unrebuilt 120K+ mile engines at better than 95% across all 8 cylinders.

Are you confident it's not the valves?

Greg

 

greg,

not having performed the test myself i am not confident of anything - you know how the saying goes if you want something doing right. i had another mechanic check compresions last year with the following result:

1)190
2)180
3)175
4)185

5)165
6)145
7)150
8)160

as you can see there isnt really a clear correlation between both sets of numbers so im not entirely sure what each individual reading actualy means.

i think overall however the picture does evidence wear and tear and perhaps more than just a little. maybe i am looking at more than just bolting on a supercharger to squeeze out some extra horses.. i do know where theres a wrecked gt, i wonder..

 

Not a lot of correlation ?? like zero , none , nada ...... the two best for leak down 6 and 7 are the two worst for compression !! I would have liked to have seen number one checked again at the end just to be sure part of what you are seeing is not just the battery wearing down . At any compression over about 100 the cylinder will fire less than that and it is a seven cylinder engine . If you shoot a bit of oil into each cylinder and the compression numbers increase then it probably is a ring cylinder wear problem and not valves .

 

Not so sure your motor is or isn't a candidate, but the compression test component seems nice.

 

yeah,

i dont know what this all means exactly. i do know that the cylinder bank with higher compressions has had the head off after a camshaft breakage (apparantly it happens on this side as the distributor drive weakens the shaft) and consequently the head was rebuilt which i think accounts for the higher compressions.

ive been on the phone to some places that can rebuild it and also to some breakers who have a gt engine and this is where im at. do i: 1) slap a supercharger on it and see what happens; 2) do a basic rebuild assuming this is possible and then supercharge; 3) drop in the engine from a gt???

perhaps i should have the compressions and leakdown done again to gain a more accurate picture.