305 to 350 upgrade needs some tuning

[84ever]

My '84 K5 305 with only 92K miles on it was running great except for the worn out cam and rings. Yes, only 92K, I bought it in '87 with 50K and the original tires. Seemed to go south fast the last couple of months until finally I wasn't sure if it would move anymore. Had it replaced it with a 350 crate engine. It's running pretty good but needs some tuning. It knocks a bit under moderate acceleration. Also noticed when I start it when it's hot it cranks a bit hard like it's got some ungodly compression and I hear it diesel for a split second until it starts. Not sure what's up with that. There's a small valve tap so we're going to readjust the valves and see if that helps.

I'm not quite sure what the timing should be for the 350, the decal for the 305 called for 4deg BTDC so that's what I set it at. The distributor is for the 305 and I haven't bypassed the ESC yet although the knock sensor isn’t working. Since the 350 didn't get the ESC I'm thinking I will end up bypassing it. I checked out the timing over the RPM range and found that the dist vac advance kicks in between 2250-2500 RPM (no load) and adds about 18deg max. At 3500 RPM no load I've got about 38 deg BTDC. Seems like a lot. I could be off by 1 or 2 deg with the measuring but not much more than that. Not sure if this timing is reasonable or not. I put a vacuum gauge on the dist vac line on the dash and noticed it knocks even with vacuum too low for the advance to kick in. The dist is brand new (yeah, the installer put in a new 305 dist with the 350, go figure) and there is no adjustment short of messing with springs and weights. The manufacturer says the advance is the same as the 350 dist, the only difference is the connection for the ESC.

I've got the dist connected to ported vac, I think. The original M4ME carb has three small ports labeled J, B, and H on the decal. Only the B is labeled on the carb. The B appears to be manifold vacuum when I measure it. The other two seem to measure ported vacuum, about the same. The decal shows the dist vac on the B port for the 305 but when I tried this with the 350 it barely idles, with way to much in the timing. Not too surprising though. Not sure why the 305 ran OK with manifold vac on the advance.

Anyone know the difference between the J and H ports on the carb? Anyone know what the original hose routing was on the decal for the 350 Federal? I think I read that the 350 was only available on California K5s for 84. Don't know if that's true or if it means that all the 84 K5 350s had computer control (and none of this vacuum control stuff) or not. The on-line parts catalogs still show two thermal vacuum switches for the 350, just like the 305, except one switch is a different part number. So I’m thinking the 350 vacuum plumbing was probably similar to the 305 but I’d like to know for sure. Don’t know if any of this plumbing could be contributing to the knock or not.

 

[jonrpick]

Is this the 290hp engine?

 

[84ever]

Don't know about the HP. I ordered a 350 crate Engine from ATK for an '84 K5. It should be the same specs as an original 84 K5.

 

[CHEVYDADDY]

hey not sure when i missed this post but i have a 85 K5 just finished a 305 to a 350 .40 swap and have alot of the same problem. not sure about the degs and fixing it yet but i bought a new battery (smallest they suggested) but have the same cranking problem. It seems cold start it will crank until the gas gets to the carb and fire right up but when it is warm or even been running for a while if u shut it off and try starting it agian it chugs hard damn near gives out. wait a sec then try agian about the same thing seems if u let it hit once then tap the gas on one maybe two next crank it fires up strong. im starting to think timing maybe a little off but engine feels good. and im useing the same dist. for the 305 in the 350 now.

 

[corey6969]

Did you set the timing with the vacuum advance unhooked? Usually when they are hooked up to ported vacuum you dont have to do this(in my experience) because there is no vacuum there at idle. It sounds like your vacuum can is advancing the timing to much. Does it ping/knock at WOT?

The way I tune those distriburators is unhook the vacuum can and start with the middle springs and if it doesnt ping under WOT replace one spring with the lighter spring and keep doing that untill it pings. When it starts to ping go back and replace the last spring u replaced with the one you replaced it with and this should give you a good mechanical advance. Next hook up for vacuum advance can and tune it untill it pings then back it off. To do this stick the supplied allen wrench in the hole where the vacuum line hooks up to and turn it clockwise to advance the timing and counterclockwise to retard the timing(pretty sure or it might be vice versa). Advance it one turn at a time untill it starts to ping then back it off a turn and your timing should be set for good power and mileage.

