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Discussion Starter · #1 ·
Thought this was going to be sweet, but now very very very upset. 350 vortec heads, small cam (isky 262/270) 3:73 gears 31" rear tire. I installed an OD tranny over the weekend and it seems to ping at 60mph on the hwy. One other change I did was change distributors to a MSD street fire. Something needs to be adjusted inside the vaccum module. Have not done that yet.

Anyway, my biggest problem is how do I get rid of detination to enjoy the added expense of the OD tranny I just added. Also added a 1800-2200 stall with this set-up. I have always run 91.. so this is not it.

Also, I have never had a distributor where you adjust the advance through the module. Is this common and DOES it need to be adjusted. I have not touched it yet.. and instructions say to use a 3/32 allen key to adjust. First start by turning clockwise (in) then out to adjust. Has chart.

I am seeming not to be able to enjoy the OD feature because of the pinging. Even when I try and pick up speed.. it gets worse.
 

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The adjustable vac advance is there for that very reason. You must adjust, test drive, adjust until the pinging is gone. when you added the 700R4 you lowered the cruise RPM even more due to it`s overdrive, which means vacuum is higher due to the lower RPM. Less throttle blade opening: more vacuum. I had never fooled with one either until the last engine I built for a friend, the kit we got for the HEI included it and I`m grateful it did. Since his engine has 10:1 compression it pinged like crazy, I took the time to adjust the vacuum advance and the result was outstanding power with no pinging. adjustable vacuum advances are common on aftermarket distributors.
There are several reasons why they make them adjustable, but I would think the biggest reason would be higher compression ratio`s, plus it being adjustable makes it where you can tailor in the amount of needed advance or set it where the engine runs it`s best.
 

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Discussion Starter · #3 ·
I kind of concur with answer #1 more so in terms of what's wrong with my problem. I think I need to adjust the vacc. on the distributor. Fbird88, I thought my cam was rather small. The rpms were not way up there but they were excessive or more than I wanted my motor to run. I was told a 3:73 is a good minimum gear for OD? that was one reason whay i went that route. Now I'm hearing no benefit or not much?

Do you agree with anything doublevision had to say.
 

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Discussion Starter · #4 ·
DoubleVision said:
The adjustable vac advance is there for that very reason. You must adjust, test drive, adjust until the pinging is gone. when you added the 700R4 you lowered the cruise RPM even more due to it`s overdrive, which means vacuum is higher due to the lower RPM. Less throttle blade opening: more vacuum. I had never fooled with one either until the last engine I built for a friend, the kit we got for the HEI included it and I`m grateful it did. Since his engine has 10:1 compression it pinged like crazy, I took the time to adjust the vacuum advance and the result was outstanding power with no pinging. adjustable vacuum advances are common on aftermarket distributors.
There are several reasons why they make them adjustable, but I would think the biggest reason would be higher compression ratio`s, plus it being adjustable makes it where you can tailor in the amount of needed advance or set it where the engine runs it`s best.

So I need to ADD more vacuum by turning it counterclockwise. I'm not sure where it is now, but instructions say turn ALL THE WAY IN FIRST, then out. I hope this is what's wrong.
 

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You`ll find you need less advance, not more. Too much is why it pings now. What F Bird says has some merit. 31 inch tires are pretty tall, so we need to know what the cruise RPM is at 55 mph in OD. The taller the tire, the higher it makes the gear. a 31 inch tire turns a 3.73 into a 3.08 as a example while a smaller tire does the opposite. What F Bird is saying is that you could have gotten the cruise RPM too low, if it`s below the power band of the cam it`s going to ping and detonate no matter where you set the timing because it`s placing the engine in a lug. The power band of your cam doesn`t come in until 2000 RPM, if your cruise RPM is lower than this at 55 mph then you`ll need less cam, lower gears or smaller tires. There are other ways you can try and compensate for it, like zero lashing the valves, or installing a smaller carb or a carb with smaller primaries like a Quadrajet. Or even possibly advancing the cam 4 degrees but overall, if the cruise RPM is below 2000 RPM at 55 mph then you`ll have to lower the power band to get the detonation out.
Have you tried it on the interstate at 70 MPH? if the ping is there at this speed then it`s over advanced no doubt, but that doesn`t mean it`ll come out at lower speeds as discribed.
 

