New Engine Help

[brian617]

Nope, hot water under the runners, see how that manifold has two holes either side of the carb flange?

[Engine07]

Gotcha now. Never used them before. Have to go look at my engine and see what I can hook them into

[brian617]

Never used that manifold and method myself, but came across a thread about it once. Almost need to have the manifold in hand to see your plumbing options. As far as I know its the only heated plenum manifold other than the 3704.

[Fast355]

That's similar to how we set up the 406 except it's running 31 total by about 3,500 rpm. A heavy truck might not get away with that much timing though. The 406 is in a 3,000 Lb. Nova and accelerates damn fast. It also likes 40° cruise timing by 2,000 rpm.

Fast - how did you determine the need to reduce timing past 5,600 rpm at WOT? Did it make better power or was that required to keep it off the knock sensor?

It was on the knock sensor pretty hard on 87 octane. I played with the timing on the dyno and even running 93 octane there was less than 2 HP difference running 26* vs 30* at those RPM levels. With the Etecs and somewhat decent quench it made peak power at only 29* total advance on 87. My combination is pretty timing sensitive. Mine really wants more cruise timing but to do that I would have to advance the physical distributor which would throw the cam sync off for the fuel injection. At about 42* it starts jumping to the previous cylinder and misfiring. It pulls the brick aero of a fullsize van down the highway at 70 mph at about 2,400 rpm pulling at around 50 kpa. My sister has a 5.3 Tahoe that I have datalogged into the 52*+ range at very light load cruise. One of the benefits I hope to soon have when I go with the EFI Connection 24x on the Express. My old 83 G20 with TPI ran up into the high 40s at cruise and was happy with that, but it was also under 9:1.

[Engine07]

Go to the top of the page click forums, then gm efi systems, then gm bin files and wiring diagrams, then find your ECM number on the list, I think it's page 2 if you have 7747, then there will be all the info you should need there. It will have wiring diagrams, bins, tuning files, etc.

[Roadknee]

It was on the knock sensor pretty hard on 87 octane. I played with the timing on the dyno and even running 93 octane there was less than 2 HP difference running 26* vs 30* at those RPM levels. With the Etecs and somewhat decent quench it made peak power at only 29* total advance on 87. My combination is pretty timing sensitive. Mine really wants more cruise timing but to do that I would have to advance the physical distributor which would throw the cam sync off for the fuel injection. At about 42* it starts jumping to the previous cylinder and misfiring. It pulls the brick aero of a fullsize van down the highway at 70 mph at about 2,400 rpm pulling at around 50 kpa. My sister has a 5.3 Tahoe that I have datalogged into the 52*+ range at very light load cruise. One of the benefits I hope to soon have when I go with the EFI Connection 24x on the Express. My old 83 G20 with TPI ran up into the high 40s at cruise and was happy with that, but it was also under 9:1.

We were messing around with the 406 one night in search of better fuel economy. It runs 70 mph at 2,000 rpm around 50 kpa if I remember right. Its a Holley Commander 950 system. We set the cruise on a level highway and started messing with timing and watching injector duty cycle. 35 to 45 degrees timing made no difference so we left it at 40. It has the wideband upgrade so we also tried leaning it out. Duty cycle decreased each time we increased AFR, indicating economy was better. At 17:1 it started missing and throttle response suffered so we settled on 15:1 AFR cruise.

[Engine07]

On the heated plenum question again...I know the older heads had the exhaust crossover the vortec style heads do not have. How are you guys with vortec heads solving the cold weather issues? The heated passage is not needed for summer right? So in theory, if I take my heater hose and reroute it through the heated plenum passage on the vortec manifold, then it would provide enough heat through the plenum in cold weather while the heater is running? I wondered how it would be while the engine was warming up but most of the time in cold weather I start the truck about 15 min before I leave anyway so the truck has time to get warm because I don't like climbing in the truck and freezing on the way to work. Would this method provide the heat needed to the manifold?

[Roadknee]

Whether the heated plenum is needed is a matter of personal opinion and preference. It would not be near as important in a carbureted application because the emulsion circuits in the carb do a great job of proper fuel droplet formation. The TBI injectors meter liquid fuel on top of the throttle plates and rely on manifold heat and vacuum to properly vaporize the fuel. I would recommend you figure out how to heat the plenum year around like GM intended it. Yes, you'll give up a few top end HP, but the increase in economy and running consistency as the seasons change will be well worth it.

[Fast355]

Whether the heated plenum is needed is a matter of personal opinion and preference. It would not be near as important in a carbureted application because the emulsion circuits in the carb do a great job of proper fuel droplet formation. The TBI injectors meter liquid fuel on top of the throttle plates and rely on manifold heat and vacuum to properly vaporize the fuel. I would recommend you figure out how to heat the plenum year around like GM intended it. Yes, you'll give up a few top end HP, but the increase in economy and running consistency as the seasons change will be well worth it.

Its actually quite the opposite. The carb needs more manifold heat than the TBI does. At part-throttle the intake is under a vacuum which reduces the fuel boiling point and creates sheer off the throttle plates. I ran an edelbrock air gap victor jr 2bbl single plane in temperatures under 20*F without any issues. If you run into pre-heating issues I would suggest using an OEM style air cleaner and a preheat tube on the header/exhaust manifold. If you were to abuse an old carb V8 right after cold start and say floor it from idle there is a pretty good chance it will stall out on you or have a bad bog.

[Roadknee]

Its actually quite the opposite.

I will agree to disagree on this point. No disrespect intended.

[Engine07]

So I guess since it needs the water bypass, I could go from pump, up to passenger plenum, out of driver plenum, into bypass port and problem solved? Guess I can see how it does lol

[Roadknee]

I think full flow runs through the heater core all the times on these trucks, and heat into the passenger compartment is regulated by the air doors in the heater box. So you should be able to plumb the heater hose on the passenger rear of the stock manifold to the passenger plenum of the RPM manifold.

[Engine07]

I was thinking that but not sure. I'll test it out in the morning just to be sure. Actually nevermind I know it does. Wasn't thinking. Heater core was out in the blazer I'm helping my cousin in law fix up and we just looped the hose to bypass it until he got a new one.

[Fast355]

Would love to see those timing tables...that would be awesome!! I had no idea where to start with the tuning.

Here is the timing table I was running with the LT1 cammed 1999 Suburban with the S10 converter. Ran GREAT.

[Fast355]

and this is what I am running on the Express