RV8 flat plane crank
Discussion
I know its been played about with in the past, but other than the crank and cam needing replacing what else is needed to convert an RV8 a flat plane setup? Would it shake itself to pieces because the 90deg Vee would cause things to be out of balance.
Just idle, drunken hypotheticals
Regards
Iain
Just idle, drunken hypotheticals
Regards
Iain
Can anyone post back to back pics of a flat plane crank and a conventional one please?
I'd have thought balance would be an obvious issue, together with the ign timing if intevals/firing order change
Didn't someone produce a flat plane crank option for the Rv8, sure I've read that somewhere...
I'd have thought balance would be an obvious issue, together with the ign timing if intevals/firing order change
Didn't someone produce a flat plane crank option for the Rv8, sure I've read that somewhere...
You don't really need pics. On a flat plane crank the rod journals are 180 degrees apart like a 4 cylinder crank, it would lie flat on the floor.
On a cruciform crank as rover the journals are spaced at 90 degree intervals so the crank couldn't lie flat on the floor. With a good push it would roll sideways but not for far
Viewed end on a rover crank looks like a cross whereas a flat plane looks like a dog bone lieing on it's side.
On a cruciform crank as rover the journals are spaced at 90 degree intervals so the crank couldn't lie flat on the floor. With a good push it would roll sideways but not for far
Viewed end on a rover crank looks like a cross whereas a flat plane looks like a dog bone lieing on it's side.
Gary,
Conventional V8 Crank:
Flat Plane V8 Crank:
Both pics stolen from http://www.brandes-online.de/engine_types.htm
Regards
Iain
Conventional V8 Crank:
Flat Plane V8 Crank:
Both pics stolen from http://www.brandes-online.de/engine_types.htm
Regards
Iain
Chassis 33 said:
Gary,
Conventional V8 Crank:
Flat Plane V8 Crank:
Both pics stolen from http://www.brandes-online.de/engine_types.htm
Regards
Iain
Thanks Iain, appreciated Conventional V8 Crank:
Flat Plane V8 Crank:
Both pics stolen from http://www.brandes-online.de/engine_types.htm
Regards
Iain
spend said:
Even with a flat plane crank you would have to change the standard inlet induction.
Why? It doesn't tune worth a d*mn anyway so I don't see that changing the firing order is going to do any harm. You might find it's worth splitting the intake into two groups of four and actually trying to tune the thing, something that would probably work OK with the flat plane but was near enough a waste of time previously.the only advantage i can see is that with a flat plane crank you can i you wish take advantage of exhaust scavenging, it's worth a great deal in hp terms .. 20-29hp in our tests .. but going for clive's exhaust is a lot more cost effective than going for a flat plane crank and associated cam, you' still need to change the exjaust anyway to take advantage of the exhaust tuning effects. 2500 pounds versus what? 10 grand maybe?
I'm not sure Clive's exhaust compares with a Flat plane alternative Joo. Since they seem to use shorter primaries and secondaries, I reckon it looks more like a 180deg separation where the secondaries join. I'm sure that kind of arrangement could be achieved much more simply than Clives full 360, simply by using 2 y-pieces to cross the V.
I was never debating what benefits it gave just whether or not it was just possible by swapping cam and crank. Exhaust and inlet could be tuned, but are optional.
...but seeing as we are going that route...those alternative grind camshafts that you see over in america occasionally, I think they swap 5 or 7 with another cylinder so they don't have two consecutive cylinders on one bank firing.
Regards
Iain
...but seeing as we are going that route...those alternative grind camshafts that you see over in america occasionally, I think they swap 5 or 7 with another cylinder so they don't have two consecutive cylinders on one bank firing.
Regards
Iain
Everything today is reminding me of funny stories so here's the one for this thread. A well known UK crank manufacturer who a friend of mine did some business with was approached by a customer to make an RV8 flat plane crank for him. No problem they told him but somehow they also agreed to get involved with the cam which although they needed to farm out the lobe profiling for they could make the blank themselves from billet steel and earn a few extra bob. That part of the job isn't so different from the crank machining.
So they make the blank, get it heat treated and give it to a cam grinder to get suitable race profiles put on. Sadly, not long after the engine got built and fired up it started making nasty rattling noises and on stripdown it was found that all the cam lobes and tappets had worn away. Red faces all round, they make another blank, double check all the material spec and heat treatment, get it ground and post it off for attempt number two.
Shortly after starting up the lobes all go the same way as the first set. Being crank manufacturers they knew a lot about cranks but not quite enough about cams it seems. The bit they didn't realise, and so never told the cam guy to do, and he didn't realise it either because it was obviously a totally new application for him so he just did what he was told was that the RV8 cam lobes, as with any other pushrod engine, need to have a very slight angle across them. This is so they contact the tappets, which are slightly domed, on one side and make them spin which evens up the wear and allows them to bed in.