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Discussion Starter · #6 ·
Have a quadrajet and as far as the timing advance goes, I was talking about the advance adjustment inside the distributor.. not initial as I believe you are indicating here. I was with you on the first post.. lost me on this one. Now, maybe I need more cam. The cam I have is pretty small. I thought.
 

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You need less cam, more raises the power band higher. I don`t think you understand entirely what timing is. At idle, you need vacuum advance, it should be connected to a full time, manifold vacuum port or a port that pulls vacuum even at idle. Next with the vac advance disconnected and plugged, set the timing at 12 degrees before top dead center, lock the distributor and reconnect the vacuum advance, check the spark timing, it should be around 24 degrees before top dead center, as a ball park estimate I`m thinking you`ll need around 18. At cruise speed, the mechanical and vacuum advance will work together. at cruise speed mixtures are leaner and leaner mixtures burn slower than do richer ones so more timing advance is needed. As the throttle blades open more the vacuum drops off giving it less vacuum advance so the mechanical advance has taken over entirely. This is why vac advance is not important at mid to wide open throttle. You can adjust the vac advance with the engine at idle, you`ll notice as you lower it, the idle will drop. This is why you`ll need to adjust, test drive and adjust. This is so you can get it where the engine likes it. I can`t give you a base line on vac advance because every engine is different. With everything set, check the spark timing, For example if it has 24 total degress, disconnect the vac advance, adjust it down, reconnect and check the timing again. Bring it down 2 degrees at a time until the pinging stops.
 

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your cam is small, its definitely not the problem- unless its too small. If you're runing flat tops it may be too small. The problem is you're overloading the engine, high cylinder pressure and low RPM do not mix. GOing up in cam size would actaully help you mroe than going down. Or just retarding it 4 degrees (cheap fix). Another temporary fix would be installing a small 2bbl carb. Pulling some timing out will get you there too. you need to lower the cylinder pressure or reduce the timing advance. But each has its limitations.
 

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The whole routine for setting the distributor up w/the correct timing curve for the engine needs to be done- not just poke and hope w/the allen wrench to set the vacuum advance. :rolleyes:

The initial needs to be set along w/the total. When that's dialed in, add in the vacuum advance- as much as the engine will stand w/o pinging.

Once the curve's dialed in, you can tell whether or not the cam is gonna be an issue. IMO, the cam should not be an issue- at least not one that can't be tuned for.
 

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its not that the cam needs to be bigger to match the gearing, but the compression. his cylinder pressure is too high for that low RPM load. a bigger cam will run worse but it won't ping. not shifting in 4th would probably be the best fix, and one that i think we all would agree on, but since he now has incredibley low gearing and big tires, and too high of cylinder pressure, pulling out timing and retarding the cam 4º seem to me to be the cheapest way out. this engine/gearing combo would only work in a very light and aerodynamic car, like a vega or a Opel GT.
 

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ap72 said:
your cam is small, its definitely not the problem- unless its too small. If you're runing flat tops it may be too small. The problem is you're overloading the engine, high cylinder pressure and low RPM do not mix. GOing up in cam size would actaully help you mroe than going down. Or just retarding it 4 degrees (cheap fix). Another temporary fix would be installing a small 2bbl carb. Pulling some timing out will get you there too. you need to lower the cylinder pressure or reduce the timing advance. But each has its limitations.
i agree with you ap, on the cam. basically it seems to me that all the OP has to do is adjust the vacuum on his distributor. i have 1 from crane in my car and untill i backed out the vacuum advance, it pinged. it took about 2-2 1/2 turns out to rectify the ping, besides going up 3 jets sizes. but i also run a holley 600cfm. a bit different than a quadrajet. back out the vacuum screw, and see how it does. if this is the stock carb that was on the engine before the performance adders (cam or anything else that was done), i guarantee its going to be lean now. bigger cam, gasket matching or porting, higher compression, headers or anything that is going to add more power is going to require more fuel. simple math, if it flows more air, its going to take more fuel. id check the a/f ratio if possible, and correct , then back the vacuum screw in the modulator out till the ping is gone. worked for me. :thumbup:
 

