NB8A cylinder compression

RX-747 · Postby **RX-747** » Tue Jan 28, 2014 6:53 pm

I am thinking of going turbo on my NB8A and decided to do a compression test before I went ahead with it. Haynes manual says that for 1.8l should be 185psi but I have seen readings up to 205psi in other peoples results so i am confused as to what the actual results should be/ are from factory? My results from my compression test are as follows bellow:

Cyl 1: 199psi
Cyl 2: 199psi
Cyl 3: 198psi
Cyl 4: 199psi

I am pretty happy with the results and am confident to turbo but just want some confirmation as to what the actual values are from factory.. Also just wondering where I can take the turbo water feed from? I know that question should be in the turbo section but thought i would ask it all in one go..

Cheers

16bit · Postby **16bit** » Tue Jan 28, 2014 9:14 pm

not sure on actual figures you should be getting, but would think that its quite inaccurate between gauges/equipment/techniques.

i think the most important thing is that the cylinders are consistent which yours are so it would appear your motor is in good condition.

no idea on the water feed.

Postby **NitroDann** » Tue Jan 28, 2014 9:35 pm

Thats way to close to be likely correct?

Dann

RX-747 · Postby **RX-747** » Tue Jan 28, 2014 10:39 pm

NitroDann wrote:Thats way to close to be likely correct?

Dann

I thought this too but its the same gauge I used on my built 16v corolla last time when it had a blown head gasket and it seemed to have worked.. I warmed up the car, unplugged the coil, took out all plugs, screwed in the comp tester, cranked the engine for the recommended time at WOT and its the result I got.. The engine does feel good, revs nicely and doesn't use any oil.. I bought the car at 95,000km did full major service myself and now its up to 130,000, I always serviced pretty much every 5,000km with penrite 10 tenths fully synthetic so i would expect it to be in good condition but I too am skeptical of the actual result.. I might try another comp tester if i can find one and see how it goes, if i get the same result I guess ill be happy haha.. But I am guessing that factory would be about 200-205psi..

manga_blue · Postby **manga_blue** » Tue Jan 28, 2014 10:58 pm

RX-747 wrote:But I am guessing that factory would be about 200-205psi..

Factory NB8A specs are standard:209psi, minimum 146psi, max difference between cylinders 28psi. I want to buy your motor.

speed · Postby **speed** » Wed Jan 29, 2014 12:10 am

RX-747 wrote:I am thinking of going turbo on my NB8A
Cheers

I'm jealous!
How much boost can you run safely with standard compression anyways?

Thought I saw something re the turbo feed pipes on one of the mighty car mods re turboing a MX5.

16bit wrote: would think that its quite inaccurate between gauges/equipment/techniques.
i think the most important thing is that the cylinders are consistent which yours are so it would appear your motor is in good condition.

Agree re the gauge.

Why is minimal variance the most important thing?
I was always led to believe this is important but have recently been told having slightly lower compression in a cylinder is no big deal and it should still make decent power.

Postby **NitroDann** » Wed Jan 29, 2014 12:34 am

lower comp all around tells you the rings are wearing out with age.

If you have one cylinder which is low something has gone wrong in that cylinder.

Damm

RX-747 · Postby **RX-747** » Wed Jan 29, 2014 1:07 am

speed wrote:I'm jealous!
How much boost can you run safely with standard compression anyways?

Thought I saw something re the turbo feed pipes on one of the mighty car mods re turboing a MX5.

I'm only going for around 8 or 9psi at the moment, mighty car mods turbo was only oil fed from what i remembered, mine is and gt28 and is oil fed and water cooled.. I'm thinking of maybe using one of the heater hoses or bottom radiator hose but ill cross that bridge when i get to it, hopefully it doesn't slow the installation..

Thanks a lot for the speedy responses guys, ill get my hands on another compression tester and post up the results, fingers crossed that it doesn't vary too much from the first test haha..

hks_kansei · Postby **hks_kansei** » Wed Jan 29, 2014 10:54 am

NitroDann wrote:lower comp all around tells you the rings are wearing out with age.

If you have one cylinder which is low something has gone wrong in that cylinder.

Damm

Like the engine in the Kingswood my GF and I have.

#3 and #4 were down a bit compared to the rest.
Take off the head and see a nice score mark in bore #3, and a mark that looked like the head gasket had failed between the cylinders.
Then there was the nice cracked skirt on piston #3.

So yeah, a low number on one can indicate something is wrong with that cylinder.
But there's some leeway between them, Manga-Blue quoted 28psi

RX-747 · Postby **RX-747** » Thu Jan 30, 2014 11:50 pm

So borrowed my mates comp tester to test the compression again, his threaded part was a bit stuffed so i used the rubber push in one and my friend recorded 190-195psi on cylinder 1 but was struggling to hold it in.. When we got to cylinder 2 we got close to 190 but the rubber bit broke off from the end and landed in the cylinder but gave the car a few cranks and it blew out on the cylinder haha so I stopped testing it after that and am going with my original results, I believe that the motor is somewhat healthy and near the original test results.. But I will never use a push in compression tester ever again haha after this experience..