Geez... that post looks like a potential can o' worms... I'm curious to see replies myslef.

What you are getting into there is way way way above my head, but my initial thought is that by the time you get into detailed numbers like that, you probably also ought to be looking at the rest of the engine, which is going to play a larger role I would think than just the cam.

Starting with the air intake, ending with the exhaust. And of course, not forgetting bore and stroke, valve size, head tuning, carburetion or injection type/setup... and of course valve lift and duration. It all plays a part, and should all be taken into consideration prior to building the engine based on what the desired outcome performance would be.

It's my understanding that putting a fancy cam into a stock engine will not necessarily be an improvement.

Again though, that sorta stuff is beyond anything I've ever done or even tried to comprehend.

-Matt
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-Matt '70 145s, '65 1800s, '66 122s wagon, others inc. '53 XK120 FHC

You've got a good point about the rest of the engine configuration playing a part...maybe I'm concentrating too much on one component, but the D vs. VV71 should be a good match up on a theoretically identical engine, such as the default "ipd" motor, a 2130cc, mild headwork & around 10:1 comp, freeflow exhaust, etc.
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Damn, down to only one exhaust pipe now!! less rice by the minute

By the numbers, the D is indeed a bit "hotter" than the VV71. The VV71 feels like it's more of a performance cam because it's lumpier at idle and comes on a bit stronger in the midrange. I think the D actually makes a bit more power above 6000 rpm. However, all that's going to depend on exactly what the rest of the motor, intake and exhaust are like.

I'm quite familiar with an otherwise dead-stock B20B that has an R cam in it. It's much, much quicker 0-60 than with the original C cam. It's also a complete lump at idle and doesn't do much of anything below 2500 rpm.

Your biggest performance gain is going to come from having the head ported by someone who has a lot of specific experience with B20 heads -- not the local guy who's been doing V8s for 30 years. Without doing that, going to a big bore kit won't give you more peak HP -- you'll get roughly the same power but at lower rpm. Not having to rev as high for power might be what you want, but it actually makes the car less quick:

Imagine two identical cars that both make 120 HP. One is stock and makes that power at 6000 rpm; the other is overbored and makes that power at 5500 rpm. The stock one can accelerate hard to 60 mph in second gear, while the overbored one can only accelerate hard to 55 mph in second gear. Which one wins the drag race?

--Phil

You've all got very good points about the rest of the engines components having a large, if not larger effect on performance than just the cam. In my head I was thinking about the comparison on a engine that has had some mild headwork(done correctly:)),etc, and the differences the cams would make on that theoretical engine. Of course, after reading these and thinking some more, that's probably not a good way either, as a particular cam that didn't make as good power on one motor, might do better with a slightly different configuration. Any way, thanks for all the replies & insights!
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Damn, down to only one exhaust pipe now!! less rice by the minute

A camshaft fine tunes an engine to produce a torque curve that you are looking for. Duration measured at .050" lift determines roughly what rpm range the engine will be best suited to. 220degrees@.050" makes a good camshaft for economy with some power in a range of 1500-4500, 240@.050" gives up some economy & manners for stronger power in the 2500-5500 range, 260@.050" is getting pretty racey with power from 3000rpm upwards. The second aspect of camshafts is Lobe Centreline Angle(LCA). This affects how much overlap & how early the intake opens. Wide LCAs like Volvos stock cams produce a wide power band with good fuel economy. Narrow angles produce more peak power & torque at the expense of fuel economy & flexibility. 260degree@.050" cams ground on wide 109 degree LCA such as Phil's MPPE produce good power across a wide range & can be made to perform form idle through to 7000rpm. If you take the cam out & have it ground to 101LCA like Volvo rally cams it will become peaky & produce more power & torque in the 3000-6000 range at the expense of being a pig around town, being undrivable under 2000rpm, idling badly & eating more fuel. Thirdly is lift, high lift produces more power & torque without affecting economy & drivability, but the cost is they don't last very long.

Cheers,
Paul.

"Imagine two identical cars that both make 120 HP. One is stock and makes that power at 6000 rpm; the other is overbored and makes that power at 5500 rpm. The stock one can accelerate hard to 60 mph in second gear, while the overbored one can only accelerate hard to 55 mph in second gear. Which one wins the drag race?"