You mentioned a 305 distrubutor, what did you mean by that? Im quite sure all small block distrubutors are the same, unless you got a non adjustable stock replacement one. New aftermarket distrubutors require tuning.

 

[CHEVYDADDY]

You mentioned a 305 distrubutor, what did you mean by that? Im quite sure all small block distrubutors are the same, unless you got a non adjustable stock replacement one. New aftermarket distrubutors require tuning.

mine is stock out of the 305 just throught that i would throw that in there 84ever said his guy used a new 305 dist with his new 350 so really just trowing that in and yes i was told they are the same thing in a stock style truck.(non-raceing) mine is a 350 .40 over 80-85 4 bolt main but was built by some one else and i put a gasket in it and slaped it in so it like comparing note for now.

 

[84ever]

What I mean by stock 305 distributor is it's a Cardone rebuilt stock distributor for 305, the one that would show up in their catalog for a 1984 Blazer 305, which should be equivalent to GM original. I checked with Cardone tech support and they confirmed that the vacuum advance and the mechanical advance for their 305 distributor is the same as for their 305 for 84 Blazer. Also there is no adjustment for the vacuum advance on their dizzys. I believe the only difference is the ignition control- the 305 used the electronic spark controller (ESC) to retard the spark using the knock sensor and vac tip in switch while the 350 did not use a controller at all. I verified the knock sensor on my 350 (taken from the old 305) does not work. The ESC is still connected but basically should not be doing anything (no retard) since the knock sensor isn't working. The ESC can only retard, not advance. Since the ESC is not supposed to be on the 350 anyway I have not bothered to replace the knock sensor and may just bypass the ESC.

I don't know that I've check for knock at WOT but I've checked pretty close to it. I've laid down the peddle enough to drop the dizzy vac to zero on the inside gauge and still get knock so I know it's knocking with only mechanical advance, let alone with vac advance.

I have the dizzy vac hooked to ported vac on the carb which is zero at idle but I disconnected it anyway to set the timing at 500RPM in drive to 4deg BTDC per the decal.

I just got off the phone with ATK tech support and they confirmed it's not unusual for a brand new rebuild to be really tight and for it to turn over real slow and knock for a split second when starting hot. So not to worry for that right now, I only have 300 miles on it.

He also said that the timing cover might be slightly different between the 305 and 350 with respect to the timing marks. We know the balancer is different and I know I have a new 350 balancer on mine with the old 305 timing cover. If the timing cover is different it might be lying and I might not really have the timing at 4deg BTDC. So I need to pull the plug and crank the motor and verify where TDC is on the timing cover marks. if that's not it then I'm really going to be scratching my head trying to figure out where this knock is coming from.

Can anyone confirm or deny if the timing cover marks would be different between the 305 and 350?

 

[CHEVYDADDY]

I just got off the phone with ATK tech support and they confirmed it's not unusual for a brand new rebuild to be really tight and for it to turn over real slow and knock for a split second when starting hot. So not to worry for that right now, I only have 300 miles on it.

Thats good for u but what does that mean for me mine is not new at all?? I did how every use the TDC way for confriming my timeing but still thinking about tweaking it. Hope things work out for u! but keep me posted will ya!

 

[84ever]

OK, here's the latest poop on the motor replacement. Pulled the plugs, cranked it over, checked through the #1 plug hole and found TDC is about 28 degrees later than what the 305 timing gear cover says. So that means the motor has been running with 28deg more timing than it should have since install which means it was maxing out at 66 deg with full advance. Ya think that might cause just a little bit of knock?

Put another TDC mark on the balancer at true TDC, retimed the motor to 4 deg BTDC, and reset all the idle speeds. A quick test drive up to highways speeds and it seems to be smooth sailing. No more knock under hard accel and no more knock when it starts up hot.

I'd still like to confirm the exact timing difference between the 305 and 350 timing gear covers because measuring through the plug hole isn't perfectly accurate.

Now on to adjust the lifters to take care of a tap and it should be all done.

What do y'all recommend for a thermostat in the 350 in the south? There's a 180 in now from the 305 but I've read 195 might be the standard for the 84 with carb.