Gross lift .539 I, .551 E
Duration 271 I, 279 E, @ .050: 219 I, 227 E
ICL 106, sep 109
LONG!
Lately I’ve been doing a lot of testing and Gonkulating on heavy, tall geared cars – what works and what doesn’t.
The combos that work and don’t work are quite different than if you had an ideal car behind the engine – light, steep gears, stick or high stall, etc. So I did some Gonkulating on the big 65 T-Bird, and it shows trends the same as I’ve seen in road testing and Gonkulating my own big heavy dog. Hopefully it will help in terms of not just “what carb” (I’d run that little Autolite on the shelf for now) but what else will make the combo work.
I don’t know the weight of your 65 Bird exactly but guessed a curb of 4350 lb, or 4550 lb down the track with driver and Feral Shop Cat (optional but a good idea).
With that, and 2” duals which I assume it has, let’s start out with a Gonkulator of its current description, with that 1.12 Autolite 4100 on top. I assumed 1900 stall which is about what I tend to observe for a stock C6 behind a 390.
In the starting condition I’ll include some Gonkulator shorthand, as it will make each Gonkulation quick to compare with the others.
Torq 393 at 3500 (35t393)
Powr 336 at 5200 (52p336)
Shifting at 5500 (s55)
2.61 60ft
10.60 at 70.2 1/8 mile
16.13 at 89.8 ¼ mile
8.35 0-60mph 8.35 60m
OK let’s compare some carbs:
500A= 1.12 Autolite 4100 500cfm
600H = Holley vacuum 600cfm eg 390GT, 390HiPo, 430 Bulldozer carb
735H = Holley vacuum 735cfm 428CJ carb
35t393 52p336 s55 2.61 10.60 at 70.2 16.13 at 89.8 8.35 60m SM+500A WT=4550
35t394 52p342 s55 2.58 10.50 at 70.8 15.98 at 90.6 8.16 60m SM+600H best for now
35t395 52p346 s55 2.60 10.52 at 70.8 16.00 at 90.8 8.17 60m SM+735H best later
The Holleys are a couple tenths quicker 0-60mph, maybe a tenth in 1/8 mile. The 600 Holley was the best of the 3 carbs, but probably NOT the best one later on if you keep reading.
While at it, I Gonkulated the stock iron “Z” intake:
31t400 47p316 s50 2.54 10.50 at 69.6 16.09 at 88.1 8.23 60m Z+500A WT=4600
The iron Z boat anchor beats out the Streetmaster all the way thru the ¼ mile (though it would probably lose the ½ mile if anybody cares). The Streetmaster suffers below 2500rpm as I noted above, so though it shines on top (20 extra horsepower, 336 vs 316) it loses the race off the line and never catches up. So I’d keep that iron Z intake around, but if you want to make the whole combo work better, here’s what’s next:
The FPA headers and 2.5” duals are good steps, regardless of other options.
Here’s a repeat of both Gonkulations, Streetmaster=SM and Z intake with the 500cfm Autolite on top, with FPA and 2.5” pipes.
Note the headers add T=17 ftlb and P=24hp to the Streetmaster combo and 18hp to the iron Z intake combo.
35t410 51p360 s55 2.56 10.31 at 72.3 15.67 at 93.0 7.77 60m SM WT=4550
32t414 47p334 s50 2.50 10.26 at 71.5 15.70 at 90.5 7.75 60m Z WT=4600
The 50 lb heavier iron Z is still quicker thru the 1/8 mi. It loses by .03 in ¼ as the Streetmaster comes to life.
What the big heavy Bird needs, especially with the cam in there (about the equal of Ford’s old C8AX-C cam in terms of loss of low-end), is either more converter, steeper gears, or an overdrive trans. The easiest fix is more converter, as it lets us keep the highway gears. But as we can see, the Gonkulator doesn’t think that stall alone will do it – more gear is also needed.