That's easy, it would be the engine which has the lightest internal components. ;)

That's easy, it would be the engine which has the lightest internal components.

If everything else were identical, of course that's right.

For the record, we did nothing whatsoever to reduce reciprocating weight in the MPPE. We did go for a much lighter flywheel, lightened timing gears, and (of course) no fan. There's a lot more potential in the thing in quite a few areas that didn't fit into the budget this time around.

To make 120 hp at a lower RPM means the overbored engine must have greater torque, and consequently it would win the drag race. If by this you mean an RPM limitation, and therefore another shift must be made, then that is outside engine performance and is more a gearing statement. On the dyno, the overbore engine wins.

Lets say a 120HP@6000rpm B18 v 120HP@5500rpm 2130 using B21 crank, rods & pistons. My money would be on the ligthweight B18 regardless of the obvious torque disadvantage. It takes considerable HP to accelerate all that stuff up & down. Also, no amount of bottom end torque is goin to help in a drag race if you are reving it up to 6000 each gear shift.

Cheers,
Paul.

Well we are really getting into hypotheticals, but as long as we are, I would vote for the greater piston surface area - and therefore its back to the 2130 for me!
Rhys

Anything that stops and starts each revolution cannot, by definition, affect "revability". Heavier pistons, for example, do take up kinetic energy, but do not contribute in any way to flywheel type inertia.

The fact that these two theoretical engines both made 120 hp means the kinetic energy loss is made up for by extra power being produced that doesn't make it to the crank.

Only part of the big end rod weight contributes to rotational inertia.

Things like alternators, which turn twice crank speed have far greater effect than timing gears, which turn at 1/2 crank speed. Smart to run a loose fan belt for this reason.

My bet would be on whichever had smaller CC intake & exhaust runners. Ability of engine to fill and empty on an increasing basis has been dubbed transient response by some of the smarter engine builders, notably Larry Widmer. It's a difficult concept to put into words.

Nothing hypthetcial about it, assuming the cylinder head is stock, I would take a B18 everytime. Assuming the head is carfully modified, I would take a B20. There's no point to a 2130, it might produce an extra 5% torque at 2000rpm, but once you rev it up, the extra weigth soon sucks that up.

Cheers,
Paul.

In your previous post Paul you talk of an eight bolt 2130. I have built them using the six bolt crank, and a further overbore to 2180. I don't believe the internals weigh any more on the six bolt. Rotating mass per se has no effect on the output, either torque or horsepower, but of course does determine the rate of acceleration or decceleration of the engine.
Rhys

Rotating mass doesn't have any effect but reciprocating mass does, you can't start & stop pistons, piston pins & the little end of the conrod for free. I also think a 93mm bore is really stretching the frendship too. I know it's splitting hairs, but more piston area sucks more heat out of the bang too. Add on a custom head gasket & you really get no return for the hassle.

Cheers,
Paul.

Ian says: Anything that stops and starts each revolution cannot, by definition, affect "revability". Heavier pistons, for example, do take up kinetic energy, but do not contribute in any way to flywheel type inertia.

Paul says: Rotating mass doesn't have any effect but reciprocating mass does, you can't start & stop pistons, piston pins & the little end of the conrod for free.

You're both right, but you're talking about two different things. Rotating mass has no affect on horsepower, which is a measure of the work done at a steady speed. Reciprocating mass does affect top speed, while rotating mass does not.

Rotating mass has a large impact on how quickly a motor can rev, obviously, while reciprocating mass is much less important. Rotating mass affects acceleration more than reciprocating mass (oversimplifying).

Interestingly, there are two principle types of chassis dynos, the inertia type (Dynojet, for instance) and the brake type (the more expensive models of SuperFlow). Inertia types measure how quickly a roller of known mass can be accelerated -- and rotating mass will influence the HP numbers obtained. A brake dyno measures power at steady speeds (again oversimplifying), and only the reciprocating mass will affect the readings.

--Phil

"Rotating mass has a large impact on how quickly a motor can rev, obviously, while reciprocating mass is much less important. Rotating mass affects acceleration more than reciprocating mass (oversimplifying)."

I have always thought there was a very noticable difference between early & late B20's, so I think reciprocating mass is important. Late B20/B21 cranks tend to be more bent then early B20 cranks & B18 cranks hardly bend at all. That bending force has to equate to more drag don't you think?

