i’m in the process of piecing together a turbo kit for my 91 ls.
i did a compression test tonight and i wanted to make sure i did everything right…
here is the procedure i followed;
removed all spark plugs
unplugged fuel pump(so cylinders wouldn’t fill with fuel)
hooked up tester.
pushed gas pedal to the floor, pressed clutch in and cranked car
continued to crank until pressure stopped rising(4-6 cranks)
repeated for each cylinder
heres my results;
cyl. 1 215
cyl. 2 210
cyl. 3 200
cyl. 4 220
these seem great considering my car has 127k.
did i do everything right? if so boost here i come!!
as long as youre within 28psi between any adjacent cylinder (next to eachother) youre within service limits. youre over 200, so i’d say youre building up good compression
one more thing. my car does use oil, about a qt every 1k. it smokes mostly on start up, so i’m leaning towards valve seals, since the compression seems good. still ok to boost?
thoughts?
shawn
your compression does seem kinda high. my ls is pulling 180+/- 5 psi on all cyls (195k miles). even my old d16 with 9.2:1 static (same as ls) was high as hell at 210psi. im also using up some oil, at similar rates to you, and i also think its valve stem seal related. i say boost it up, and go from there, thats what im going to do
Those numbers seem fine to me. Although in the long run, it looks like cylinder #3 would be the first to burn oil. If you’re worried about those numbers, do a leak down test before you boost.
Also, just curious–how many cranks did it take for cylinder #3 to get to 200psi, in respect to the other cylinders?
Also, if you do plan on boosting ALOT of psi, in the near future you might want to consider re-lapping the valves, a new head gasket, piston rings, and CS and rod bearings–just to make sure everything is smooth and reliable.
Also, some may find this unorthodoxed, but if you want to seal-up those piston rings which you have in there right now, try Restore oil additive. On my 2nd LSvtec, one cylinder jumped from 265psi to 277psi. This could help reduce piston ring blow-by when you begin boosting. (And on my old turbo 4G63t motor, the cylinders jumped from 205 to 210.)
i did this test a while ago, but i cranked all the cylinders about 6-7 times. most of my burning is on cold start ups. hoping valve seals, but i’m never that lucky. i plan to boost between 8-10 lbs. whats re lapping valves mean?
so restore might work?
There is valve lapping compound which is a very very fine paste which has a fine sandpaper like texture to it. When you re-lap in your valves, this will clean out the imperfections between the valve seat and the cylinder head.
Doing this allows for less wasted power, when explosion occurs at top dead center. The benefits will also show-up in compression tests. When I relapped in my valves on my 2000 B16 head on my Lsvtec, the psi jumped about 5 to 7 psi in each cylinder respectively.
(The constant smacking of the valves over several years of usage and high revving, the valve seats tend to develop imperfections.)
In in terms of the Restore oil additive, I still haven’t found a reasonable argument as to why it’s bad, other than it changing the oil viscosity.
(IMO, the parasitic power loss from the slightly higher viscosity oil drag, is a good trade-off for increased and evened-out cylinder compression.)
i bought lapping compound but stopped after doing one valve after hearing that some people choose not to do it. they say that it can leave bits in the seat. i think an old school domestic guy said this. it never came to a final conclusion, so i just left it .
i dont trust any additive. i think it’s a much too complicated subject to leave to people other than the oem or at least oil manufacturers.
The exprienced engine guys at the machine shop here in Santa Cruz CA, say that valve-lapping is the next best thing to full valve job by them. I think as long as you clean off all of the valve lapping compound afterwards, you should be fine. IMO, valve lapping is a good way to clean-up the valve seats, if you don’t to spend $400 on a valve job.
My understanding is also, whenever you get new valves, i.e. aftermarket valves–portflow, ferra, crower, skunk 2, redline, etc…you are supposed to lap in the new valves, with lapping compound.
In terms of oil additives and their effects on dynamic oil viscosity “N,” as XDeep pointed out, this is a complex, and never stagnant matter.
Obviously, a highly viscous fluid looses viscosity as temperatue increases, and gains viscosity as temperature decreases.
This slower movement of the oil, is what I read as one reason why Honda designed Vtec to not engauge during cold oil temps.
In terms of the Restore oil additive affecting the chemical composition of the combusting air-fuel mixture, this can also have an affect on emissions regulations, especially if there is slight piston-ring-blow-by. As the Restore additive adheres to the cylinder wall, after the flame front from top-dead-center, the Restore additive can be burned in the air-fuel mixture–even more so than the oil itself.
What I experienced with my LSvtec which initially had ~240 psi in the #3 cylinder, was that after I added Restore, the pressure in that cylinder was the HIGHEST of all of the 4 cylinders, when previously, it had been the lowest. After Restore, it was ~280 psi.
Although what I did notice, was a slight increase in oil burning, but an increase in static compression.
On the other side of the coin, the Restore additive can be looked at as a “Band-Aid” product, which would just mask the inherent engine problems. This could also be the case with MANY other oil additive products.
(I hope I didn’t ramble on too long. Anyhow, if anyone has any other insights about change in oil viscosity affecting static and dynamic compression, please add.)