52 replies to this topic

[Johno]

Is that to do yourself or send it away to get done?

[yel327]

Sent away. Xtreme fuel Systems, Hume Performance. Both Sydney region. Others in Melbourne too.

[Johno]

How hard is it to do it yourself?

[yel327]

A lot harder than $350-odd. To me anyway.

[lemonaro]

Get on youtube and watch a couple of videos on how to rebuild a Edelbrock 600 carby. I rebuilt a Rochester 4 barrel after watching a couple of videos, easy as and ran like a dream. There not rocket science.

[Shtstr]

I got the following compression test results will all plugs out and throttle wide open. 355 stroker with fairly lumpy cam. What do you make of this? I’m happy there’s no one cylinder that’s really low and all are within a reasonable range.

Drivers side:
120
110
120
120

Passenger side:
120
110
110
130

I noticed the compression tester looked like it couldn’t screw in all the way to the rubber o ring to seal it. Not sure how to get around that as I’m only meant to screw it in finger
tight.

That engine would be better off with a smaller cam.
120 TO 130 PSI dynamic compression aka cranking compression is way low.
A good healthy engine that will make good power and torque should be up between 180 to 200psi on a compression test.
I aim for 190 to 195psi myself.

[LJ RB30]

If the throttle shafts have no movement  ie up & down, then they are easy to rekit, otherwise send it out to be fixed.

Yes watch some youtube as stated above to get an idea of the procedures & set ups 

Just remove all residual gasket material, clean EVERY passage with carb cleaner & compressed air.

Safety glasses are essential as there's a 99.99% chance you will have a passage pointing towards your face as you squirt/blow through it!

Put a straight edge across the surfaces to check for flatness, check condition of threads & idle mixture screws.

Reassemble with new gaskets & power valve ( some kits even have new idle mixture screws)  & it should be good.

[yel327]

I’ve done Quadrajets before too. But by the time you clean them, buy all the parts, frig around rebushing the shafts etc it isn’t worth it. Rebuilders do them perfectly and you get them back recoloured as per original, they are run tested and work like clockwork.

[LJ RB30]

Yes a Quadrajet is much more involved than a Holley, especially if it requires rebushing & you want it recoloured as per stock then definitely send it out.

That's why i said if the shafts are flogged send it out otherwise if its a basic rekit the its not a bad thing for a beginner to have a go at.

Will give them a greater appreciation of how things work.

Ive done a couple of my own Quadrajets (rebushed, coloured & kitted) & some single strommy's &  the colour is certainly not correct.

Wasn't going to try multiple brands of colour's to get perfection because it was mainly just for me.

Certainly wouldn't do enough to recoup costs & time involved but at least the zinc plating kit has been very handy on nuts & bolts lately.

[Johno]

That engine would be better off with a smaller cam.
120 TO 130 PSI dynamic compression aka cranking compression is way low.
A good healthy engine that will make good power and torque should be up between 180 to 200psi on a compression test.
I aim for 190 to 195psi myself.

Would this indicate worn rings all round, given that it’s even across all cylinders?

Perhaps there’s a chance my compression test wasn’t sealing properly in the plug holes. I screwed the tester in hand tight but the thread on the tester was way longer than the thread on the spark plugs. So the tester couldn’t screw in far enough to hit the o -ring to seal it as in the pic.

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[Johno]

Disregard the above, I re-did number 2 cylinder and it was seated fully, it just looked like it might not have been due to where the oil mark is ion the screw in part. Was hoping maybe I’d lost 30 PSI somewhere.

Are we thinking generally worn rings? Is it common to be consistently low on all cylinders?

If it’s generally worn rings I’m hoping I can get away with driving it as is until I can save the money for an engine rebuild. With a tune and maybe not as much power as it should have, I’m hoping I can drive it for a while without any show stoppers.

At least it’s not dropped one cylinder or anything.

Edited by Johno, 12 April 2023 - 10:58 PM.

[Shtstr]

Would this indicate worn rings all round, given that it’s even across all cylinders?

