[srgould41]

Two years ago I bought an '83 305 that was advertised as low miles on a rebuild. At that time I installed a Summit K1102 cam kit and an Edlebrock Performer manifold along with a Quadrajet. The engine ran pretty good, but I could never get more than 17 inHg in vacuum and it always ran too rich. I leaned it out a bit, but that brought vacuum to 15.



This weekend I decided to pull and inspect the plugs, check compression, and work on the timing to see if I could add some more advance for better vacuum. The plugs showed carbon from running rich. Compressions was 165 to 175 except number 3 at 110. So it seems I have a broken ring, burned valve, flat cam lobe, or (I did run through a cam breakin procedure)? I tried measuring the intake and exhaust lift at the valve retainers and the intake didn't compress as far as others. In any event I have a motor that is a little sick and needs something.

I did mess with timing and found some weird stuff. I had the timing set at about 10. I plugged in a new timing light with a degree feature then started adjusting the timingfor max vacuum. It was about 34 degrees. Is that odd? I backed it down to 20 and left it there. Ran fine with no pinging.



Please don't diss the 305's, I know all the arguments and happen to like the 305's. They have all the power I need for my purpose. More power means more broken parts as this is in a Toyota 4x4 trail truck.

I have wanted to change things up for a while now so this might be a good opportunity. I hate flat tappet cams. I have removed several cams with flat lobes. This morning along came an add for an '89 305 TBI motor with 140k miles. I can get it complete with the ECU and harness. I know the TBI engines suck on HP because of the swirl port heads.

Questions. On the '89 motor.

1. Could I swap my current 416 heads onto it (assuming no burnt valve)? How much effort would it be? Same push rods, etc? Have to drill the intake center bolt holes? Will it make a big difference?

2. I don't have to pass smog on my old truck so can I delete stuff like the air pump, etc? What will that do to the ECU? I want to keep the TBI for 4 wheeling.


Thanks.

Steve

[DoubleVision]

Are you using vacuum advance? If not you should be as this is where part of the problem lies. At idle, the timing should be 12 degrees before top dead center with vac advance disconnected and plugged.
Next connect vacuum advance to a manifold or full time vacuum source, this is any source that pulls vacuum full time, including idle. Once it's connected to a manifold vacuum source right away it will idle up, return the idle speed to the normal 750 and recheck timing, it should be 20 to 24 degrees before top dead center. Your mention on vacuum confused me somewhat, as you want to shoot for higher vacuum at idle, not lower, the higher the vacuum reading at idle the better. This is why it's popular to use a vacuum gauge to set the idle speed as it's a simple procedure, set it to it's highest idle vacuum. The lower compression on one cylinder could be caused by several things, however if there was a broken ring or the like you'd know it by now. Pull the plug, shoot the cylinder some oil, redo your compression test with power wire off the distributor and the throttle set to wide open. Last, if your pulling 20 degrees base timing without vacuum advance in use then a hot start condition will likely be a side effect.

[srgould41]

Thanks for your reply.

The vacuum advance was disconnected when I set the timing. Stock timing is 8. I had it at 10 for a couple years. However I was recently reading that the cam I used needs at least 4 degrees more timing over stock so I was going to set it to 12. Further reading led me to believe I could use up to 20 degrees initial depending on how the engine ran. I bought an advance kit and was going to add softer springs and a variable advance can and remove some vacuum advance. I didn't install it yet. I also read about the old school method of advancing to max vacuum which gave me thirty something degrees initial.

I have the mixture set to lean drop off. Idle vacuum is now 17.


Anyway, beyond the weirdness of the engine as it sits now I need to do something to resolve the bad cylinder. That was the real reason of the post. Could I swap heads on the TBI motor without needing to burn a new chip...

