Have seen this modification done quite a few times on various engines. Have googled it but didn't really find any conclusive answers.
Anyone?
What's a stroker kit?
What's a stroker kit?
George - Nurburgring pax lap whore and co-pilot extraordinaire
There are two types of stroker kits, one is normally found in Soho, Vegas etc :P and the other is...
A kit that increases the stoke of the engine. This is normally accomplished by changing the crank and/or con rods and so increasing the distance traveled from bottom dead center to top dead center.
Increasing the c.c. of an engine this was is normally cheaper (size increase to size increase) than having the same engine re-bored and new pistons etc.
I'm sure there will be someone come along who is more technically suited to give a better answer
A kit that increases the stoke of the engine. This is normally accomplished by changing the crank and/or con rods and so increasing the distance traveled from bottom dead center to top dead center.
Increasing the c.c. of an engine this was is normally cheaper (size increase to size increase) than having the same engine re-bored and new pistons etc.
I'm sure there will be someone come along who is more technically suited to give a better answer
One of the technical blokes will be able to explain it precisely but basically Gary has summed it up.
Imagine when the piston is at halfway through its travel and the crankshaft is sitting horizontal, the greater the distance between the crankshaft and the bottom of the con rod means the greater the stroke and the greater the stroke equals the greater the torque.
Hope that helps a bit but i am poor at explaining things!!
Imagine when the piston is at halfway through its travel and the crankshaft is sitting horizontal, the greater the distance between the crankshaft and the bottom of the con rod means the greater the stroke and the greater the stroke equals the greater the torque.
Hope that helps a bit but i am poor at explaining things!!
-
Bladerider
- Posts: 1597
- Joined: Sat Aug 26, 2006 2:51 am
- Location: nowhere !!!
- Contact:
Gary is in the right direction.
Only major thing wrong is that its not cheap - by no means as cheap as just a set of pistons and a rebore.
Volume of an engine is the number of cylinders x the bore size x the stroke length of the swept area - ie the space where at Bottom Dead Centre the mixture of fuel and air is held before getting compressed. The only ways to increse the capacity (or cubic capacity or cc = litre of the engine like 2.6 for a sklyine) is by increasing outwards (over bore) or up/down by extending the stroke length, and maybe adding a thicker head gasket or in extreme examples a spacer plate like the OSGiken RB30 conversion.
There are several things that also need to be taken when stroking an engine. The pistons are travelling further so often the gudgeon pin needs a slightly different position to allow for the change in angle during the stroke. Bigger pins are sometimes used as the piston velocities are greater at the same revs as the piston will have travelled a further distance in the same amount of time creating more stress. Sometimes you get a change in engine characteristics, for example the RB26 has harmonic damping issues with crank flew and stress at around 7400rpm, this changes when you go for a Stroked OSG engine, and chages again if you use the long block RB30 from Oz.
Performance properties of engines usually follow a simple rule that the more oversquare an engine is ("square" engines are those with the same piston bore as stroke length, like the RB26 for example at 86mm, "oversquare" means that bore size becomes greater than stroke length) the revvier its characteristics as the pistons travel less distance and hence dont have such great forces acting upon them at high revs, so they can rev more. If they are "undersquare" then they rev less but develop more torque as the piston is travelling further, therefore cannot rev as freely but has slightly more momentum giving better torque response. Getting the right compromise for an application is where the clever people earn their money and I dont begin to pretend to know enough to discuss that at length. Suffice to say that a little lightweight car such as an F1 car revs to 20,000rpm from a 2.4litre V8 with 8 tiny little pistons hurtling up and down like maniacs with very little stroke, hardly any torque, but as their effective rev range is from 13,000 to 20,000 they hardly need worry about that !!! Same with a big diesel engine for a lorry - its making maximum torque at 900rpm, its pretty much done and dusted by 1500rpm and will shake apart at 2000rpm !!
The best discussion comes when you "stroke" a turbocharged engine though. This has all the minefields as above, but with one major turd in the water hole - the turbocharger !!!! Turbos use the waste exhaust gas to spool up and then force feed air into the engine. Stroking the engine you might think is great as effectively more air is going in and out, but the trick is the actual airflow speed, the responsiveness of the engine, and the inertia of the components inside that all have a bearing on how quickly the turbo will spool up. As its the turbo that primarily gives the engine its real power this can become an absolute nightmare problem to get just right, especially when you add cam timing, duration, ignition advance and a whole host of other issues, all of which need to hold hands to make the party a successful one !!!
I guess I have just answered one question with about another 6 but at least it could make for a fun thread !!!
j.
Only major thing wrong is that its not cheap - by no means as cheap as just a set of pistons and a rebore.
Volume of an engine is the number of cylinders x the bore size x the stroke length of the swept area - ie the space where at Bottom Dead Centre the mixture of fuel and air is held before getting compressed. The only ways to increse the capacity (or cubic capacity or cc = litre of the engine like 2.6 for a sklyine) is by increasing outwards (over bore) or up/down by extending the stroke length, and maybe adding a thicker head gasket or in extreme examples a spacer plate like the OSGiken RB30 conversion.
There are several things that also need to be taken when stroking an engine. The pistons are travelling further so often the gudgeon pin needs a slightly different position to allow for the change in angle during the stroke. Bigger pins are sometimes used as the piston velocities are greater at the same revs as the piston will have travelled a further distance in the same amount of time creating more stress. Sometimes you get a change in engine characteristics, for example the RB26 has harmonic damping issues with crank flew and stress at around 7400rpm, this changes when you go for a Stroked OSG engine, and chages again if you use the long block RB30 from Oz.
