340 cam change, carb rejet suggestions.
I am going to use 292/508 mopar cam. Will put in advanced 4°advanced to get better low end. This cam will have a pretty choppy idle but should get me nice power. Thermoquad i run with .101 primary jets, .145 rear jets and 1966 metering rods. For intake i will be using the holley strip dominator single plane. Rear gear will be 3.91's. Not set up this way yet but plan to do so in the near future. Now have a 280/474 cam & 3.55s but not too impressed. So will experiment with new set up. Just thought I would share.
1)That 280 cam wants about 10.4Scr with iron heads, and 11.4 with aluminum. And you're right about 3.55s; that cam is way past 3.55s. Try 4.30s; those will wake her up. With an automatic, she'll want some serious stall just to get moving.
A well-engineered 280*cammed 360, should spin street 275s to well past 60mph, in an A-body, with street suspension. BTW, 6800 at the top of first should be close to 60 mph.
With 3.55s that's a bit of a problem if you short-shift her. When you hit second with an automatic; if you don't stretch out first gear,the Rs fall too far. You're gonna have to get into second at around 4000/4500. That means yer gonna have to wind her up to about 6800 in first. If yer shifting at 6200, yer choking it, and bringing second in at 3700ish, and nobody is home down there. The ponies are sleeping. So you have to wait for the alarm to go off up around 4000; then they start rubbing the sleep outta their eyes.And they don't really wake up until maybe 4800. Now 900 rpm doesn't sound like much, but with 3.55s in second gear, this is from 55mph to 71mph, and that poor engine is starting to feel the wind. So yeah, you gotta wind em up in first,with an automatic. This is also why an automatic doesn't really like a tight 108LSA. When it falls off the curve, it falls harder than when it falls off a 114LSA. Doesn't sound like a big deal, but you'll feel the 108 fall right away. Actually you'll feel it more on the approach side as the 108 cam has a decided two-stroke power band; there's; nothing....nothing... I think it's coming..... and then KAPOW! it's here and then it pulls really hard for about 1500 rpm and then KAPOW!,it falls off the other side of the curve.This is why this cam is not well-suited to an automatic; and it only gets worse with the 292* cam
2) If you're gonna spend more than a little time in the 6000s, then you need to prep your oiling system to survive it.It's not hard, but the engine has to be torn down,completely.
If you put the 292 in you're gonna see that it wants to be shifted at past 6800, so the engine won't survive that very many times and then the rod bearings are gonna spin; unless you do the oil-system mods. If you also short shift this cam, then it would have been far better that you had a 268 cam, cuz if you line up with the guy that does, he might clean your clock.
3) The 292 needs 10.7 Scr with iron heads,and about 11.7 with aluminum.With iron heads the bottom will be soft;not may be soft , but, will be soft. How soft? Like a factory 360 with a 2bbl cam, and the compression pumped up to 8.6. This effect diminishes with rpm and by 3000/3500 the 292 will be picking up, but it's not really awake til it gets up in the high 4000s. So your 3400/3600 will really help you get past the low-rpm doldrums.
If you run the 292, I'm assuming your car is a race car, so my comments don't apply; but I can't see a 292,a360,and 3.55s in a racecar.
I highly recommend not to run the 292 with an automatic,as a streeter.
Your results may vary.
4) My experience;
The 292 makes lotsa power from 5000 to 7000, at or near sea level.
In my street-367; it had nothing below 2000,and from 2000 to 4000,a good stock 360 I think was better. I ran it at 11.3 Scr in a 367 with OOTB Eddies
When I had that combo, I ran a regular A833 and with 3.55s, I couldn't wait until 5000rpm/
42mph for the power to show up. Like you say; "I was not too impressed". I swapped in 4.30s which were nice, but they sucked on the hiway,lol. Finally I conceded that the 292/108 was not for me, and I pulled that lazy-azz 292 out before the end of the summer..
5) After that I installed a 270* cam, which I liked a lot. But 4 years later it dropped some lobes and I had to kiss her goodbye.
I currently run a 276/286/110 in my now10.9Scr, aluminum headed, 367, with a starter gear of 11/1.. This is still pretty tame in a streeter, but she's a wild ride. I run it with 3.55s but I have the A833 with the 3.09 low gear, and I have a gear-splitter. If I was stuck with a regular A833, there is no way I would run it with 3.55s. No way.And it's only a 276*, and it has an adjustable "stall",lol.
6) IMO,
if/then
IMO,
if you need more power in a street-360,than the 280 can muster,and if your compression is up where it needs to be,
then; IMO; you need more head or a bigger engine...........................or you need to supercharger it.
7) If you're really gonna do it, remember the power doesn't start 'til she's really singing, and the rest of the time, without compression, you'll be disappointed, again. But if you install 4.30s and with your 3400/3600TC, then once she hits 4800, yer gonna .....giggle like a schoolgirl.
