It could be the heat range of your plugs as BuzzLOL mentioned, or a lean mixture at WOT.

I thought that Chassis Dynos use High Gear for Dyno Pulls. You let the trans shift into high & rev to Max RPM with no load on the rear wheels, then they add load until the motor RPM drops. It's very hard on a drive train, because it sees the maximum torque of the motor for a long time. It's actually worse than a Drag Race.

 

Hmmm...good point on the plugs.

Anyone have a recommendation and P/N for one heat range colder plugs for 302C Aussie heads that they like?

 

The 18 degree stop has fixed the ping. 30 degrees total. Winning.

Started adjusting the modulator (1/2 turn clockwise increments; then test-driving...I'm turned in one full turn CW now)...shifting at 4800 now...another half turn and will report back. Gonna take it slow. Going for ~5500

 

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2 tons of Ford fun!

 

4,167 to be exact! It's a tank!

I'm actually amazed how well it pulls for its size and gearing.

 

Hey Y'all I'm just gettin' back into this forum after a long hiatus. So...Please go easy on me. About the motor not pulling to 6 grand;it sounds like you're nosin' over lean! That motor build is goin' to require a carb in the 700 cfm range to provide enough flow to keep it pullin' on the big end.

 

Flow calculations do not support that theory, even at 100% volumetric efficiency.

 

Have you ever dropped 'er down into 1st- went to the wood with it..and seen where it stops pulling? I mean, to the point where you've got to lift in order for the manifold to belch the carb back out? If I remember correctly..an adjustable vacuum modulator will only hold it in gear for about 80% of what it'll pull to before it loses enough of the vacuum signal to hold it against the spring. Whether it noses over from valve float, lean mix, air restriction(no longer able to extract fuel through the carb) or electronic skips,makes no difference, all "calculations" aside. Someone can check me on that but it seems right to me. So..if it quits pullin' at 6500 rpm then -20% is goin' to put your best possible tweak at around 5200. That's pushin' the realm of vacuum diaphragms. Any thing that will cause the motor to "tick" like detonation,oil pump belch, hall effect skippin', or firin' pin glow..so on.. will cause a loss of vacuum signal within the "Air pump" and let the modulator think the load is gone. Get yer shift then like it or don't. I took the liberty of copying this carburation calculator: entering a conservative parameter for your build, and maxed rpm's at 6500. Does it jive with the calc. you were talkin' about?
Formulas and Calculations

CFM Calculator
Engine Size like 350 or 454 etc.


Your Engines Max RPM like 6000 or 7000.

( Better to guess a little high )
Engine Type


.

.
Aprox 728 CFM Needed for a 408 CID Mildly Built Engine

 

http://www.carburetion.com/calc.asp Sorry.This is the web page where I got the carburetor calculation "guess" from.

 

Odd. Put a max rpm in of 7000, with a C.I. of 408 and mildly built and got 785.
suggest though that 7000rpm on even a mildly built 400 is xtremely optomistic.
Used Rpm limit of 6000 and that came out at 672 cfm.

Tim Meyer on his website has suggested it takes a lot of valvetrain (and other) work to get past the 6000rpm mark easily and reliably. Dimora has a pretty close build to mine (mine is a 72 galaxie 4dr) except the lucky bugger managed to get a set of roller lifters/rockers in there.
I am running a 725 holley, but also running propane. Broke the engine in on gasoline, and since I have been running it for a while on propane the carby is being a PITN!! It did go very well up into the 5000rpm mark but it is a little bigger than needed-i did it that way for the propane setup.

Done a little digging and found (on several sites including Holley, (so a little cut and paste was probably going on) that it can depend on the weight and axle ratio of the vehicle.
A heavy vehicle can actually benefit from a smaller carb than a lighter one.
A lot of other factors were mentioned but that was the power-point version.
The upshot of this and all the other research I've done over the last few years is that a 400 does not need much more than a 600-650cfm carby.

 

You're probably dead on with the "upper" limits of a "mild" build, even though DiMora's is considered, probably, on the top side of MILD. I was just responding to him wanting a higher "SHIFT POINT" from a C-6/408 pushing a land yacht with 2.75 gears! But, you're right. I wouldn't want to twist my 400 (without any oiling mods) to any where near 7K, or expect the transmission to pull over 5k before shifting! He's already stated that the barge is banging between 4k and 5k, which I was pointing out would screw with the vacuum signal given to the trans. I also noticed that in his videos he has the little red tab set at 6k on his tach and even that is probably on the top side of that Edelbrock carb/Performer best. There have been one OR two others on here that believe he's goin' a little lean on the big end as well, and I'm just thinkin' that he may be gettin' a glow on the buisness end of his firin' pins! "SHIFTING" at 5500 rpm with that combo? I don't know...maybe it's like my Mammaw always told me when I wanted something I was clearly never gonna get-"Won't Ya wish for it in one hand and crap in the other, see which one fills up first!" Peace out

 

Like I said, my build is similiar. Car a little earlier but no lighter, approx 2200kg. C6 (40yrs old) with the 2.7 diff.
Holley street dom single plane (for the Propane) and slightly bigger carb (725 vs 600) than ideal.
Not quite as snappy down low-still ok-but does start to wind up later and still shifts around the 4500rpm mark at wot.
In saying that, I bought the car with the old engine and rebuilt it myself and it definitely goes a LOT harder than before even down low so who's to say it's not as snappy. What I have on it would suggest a slightly smaller carb and a decent dual plane would increase low down torque.
I did build it to suit h/way speed and propane use though.

 

Those carb calculators are out-dated. I've seen plenty of Ford 302's do well at the drag strip with a 750 holley! As in faster than the 600-650 they had ran previously.

FWIW I'll be running a 750 holley on my 408 build for my truck. I'll let you know how it works out.

 

Try driving that 302 with a 750 Holley in city traffic! A drag strip only tests one function of a carb. That's WOT. A proper sized carb will work in stop-and-go traffic, and at part throttle, as well as WOT.