I've got a block that I'm about to build for my club car and I was wondering if there is an issue with using the B21 pistons in a B20 motor at the higher end of the rev band.

I want to build a motor which can stand 7-7.5k rpm but if i can use the B21 (does B23 fit?) pistons then that would be great but I've only heard about them only going to 5500rpm reliably. Is this true?

Thanks!
--
Alex Shevlin (Sydney): '71 142S, '72 144S, '81 244GLE, '81 244GL, '01 V70XC

I built a B20 with the ipd overbore kit (six bolt crank) some years ago. It had all the good stuff and did 7000 easily, although the power tailed off after 6500. After the upshift it sure pulled hard though. As stated by others, the limiting factor is the cylinder head, and the camshaft profile that would make power beyond 6500 even with an excellent cylinder head. The cam that would do that will not make good low end power, so unless the engine is not expected to chug around town and give any sort of fuel mileage then go for at least an R cam with double valve springs, lightened valve train, side-draft Weber style carbs, electronic ignition, steel timing gears, balanced reciprocating assembly and so on. If not use a milder cam from ipd, and build a nice torquey engine that will be fun to drive and not frustrating when the revs are below 3000.

Since low end torque can be boosted by exhaust backpressure, maybe
a cable-operated cutout or restriction might be a great idea.
In fact if you could get it rpm controlled some way it might
widen the torque curve a lot.
--
George Downs, The "original" Walrus3, Bartlesville, Oklahoma

BMW use this in most of their new 6 cylinder models with twin exhaust outlets. It closes off the entire second tailpipe until vaccum starts to drop to the unit (which is controled by the computer i think, by comparing load, revs and throttle) The low end torque is boosted by increased back pressure, noise reduced and at higher revs the exhause flows better.

I'm wait on one to play with from a mate who works at BMW (still waitng for a "warrenty" part) so i can see if I can adapt it to suit my car. It just needs to have a new stop put on it so it doesn't close fully and a slightly weaker spring so it opens quicker.

I'll keep you posted when i get one

--
Alex Shevlin (Sydney): '71 142S, '72 144S, '81 244GLE, '81 244GL, '01 V70XC

Vacuum solonoid? If you use a small hole between the solonoid and
the intake vacuum and a medium sized vacuum resevoir and have the
obstruction pulled out of the way when there is no (low) vacuum.

Think I should apply for a patent? I guess it's too late now that
it's published...
chris

I regularly run up to about 6500 rpm with the big bore B20 engine in my PV. But the power is waning and there wouldn't be much point in going up further. If you plan on spinning a 2.2 liter bottom end that fast you'd better be prepared to spend a lot on cylinder head work - big valves, porting, double valve springs and a very aggressive cam will be needed to produce any power at that rpm.

As for the postons handling the speed I don't really know - but I wouldn't imagine the B21 pistons being that fragile. Volvo usually tend to overbuild things pretty well. Just balance things exceedingly well (Volvo factory specs were suprisingly loose!) and get the bearing clearances spot on (use that plastigauge stuff) and it should hold together just fine.

As for building up a 2.2 liter engine - now that IPD no longer supplies 6 bolt kits - www.kgtrimning.com has all the goodies. Big bore head gaskets for $60, and either special conrods that fit a 6 bolt crank and std B21 pistons ($20 each) or special 92 mm pistons that fit the 6 bolt con rods ($58 each). As well as lots of other goodies like modified heads (lots of experience with Volvo pushrod heads there), cams, steel timing gears, stroker cranks, Weber carbs (DCOEs), and lots more.

Good info!
--
George Downs, The "original" Walrus3, Bartlesville, Oklahoma

I'm either going to build a 2.1/2.2 block or going to build up a straght B20 with lighter pistons and conrods from kg trim. I'me starting from a bare block so I want to check all the options before I start building it.

I like revving up alot and I've found my B20 and B23 both take it very well, especially the B20 even though it's so heavy.

If I go down the lighter piston/conrod track then is there any way I can get an idea of what the max rev's I could take it to safely or is it trial and error?

What else should I be looking into modifying for high revs? I already want to put the double springs, bigger exhaust valves and get the engine balanced.

