Thread: Too much crankcase pressure, novice engine builder

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Originally Posted by jerry clayton

How much gas do you have in the tank right now??????????If you could lower the level to near empty you could just add 5 gallons of a higher octane to see if it helps-------BUTTTTTTTTTTthose higher octane fuels do need to have jetting increased--------

Ya' know Jerry, with due respect I disagree. If NegativeZero is wanting to run 91octane then adding 93 to the tank (or a bunch of octane booster) and then rejetting the carb to get the AFR right isn't really going to help, other than telling him that it's detonation. To run on 91 he's going to have to back out the jet changes, and solve the problem with timing/compression/repairs to rings or something else. Instead of "contaminating" the tank with different fuel I would back out some timing.

I believe that with aluminum heads and a 10.0 compression ratio running 91 octane should be good. I also believe that the compression leakdown test that you first suggested is the best next step to learn more about what's going on in each cylinder.

I hope that you don't get your knickers in a knot about someone disagreeing with you..............................

Originally Posted by rspears

Ya' know Jerry, with due respect I disagree. If NegativeZero is wanting to run 91octane then adding 93 to the tank (or a bunch of octane booster) and then rejetting the carb to get the AFR right isn't really going to help, other than telling him that it's detonation. To run on 91 he's going to have to back out the jet changes, and solve the problem with timing/compression/repairs to rings or something else. Instead of "contaminating" the tank with different fuel I would back out some timing.

I believe that with aluminum heads and a 10.0 compression ratio running 91 octane should be good. I also believe that the compression leakdown test that you first suggested is the best next step to learn more about what's going on in each cylinder.

I hope that you don't get your knickers in a knot about someone disagreeing with you..............................

I tend to agree. I don't understand how running higher octane gas relieves the crankcase pressure problem. If an engine is not allowed to breathe, IMHO, it's bound to blow up just like what happened to the 57 Ford I had.

OK guys-here's the deal---by taking out as much fuel from the tank as possible, it will only take a few gallons to raise the octane level of whats then in the tank!!!!!!It won't be contaminated-------and as the fuels get more to the higher level octanes, you need to richen up the jetting---------the AFR will be different with race gas-------now he hasn't told us anything about his timing except he don't know???????

His higher crankcase pressure at higher RPM levels point to detonation--------ignition timing and jetting/octane is the cure--------

Should I list my qualifications for him??? or would that make me liable for damages???????

Ken-about your 1957 Ford-------The 57's didn't have factory pcv system-they had a vent tube breather system----the mods done for smog probably removed/sealed that and then pressure would build up------and-----------the oil system-------especially 2 qts low-didn't have enough pressure to overcome the positive crankcase pressure to have oil flow to the crankshaft-----

Originally Posted by jerry clayton

OK guys-here's the deal---by taking out as much fuel from the tank as possible, it will only take a few gallons to raise the octane level of whats then in the tank!!!!!!It won't be contaminated-------and as the fuels get more to the higher level octanes, you need to richen up the jetting---------the AFR will be different with race gas-------now he hasn't told us anything about his timing except he don't know???????

His higher crankcase pressure at higher RPM levels point to detonation--------ignition timing and jetting/octane is the cure--------

Should I list my qualifications for him??? or would that make me liable for damages???????

Jerry, no one's saying it's not a possible detonation problem, but the guy has said he's running ethanol free 91 octane and would like to keep that as his fuel. With aluminum heads and 10.0 to one compression he should be fine with 91 as far as detonation is concerned, in my opinion and as has been stated often here in the past (TechInspector1 comes to mind). Since "...ignition timing and jetting/octane is the cure--------" that leaves ignition timing and jetting as the options.

Let's not drive another new guy away by refusing to listen to what he's asking and arguing.

Originally Posted by jerry clayton

Ken-about your 1957 Ford-------The 57's didn't have factory pcv system-they had a vent tube breather system----the mods done for smog probably removed/sealed that and then pressure would build up------and-----------the oil system-------especially 2 qts low-didn't have enough pressure to overcome the positive crankcase pressure to have oil flow to the crankshaft-----

It was only 2 quarts low after the dipstick blew out. Funny thing, Ca has been "fighting" smog since the early 60's and they still have smog. A guy I worked with at Douglas said "that as long as there is a smog commission we'll have smog". No truer words were ever spoken.