Perhaps there’s a chance my compression test wasn’t sealing properly in the plug holes. I screwed the tester in hand tight but the thread on the tester was way longer than the thread on the spark plugs. So the tester couldn’t screw in far enough to hit the o -ring to seal it as in the pic.

Not necessarily. Do you have blow by?.
If not this is what I'm thinking
To me it shows an engine that has about 9.5 to 1 or 10 to 1 static compression ratio and a cam that is to big bleeding off dynamic compression.

[Johno]

I did the compression test because I suspected it had too much blow by.

I put a breather on one of the rocker covers and noticed it emitting smoke that I suspected may be blow by. But wasn’t sure if it was just condensation.

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[Heath]

The compression figures from your test are low... concerningly low, but unless you've seen other evidence of the motor being rooted (is it haemorrhaging oil via leaks? Or blowing oil smoke? Is the crankcase copping heaps of blowby when it's under load?)

I'd hesitate to pull it to bits. You're likely gonna spend $10k on it by the time you open it up properly and I do wonder if it's worth just trying to get it working better.
Cars like Toranas with built 355 motors rarely get out of the shed enough to wear things out. Never say never of course! But normally cars like this get put in the naughty corner when things like carbies and ignition systems start playing up.

[Johno]

It’s not mixing oil and water and not putting out blue smoke or anything to my knowledge. It’s running not quite right but suspect the timing is a bit retarded. Timing is next on the list.

The other thing that’s a concurrent issue is that it’s got about half the vacuum it should have. I’m yet to find that vac leak.

If I can get the car tuned and running I’m happy to just keep running it as is with less power while I continue pouring money into the overall rebuild.

[N/A-PWR]

Check that #1 piston is at top dead centre to the Harmonic balancer mark,

 

 and the #1 tappets are floating.

Edited by N/A-PWR, 13 April 2023 - 04:48 PM.

[dron]

If you want to check the rings repeat the compression test wet. Small ammount of oil down the spark plug hole, Spin it over foe 2 or 3 seconds to coat the cylinders and retest. The oil seals the rings. If you get another 30 or 40 PSI the rings are on the way out if not there is no problem with them.

 

The highest compression I have had was on a 253 I built for gas, 250 PSI. To get that the block was decked to the point the piston was proud about 3th at TDC and the heads had a lot off them. A stock 308 or 6 cyl can be below 130 from new and anything over 110 will run well .    All depends what the last person built the stroker for. Hi torque, Long life or to raceing etc. The numbers you have are good if that is how the engine was built.

 

    Try the wet test and if you only get an extra 10 or so PSI all is good.

[Shtstr]

To back up what I said earlier about the static compression ratio and the dynamic compression ratio.
V8
4 inch bore
3.48 stroke
5.7 rod
Inlet valve closing at 85 degrees after bottom dead centre.
Will give you a dynamic compression ratio of 136 psi if all is perfect and rings have perfect seal.

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[Johno]

Great info thanks!

I should have done the wet test while I was at it but was just slack.

I’ll do a wet test on number 2 that’s really easy to get to and see what it does.

[Johno]

This is a short clip of it idling:

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[rexy]

Sounds like a lumpy holden should?

 

Your vac reading isn’t unusual with a cam that sounds like that.

[Johno]

Rexy do you mean vacuum or compression is normal for an engine with a cam like this?

If there’s no vac leak I’ll give up looking for it 😆

[ozyozyozy]

As said before, leak down test, can see exactly where the compression is going or if it shows low leakage eg 10-15% it’s just a low comp engine.

[N/A-PWR]

Rexy do you mean vacuum or compression is normal for an engine with a cam like this?

If there’s no vac leak I’ll give up looking for it

Yep,

 normal.

My ones the same,

and need the double diaphragm brake booster to have enough Vac for assisted brakes.

[Johno]

Wow ok that’ll save the headache of looking for a vac leak that doesn’t exist 😂

Noted the double diaphragm.

Thanks for all the info, learning a lot!