It should, shouldn't it? With the 3.42's and the TH400, I got 7-8 mpg. With the 3.55's and 700R4, I got about 10 mpg on my way to Dallas - all highway miles trying to be conservative to make it to the next place that sold 93 octane. And now with the new heads and properly fitting gaskets, it wasn't any better. Still 7-8 mpg. That's with some good on ramp pulls as well as just highway cruising. Right around 100 miles per tank. Lots of smiles too, but not many miles. So that was the first of 2 remaining problems after the head swap.
But then came the second issue. As I was pulling into my driveway after a test drive, I heard a strange noise coming from the engine bay so I popped the hood and watched as my A/C belt fell off. WTF? I had personally tightened the belts during the motor reinstall. Pulled it out and saw this:
The teeth were delaminating from the rest of the belt. How weird. The belts were reused and I didn't actually know how old they were. So I chalked that one up to an old belt, replaced it, and considered how lucky I was that it happened in my driveway instead of while driving where it'd undoubtedly knock off all the other belts.
Next time out, almost the exact same story. As I was turning the corner into my neighborhood, I noticed my voltmeter drop down to 12V and heard a similar sound as the previous day. The alternator belt had liberated itself from the car. Went back and found it laying broken in the road:
So... that one was probably just old too, right? Replaced it, went on with my life.
Next couple drives were ok. I was about to return focus to the rich running carb when it happened again - this time in the way I had feared. On the highway, just after doing a nice pull on the on ramp. Belt flies off, knocks all the rest of them off. In an instant I'm down to 12V, with no power steering, no water pump, temps climbing rapidly, the whole 9 yards. What. In. The. World?
Replaced all the belts. Got them all nice and tight. Nothing appears out of alignment. I'm not super impressed with the quality of the belts I'm getting from O'Reilly, but my pulley grooves are pretty darn skinny and these are the narrowest belts I can find in the size I need. I think I've narrowed it down to happening only at high RPM. I can cruise around mildly all day with no issues. I'd go for drives and keep it below 4,500 RPM. Then 5,000. Then 5,500. All fine. It's only if I get in the 6,000 RPM range that the belts will fall off. It's consistent at this point and I become an expert at changing belts. The confidence I was supposed to have in this motor after all the upgrades is shattered.
I switch to made in the USA Napa belts. They look and feel much higher quality. Maybe it was just an issue with the lesser belts. May have helped a little, but it still happens. Other than that first time, it seems it's always the alternator belt that fails first. Wish I had a way to see what was happening in the engine bay under load at high RPM and figure out exactly what was going on. The only thing I could tell from looking at it is that the belts sit kinda high in the alternator pulley. Like I said the groove was pretty narrow so the top of the belt would stick out above the top of the pulley groove by a few mm. So I removed that and turned down the grooves on a lathe to fit the belt better.
Happy to say that after 20+ full throttle, high RPM pulls later, I have not had any further belt issues. Whew. Confidence returning..
So back to the first issue. Took the car to a chassis dyno because I wanted to see what my drivetrain losses were now that I knew exactly what the motor did on the engine dyno.
I don't remember the exact numbers but it was lower that I was expecting - down about 25% from engine dyno number vs the 18% or so I was hoping for. Guy running the dyno also mentioned how rich it was. I knew it was rich from the smell, the black soot in the exhaust, the narrowband O2 sensor reading, and the aforementioned terrible gas mileage. This was the final straw that got me motivated enough to learn enough about carburetors to fix it. Of note, the dyno headers were also bigger than the ones in the car, plus it has a full 2.5" exhaust, air cleaner, water pump, power steering pump, fan, alternator, and A/C compressor to spin. I'm guessing all that is why the mixture changed as much as it did from engine dyno to in car.
Anyway, got home, pulled a plug, and this is what it looked like:
I'm no expert at reading plugs, but I'm pretty sure they're not supposed to look like that!
So after researching tuning carbs, all the reading plug colors, evaluating sounds, smells, vacuum, etc. seemed too imprecise to me. So first up I ordered a wideband O2 gauge/sensor to replace the narrowband rich/stoich/lean gauge that I had. (And because nothing is ever easy, the bung in my exhaust had some material leftover from the weld that prevented the new wider sensor from screwing in at first until I drilled it out..) Also added a fuel pressure gauge and regulator right before the carb that you can kinda see in the engine pics in my previous post.
Installed in the pillar pod:
If you have a carbureted engine and take nothing else away from this build log, take this: GET ONE OF THESE! Seriously. Having real-time air/fuel data there right in front of you as you're driving at all throttle settings/load conditions is invaluable for tuning the carb. This made it SO much easier.
Setting the idle mixture was a snap. It needed less than the standard 1.5 turns of the idle mixture screws. With the high line pressure of the transmission, the converter is tighter than its rating suggests and I found that the motor likes it a bit rich and a little faster at idle so as to not approach stall when in gear with the a/c running, lights on, etc. So it's set in the high 12's A/F ratio-wise.
Next it was time for a drive to see what it looked like under cruise, part throttle, and full throttle acceleration. Cruise wasn't too
bad, in the low 13's. Part throttle acceleration was the worst - 10.0 was as low as the gauge goes and it would hit that often. At full throttle it'd lean out a little to mid 11's. Pig rich, all around.
My plan was to adjust full throttle to within the realm that I wanted first by changing secondary jets, then fine tune that along with part throttle by adjusting primaries, and then see what that did to the cruise A/F ratio. Called Holley to see if they had any starting recommendations, and they said to change the power valve. After looking that up, I realized why. This carb came with a 10.5 power valve. The motor only pulls 7-9" of vacuum at idle depending on load. So basically the power valve was open almost all the time except very light throttle cruise or coasting. Things are starting to make sense...
Put in a 4.5 PV and started swapping jet sizes (after readjusting the idle circuit). Eventually settled on 66 primaries and 75 secondaries if memory serves. Down 8-9 sizes from out of the box (74/84). This gave me high 14's at cruise and a solid 12.5 at WOT. Part throttle mixture still gets rich (down to high 10's / low 11's) when the PV opens, so when I get home I'm going to swap the 4.5 for a 2.5. It'll be cooler so I might jet up a size or two as well. I'll make that decision based on the lovely real time data from the wideband.
- This carb was real rich out of the box. Obviously. It's made for boost and richer is safer for boost so I get it, but I do question the use of a 10.5 PV.
- I can see via the readout the moment the PV opens. A/F ratio drops about a full point. The vacuum rating of the PV is accurate.
- The car sounds and feels much happier and healthier. More eager to rev more quickly, no bogging. (Before this, I wouldn't have described anything the engine did as bogging, but in comparison, with the corrected mixture it just seems so much peppier)
- Gas mileage is DRASTICALLY improved. Instantly doubled - on the highway I now get almost 200 miles per tank (almost 15 mpg vs 7-8 mpg before the tune)
- The engine runs hotter. It was using so much gas before that the fuel was contributing noticeably to cooling. Coolant temperature is probably an average of 9-10 degrees hotter now. This is the one thing I'm not as excited about. Idling in traffic in the hot Texas sun with the A/C on, it will climb over 210 degrees and that makes me nervous.
Regarding the last point, I'm interested in what you guys would do to address it. I've started using a higher ratio of pure water in the coolant. Helped a little. Have a 180 or 185 degree thermostat from Napa that's supposed to be their performance line. New aluminum radiator? Expensive electric fans? Other options? Richen it back up some?
BTW, here's what the plugs look like now:
Can't wait to get home, get the new PV in, make any other minor mixture tweaks that may or may not be necessary, and give it another go on the chassis dyno. Overall it's running so much better!