Results? Pros: Tapping noise is gone. The engine seems to rev a little smoother, and it revs well to 7000+
Cons: Lost power. At first I wasn't sure, but I just took it to my test hill where I push it hard at 3200 rpm in 4th gear. I use this spot to listen for knock when setting up my timing map, and I do have to progressively pull a fair amount of timing out at high loads (drops to 22.5 degrees advance at 2500rpm, 24 at 3000, 26.5 at 3500, 30-32 at 4000 at 70-100% of throttle. For comparison, low load/cruise timing is 28 degrees at 2500, 33 at 3000, then 37 from 3500 onward). Before, if I hit it hard at 3200 on the hill it pulled (as long as it didn't knock! Thus the above adjustments); now, it goes flat, and has that flat blaaaa kinda sound where pushing the pedal makes no difference in the car, and then it begins to catch up. The engine doesn't strain (in fact it feels "safe"), it just seems "thin" there, like it's off the cam. You can feel it on the flats as well, but that's what makes the engine feel smoother. Top end may be the same, I need to try some high speed runs in my test place for that, but the 3200 rpm grunt is missing.
Then I realized, it's a feeling I've felt before. And sure enough, I looked back through my previous posts about dynos and cams etc, and there were my own words talking about how much better the Isky was at 3200 rpms. Then I looked over my own dyno charts from over the years, and while the engine has evolved in many ways run to run, I did have an early 2004 run with the RB cam with 48mm SK RACING carbs w/39mm chokes, stockish compression, ported head but standard valves. At 3000 rpms it was making about 120lbs torque. But then it dropped down to 105 at 3500, before climbing back to about 128 at 4000 then peeks at 130lbs at 4600. Then it drops off to 120-118 at 5500 (believed to be carb related at the time). That first drop at 3500 seems to still exist. Why? Not sure, but that's what happens. At the time we attributed it to carb and/or timing issues. Note the big 39mm chokes. Compared to the Isky cam dyno runs in 2019 (more modified engine, 11.7 compression, bigger valves, crank fired ignition, Dellorto carbs with 37mm chokes, unfortunately it ran too rich on the dyno) at 3000 rpms it only had 105lbs, but by 3500 it's at 125 and hits 130-134 at 4000rpm and carries on 4700. At 5500 it's still making 128, but the engine was drowning in fuel, like 10.5 to 1 and it was struggling to rev and choked off at 6200rpm... I need EFI! And that started THAT adventure
. Today, with EFI controlling the fuel mix, we know it's not a fuel ratio issue. It might be a result of the size of the intake (39mm venturis in the carbs back in 2004, and the now I run 40mm throttle bodies) but I kinda doubt it. I do wonder about ignition timing, so I may try a bit more advance under load than I ran with the Isky. Maybe the change has created a condition where it wants more timing? It's my understanding that reduced timing can make the engine response "lazy" but she must not knock! If that doesn't work, well... somehow I will have to figure out how to run the Isky. The car's not horrible or anything with the RB, but there was a response I could count on that I really liked, and it's different enough that I notice it. As many know, I have had this car a very long time (my third car ever owned). This summer I kept noting how often I felt like I was in 4th gear only to see I was in 5th because the car was just more responsive. I attributed that to the EFI, but the cam seems to be a big part of it. I may have to have Delta cut a smidgen off the lift to say .520 lift and not run the lash so tight (6 and 8 cold, could go stock 8 and 12) and maybe that will give me the clearance I need.
So there's the story... thanks for reading my dribble. Of course I'll keep you posted... I can't help myself
