Got a couple of interesting things I wouldn't know how to search for.

1. Put a crate motor in, and still learning the ins and outs of carb goodness. I found out that there is a way to tune the carb other than by sound! Never new it before, but never worked with carb, so I didn't feel bad. At idle, it pulls 18 or so, with it properly tuned. Curious if that's a good number.

2. When I take the gas cap off to fill the car up, it lets out way way too much air. When it was the ol TBI, it would fart, then nothing. This is a strong sound, real pressure, and lasts about 5 or more seconds. Charcoal canister was never disconnected, but I'm gonna take a look at it tomorrow to see if everything is still ok.

3. When I turn the car off with the hood open, I can hear the engine sucking in air. The car is completely off, and I narrowed it down to the PCV valves. I took the valves out, and it still hisses like its hungry for more air. I don't know why it would do that.

Still trying to tune the beast, but it's tough checking out the daily driver for any possible tunability problems when the 350 is new, and I have no experience with carbs. Still needs lots o goodies, but it's still faster than that stock lo3 turd.


GMPP 350 HO
Edelbrock 1411 750 cfm

 

A steady 18 inches of vacuum is generally considered pretty good. Other things will affect that though. Lumpy cams will have lower vacuum, mis adjusted valves will have vacuum issues (dips or fluctuations in vacuum), advancing and retarding ignition timing will change vacuum readings.

The fuel tank is pressurizing because the vent has been modified in some way. The charcoal cansiter is still hooked up, is it hooked up to the tank and the engine? Those usually have a large vent tube and some kind of switching or solenoid tube to control when fumes are actually taken up by the engine. All tubes are hooked up to something that will actually make it function like it was intended to?

Does the PCV rattle when you shake it, it's not clogged? Some of them have a calibrated spring in them, only open at a certain weight of vacuum. The PCV uses engine vacuum to pull fumes from the crankcase. I wouldn't think it would be doing much without the engine running, no engine vacuum.

 

The crate engine is straight from the crate. No modifications have been made to it other than new carb. I don't know the specs on the cam, but it came with the engine, and I'm unfamiliar with cam lingo so I don't know what kind of vacuum this should pull.

I looked at the charcoal canister, and nothing has been removed. Still stock as the day is was made. Could the solenoid perhaps be dead? I think I'll go check to see if it's still opening and closing.

PCV valves are new, less than 200 miles on em. They rattle, and the bottom piece has free movement. I pulled the PCV valves off the engine, and the engine itself was making a sucking sound. Something inside the engine is sucking more air in. It doesn't make any sense to me either, the engine shouldn't be making any sucking noises without it being on, and it's coming from inside the valve covers.

 

Also, is there a specific way to tune the distributor? All I've ever heard of is the ol' how good it sounds method. Is there something I can hook up to find the best idle advance?

 

Nobody knows how to properly tune a distributor?

 

Aftermarket distributor?

https://www.thirdgen.org/forums/tech...or+spark+curve

 

Aftermarket? That depends on how you look at it. The engine is aftermarket, but it is GMPP. The distributor came with the engine, so it's a vacuum advance HEI from AC Delco.

 

18 vacuum is about stock numbers.. (dont take my word for it, my stock motor only made it home before it was yanked)

as for the distributor thing, a timing light is pretty much your only option to help tune it.. there is also little bushing type things that limit the advance on the vacuum advance as well as springs to make it advance earlier or later on the rpm range.. finding the right curve is another story..

 

I'd like to learn that story. I haven't looked under the cap, but I thought it would have springs for the timing curves. How would I go about learning what the engine likes timing wise for base/curve@RPM? What do the professionals do? How do the GM engineers know what to set the cars' timings at from the factory?

 

well since my motor is about 70/30 street/strip i wanted it to advance quickly.. so by 2000 rpm, i'm at full 36* advance.. with about 12* initial on the lower rpms.. this was achieved with the small, light springs.. and a bushing that went from 12*-36*.. basically the bigger the bushing, the less advance you will get and vice versa.. so all i know is that strip motors like advance quickly.. i dont see why a street motor wouldnt like quick advance as well.. oh, i dont run vacuum advance either.. just a vacuum advance distributor without the vacuum hooked up and relying on the mechanical advance inside.. dont have nearly enough vacuum to even flicker the vacuum advance.. damn huge azz solid flat tappet cams.. lol

 

So nobody can tell me how the engineers figure out how to tune a car when they build an engine? How do the professionals at the factories figure out the best timing?


Also, I got the correct PCV valve for the valve covers, and engine still does the same thing. When I turn the engine off and pull the PCV valve out, it equalizes. It makes a noise like if you got the wind knocked out of you. whoooooo... Nobody knows what this is

 

Testing.

Sounds like you don't have a proper air inlet on the other valve cover.

 

Yea, I was curious why you said "PCV ValveS". Make sure you have a breather on the other valve cover, some crate motors aren't set up for that.