Originally Posted by DoubleVision

Are you using vacuum advance? If not you should be as this is where part of the problem lies. At idle, the timing should be 12 degrees before top dead center with vac advance disconnected and plugged.
Next connect vacuum advance to a manifold or full time vacuum source, this is any source that pulls vacuum full time, including idle. Once it's connected to a manifold vacuum source right away it will idle up, return the idle speed to the normal 750 and recheck timing, it should be 20 to 24 degrees before top dead center. Your mention on vacuum confused me somewhat, as you want to shoot for higher vacuum at idle, not lower, the higher the vacuum reading at idle the better. This is why it's popular to use a vacuum gauge to set the idle speed as it's a simple procedure, set it to it's highest idle vacuum. The lower compression on one cylinder could be caused by several things, however if there was a broken ring or the like you'd know it by now. Pull the plug, shoot the cylinder some oil, redo your compression test with power wire off the distributor and the throttle set to wide open. Last, if your pulling 20 degrees base timing without vacuum advance in use then a hot start condition will likely be a side effect.

[vinniekq2]

I agree with you 100%,the 305 is the correct engine for that truck if its just for fun.If the enging in your truck worked well,just freshen it up. If it needs a cam you have a lot of choices.If you find a 305 roller engine then out of 2 engines make a good one,or rebuild the best one.A low rpm roller cam motor will give reasonable mileage and have more torque

[cobalt327]

Originally Posted by srgould41

Thanks for your reply.

The vacuum advance was disconnected when I set the timing. Stock timing is 8. I had it at 10 for a couple years. However I was recently reading that the cam I used needs at least 4 degrees more timing over stock so I was going to set it to 12. Further reading led me to believe I could use up to 20 degrees initial depending on how the engine ran. I bought an advance kit and was going to add softer springs and a variable advance can and remove some vacuum advance. I didn't install it yet. I also read about the old school method of advancing to max vacuum which gave me thirty something degrees initial.

I have the mixture set to lean drop off. Idle vacuum is now 17.


Anyway, beyond the weirdness of the engine as it sits now I need to do something to resolve the bad cylinder. That was the real reason of the post. Could I swap heads on the TBI motor without needing to burn a new chip...

As long as the vacuum remains about the same as what the chip was made for, the heads can be swapped out and there will be no issues.

Just don't go crazy w/a huge intake port volume, all you need is 160-170cc. Most any production head having the combustion chamber size you need (<64cc) will be about right, port volume wise.

If the valve isn't opening as much as the rest, you know the problem.

The only fix is to replace the cam and lifters. Info on breaking in the cam is here. There are useful links under Resources there that will also help.

Info on timing and the GM HEI can be seen here.

Good luck.

[ap72]

Originally Posted by srgould41

Thanks for your reply.

The vacuum advance was disconnected when I set the timing. Stock timing is 8. I had it at 10 for a couple years. However I was recently reading that the cam I used needs at least 4 degrees more timing over stock so I was going to set it to 12. Further reading led me to believe I could use up to 20 degrees initial depending on how the engine ran. I bought an advance kit and was going to add softer springs and a variable advance can and remove some vacuum advance. I didn't install it yet. I also read about the old school method of advancing to max vacuum which gave me thirty something degrees initial.

I have the mixture set to lean drop off. Idle vacuum is now 17.


Anyway, beyond the weirdness of the engine as it sits now I need to do something to resolve the bad cylinder. That was the real reason of the post. Could I swap heads on the TBI motor without needing to burn a new chip...

Regardless of your initial timing you don't want your max timing to exceed 36 degrees, and 34 or 35 may be more appropriate. If it does exceed 36 degrees then you can play on doing a rebuild in the short future.

[techinspector1]

It seems to me that the low-rpm swirl heads would be just the ticket for your kind of driving.

[hcompton]

Just removing air pump and other emissinons gear will make the engine run like crap. Sorry dont actually no how to remove everything and not mess up the engines tune. Smeone else may be able to help. But if itsworking right i would leave it in place until it fails then tackle that issue.

I did see a good write up on one of the corvette forums. But it did not look straight forward.

[srgould41]

That's kind of what I was thinking. I guess if I am going to TBI I am just going to have to pay for a good computer.

Originally Posted by hcompton

Just removing air pump and other emissinons gear will make the engine run like crap. Sorry dont actually no how to remove everything and not mess up the engines tune. Smeone else may be able to help. But if itsworking right i would leave it in place until it fails then tackle that issue.

I did see a good write up on one of the corvette forums. But it did not look straight forward.