Same comparison as above, FPA headers, but 2200stall
35t410 51p360 s55 2.39 10.00 at 72.7 15.34 at 93.2 7.37 60m SM finally holds its own
32t414 47p334 s50 2.36 9.99 at 71.8 15.41 at 90.7 7.40 60m Z hangs in there even +50 lb
The 2200 stall picks up 3 tenths in the ¼ mile, about 3 carlengths, and even 3 tenths as early as the 1/8 mile, about 2 carlengths.
Note that the Streetmaster finally has a clear ¼ mile win, but in the 1/8 mile the Z is still a few inches in front.
Also, right in here somewhere, before buying a converter, I’d either swap to a C6 trans (I assume they fit the Bird but not sure), or get some beef in that MX trans before it self-destructs like ours did. I don’t know if a gear vendors C6 overdrive would fit the Bird or not, or maybe a built AOD trans, etc. It’s hard to have a heavy car that cruises and also has steep gears off the line.
Let’s try more stall at 2500, though now we would be cruising “on the converter”, kinda slushy and building heat at cruise:
35t410 51p360 s55 2.31 9.81 at 73.0 15.14 at 93.3 7.12 60m SM better 1/8 mi on.
32t414 47p334 s50 2.29 9.83 at 72,1 15.24 at 90.8 7.18 60m Z better <330ft
This time we only gain .20 seconds (or less) ET – diminishing returns, but that’s still 2 carlengths for a total of 5 carlengths ahead of where the big Bird used to be. A huge difference. The Streetmaster has come into its own (barely), and now beats the iron Z intake everywhere except across the intersection (60ft). Now we need gears.
Next in the Gonkulator I “swapped in” a 3.50 gear, with Traction-Lok while we’re at it. Not needed with the 3.00 gears but now it will help:
35t410 51p360 s55 2.18 9.53 at 74.2 14.83 at 92.6 6.68 60m SM finally better >330ft.
32t414 47p334 s50 2.14 9.55 at 73.3 14.98 at 90.9 6.80 60m Z WT=4600 still wins <=330ft.
The 3.50 gears wake up the combo yet again, making it another 3 tenths quicker. The Streetmaster is winning, but the iron Z still does a respectable job up thru the 1/8 mile, which I commonly use as the cutoff for “street” performance. Unless you live in “flyover country” (pun intended for Ross), that’s probably more important than what the car does at 90-100mph. We have over 40,000,000 people here in CA, and sometimes I do indeed miss flyover country. Empty open road!
Now let’s try a couple different carbs again to compare to the 4100 Autolite’s 14.83 at 92.6mph:
240d 35t412 52p367 s55 2.16 6.14 9.43 at 75.0 14.69 at 93.4 6.51 60m SM+600H
243d 36t414 52p373 s55 2.16 6.14 9.43 at 75.2 14.67 at 93.7 6.49 60m SM+735H better in ¼ mi
The Holleys are a tenth or two quicker than the little 4100 Autolite, but that seems a tiny amount compared to what the converter and gear did. Those are the big decisions as I would see it. It looks like you could choose either a 600H or 735H and run about the same, depending on where you score a super swap meet deal. Half the fun in our hobby is scoring a good deal, right?
I Gonkulated one more combo just for fun – the Rodney Dangerfield (Performer) intake:
232d 33t422 48p350 s51 2.11 6.08 9.38 at 74.8 14.69 at 92.7 6.47 60m Perf+735H, 1” 4h better to 1/8 mi
This intake, with a 4-hole 1” spacer to make it the same height as the others, and a 735 Holley, beats them all to the 1/8 mile and 0-60mph. A good street combo if you come across one. I’d keep that in mind to try it – you could always sell the intakes you don’t like after that. But I’d keep both carbs – the Autolite for gas mileage, and the Holley for summer fun. You gotta have a good running backup carb anyway.
The big heavy Bird is not going to be Top Stock Fast no matter what you do (neither is my super tanker wagon) but it’s fun knowing a car is doing all it can, while still being a good fun cruiser.