Cheers,
Paul.

Paul,

I agree that reducing reciprocating weight is beneficial for horsepower. However, there are a lot of more important things that take precedence over the budget.

Question, because I really don't know: Why do late B20s have more reciprocating weight than early ones? Where is it?

Why would more mass bend a properly balanced crank sitting if properly aligned bearings? I don't see the dynamics of this, unless harmonics enter the picture.

As for heads, ports don't need to be all that big to take advantage of higher displacement. It's more a matter of combustion efficiency -- how much energy you get from a charge of air/fuel -- than of sustained flow. The quality of the burn is just as/more important than the quantity. That being said, with a well-matched cam and header/exhaust and some resonance tuning of the intake, you can get excellent VE without huge ports.

I'm running 93mm pistons, heavy "M" rods, big heavy valves, a B20F head with ports that still match the OE manifold gasket (although they have been reworked considerably for shape), and I can tell you it goes just fine, tolerates 7000 rpm no problem, and gets better gas mileage than a stock B20 when driven at similar performance levels.

YMMV...

"I agree that reducing reciprocating weight is beneficial for horsepower. However, there are a lot of more important things that take precedence over the budget."

You could have used the early rods which are lighter & stronger than M rods for no extra cost.

"Question, because I really don't know: Why do late B20s have more reciprocating weight than early ones? Where is it?"

They have B21 rods in them with the heavier style piston.

"Why would more mass bend a properly balanced crank sitting if properly aligned bearings? I don't see the dynamics of this, unless harmonics enter the picture."

Inline 4's are never really balanced unless they have a balance shaft or two in them, it just natural that they are rough. When you balance the crank, it is balanced alone with disregard to what the pistons & rods weigh. The heavy the pistons & rods are, the more they jump up & down as there is nothing to counter them like there is in 6's & 8's.

"As for heads, ports don't need to be all that big to take advantage of higher displacement. It's more a matter of combustion efficiency -- how much energy you get from a charge of air/fuel -- than of sustained flow. The quality of the burn is just as/more important than the quantity. That being said, with a well-matched cam and header/exhaust and some resonance tuning of the intake, you can get excellent VE without huge ports."

Port velocity determines what is possible. Port velocity is controled by how big the ports are compared to the capacity. It's hard to get power out of a B20E head under 2000rpm purely because the port velocity is too low. Equally hard above 6000rpm because the velocity becomes too high. Making the engine bigger just moves the possible powerband downwards.

"I'm running 93mm pistons, heavy "M" rods, big heavy valves, a B20F head with ports that still match the OE manifold gasket (although they have been reworked considerably for shape), and I can tell you it goes just fine, tolerates 7000 rpm no problem, and gets better gas mileage than a stock B20 when driven at similar performance levels."

Yes, but it is full of comprimises. If you closed the LCA of your cam up to 100 & change the headers to 4-1 you would end up with an engine that develops more power at less revs.

Cheers,
Paul.

As you guys know, i'm not as experienced as the two of you who are having this BEAUTIFUL conversation that i'm loving, but i'd still like to pipe in. Sorry if it is causing any annoyance or the like. Can't you use a forged piston and that would bring the weight levels back down to an "early" b20 piston? Also, I'm sure i've seen people shave and shape the bottom of their pistons within reason to reduce the weight of them. Would that be possible with either a forged b21 or regular b21 piston? And then lastly, doesn't a good 4-1 header produce power at a higher rpm than a properly tuned 4-2-1 which produces a wider, albeit slightly lower max hp?
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Kyle - attending Ore. State, while my lil 68 142 (74 b20, m40) AWAITS ME OUTSIDE!!! (check out my cardomain site, kneedsacar)

Hi Kyle,

You can get someone like Wiseco to make custom forgings, but they cost a zillion dollars & give very poor bang for the buck. The difference in HP & Torque output between bog stock bottom end & one that has had stacks of money spent on it is pretty close to nil. The place to spend the most money is in the cylinder head & even then standard B20E valves are all you will ever need on the street especially since standard valves & guides will last about twice as long than their stainless steel & bronze 'race' counterparts.

For headers, you will not likely find any advantage from 4-1 until the cam gets very large and has a lot of overlap. 4-1 are generally easier to tune, but are peakier like you say.

Cheers,
Paul.

