B20 D vs R camshaft

[James M]

I've pretty much finished rebuilding a B20 for some more power in my Amazon, just needs covers and pan put back on but now I'm questioning cam choice. I've got a used D cam in it now, but can get a new (reproduction) R cam pretty cheap locally. Info seems to be a little sparse so I've got a few questions. The majority of my background info comes from this 1800philes article, so any differences in thinking from this collection of information would be nice to know as well.

My specific questions:

• Would an R cam be too much for the motor to the point of uselessness or hinderece?
• Will running a R cam require aftermarket valve springs or changes to the valve guides/stem seals? (as hinted to in the linked article)
• Has anyone ran one and gotten an estimate of where the power band is? (For example is it useless to run with stock lifters/pushrods only to 6k RPM)

To give some useful information the motor is:

• 75 B20f
• Decked block for flush piston/deck clearance
• Elring 419763 Head gasket to match F combustion chamber shape and have .8mm ~.032" squish
• Head shaved to either 50 or 52cc, I have forgotten but the result should be 10:1 compression,
• Hardened valve seats and valve job, obviously Kjet ports welded closed
• Some portwork done to address F head restrictions
• Will be running Chinese Weber knockoffs, assuming they function

It's going to be a fun motor in a fun car, I've got enough volvos to last me the rest of my life and I'm young enough to deal with it not being the most "daily drivable" low end torque. I just don't want to waste the time and money if it won't help, or miss out on gains for cheap while it's still yet to be sealed up

 

[cwdodson88]

Never ran an R, but I can say that the D is a great street runner. But from the looks, it would be hard to pass on if the price is right.

I’d vote with your compression and that carb setup, it would be a good bump. But it might make low rev a little less streetable.

 

[spock345]

How much did you end up taking off the F head? Also which machine shop?

 

[James M]

Never ran an R, but I can say that the D is a great street runner. But from the looks, it would be hard to pass on if the price is right.

I’d vote with your compression and that carb setup, it would be a good bump. But it might make low rev a little less streetable.

This is the way I'm leaning so it's nice to not be shot down right away. Like I said it's a fun car so having to rev it out a little more than stock isn't too troublesome.

How much did you end up taking off the F head? Also which machine shop?

I wanna say it was close to the 0.070" discussed elsewhere, but I couldn't tell you off the top of my head.
One man shop we go through for work in Sac, although he is not well versed in these motors. I had to convince him to take off that much off

 

[mitch1971]

A R cam in a B20 is a fast road cam area I believe. A guy in Sweden runs one and loves it. Not used one myself though.

 

[OttoB]

10:1 is abit low compression for R cam.

 

[JohnMc]

I ran for a while in the PV, until one of the lobes flatted. More my fault there, IIRC the cam nut loosened, and the cam slid back slightly and the front bearing started chewing up the edge of the front lifter, which in turn chewed up the lobe.

But it was a fun cam. Obviously, as you'd expect from the specs, there's a bit more tradeoff or low end torque for high end power. More of a pronounced feel as it hits a bit over 3000 and really starts going. A bit lazy under 3000, but if you're just puttering around, no problem, and if you're wanting to go fast, you're only under 3000 for a little bit taking off, then you keep the revs above that as you shift.

IIRC the peak on my setup was around 6500 rpm, it would start to trail off above that.

I'm currently running an Isky VV81 - more because it was cheap and available the last time I needed a cam. It's a little bit zoomier than the R was, comes into the power band a little later, more like 3300, and will pull pretty hard as fast as I bother to spin the PV's motor - 7000 rpm regularly, 7500 occasionally (still pulls hard there). But, like the 'R' cam, it's an 'old fashioned' cam profile, with a pronounced trade off of low end torque for high end power. I've always wanted to try some more modern cam profiles and see if they have less of a trade off.

 

[James M]

I've heard great things about advancements in cam profiles, I'd also love to try a newer one out but time/money/ease of access isn't in that moves favor.

I'm fine with that low end < top end trade off, but I guess peak power above the operating RPM of my lifters isn't ideal. I don't really want to shell out anymore (otherwise I would simply look into modern camshafts) but it seems that lightening the lifters will help increase their useable max RPM. Has anyone here done something similar?

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For some reason the "start video at" line isnto working, but he goes over it at 19 minutes in

10:1 is abit low compression for R cam.

If I tear it down sometime later I could always trim a little more, or the next motor (with a more modern cam of course). With proper squish (0.032") and stable timing what would you say the right (read max) static compression ratio to aim for with CA 91 octane gas would be?

 

[142 guy]

You might want to check your CR calculations. On my B20E with 45cc chambers and a 0.030 overbore the CR is 10.5:1 with my non decked block. Assuming with your decked block you decked to the lowest piston and machined the crowns to give zero deck clearance volume and that you have stock bores. Using a B20B gasket with 0.028" installed height gives a gasket volume of 4.38 cc. With a 52 cc chamber volume your CR would be 496.8+4.38+52/4.38+52 = 9.8. A chamber volume of 50 would give you a CR of around 9.9.

The D cam duration was matched up with a nominal 10.5:1 compression ratio on the B20E engine. The 1979 Volvo R sport catalog 'special I' B20 engine used the F camshaft with a compression ratio of 10.5:1. The 'special III' engine used the R camshaft with an 11.2 compression ratio. The odd part is that the 1979 R catalog indicates that both these packages used a 1.2 mm gasket which would be equivalent to the fat B20F head gasket. That might have been because the thinner gasket was no longer a Volvo catalogue part be 1979?