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Ok I'll Bite

Some of what has been mentioned I agree with, some of it I don't. To big a cam, NO. Wasting your time with the overdrive, take it out, or run it in drive only, NO. Not enough gear, NO. Too much timing, YES. Too lean on jets, YES.
Okay, now that I've made some smile and pissed off others, I'll throw in my two cents( I only have two). I've got a feeling that you've got the piston tops loaded with carbon from your previous mis-adventures with this built, hot spots. Might just need to run the ca-ca out of it to blow it out. Put a 160 degree T-stat in it and make sure the cooling system is up to snuff to keep it real cool, it is a hotrod motor. If you're running a stock 350 Q-jet, find a big block Q-jet from anything and get the primary metering rods from it to replace yours. As long as they are alot thinner than yours and are the same length and steps, they'll work fine. This ain't rocket science, just get it richer on the primaries. Back the timing down to about 8-10 degrees initial,with no more than 32-34 total. The vortec heads have such a fast burn rate they don't require old school timing #'s. If you wanna have fun on cool fall nights, get some octane booster or race gas, jack the timing up and run the piss out of it. Lower the timing back down and drive home enjoying your overdrive and MPG. :thumbup: olnolan
 

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Discussion Starter · #14 ·
F-BIRD'88 said:
The cheapest way is to run the engine at its most efficent rpm, and optimize the spark timing and carb jetting for best mileage at that cruise rpm wher ehte motor is happy. ( this motor with this cam is not happy running at 1700 rpm. Leave the cam alone. Run the thing in "D" or re-intall the th350 trans. You didn't/ and don't need overdrive at all. It will not save you money.
but it will help give my engine a little more ife by not being stresses etc. I am surprised at your comments.. meaning, I value them and always have, but not liking what I'm hearing from you on this one. Don't get me wrong.. I value your opinions and have taken heed.. but on this one, I have to look for other solutions. Mainly because OD is not a bad thing and if I can get the kinks worked out.. it's actually pretty nice. Now again, I MAY NOT experience any savings in the pocket as far as money goes, but the payoff for me is having my engine run easier (at higher speeds). So come on dude.. and help me here. The OD is not going away.

Now as for updates. I had the truck out Yesterday and I noticed it likes to be above 70 in order not to det., but when you are going 70ish and accelerate you get it a little. I talked with a mechanic yesterday and he said chevy’s get wayyy too much vacuum. Told me to pull the plug on the distributor and see if that helps. If not, he suggested what others have already in regards to setting the timing and advance correctly for my set-up. Says he doesn’t see anything way off or out of the ordinary, but that when you do things like this, some adjustments need to take place. It’s not just a plug/play type deal. I don’t think we’re too far off. The tranny shifts good and when I ‘m going fast enough to utilize overdrive.. IT IS SWEET. That baby just drops right down and the engine is at ease.

It’s funny because I contemplated this idea for a while before I actually added OD. Only one shop recommended I KEEP my th350. All others seem to think OD was beneficial. For me, it’s not just a gas savings issue. I built a pretty nice motor and if I can relieve the stress put on it doing hwy driving , then having it to me is beneficial. Gas is gas and will be used no matter what tranny is used. Another thing it adds is modernization. Another thing it adds to an older vehicle is modernization. I could not do what I did this morning.. without appearing to be speeding down the fwy like a mad man. The OD allows you to pass in comfort. It felt good passing cars.. something I could not do well with the th350 because the rpms were always too high. Besides, on the streets, I drive it like a th350. OD only for the hwy.
 

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Discussion Starter · #15 ·
Lean, YES, I could buy that. Timing and advance set properly YES. This is the only thing wrong with it IMO. Now backing down the advance inside the vacuum module is counterclockwise or clockwise on the distributor. My instructions say turn all the way in. Does clockwise add or take away advance. Also, I was told by a ole time that I needed to richen thigs up when added headers. The truck went from a good muscle truck tone to almost too quiet. He said it's breathing almost too good now.. because it's too quiet. I will admit those vortecs breath much better than I thought they would.. I thought about adding more cam just to get some sound back in exhaust, but the new tranny and stall (1800-2200) has helped tighten things up and it sounds idles better now. The old tranny really was shot and wasn't helping much.
 