It's a few gallons of fuel, I have a syphon though. It's not hard to empty. I have larger jets for my carb which is a 750 cfm 1411 Edelbrock. The manifold is a dual plane high rise also from Edelbrock. I don't know the flow number off the top of my head. Exhaust is a 2.5" diameter, H-pipe, with 1 5/8" full length headers. The AFR gauge is places about 6" behind one of the headers. No known leaks from the exhaust.

As is stands, since I have people here telling me this is likely a tuning issue, I'm going to go ahead and take my car to a tuning shop. I will get in touch with them before hand about all of this and give them the update and see what they would like me to do and what fuel they'd want me to have in the tank. I do plan on doing a leakdown test first however. When I get the equipment and do it, I'll be sure to post results here.

I'm interested to see if you think this is the right call, and I also appreciate all the info.

Read your plugs, they will tell you if detonation is present by specks on the porcelain (or worse melted). The plugs will also tell you your tuning.

Leak down test is a must do.
JMHO, your compression test shows a problem.

Originally Posted by NegativeZero

Static compression ratio is 10.1:1 Results of a cylinder compression test are as follows:
cyl1 - 135 psi lower mid of 10% compared to highest
cyl2 - 130 psi very low side of 10% compared to highest
cyl3 - 139 psi upper side of 10% compared to highest
cyl4 - 132 psi borderline low side of 10% compared to highest
cyl5 - 133 psi borderline low side of 10% compared to highest
cyl6 - 137 psi mid side of 10% compared to highest
cyl7 - 125 psi below 10% compared to highest
cyl8 - 143 psi highest

don't mix the plugs up when you remove them -keep them in the order they are in the engine------the best plug reading results are when engine is shut down while doing its best ---like going for a drive and running it up thru the gears hard and shooting off, coasting down to a stop in neutral and pulling plugs while even still hot------have another set with you already gapped so you can install them and keep the others as removed-

and do you know what your timing is set to???????? did you verify the tdc mark ?

Originally Posted by NegativeZero

I will get in touch with them before hand..... and see what they would like me to do and what fuel they'd want me to have in the tank.

Just my $0.02 if they tell you to have anything other than the fuel you want to run I'd be asking them why they would tune with different fuel. Just doesn't make sense to me. You'll end up with your timing too far advanced for the fuel you plan to run.

Originally Posted by 36 sedan

Read your plugs, they will tell you if detonation is present by specks on the porcelain (or worse melted). The plugs will also tell you your tuning.

36 sedan, not too awfully long ago you posted one of the best picture references on reading plugs I've ever seen. Is that something you might have close and could repost here. It was the best.

Found it...

Originally Posted by 36 sedan

Read your plugs, they will tell you if detonation is present by specks on the porcelain (or worse melted). The plugs will also tell you your tuning.

Leak down test is a must do.
JMHO, your compression test shows a problem.

I've done a lot of reading on this and can't seem to find an exact answer, but cylinders within 15% of each other seemed to be the general consensus for acceptable.

A leak down kit has been ordered and I'm sure will give some results to consider.

Originally Posted by jerry clayton

and do you know what your timing is set to???????? did you verify the tdc mark ?

TDC mark is verified. I don't understand timing enough to give you an accurate number on "what it's set at". Between the vacuum advance, mechanical advance, and just regular setting. I'm not 100% sure. My strategy largely reliant on looking at what other's did on the internet and adjusting it until I didn't hear any knock anymore. I do have a timing light, but this is why I am planning on going to a tuner since I'm not at all familiar with this.

Originally Posted by NegativeZero

I've done a lot of reading on this and can't seem to find an exact answer, but cylinders within 15% of each other seemed to be the general consensus for acceptable.

A leak down kit has been ordered and I'm sure will give some results to consider.

15% is a pretty wide spread. I would question anything more than 10%, especially on a new motor. Did you follow with a wet test?
Probably irrelevant, the leak down test will tell more.

Originally Posted by NegativeZero

My strategy largely reliant on looking at what other's did on the internet and adjusting it until I didn't hear any knock anymore. I do have a timing light, but this is why I am planning on going to a tuner since I'm not at all familiar with this.

You may have just found the problem! With the engine warmed up and running at idle unhook the vacuum line to your distributor and plug the hose (pencil or golf tee work good). With the engine at idle adjust the distributor position to your base timing with your timing light - I would start at 12 degrees before TDC for your SBC, tighten the distributor hold down bolt and recheck to be sure it didn't shift with tightening. You can rev the engine a bit to see with your timing light that the mechanical advance is working, then hook up your vacuum line and you're good to go.