If you just grind the lobes dead flat they only touch the tappets in the centre so the tappets never rotate and the whole plot disintegrates in minutes. Someone took pity on them in the end and told them what they were doing wrong but I imagine by then it had wiped out all the profit on the actual crank.
So they make the blank, get it heat treated and give it to a cam grinder to get suitable race profiles put on. Sadly, not long after the engine got built and fired up it started making nasty rattling noises and on stripdown it was found that all the cam lobes and tappets had worn away. Red faces all round, they make another blank, double check all the material spec and heat treatment, get it ground and post it off for attempt number two.
Shortly after starting up the lobes all go the same way as the first set. Being crank manufacturers they knew a lot about cranks but not quite enough about cams it seems. The bit they didn't realise, and so never told the cam guy to do, and he didn't realise it either because it was obviously a totally new application for him so he just did what he was told was that the RV8 cam lobes, as with any other pushrod engine, need to have a very slight angle across them. This is so they contact the tappets, which are slightly domed, on one side and make them spin which evens up the wear and allows them to bed in.
If you just grind the lobes dead flat they only touch the tappets in the centre so the tappets never rotate and the whole plot disintegrates in minutes. Someone took pity on them in the end and told them what they were doing wrong but I imagine by then it had wiped out all the profit on the actual crank.
spend said:
I'm not sure Clive's exhaust compares with a Flat plane alternative Joo. Since they seem to use shorter primaries and secondaries, I reckon it looks more like a 180deg separation where the secondaries join. I'm sure that kind of arrangement could be achieved much more simply than Clives full 360, simply by using 2 y-pieces to cross the V.
As far as linking the ports which fire an engine rotation apart they are exactly the same of course, and i always said to clive during the development period between us that in the V8E version with the lonnnnnnng primaries we were going to see the benefit of the momentum scavenging effect rather than aa quantifiable gain from the tuned length. I'm not sure how much effect a "tuned" length has, and whatever effect it does have i'm fairly sure (but not completely sure) that it only occurs over a very small rev range anyway. however the momentum of each slug of gas is something you can take advantage of over a much wider rev range (i think, and i have to explain that in no way am i anything like up to speed on proper exhaust dynamics). I do have a plan for an evolution of the RV8 crossover manifold with much longer secondary pipework though, because when we shortened the secondaries for my own V8S version there was little change in the hp over the previous version. Now from my understanding there should have been a noticeable quantifiable gain from such a move, unless of course the secondary pipework was already too short .. so more development needed on that just as soon as clive finishes all the other projects we're working on lol 
Chassis 33 said:
I was never debating what benefits it gave just whether or not it was just possible by swapping cam and crank. Exhaust and inlet could be tuned, but are optional.
...but seeing as we are going that route...those alternative grind camshafts that you see over in america occasionally, I think they swap 5 or 7 with another cylinder so they don't have two consecutive cylinders on one bank firing.
Regards
Iain
I did some 'what if's with the firing but couldn't see any significant improvements....but seeing as we are going that route...those alternative grind camshafts that you see over in america occasionally, I think they swap 5 or 7 with another cylinder so they don't have two consecutive cylinders on one bank firing.
Regards
Iain
Chassis 33 said:
I was never debating what benefits it gave just whether or not it was just possible by swapping cam and crank. Exhaust and inlet could be tuned, but are optional.
...but seeing as we are going that route...those alternative grind camshafts that you see over in america occasionally, I think they swap 5 or 7 with another cylinder so they don't have two consecutive cylinders on one bank firing.
Regards
Iain
You always have two consecutive cylinders firing on the same bank with a crossplane V8 regardless of what you do to the cam. Your only choice is which cylinders. There are several different possible firing orders but all have two cylinders firing consecutively on one bank followed by two on the other bank later in the same cycle. That's what stops the exhaust systems being able to pulse tune effectively compared to a flat plane which is basically two straight four cylinder engines arranged side by side....but seeing as we are going that route...those alternative grind camshafts that you see over in america occasionally, I think they swap 5 or 7 with another cylinder so they don't have two consecutive cylinders on one bank firing.
Regards
Iain
Not that long ago I wrote a detailed analysis of the differences between flat plane and cross plane V8s in terms of firing order and pulse tuning but I'm damned if I can remember which forum. If I can find it again I'll post it here.
It's been done before and rather successfully.
How successful - well it won the Formula 1 world championship .. twice.
1966 - Jack Brabham
1967 - Denis Hulme
The company - Repco Brabham.
