So unfortunately I've been laid up with a severe eye injury for the last week. Getting alot better though. But when I get bored my mind starts wandering. So got thinking about the turbo 4.3 in the s10. Lately I've been playing with timing. Originally I was running 14 degrees of centrifugal advance all in real early 2000-2500 along with the 4-8 degrees of base timing. I turned up the boost a few lbs now running around 9-10 lbs up from 6-7. Then had to back timing down about 6 degrees to keep the rattle out when the trans shifts gears... made it pretty sluggish off idle at that point with a slight stumble sometimes. So I thought as low as my timing is why not lock centrifugal out. Pulled distributor and tinkered a bit with it and found the play in the distributor was allowing the shaft to walk up the stops I made and bevel them allowing probably 2 more degrees of timing... so I locked it out and set it at 18 and took it for a drive. When it was nice and cool outside it ran like never before! Once it got hot out 90 plus with high humidity it seems to intermittently rattle upon shifts. So I backed down to 16 and got rid of the rattle. So now I'm running 16 degrees with locked mechanical and 18 degrees of vacuum for a total of 34. Which makes it cruise much nicer and brings up my fuel economy. My question is would in be worth switching to something like the msd programmable box to get a better timing curve into this and be boost referenced to pull timing under boost or would it not be worth the cost vs the gain? Am I better off to keep it simple with my hei and be happier with the extra 500 bucks in my pocket? Let me know what you guys with experience in this think.
Thanks
Joel

 

Just depends on what you want out of it. You can optimize drivability with programable, get the full 40-50° of timing at cruise, have full timing off boost, change timing at rpm so it doesn't rattle at the shift, optimize power everywhere.

If the truck is just a toy, not worth it, if it is your driver worth it.

 

So far it is just a toy, but a fun one at that. Drive train may find its way in to an older car someday as the s10 isnt that nice. It does pretty decent for economy averaging 13-14 while putting dents in the floorboard under the gas pedal from dang near every stop sign! Haha maybe there's more though...just not familiar with the more hi tech stuff with hot rodding now days...I was raised to make it work with we had readily available. Definitely been a learning curve on this one though. I guess when it comes down to it its a matter of opinion on whether or not its worth the money for the optimized performance. But...will the performance gained be that noticeable?
Joel

 

Programmable ignition is absolutely worth the time and money.

 

couple questions
what year motor is this?
what oct fuel?
when it knocks at the shift, is this light throttle/cruise, or woT on boost?

 

1988 engine always running 93 from the same station due to issues I had with anothers fuel. Engine is completely stock with around 170000 on it but mechanically stable. Don't seem to have the knock at light throttle anymore with my locked timing that I previously had while using the centrifugal advance. But under hard acceleration occasionally it rattles when trans shifts from 1st to second, which with the 700 r4 is a decent jump. Knock seems more frequent with higher temps and humidity as well. Been waiting for a nice cool night to go out and play a bit but haven't gotten the chance yet, especially with my new found eye injury. Just waiting to heal up a bit and get after it again.
Thanks
Joel

 

I cant remember what your setup is.

What is the timing and boost at the moment it knocks?

I havent really played with 93 oct on one of these.
I can tell you the 4.3 I just pulled the heads off has 180k on it and the quench area of of the piston and head where both packed solid with soft carbon from pcv oil. Prime cause of auto ignition /detonation. Might take a look at the top of the pistons through the spark plug hole.

 

With timing locked at 18 and high outside air temps with high humidity it will rattle as soon as it hits second. At that point boost is dropped to around 6-7 lbs but climbs right back to 9-10. Timing shouldn't move due to the distributor being locked at this point. Before the shaft had walked up and tapered the top of my stop so I think it was adding more than what I thought. Now today it's warm but not super hot with lower humidity and I was able to increase from my "safe" 16 to 18 without even a hint of rattle. Also noticed the tires broke loose into second not just chirped but maybe the extra slipping takes the load off a bit to not rattle it? My setup is just the stock 4.3 with an h1c turbo blowing thru a 500 cfm edelbrock with a cheapo hei, which is now locked mechanically but still using the vacuum with check valve setup. That definitely helps cruising with the added 18 degrees with vacuum. My afrs read a bit on the rich side but sometimes I wonder if my wideband isn't reading actual. High tens to low elevens seems to make it the happiest. I've tried to bring it up to high elevens but it seems to not pull as good and wants to surge like it's lean, so I went back to where it was and that seems good, plugs look ok with just a bit of black around the outside. My pcv is hooked up with a check valve and catch can which rarely ever has oil in it. I will have to pull plugs and look in cylinders to see what I can and go from there.
Thanks for the input! I'll keep you posted as to what I find.
Joel