Try to find a vented gas cap at the parts store. That's a quick easy fix for the gas tank "wheeze". You don't even have to fully understand the problem to fix that one

Oh hey, 5678TA, have you looked at the Crane adjustable vacuum can? You can adjust how much vacuum it takes to kick on the vacuum advance, so much lower than stock, for a big cammed car. Might help with highway mileage, if you had any interest in that, for the 70* street driving that it sees.

 

sonix, i used to get about 9ish mpg highway.. which is ok by me.. and i just figured out that my jetting over 10 off.. so i should save alot of gas from that.. the TA only sees up to 100 miles a week, max.. but thanks for the tip.. i may do that for another motor if needed.. i dont even use the vacuum advance.. just the mechanical part of it.. right now, i believe i'm somewhere around 18 initial and 36 total with full advance around 1800rpm.. seems to be working great..

 

Holy cow!!!! 9mpg?? haha Ok, granted you've got more cubes, bigger heads, and gigantic cam apparently, but that still seems low. Especially with overdrive... man!
Alright, your call, just that i've heard you can increase your mileage about 2MPG on the highway with vacuum advance, and keep your plugs from fouling up as fast with it. I have that vac can and it's a nice piece.

 

surprisingly, i havent had a problem with plugs fouling.. i guess because of all the "spirited driving" that i do keeps the cylinders clean.. i'm not really concerned about gas mileage though.. i have an 03 s-10 so that is my gas saver.. my car has enough stuff under the hood as is.. dont really want to add more to it..
heres a most recent shot as of winter time.. i'll probably sell the strut brace.. but i do like it there for those valve adjustments..

 

I'm sure the pros test it. Come on. So the pro's have really sensitive right feet for the peddle and sensitive ears for how it sounds?

I thought you could only have one kind of gas tank ventilation. Either gas can that operates with vacuum, or vented gas cap. Wouldn't one defeat the other?

My gas mileage is around 11.5 MPG city/highway. I know it's not perfect right now, but I hope it goes up a bit. Seems like a real thirsty engine.

I was told running the two PCV valves was better than a breather. Does it matter which side the breather goes on?

 

Pro's use a dynometer. Or go the track at test and tune and adjust timing, bushings, weights and springs untill you get the highest trap speed and/or lowest time.

Breather goes in the valve cover on the opposite head as the pcv valve.

 

Yea, you can't run two PCV valves, that'd be like using a can that operates with vacuum or the vented cap - one defeats the other. (The gas tank ventilation i'm not sure if one defeats the other, but for the PCV - yes).
A PCV basically only lets the air out, not in. Letting air in needs to have a breather.

 

Cornholio I'm running the 350HO crate as well, have had it for about 3 years now. my timing is 16 initial, 20 degrees mechanical, with a 800-3200 curve. crane hei kit with vacuum advance locked out at 15*. 31 degrees at idle@ 800 RPM. pulling about 18* vacuum at idle as well.

this is all from a reman HEI dizzy, msd cap/rotor, proform coil, msd superconductors, and r44lts'.

what intake you running? RPM?

stock stall with 2.73's?

 

I did put a breather on one side, and vacuum went down, so it made sense to me. Now at about 15.

I don't know how to jet a carb and such, but I'm ordering an o2 sensor with air/fuel ratio monitor to properly tune it, and a calibration kit. I figure it could really use a proper tune.

The carb is a 750 CFM Edelbrock, and I expect it's too big for the current setup, but I've got plans to beef up the top of the engine. I wanna get aluminum heads with better stats, and everything above it. I'm taking welding and I hope to be able to do my own true dual exhaust.

My car diesels every now and then after shutoff, so i dunno if i can shoot the advance so far as 16.

Ive got the 350HO 'stock' intake manifold.

I upgraded to an Edge TC with 2500-2800 stall, but havent pushed the rear up to the 3.73 gears yet. I'm still learning about gears, but scouring the classifieds for a posi set.

I upgraded the wires to custom Accel 300+ wires. How is the Coil? Any difference? MSD box help this setup at all? I've got a 6a box layin in the garage...

What TV cable do you use? I got a Bowtie Overdrives cable, and it wears on itself and eventually moves less, resulting in bad shifts. I have to take it out of the car and reset it every now and then, not fun.

 

I used to have an edelbrock carburetor, messed with the calibration up, down, and sideways. could never get it to run right. ended up selling it on ebay.

i wouldn't spring the cash for a new msd box, but since you have one sitting the garage i would use it.

I'm using a stock TV cable, with the corrector brackets and such. I still get my double downshift, but light throttle shifts are a bit delayed.

what distributor are you running?

 

I had the same luck with the Holley carb that came with the motor, so I switched to edelbrock. I guess everyone has good and bad experiences with the same carbs.

The crate motor came with the distributor and coil from GMPP.

In a perfect world, I would put a build 4l60e on the car and just program the shift points to an exact science. The cable is not my favorite, but i guess it's better than vacuum. Possible to hook a TPS sensor to a carb, or would I have to hook a TV cable to a modified tranny?