[chiphead]

Here's the #7 plug from my 400 with 62 heads. All the R45S plugs look exactly the same. Slight bit of oil on the threads, some carbon, white insulators. Car runs really well, just obsessing on the tune.

400, 62 heads, 2802 cam, RPM intake, headers in a 67 Lemans.

QF750 DP
70 primary jets
64 PVCR
79 secondary jets
.030" IFR
66 LSAB
30 HSAB
93 octane E10 fuel

16* base, 35* by 3400 RPM, 12* vacuum advance
wideband shows AFRs of 14s at cruise and 12.3 at WOT. Will easily roast a set of 275 drag radials with 3.25 gears.

[johnta1]

I'd try a R44S plugs and see what they look like without a lot of idling. Idling makes it really hard to color the plugs correctly.

[chiphead]

I did just change to the NGK XR5, which is supposed to be equivalent to the R44S plug, one heat range cooler than the R45S. The 389 plug heat range thread got me thinking about plug heat ranges, so I figured I'd start a thread about my own situation. It also dovetails with my QF 750 tuning thread from a few weeks back.

[steve25]

Info.

[chiphead]

I chopped the #3 plug, as it looked the leanest. There is no fuel ring at the bottom, the whole insulator looks as white as the pictures. So it's lean and plug range is hot. I guess leaner is meaner, because it's been running awesome in 50F-60F weather we've had here.

Should I give the NGKs a rip around the block and see if they color up, or go immediately to adding fuel?

[Kenth]

Do the "tip-in" test with the choke-blade or the palm of your hand at 2200 rpm and see what it shows.

If the engine picks up more than 150 rpms you may want to enrich the mixture, as in larger main jets.

And, the .030" IFR seems somewhat small, they may be opened a couple of thousands.

[steve25]

With hotter weather on the way I would drop down one heat range and proceed as in the post above.

Deliberately de-tuning out 4 Hp by running a hair on the rich side will keep your rod bearings alive in adverse conditions.

[chiphead]

With the Proform metering blocks, the primary boosters have been slow to come on. At cruise as I add throttle, the AFR goes to 15.5s before it drops down into the 13s at about 2600 RPM. It doesn't surge, but there is a slight grumble at 2500 RPM, and AFR goes into the 15s, that indicates it's on the edge of lean surge. This is right as the transitions taper off and the mains try to start.

Would decreasing the top emulsion bleed from .028 to .025" encourage an earlier pull-over? The boosters need to start before the transition circuit tapers off. I'll increase the IFR from .030 to .032, but the mains need to show up to the party on time.

[chiphead]

How much plug coloring is realistic with E10 fuel?

With the carb changes I made (.031 upper emulsion, one step larger jets, up on the fuel level, increase IFR), the AFR gauge is showing 0.5 to 1 AFR richer at cruise and heavy accel on the primaries. I went for a 50 mile back highway rip, and the plugs barely have a fuel ring at the bottom. The XR5 plugs look brand new.

If the AFR gauge says 12.x to 13.x, the car runs crisp, but the plugs are bone white, do you add more fuel or not? How long do you drive a street car to judge jetting?

[triathlonx13]

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