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-   -   B21F Carb Cam? (https://forums.turbobricks.com/showthread.php?t=360178)

TouringMusician 05-02-2021 12:41 PM

B21F Carb Cam?
 
Howdy friends,

So I installed a Weber 38/38 downdraft on my 76, and itís running incredibly well. Definitely gained 10 pants seat hp from the tired Kjet.

That said, I was curious if I could squeeze any more out of this motor with a cam-Iíve got an A cam in my 93 EFI, and it definitely was an improvement over the M, but this 76 comes with a B already, which appears pretty similar to the A, though I donít really know how to read cam specs.

I spiritedly but wonít be anywhere near the redline, so Iím hoping to have good daily drivability with as much fun under 5k as possible.

Also, I live in CO and elevation is a thing. The more air the better.

FWIW the car has incredible low end response now, so Iíd love to hold onto that. Honestly Iím not a Weber guy, but the 38/38 really woke this motor up.

Thanks!

mikep 05-03-2021 01:52 PM

K or one of the big enem cams.

John242Ti 05-03-2021 03:54 PM

K cam has a useful power band from 2000 rpm to 6500 rpm. So, not that great of a match for below 5K rpm acceleration. Also helps to have more displacement than 2.1 liters with the K, which is why the Penta engine that got the K cam was the AQ145, which was based on the B23E, but with dual carbs.

Personally, I'd swap the A in the B230F out for the B that's in the now-B21A engine. Drop the A cam into the B21A.

dl242gt 05-03-2021 04:01 PM

Volvos hotter engine with the kjet setup was the D cam. That was in B21E kjet engines and made about 125hp. It will do what you want but you may give up some low rpm grunt. The B21 loves to rev and the only reason for not using redline when you want to is if your engine has a lot of miles on it. Then keeping the max revs to about 5 to 5.5k is probably a good idea.

Broke4speed 05-03-2021 06:39 PM

I like the D cam in my B21A/AQ140 with the dual ZS carbs. It sounds insane on cold start, with the carbs.

mikep 05-03-2021 07:51 PM

K cam is not a wild cam.

PCH 05-03-2021 10:06 PM

I loved K-cam on my '76 but it had a manual. The rear axle ratio probably also comes into play when you are talking about low end feel.

spock345 05-04-2021 12:05 AM

I agree, the K cam is not all that wild. I ran one in my B230 for a bit. Advanced it a bit. Low end torque wasn't really a problem. It just pulled itself gently to 2k rpm and then took off.

John242Ti 05-04-2021 04:06 AM

Owned a B23E with one in my original 242. It's decent in that application. My current 242 has one in it. With a B23FT. A bit less decent, due to the lower compression (8.7:1 compared to 10:1), but still accelerates as long as the engine speed is above 2K. And, yes, the K cam is the second hottest stock cam available for the B21/23 series engines. So, it's not a mild cam.

An 8.5:1 compression B21 might not work very well with a K cam, especially when it's living at 6500' or above. Remember, the OP is not at sea level. So, having a higher peak rpm for torque (A K cammed B23E is at 4500 rpm, not the 2500 rpm of a B21F) probably won't be as desirable. Adjusting the cam timing might help, but the reason the OP asked the question was to expand on a suggestion I had on his IG account, which was for more low-end torque, not high rpm horsepower.

A B21A with an A cam and 8.5:1 compression has 96 hp and 121 ft.lbs of torque. The B cammed version with K-Jet is 102 hp with 114 ft.lbs of torque if without a catalytic converter. 99 hp with a cat. So, by going from the B cam to an A cam, there's an extra 7 ft.lbs of torque at 2500 rpm. Some slight loss in peak hp.

With the Weber DGV series Outlaw carburetor and Bosch breakerless ignition, it may have more power, but I seriously doubt that a hotter cam is going to be desirable in the rocky mountains with a naturally aspirated motor, in either a carb or FI configuration. In Santa Cruz, Ottawa, or Baltimore, sure. At the 11,312 foot Monarch Pass in CO, probably not.