 

Any idea what your air intake temps are? Where are you pulling your turbo inlet air from? Any room for intercooler?

 

The check valve setup. Does it have some type of bleed on the distributor side of the valve?

Ive found when using check valves on trans vac. modulators, when the valve closes, it will trap the vacuum and the trans wont upshift under boost.
To fix this I drill a .015 hole on trans side of the valve so it bleeds the vac. off when the valve closes.

If this is the case on yours, its holding the vac. timing, causing the knock.
A test method would be disconnect the vac. advance and see if it doesnt knock.

 

I just have a tee in the vac line with the check valve vented to atmosphere that way under boost the line isn't pressurized to the diaphragm. I would think if it's holding vacuum that it would rattle tremendously in first gear due to the large amount of timing added by that. As far as iat I couldn't tell you for sure. I know that after a decent beating the carb hat is warm enough that most people won't leave their hand on it for long. I can though but being a mechanic for a living you tend to loose your sense of "ouch that's hot!" Haha my air inlet is right off the turbo and down behind the headlight. Probably an 8 inch drop with an open k and n but still not getting much from outside. Been pondering cold air inlet of some sort with a sealed air box to the outside which I imagine would help alot. Also been thinking about the intercooler but haven't decided on optimum placement and plumbing. Would like to try outside air first.
Thanks for the replies.
Joel

 

Do you have any pics/part numbers for your check valve setup? I've been trying to figure out a way around the $400 MSD upgrade. Right now running no vac advance and I'm certain it's hindering my performance considerably.

 

pic of check valve on car please

 

Transgo t34161e will solve the trans vac issue

Colder air intake would do you a lot of good.

The hot carb makes me think your intake temps are your main detonation problem. You need to get the heat away from the system, a phenolic spacer and a cool intake source could really help. An intercooler would be real good.

 

#ad
here is a pic of what I'm using. It seems to work for what its worth. Just a cheapo universal check from advance auto help board that vents when boost is present. Doesnt seem to leak fuel under boost. Without a decent amount of cutting and fabbing not much I can do for cooler intake air right now. On light duty for a couple more weeks due to the eye injury.
Thanks
Joel

 

same check valve ive used from what i can see of it. If it has two connections, and there isnt another hole in it on the distributor side, it will trap the vacuum.

 

Only one connection have it teed into vacuum line going to distributor. Only allows flow out to atmosphere but no flow in under vac.
Joel

 

You could easily hook up a meth injection kit.

https://www.summitracing.com/parts/...8wvnITHw1mn6088xNP_CPl1le2_6xiYkaAiKqEALw_wcB

you will need a carb spacer also,

https://www.summitracing.com/parts/...D8yNPYwsw0sub1VZS55cxVGDJCYYCpnIaAiYVEALw_wcB

 

Hmm didn't know under carb was an option for such a setup....I like that for the simple fact the my intake tube from turbo to carb is real short and has alot going on with bowl vents tied in and bov right there as well. Will it work ok there? Always read, never tried though, that it needed to be closer to the carb. Not sure though. Also are the nozzles a bastard thread or just npt? The spacer is nice but the price not so much and I've got a couple laying around which cold be modified if they are npt...
Joel

 

So you're venting the vacuum pressure to the atmosphere? How do you prevent boost from entering your distributor if that's how you're using your check valve? I'd think between your tee and carb you'd need another check valve that only allows the flow of vacuum. Unless I'm missing something.