Performance properties of engines usually follow a simple rule that the more oversquare an engine is ("square" engines are those with the same piston bore as stroke length, like the RB26 for example at 86mm, "oversquare" means that bore size becomes greater than stroke length) the revvier its characteristics as the pistons travel less distance and hence dont have such great forces acting upon them at high revs, so they can rev more. If they are "undersquare" then they rev less but develop more torque as the piston is travelling further, therefore cannot rev as freely but has slightly more momentum giving better torque response. Getting the right compromise for an application is where the clever people earn their money and I dont begin to pretend to know enough to discuss that at length. Suffice to say that a little lightweight car such as an F1 car revs to 20,000rpm from a 2.4litre V8 with 8 tiny little pistons hurtling up and down like maniacs with very little stroke, hardly any torque, but as their effective rev range is from 13,000 to 20,000 they hardly need worry about that !!! Same with a big diesel engine for a lorry - its making maximum torque at 900rpm, its pretty much done and dusted by 1500rpm and will shake apart at 2000rpm !!
The best discussion comes when you "stroke" a turbocharged engine though. This has all the minefields as above, but with one major turd in the water hole - the turbocharger !!!! Turbos use the waste exhaust gas to spool up and then force feed air into the engine. Stroking the engine you might think is great as effectively more air is going in and out, but the trick is the actual airflow speed, the responsiveness of the engine, and the inertia of the components inside that all have a bearing on how quickly the turbo will spool up. As its the turbo that primarily gives the engine its real power this can become an absolute nightmare problem to get just right, especially when you add cam timing, duration, ignition advance and a whole host of other issues, all of which need to hold hands to make the party a successful one !!!
I guess I have just answered one question with about another 6 but at least it could make for a fun thread !!!
j.
-
Bladerider
- Posts: 1597
- Joined: Sat Aug 26, 2006 2:51 am
- Location: nowhere !!!
- Contact:
On skylines....
The recommended maximum overbore before you start weakening the block is 1mm to take it to 87mm. You will find that the bigger tuning firms make forged pistons upto 88mm though if you really want to go bigger but this will mean you have to start reinforcing the block - usually with resin.
They also do 88mm short skirt "drag" pistons that can cope with huge loads, have minimal weight and destroy your engine faster than a bag of sand, but give the outright most performance all other things being equal for their prescribed use.
The 2.8 kit that Abbeys do alot of is the HKS kit. This still isnt as simple as you might think as it comes with a couple of choices (from memory) for the exact spec - Step1, step2 or step 3. Step 3 having a full counterweighted forged crank with bigger journals (I think), forged pistons and rods with bigger pins and relocated gudgeon point. This is "safe" to 10,500rpm and 1000bhp apparently. The step 2 kit doesnt have such a serious crank and uses standard rods i think - but I cant remember exactly.
2.7 kit by Trust was the original flavour of choice as fitted by Abbeys to rocket rons original engine, henrys and Ruperts sister cars to Ronnies and several others besides. Ged ran the first 2.8 I think and still pootles about with 670bhp and a hollinger with the massive first gear. I dont know anyone in the UK with an Apexi 2.9kit (which uses 88mm pistons from memory) and certainly no tuner has fitted one over here to my knowledge.
OSGiken use a standard diameter piston with long rods and a long throw crank to make use of the circa 20mm spacer plate - which I seem to remember gets machined down into the block first.
"RB30's" from Oz use either a Holden or Nissan Patrol block and then it starts to get a bit tricky with galleries and oilways needing to be "massaged" although these are the cheapest and possibly best performance per pound option upto around 800bhp at which point they get a bit unhappy I think.
I could - and probably am - talking bollox about some of this though.
J.
The recommended maximum overbore before you start weakening the block is 1mm to take it to 87mm. You will find that the bigger tuning firms make forged pistons upto 88mm though if you really want to go bigger but this will mean you have to start reinforcing the block - usually with resin.
They also do 88mm short skirt "drag" pistons that can cope with huge loads, have minimal weight and destroy your engine faster than a bag of sand, but give the outright most performance all other things being equal for their prescribed use.
The 2.8 kit that Abbeys do alot of is the HKS kit. This still isnt as simple as you might think as it comes with a couple of choices (from memory) for the exact spec - Step1, step2 or step 3. Step 3 having a full counterweighted forged crank with bigger journals (I think), forged pistons and rods with bigger pins and relocated gudgeon point. This is "safe" to 10,500rpm and 1000bhp apparently. The step 2 kit doesnt have such a serious crank and uses standard rods i think - but I cant remember exactly.
2.7 kit by Trust was the original flavour of choice as fitted by Abbeys to rocket rons original engine, henrys and Ruperts sister cars to Ronnies and several others besides. Ged ran the first 2.8 I think and still pootles about with 670bhp and a hollinger with the massive first gear. I dont know anyone in the UK with an Apexi 2.9kit (which uses 88mm pistons from memory) and certainly no tuner has fitted one over here to my knowledge.
OSGiken use a standard diameter piston with long rods and a long throw crank to make use of the circa 20mm spacer plate - which I seem to remember gets machined down into the block first.
"RB30's" from Oz use either a Holden or Nissan Patrol block and then it starts to get a bit tricky with galleries and oilways needing to be "massaged" although these are the cheapest and possibly best performance per pound option upto around 800bhp at which point they get a bit unhappy I think.
I could - and probably am - talking bollox about some of this though.
J.