Thanks!
--
Alex Shevlin (Sydney): '71 142S, '72 144S, '81 244GLE, '81 244GL, '01 V70XC

I'm pretty sure the valve train is the limiting factor as far as high rpms and B20's go. Double vavle springs work pretty well, but even then they have to rebound against the mass of the valve, the rocker arm, the push rod, and the lifter. At some point they just start to bounce around instead of closing fully. KgTrimning sells lightened stock lifters, though, probably helps.

Another more critical factor will be the breathing of the cylinder head. To make any significant power at that rpm it needs very good flow. And in particular the exhaust ports on B20 heads are not that great. They make a fairly sharp 90 degree bend - the port is too far down in the head to make a more flowing curve from the vertical valve to the horizontal port. Bigger valves help somewhat, the only problem with them is that the valve itself is in they way when open - multiple valves are much better in this respect. Like the VW 1.8t engine - 3 little intake valves and 2 exhausts, despite also having a turbo to keep things moving.

KgTrimning crams as much valve as will physically fit (46I, 40O)into their top line heads, but you still shouldn't fool yourself into thinking it will flow as well as a multivalve head will. And the pushrod valvetrain won't ever spin as high as an OHC setup will - just too much moving metal. Not to say a modified B20 won't be powerful, just not as powerful as, say, the 2 liter 240 HP 8900 RPM redlined Honda S2000K motor.

So instead of reaching for unreasonably high RPMs the best approach is to maximize the tourque available in the moderately high rpms. In addition to increasing the bore consider a stroker crank as well. That will give you nearly 2.4 liters of displacement. Top that off with a modified head and a race cam and you will have an engine that still won't rev (with power) up to 7500, but will be as powerful as possible up to that point.

NOTE: In my PV I have a 2.2 liter bottom end (built a long while ago with an IPD kit), a stock 'D' grind cam (great for city driving - lower peaks but a wider curve than the IPD 'Street Performance' cam I used to have), and a stock 'F' head. I need to shave a bit off the 'F' head as my compression isn't very high, but putting an 'E' head (10.5:1 cr) on top of a big bore bottom end might be cause for a little trouble - without changing anything else it wold put the CR up to slightly over 11:1. Thats into the danger zone for pump gas and an iron head (aluminum heads can run about a point higher because they manage hot spots better). Do-able but a bad tank of premium (happens at the best of stations) will have it pinging. (FYI - big bore AND stroker crank puts an 'E' head at 11.8:1!)

My future plans for my engine would be a mid tier head from KGTrimning and a mid tier cam. At that point probably the limiting factor would be the SU carbs, but I'll just live with it. Probably around 180 HP? --Possibly-- might think about a stroker crank. Or even less likely on of John Parker's B20 supercharger kits. As is it probably has around 150 HP and really scoots the 2,250 lb PV around nicely.

If you do change the weight of the pistons and rods, be sure you find
someone who can do a good job of balancing it. That will be the key
to high rev durability.

I've not used any valves bigger than come in the B20E, and they were
enough for the way I drive. Likewise I have not gone to heavier or double
springs or light retainers. So I guess I am somewhat limited by valve float
but I rarely encounter it. I'd guess my max rpm is somewhere between
6K-6500. That sounds scary enough most of the time.

What I guess I am saying is that you need to talk to someone with racing
experience, which is not myself.
--
George Downs, The "original" Walrus3, Bartlesville, Oklahoma

Two points to correct.

No amount of weight removed from rods and pistons will require rebalancing the crank. 4 cyl counterweights are there just to offset the weights of the throws. The pistons coming down balance out the pistons going up. If you reduce the weights evenly, nothing has changed.

The b23 parts (pistons, rods) are *much* heavier than standard early 6 bolt b20 stuff. Someone stated the opposite in passing.


Stay away from the 74-75 cranks (and the blocks are little if any better) stay with 6 bolt stuff. Bore the pin ends out if you feel you have to use b21 pistons. The only problem I foresee with using b21 pistins in this app is that the rings will flutter. The rings Volvo used are thick, old-tech stuff.