Short answer is that at a minimum you should probably be targeting a CR of 10.5:1 if you stick with a cam with durations like the D cam. If you move to the R cam a higher compression ratio would seem appropriate.

I would also note that while the Ehlring B gasket is listed with a compressed height of 0.028", if you search around a number of builders have advised that the actual compressed height is more like 0.034". I have not installed one and removed it to measure so I cannot confirm that. That is something that you might want to confirm as you review your calculations as it will affect your quench depth and if you push the CR up as I suggest correct quench depth is going to become critical. A Cometic gasket might give you a more reliable compressed height value. 0.032" seems to be a consensus value for correct quench depth; but, I have seen individuals advocating for less. You get to pick that number out of a hat. The 1979 Volvo R special engines all appeared to use stock blocks. That suggests they had quench depths >> 0.032" with the 1.2 mm gasket. Go figure!

The R sport catalogue notes that the special III engines use special lightened lifters and use dual valve springs. The R cam engines also use a 46mm / 38mm valve combination so you may need additional head modifications if you want to make full use of an R camshaft. No mention is made of whether the dual valve springs are shorter to accommodate the higher lift of the R cam. The catalog lists the special I engine with a torque peak around 4500 RPM. The listed torque peak for the special III engine moves up to 5000 RPM.

 

[JohnMc]

Yeah, the Cometic gets you a very incredibly precise .032", but that might be precision that's not due to a thumbnail number like .032" in the first place. (Of course, that's with zero deck height pistons, measure and adjust accordingly).

And the piston height is measured along the center line, but the quench pads are on the sides. Supposedly the .032" accounts for lengthening of the rods as they warm up (TWSS), as well as some springy stretch at TDC(???), and some rod bearing clearance maybe. But probably a bigger variable is how much the piston tilts in the bore as it gets rather violently slowed down at TDC/high rpms. That affects the pistons height probably more than those other factors, and that's most pronounced where the quench/squish pads are.

Still, I go with .032", it's close enough to work well. Would a bit closer work better? Maybe, but I'm not wanting to experiment with it.

 

[mitch1971]

Along with the CR the standard head flow has a limit and adding a higher lift cam can actually decrease max power. I’ve however never seen any specs for this, what is the max cam lift for standard heads before increases make no difference or decrease power. That would be great to know.

I’m going to have a guess and say for a E or F head the max lift before loosing power is about 0.450”. I’m sure more knowledgable folk will know if this is right.

 

[OttoB]

142 Guy is at the same track what I would have said about compression ratio. I'm not so familiar with CA 91 octane, is that MON or RON?

Small bore (89 mm) B20 and high lift might not be the best combo. Cylinder wall is too close and it restricts flow when valve goes beyond cylinder head level, say 10-12 mm. For 89 mm bore B18 head is better starting point, valves are more centered, and 42-44 mm valves are big enough.

For 92 mm bore B20 head is good choice.

There is few good threads in sävar and amazon forums about B20, but they are in Swedish.

 

[dl242gt]

In the US they add MON and RON together. Then divide by 2 and you have the useless octane number used in the usa.

 

[OttoB]

In the US they add MON and RON together. Then divide by 2 and you have the useless octane number used in the usa.

MON is a very good method if you have to show how good lead is as a octane improver. MON test destroys advantage of alcohol by external heating of the mixture.

 

[gsellstr]

Jimmy...if you get a few minutes, run over to Parrish Automotive up near Niello, talk to Mike. He has a cam guy on tap down in socal that can do custom crap for whatever you need, decent price and turnaround as well. We got to talking about options for the Dodge a while back. Might be a way to get a much more modern profile without a long wait or huge price tag.

I wish I knew more on what VPD sent me as that thing is nuts. On the dyno, torque was a tabletop from 2k-6k where we stopped the pull, HP was still climbing like a mountain at 6k, and that's with a lot more tuning on the table. If I can find a good tuner over here, I need to get it properly tuned at some point. It definitely has the low end that my old VV61 had but it never hit the wall like the VV61.

 

[spock345]

Jimmy...if you get a few minutes, run over to Parrish Automotive up near Niello, talk to Mike. He has a cam guy on tap down in socal that can do custom crap for whatever you need, decent price and turnaround as well. We got to talking about options for the Dodge a while back. Might be a way to get a much more modern profile without a long wait or huge price tag.

I wish I knew more on what VPD sent me as that thing is nuts. On the dyno, torque was a tabletop from 2k-6k where we stopped the pull, HP was still climbing like a mountain at 6k, and that's with a lot more tuning on the table. If I can find a good tuner over here, I need to get it properly tuned at some point. It definitely has the low end that my old VV61 had but it never hit the wall like the VV61.

Gotta get that thing on a jig to measure the profile.

 

[gsellstr]

Yeah, don't feel like tearing it apart though. lol

 

[James M]

Define huge pricetag? I was hoping to get the motor the rest of the way together without spending $200.

Seem like as it sits the D cam better matches the motor I've built than an R, cheap or not. Definitely going to bump up the compression next time (to what, I'll have to make another thread it seems) and likely go to 92mm bore. At that point I'll consider contacting the Mike you mentioned, but as it sits I evidently haven't gone far enough to justify moving much past the D cam.

 

[bongo]

Check out the AGAP 238, the KG Trimning KG10, and take a look at Tinus Tuning if you havent done any port work as they have cams designed to work with stock ports. k

 

[JohnMc]

I wanted to use a KG19 last time, but they weren't in stock and it was going to be a several month delay. Looking at KgTrimning's site, all their 'KG' cams are out of stock currently.