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Vac Advance Adjustment

Hey Carlos, Clockwise decreases timing, counter-clockwise increases. You might try just tweaking it. Turn it clockwise 1/2 turn at a time, test drive, listen for ping. Repeat till it quits pinging. As you decrease the timing with the vac adv adjustment, you'll need to bring idle speed up to desired idle. I could go in to alot of detail on mechanical/vac advance curves, but it doesn't sound like you understand it well enough to set it up. This doesn't mean you can't tweak it to stop the pinging though. Or you could bring the vehicle and the instructions for the distributor to a good mechanic(that also knows how to tune a hotrod engine,some don't) and have him set your advance curve up and check the carb jetting. If you can get it to stop pinging and you're happy with the performance then so be it. But without a pro tune you may be leaving some horsepower on the table. Good luck with it, whatever you decide. :thumbup: olnolan
 

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Carlos9 said:
Lean, YES, I could buy that. Timing and advance set properly YES. This is the only thing wrong with it IMO. Now backing down the advance inside the vacuum module is counterclockwise or clockwise on the distributor. My instructions say turn all the way in. Does clockwise add or take away advance. Also, I was told by a ole time that I needed to richen thigs up when added headers. The truck went from a good muscle truck tone to almost too quiet. He said it's breathing almost too good now.. because it's too quiet. I will admit those vortecs breath much better than I thought they would.. I thought about adding more cam just to get some sound back in exhaust, but the new tranny and stall (1800-2200) has helped tighten things up and it sounds idles better now. The old tranny really was shot and wasn't helping much.
the 1 i got from crane came with the screw all the way in and in the instructions, it said to turn counter-clockwise until detonation stops. now like i mentioned before, if the engine flows more air, its gonna need more fuel. plain and simple, so you it may not make a difference till you up the jetting.
i run a 700 in my cars ( 72 and 76 pontiac venturas that came with chevy drivetrains), and i think theyre a great trans. yes they need attention on parts to make them durable and to give them longevity, but the overdrive is just so nice to have on the freeway like you mentioned, and the added gas mileage is great too.
with 3.08 gears and a 25 in. tire, im running maybe 2100 rpm @ 70 mph in the 72 that i did the exact adjustments i mentioned earlier and the car runs great, no ping, and im running roughly 16* timing on ported vacuum.
 

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Did it ping with the old setup? You should be able to tune the ping out of it. Since you haven't touched the carb, leave that alone.

* Set base timing with vac advance disconnected. It helps to have an adjustable timing light so you can see how much mechanical advance you are getting.

* Drive it with the vac advance disconnected & plugged. Don't use OD at this time. Try to listen for ping at both part-throttle & full throttle (WOT). If no ping on both, your initial advance should be ok.

* Drive it in OD now with the vac advance still disconnected. Double check your part throttle ping & WOT again.

* Adjust your TV cable (with the vac advance disconnected). Follow the directions that came with the trans kit. This is an important step. You want to get it shifting right.

Once you determine the engine doesn't ping, & the trans shifts ok, it's now time to hookup & adjust the vac advance. I would back off the adjustment & start 1 turn at a time. You will get a part throttle ping if you go too far.

Just try to be systematic & go step by step. Only make one change at a time before you test it.

Good luck!!
 

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Discussion Starter · #20 ·
I bought the bowtie overdrive tv made ez kit. All of the comments on tuning make sense and I know something that needs to be done. It needed to be done with other set-up because the car has always been set by ear/start type timing. The guy I deal with is not up on thechnology of the vortec heads and their need for less timing than conventional chevy heads.

I also came to the conclusion driving on the way home that I am riding lean. It's not a racer, but has good enough components as mentioned to require more fuel. Makes sense to me now. My dad also used to say better to be too fat than too lean. I am definitely lean. The plugs could stand to be richened up a bit.. they don't look bad but could use some richening. You get so focused on other things and forget about this.

I will tune it but not until I can get carb fattened up. I honestly don't think I am too far off and what was recommended should fix. Matter of fact I know it will. I just need to get a mechanic on it that knows what time it is with what's involved.

Someone mentioned I could change the metering rods from a larger carb. Is this all that needs to be done. I am running a quadrajet. I was told it's not the biggest.. but the best one because it does not have all the junk attached to it. I'd like to learn more about how to richen/fix the carb situation now before I make any moves.
 
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