-Ian
(with 'stroker' 544)

Ian -

Hello there again (we exchanged in e-mail earlier this spring, remember?. You sparked my curiousity. You imply that the 8 bolt and later blocks may be overated. I have heard repeatedly that the 74 and 75 blocks have thicker walls. What I have not read is of someone that have actually measured one. Walrus3 indicated measurements from his earlier block that coincide with specs I have measured on an ealry with an ultrasonic device (my machinest did it..I can't recall the proper name of the device). I guess my question to you is, what is the basis for your implication?

As for the 8 bolt, what I have discovered, for a fact, is that the rod journals are narrower than the six bolt. Other than that what's the deal?

thanks for your input.

Tremmelle

That is helpful info. I can balance pistons and rods to each other
fairly easily.
Thanks,
GFD III
--
George Downs, The "original" Walrus3, Bartlesville, Oklahoma

Why would it be better to stick with a 6 bolt crank?

What are the main differences?
--
Alex Shevlin (Sydney): '71 142S, '72 144S, '81 244GLE, '81 244GL, '01 V70XC

I hope you are not planning to run that speed continuously.
To the best of my knowledge the biggest you can go for big bore is
2200cc which is about 3 11/16". B21 bore is 3.622" Standard B21
pistons will only work in an 8-bolt engine. IPD used to sell pistons
for 6-bolt engines but I don't know if they do now or not. If not,
there are Chevrolet pistons that can be made to work (removing the
small end bush and honing a bit) that start at 3.570 and can be gotten
in oversizes up to 0.060", which gives you a bore of 3.630, same ballpark.

The main structural thing that limits rpm (NOT Torque!) is piston weight
and as far as I know the pistons weigh about the same.

You need to have your block bored by an experienced machinist because
there is a possibility of a cylinder being cast slightly eccentric and
thus the boring bar needs to be moved laterally so that the bore corresponds
to the water jacket. As the cylinder becomes thinner with bigger bores,
this becomes a lot more critical. The one big bore I had ran great and was
for 10 years the best engine I ever built. But when I ran a 5/16" hex nut
through #2 cylinder, the BLOCK was destroyed, without substantial damage to
either the piston or the head. The nut got between the flat portion of the
head and the piston, cocking the piston in the cylinder, and splitting the
cylinder from the bottom to the top, an opening you could stick a spoon
handle through. The block appeared to be about 3/32" thick where it split.
That was a 0.122" overbore or only 0.061" removed from each side. In my
opinion, even 0.150" (the original thickness) is marginal for a good stable
cylinder. Looking back, I'm surprised it ran as well and as long as it did!
--
George Downs, The "original" Walrus3, Bartlesville, Oklahoma

I hope you are not planning to run that speed continuously.
To the best of my knowledge the biggest you can go for big bore is
2200cc which is about 3 11/16". B21 bore is 3.622" Standard B21
pistons will only work in an 8-bolt engine. IPD used to sell pistons
for 6-bolt engines but I don't know if they do now or not. If not,
there are Chevrolet pistons that can be made to work (removing the
small end bush and honing a bit) that start at 3.570 and can be gotten
in oversizes up to 0.060", which gives you a bore of 3.630, same ballpark.

The main structural thing that limits rpm (NOT Torque!) is piston weight
and as far as I know the pistons weigh about the same.

You need to have your block bored by an experienced machinist because
there is a possibility of a cylinder being cast slightly eccentric and
thus the boring bar needs to be moved laterally so that the bore corresponds
to the water jacket. As the cylinder becomes thinner with bigger bores,
this becomes a lot more critical. The one big bore I had ran great and was
for 10 years the best engine I ever built. But when I ran a 5/16" hex nut
through #2 cylinder, the BLOCK was destroyed, without substantial damage to
either the piston or the head. The nut got between the flat portion of the
head and the piston, cocking the piston in the cylinder, and splitting the
cylinder from the bottom to the top, an opening you could stick a spoon
handle through. The block appeared to be about 3/32" thick where it split.
That was a 0.122" overbore or only 0.061" removed from each side. In my
opinion, even 0.150" (the original thickness) is marginal for a good stable
cylinder. Looking back, I'm surprised it ran as well and as long as it did!
--
George Downs, The "original" Walrus3, Bartlesville, Oklahoma