The Oldsmobile block was used with a single plane crankshaft.
3.0 F1 engine was 3.5 inch bore with 2.375 inch stroke
2.5 Tasman series engine was 3.34 inch bore and 2.165 inch stroke
These both used a single over head cam shaft...
How successful - well it won the Formula 1 world championship .. twice.
1966 - Jack Brabham
1967 - Denis Hulme
The company - Repco Brabham.
The Oldsmobile block was used with a single plane crankshaft.
3.0 F1 engine was 3.5 inch bore with 2.375 inch stroke
2.5 Tasman series engine was 3.34 inch bore and 2.165 inch stroke
These both used a single over head cam shaft...
Stolen from the link further up the thread...
"There are two types of V8s which differ by crankshaft. The V-angle is always 90°. The two types are called cross-plane (crank pins at a 90° angle) and flat-plane (crank pins at 180°). V8 engines have the advantage of not being in need of split crank pins in order to avoid vibrations between cylinder banks.
With a cross-plane V8, however, the last cylinder is not in the same position as the first, so there is end-to-end vibration again. That can be solved by adding counterweights to the crankshaft which cancel the forced created by the pistons. That is possible only in a V-engine with a V-angle of 90° and without split crank pins. These counterweights, fitted to an inline engine, would move to the side when the piston moves up or down and therefore generate additional vibration. But in a 90° V-engine there are pistons on the same crank pin which move exactly into the opposite directions of the counterweights (because of the bank angle) and their forces can be cancelled. Cross-plane V8s are therefore running quite smooth but because of the heavier crankshaft they are not as revvy.
Flat-plane V8 engines do not have those problems. They are also more responsive because of less rotational inertia. That increases maximum rpm and top-end power. In addition the crank case can be smaller which lowers the center of gravity.
But why are the flat-plane engines used in sports cars only if there are so many advantages? That's because of the crankshaft itself, the disadvantage of the flat-plane type. As you can see, the arrangement of crank pins is identical to a four cylinder engine which means there are also vibrations, only stronger, as basically two inline-four engines are running simultaneously. In sports cars those vibrations are reduced by using very lightweight pistons and connecting rods. That is of course expensive and because ride quality isn't too important either, the rough characteristics (compared to a cross-plane) are tolerated. Because of the crankshaft, the sound of such an engine is the one of two four cylinder engines. A (typical American) cross-plane burbling cannot be achieved."
From a tuning POV, I would expect it means you can essentially treat the engine as two separate 4pot engines, and not get the interferance between cylinders that you get on a normal RV8 where 5&7 fire consecutively, which I believe causes cylinder 7 to rob cylinder 5 of air charge, I'm sure the boffins could confirm this for me.
Regards
Iain
"There are two types of V8s which differ by crankshaft. The V-angle is always 90°. The two types are called cross-plane (crank pins at a 90° angle) and flat-plane (crank pins at 180°). V8 engines have the advantage of not being in need of split crank pins in order to avoid vibrations between cylinder banks.
With a cross-plane V8, however, the last cylinder is not in the same position as the first, so there is end-to-end vibration again. That can be solved by adding counterweights to the crankshaft which cancel the forced created by the pistons. That is possible only in a V-engine with a V-angle of 90° and without split crank pins. These counterweights, fitted to an inline engine, would move to the side when the piston moves up or down and therefore generate additional vibration. But in a 90° V-engine there are pistons on the same crank pin which move exactly into the opposite directions of the counterweights (because of the bank angle) and their forces can be cancelled. Cross-plane V8s are therefore running quite smooth but because of the heavier crankshaft they are not as revvy.
Flat-plane V8 engines do not have those problems. They are also more responsive because of less rotational inertia. That increases maximum rpm and top-end power. In addition the crank case can be smaller which lowers the center of gravity.
But why are the flat-plane engines used in sports cars only if there are so many advantages? That's because of the crankshaft itself, the disadvantage of the flat-plane type. As you can see, the arrangement of crank pins is identical to a four cylinder engine which means there are also vibrations, only stronger, as basically two inline-four engines are running simultaneously. In sports cars those vibrations are reduced by using very lightweight pistons and connecting rods. That is of course expensive and because ride quality isn't too important either, the rough characteristics (compared to a cross-plane) are tolerated. Because of the crankshaft, the sound of such an engine is the one of two four cylinder engines. A (typical American) cross-plane burbling cannot be achieved."
From a tuning POV, I would expect it means you can essentially treat the engine as two separate 4pot engines, and not get the interferance between cylinders that you get on a normal RV8 where 5&7 fire consecutively, which I believe causes cylinder 7 to rob cylinder 5 of air charge, I'm sure the boffins could confirm this for me.
Regards
Iain
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