Since his A cam is already paid for, and the B cam works fairly well in a B23/230F application, I would do that first. All he's out is the cost of shims and the tool. If there's more high end power desired, then maybe go to a D or a VX cam.

mikep 05-04-2021 04:17 PM

Quote:

Originally Posted by John242Ti (Post 6181178)
A B21A with an A cam and 8.5:1 compression has 96 hp and 121 ft.lbs of torque. The B cammed version with K-Jet is 102 hp with 114 ft.lbs of torque if without a catalytic converter. 99 hp with a cat. So, by going from the B cam to an A cam, there's an extra 7 ft.lbs of torque at 2500 rpm. Some slight loss in peak hp.

I'm not following you here. They are almost identical, with the B having one mmm more lift and a tiny bit more duration. You say the B is higher hp, but that the A will make more at 2500. also, the carb vs k-jet is apples vs oranges.

I did back to back A, B, V, K, in an LH car, and it was a snoozefest. All were fairly normal to me, with the V and K being more like an early Datsun stock cam, and the A/B being more like 60s british stock cams.
Even a K in a well-tuned megasquirt car was still fairly mild. In a decently tuned car, the V was my favorite. I loaned it to Norcal740 or whatever his name was, never saw it again.

So. OP, in my opinion, leave the cams where they are.

dl242gt 05-04-2021 06:51 PM

More low end torque is available with higher compression. That 8.5:1 of that engine is low. Even my non egr B21F with a B cam had 9.3:1 compression. A boost in compression would help and you'd get a mileage increase, too.

TouringMusician 05-05-2021 02:38 AM

Quote:

Originally Posted by dl242gt (Post 6181344)
More low end torque is available with higher compression. That 8.5:1 of that engine is low. Even my non egr B21F with a B cam had 9.3:1 compression. A boost in compression would help and you'd get a mileage increase, too.

If I had the time, the flat top pistons would be in in a heartbeat. My eventual plan was to up CR with a little head shave too, just was curious if anyone had any experience with cams in a carbed setup like this, since technically the B is a Kjet carb.

All this has been great info, yíall. The A cam is an easy try as I have one, although it does have a bajillion miles on it. And Iím
Not against revving to get power, I just donít want it to be grumpy in downtown traffic.

John242Ti 05-05-2021 05:48 AM

^That's the main reason why the K cam might not be desirable. With lower CR engines, it feels weak below 2000. But, when it comes on cam at 2000, it can get explosive, 240-wise, in acceleration, pulling strongly to the redline (and past that on cars without a rev limiter). Whereas I can putter around at 1500-1700 rpm in the 245 with its stock B21FT, I frequently have to downshift the 242 to get it above 2000 rpm, otherwise it'll actually slow down. 242 has a factory reman B23FT block with SCP 398 K-Jet turbo head and a K cam. Both are running K-Jet. B23FT has the stock B23FT intake on it, B21FT has the stock pancake B19K style manifold with the downdraft throttle body.

One benefit of the A cam over the B cam is that the overlap of the B cam is gone. Slightly milder grind, yes. You could run a K cam in the blue 245 and swap the A cam into the white 245, running the B cam in the silver 245, if the wife's car still has the M cam in it... With its 9.8:1 cr, it'll be adequate, acceleration-wise, in city driving, but will be fun on US 24 headed up to Woodland Park, etc... I ran one in our old beige '85 245DL, and it did wake the B230F up in that car. Set the ignition timing to 8 deg BTDC, which was enough to avoid severe pinging on hills if someone didn't fill it up with 92 octane. Had a slight lope at idle, almost sounding like a B20F at idle, but quieter. Under acceleration, the typical B230F whine was gone, replaced by throaty intake noises. Mileage dropped from 32 mpg highway to 26-27 mpg highway, mainly because the car was more fun to drive hard.

Jussi Alanko 05-06-2021 12:13 PM

Any "letter cam" is not a "hot" camshaft...


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