Kyle, all good questions... and I don't have direct answers for them.

What these occasional discussions always illustrate is that there are a lot of ways to build satisfying motors, and that every expert has evolved his own systems that work for him. There is no one best way -- which actually goes back to the original question in this thread.

Every motor is full of compromises; it's the nature of internal combustion engines, from the factory as well as modified, old and new.

My motor was designed by a Swedish builder who has done nothing for 25 years but build Volvo high-performance motors, pushrod, OHC, NA and turbo, street motors, race motors of all sorts. I had a specific set of requirements and a certain budget to work with -- and cost is always a factor. It meets or exceeds all those requirements, and didn't end up costing too much more than the initial budget. I could have spent more improving one area and less improving another -- which ones give the most bang for the buck to meet my particular requirements was my expert's decision. Other experts would make those decisions differently, no doubt about it.

My guy says the M rods are stronger and worth the weight penalty; Paul says they're weaker and puts more emphasis on weight to begin with. I don't know about the strength one way or the other.

I'm sure Paul builds fine motors and I know he's put a whole lot of work into development and testing. John Parker builds motors that are entirely different again. Parts that work perfectly in my design wouldn't be at all right in one of Paul's or John's motors. It's how it all works as a system, as you know.

Where this gets silly is when someone makes specific recommendations about someone else's motor, without really understanding what the system theory is behind it, what the specifics of the head work are, etc. It just doesn't work that way. You gotta pick one expert per motor, and ignore what anyone else says until that one's done.

--Phil

There's a big difference myself & other builders. I am just a hobbyist & have no hidden agenda to make money. I have made all the newbie mistakes & know what gives the most bang for the buck & what is just gloss. I still CRINGE badly about things such as IPD's extraordinarily overpriced DGV Weber conversion kit which has no advantage over a pair of properly maintained SU's. Same goes for things like 46mm intake valves which seem to have no obvious purpose to me other than to suck money from your wallet.

Cheers,
Paul.

"You gotta pick one expert per motor, and ignore what anyone else says until that one's done."

Lovely. =D Makes sense. Maybe when i'm rich and famous we can all work on putting the best into one motor, and making it work the GREAT! as a system... That'll be the day... Oh, and of course, it would be my motor. I'll let you all drive it of course. (under 30mph on a closed course in a large open parking lot) Haha, awesome guys. I love hearing this stuff. Thanks!
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Kyle - attending Ore. State, while my lil 68 142 (74 b20, m40) AWAITS ME OUTSIDE!!! (check out my cardomain site, kneedsacar)

are you saying you would take a stock bored b20 over a 2130 or 2170cc b20, considering both have the same, quality head modifications?
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Kyle - attending Ore. State, while my lil 68 142 (74 b20, m40) AWAITS ME OUTSIDE!!! (check out my cardomain site, kneedsacar)

Pretty much. I wouldn't go to 2170, that's really getting cheeky on bore thinkness, so a 2130 is only 5% more capacity than a 2030 for which you would gain 0% power. It just isn't worth the hassle of finding or making a head gasket. I have had 2130's & 2400's & neither actually goes better than 2030cc's once you get into the engines rev range because the cylinder head just isn't big enough.

Cheers,
Paul.

Not saying this has much to do with it, but what about the new S2000's motor that is now a stroked version of the earlier versions motor? I wondered why they didn't bore it out, because boring it out would make it more oversquare(is that correct? or undersquare?) vs stroking it which would make it the opposite... I don't know, maybe this is why they chose stroking it over boring it for the extra displacement? It still revs to 8000rpms, and makes the same power as the other one which revved to 9000...

Oh the pondering...

So Paul, are you saying you would take a stock bored b20 over a 2130 or 2170cc b20, considering both have the same, quality head modifications?
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Kyle - attending Ore. State, while my lil 68 142 (74 b20, m40) AWAITS ME OUTSIDE!!! (check out my cardomain site, kneedsacar)

I don't care about 1/4 mile... I want the hole-shot and the overbored torque-monster will deliver!

Mike!

I want the hole shot AND the quarter mile! OVERBORE AND HEADWORK! that's the way to go... ;)
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Kyle - attending Ore. State, while my lil 68 142 (74 b20, m40) AWAITS ME OUTSIDE!!! (check out my cardomain site, kneedsacar)