3.09x2.96/2.66= the same as 3.44s with a regular trans. The factory 340 sticks came with 3.55s and were terrors with their 268 cams. Run whatever you want, with that 3.09, you got a clutch.
But not a 292/108
I have that trans and run 3.55s cuz with my GVOD, it is revved out at 60 mph in First-over. And cuz it gets me 93mph in the 1/8 at 6150 in second-over.With a 3.55x3.09=10.97 it takes off hard, like a standard box would with 10.97/2.66=4.12s And finally because, because I can idle it down to 550rpm and the car moves at a fast walking pace of 4mph. Those are the only reasons I run the 3.55s.
My current cam is a Hughes HE 3037 with 230/237 @050 and 276/286/110
[email protected]
With this combo and 10.9Scr with aluminum heads, taking off is a dump it and go deal. I literally blip the throttle and let the heavy factory flywheel launch the car just feathering the clutch in, NO drama whatsoever. I would like to run 3.23s, but the cruise rpm would put that cam back into reversion and help nothing with fuel-economy. I know the engine would pull 3.23s just fine. But my 500rpm walking speed would increase to 4.4mph, and few people can walk that fast, making parades impossible for me.
Would she pull 2.94s? Absolutely yes, And I'm pretty sure she could spin BFGs most or all of the way thru second, ending at 75/80 mph.
So run whatever hiway cam you want.
One thing I see potentially screwing your combo up, is a lil too much overlap and not enough rpm. This will cost mileage more rapidly than hiway gears can make up. In some situations, my engine makes better fuel economy in direct than in overdrive. This is another reason for me to stick with 3.55s, the cruise rpm is high enough to eliminate reversion, at ~2200 rpm. 2.94s would drop that to ~1860, and my manifold vacuum down there is a lot less, indicating the engine is still in reversion.
So, if you want to push the envelope and still maintain economy, my 276/286/110 would not be a good choice; 61* overlap is really hard on fuel at 2200rpm.
Now, having said that, the previous cam in this combo was a Hughes HE2430 with 223/
[email protected], and 270/276/110 advertised, and had 53* overlap . And this combo ran,point to point over 600 miles averaged over 30 mpgUS running at 85=2000rpm...... I know, just 9* less overlap. In the home country, our speed limit is 62mph(100kph), and the Rs were 1515, and swapping to a 750DP from the 600VS cruisercarb.. the economy was not there.Why? Because at 1515 she was back into reversion, and the DP was not set up for mileage.
So, be careful; that 2.94 can bite you in the azz, if you run the wrong cam , with the economy going backwards, depending on the cruise rpm.
So that was hiway talk;now lets talk about
city work.With 2.94s,
30mph will be about 2200 in second gear A big fat cam at 2200 will be a big fat disappointment in every way. To accelerate briskly will require a downshift, and the Rs will jump up to 3520, and away you go. The question is do you really want to spend your whole life shifting up and down in traffic? Probably not. So in this case, married to the 2.97s you would want a hi-torque cam, something with very little overlap, and something to keep the cylinder pressure way up, so you can leave it in second.
How about 50mph? This is another popular posted speed limit. Now you are in third@2690 rpm.A downshift into second will get you 3690, and away you go.So again, the big fat cam is not a good idea.
So the solution would seem to be a short overlap,hi-torque cam.
Ok well remember the OEM 340 cars got horrible fuel economy with their 268 cams that had just 44* overlap. I had a few of those in my life, so I can attest to the poor economy, with 3.55s where the cruise rpm was already almost 3000.
So far, two things we know; 3000rpm is bad and so is 51* overlap at 1515 rpm,lol. And 44* is not too good either.
Stock 2bbl 360s had,IIRC, a 252/260/112 cam and even at 8/1 Scr could be tuned to make pretty good mileage with the 3.23s or less, that they often came with. That would make overlap of 32*, and a cruise rpm of around 2500. I have tuned those to rival teeners.
So now we know that 32* overlap and 2500 are good things. Your 2.97 will cruise at 65=2500 so you are part way there.
Ok but that 252/112 cam is a little puny in a 340 right. Well not for your application. And especially if you juice the cylinder pressure up. Aluminum heads will support pressure close to 200psi on pump gas.
Ok but your engine might come in at just 10.5, maybe a tic less. So that 360 cam with an ICA of just 59* might pump you up to 180psi; perfect.
With a VP index of
149 this will be a high torque engine, so will easily cruise at 2500 with the throttle barely open. I'm pretty sure that if you had a mind to,you could run a 2.45 on the hiway.But that 252/260/112 is gonna power-peak pretty early and rpm makes power so, your power is gonna be limited.
Let's pump it up a bit, with a 262/270/108.. This cam makes overlap of 50* and about the most your application will accept, as to hiway economy. Check this out! your ICA moves from 59* to 55* and the pressure rises to 184psi with a new VP of
158! So now you have a torque monster, that makes pretty good fuel mileage@2500, and the power peak is around 5000, and a 1-2 shift rpm of about 5700 when you get on it.
Now back to 30mph@2200 and 50mph@ 2690. Just leave it in gear, and with a VS carb, press on the pedal as hard as you need to, she will torque away.
Well that brings us close to,
the conclusion;
My numbers are worked out with an Scr of 10.5 and with 184psi@800ft elevation, you have a bit of headroom. So if you end up a quarter point over or a half a point under, you will still be alright. Here's the rub; I used the advertised numbers to bring accuracy to the ICA, and the cylinder pressure. However, the .050s can vary widely and with it the power. Which you didn't even allude to. But with aluminum heads Ima thinking you still want to have something when you are done. So talking about a 262 hydraulic cam, the .050s could vary from a scary 204 minimum to perhaps 224 at a maximum. That is a range of 20* or 3 actual steps in performance.Most likely you will find 218 to 220; I would target no less than 218. This will get you a well-rounded engine making gobs of torque, and reasonable power, and with a good tune make great mileage, and if you paid attention to minimizing your Quench during the build, I'll bet you can run 87E10, for still more savings. I know my 367 did.
Wonky specs
The numbers are kindof funky; 262/270/108, with an install of 105*. You won't find an off-the-shelf cam like that; not even close. So talk to your grinder and see how close he can get to that. The primary focus of this cam is to make pressure, to take advantage of the aluminum heads, so you can use those 2.97s at 30 mph, and not have to be back-shifting in traffic. I left Power as of secondary importance.
I chose the
8* degree split so it would get me some overlap (50*), and together with the
108Lsa, make a nice little power boost with your headers, at 55/60 mph in second gear. First gear will be a throw-away gear cuz she will spin right thru it at WOT. To get to the power bulge faster, you might have to hold first a little longer than you might think, perhaps 6200/6400, so be sure your valve gear will go there,reliably. That shift-speed will put you very close to the torque peak,after the shift, and so the car will continue to blast to 65Mph with that lil power bulge. You need that boost because the Rs at 65 will be just 4800, in second gear.
This is the LARGEST cam I would put in the on account of the 50* overlap. You could open up the LSA to 110, and trade away a bit of that almost excessive torque, for 4* less overlap (now 46*), and possibly maybe gain a little more economy, but the power bulge will also go away.
That's the best I got, and the back-story to the getting of it.
And finally;
That VP of 158 is in BB territory, so when you floor it at 30mph, hang the heck on, cuzchit is gonna happen!
Read about VP here;
V/P Index Calculation
