Jump to content
SAU Community

Recommended Posts

Just wanted to share my comp test result. First time I done one and I kind of shit my pants as nothing would read past 60psi. Turns out you gotta crank for about 15 seconds as the motor seems to push the pressure up about 30psi each time it goes around.

Anyway these are my results

160, 155, 160, 155, 153, 153.

I don't know if 5 and 6 are of a concern but I do have to keep my eye on it all. The spark plugs looked fine. I was abit worried as the car has seen a couple of instances of +100 knock and a couple around the 90 mark.

For the noobs who are doing their first comp test, be careful. The engine is at operating temp when you start so your hands are prone to being seared. Also have another car with jumper leads hooked up to your car as the battery will go fair quickly. Crank it for about 15 seconds or position the gauge so you can see it in the cabin when it stops rising. Its not always easy to position it so you can see it so when you aren't sure just crank it a few more times. Remember to disable fuel.

Link to comment
https://www.sau.com.au/forums/topic/382795-my-comp-test-result/
Share on other sites

Pistons and rings won't be expanded on a cold motor, valves and guides as well. You'll generally get lower readings and a lot more variation between cylinders. {lus as SargeRX8 says oil as well. Motor needs to be at operating temp - or at least very warm.

Because of the intake plenum design on the RB engines, lower compression in the last cylinder is normal as it's usually the "lean cylinder".

are you referring to Rb26's here with the front facing plenum or all RB's? (25 included- such as in the example of this thread?)

I can see this being the case with the FFP of the 26's but not 25's. I thought the symettrical plenum on the RB25's would avoid this?

More air into rear cylinders due to manifold design, and all cylinders get same amount of fuel= leaner air/fuel ratio at the back, more heat, more prone to det.

Nismo plenum fixes it. We just run a bit more fuel in the rear cylinders.

I would have thought that since the runners are further back, the air would be forced into the cylinders closer first but after thinking of it logically, the air would be gushing to the path of least resistance so it would be building up at the back of the plenum.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


  • Similar Content

  • Latest Posts

    • I'm normally copping my own abuse from neglecting my daily drivers. "Those suspension bushes will last a bit more", "Don't worry about the oil leak, just keep topping it up". The project cars I'm always doing things slowly on them as I'm wanting them to be done better, and neater, and nicer. Luckily I don't have to deal with 18 year old Matt's "Learning to wire" stuff in the project cars. And there's only one piece of wiring I'm displeased about in the Landcruiser, and it's about to be cut out... However, the box loads of parts that have been going through this place lately for the Landcruiser... Brake pads Brake Rotors Full handbrake overhaul Wheel Bearings Seals Swivel hubs Steering Boxes Half the suspension joints Shocks Air bags (Ones to go in the rear springs for towing) Water pump Timing kit Lower timing case Harmonic Balancer Radiator Lots of other little seals and shits Gas struts for the bonnet New power window switches And god knows what else I've forgotten... Ha ha ha I have my fingers crossed the pinion seals don't start leaking on the diffs, that the transfer case doesn't leak, and the gearbox input shaft doesn't leak, nor the rear main seal. As they're about the only seals I haven't replaced in the driveline! I'm seriously eyeing off buying new caliper rebuild kits front and rear brake calipers... I'll probably recheck all the valve clearances soon too, and hopefully, it should be all good and sweet to haul some long distance trips again!
    • Every time I pull my 3x gauges out of the console and see the crack-addict way that I did the wiring, and I just can't bring myself to tear it all apart and "make it nice", because it is currently working. In fact, the last time I was in there I probably made it worse.
    • The best part is when you own the car long enough that you look back and find your OWN ham fisted amateur shit!
    • The annoying part about neglect, is when you start to replace one thing, and find ten more broken things. Ham fisted monkey repairs you normally only find out about when trying to do something unrelated! Ha ha   Neglect you can kind of anticipate the huge costs to fix it all. Ham fistedness is normally a shock the first time your work on a new old car, as everything "looked" good before.
    • For DBA, check out their guide table here. https://dba.com.au/wp-content/uploads/2023/01/Direct_Replacement-Guide-2021.2.pdf   Additionally they have some other guides and info on how to make sure you choose the right pad.
×
×
  • Create New...