Idiots Guide To Stroking Needed.....
16 April 2003, 10:55 AM
#1
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Where do I start ??
Perhaps to clarify "stroking the engine" before any wise cracks come out of the woodwork !!
Anyways, whats involved in say doing a 2.2L stroker to the EJ20.
how much gain in power/torque
how much/at what revs
flywheel or driving wheels
any change in compression ratio
*any* disadvantages etc
anyone done it/thoughts/comments
should be enough to raise some questions.
velohead
[Edited by velohead66 - 4/16/2003 10:55:55 AM]
Perhaps to clarify "stroking the engine" before any wise cracks come out of the woodwork !!
Anyways, whats involved in say doing a 2.2L stroker to the EJ20.
how much gain in power/torque
how much/at what revs
flywheel or driving wheels
any change in compression ratio
*any* disadvantages etc
anyone done it/thoughts/comments
should be enough to raise some questions.
velohead
[Edited by velohead66 - 4/16/2003 10:55:55 AM]
16 April 2003, 02:20 PM
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I'm not an expert, but I'll try my best.
Potentially all other things being equal (and I am conveniently ignoring some confounding factors that I am aware of and no doubt some I am not) you would gain 10% power/torque across the range. The main attraction is that you can run 9% less absolute manifold pressure for roughly the same charge. You could get a wider power band for the same power, and potentially run on lower octane by turning the boost down. Increasing the compression ratio can be done in various ways, but can improve off boost performance, but also increases octane requirements for the same on boost timing. As always a compromise.
Stroker engines at the same RPM will have higher forces on the rotating assemblies, which if keeping the strength the same would advise a lower rev limit. But then most people uprate the rotating assembly - particularly the conrods and keep the piston weights down.
You will benefit from forged lightweight aftermarket pistons by having stronger ring lands and crowns which are more resistant to high temperature and detonation damage, but for high specific outputs you still have to be almost paranoid about detonation to make the engine last.
Closed vs open deck block is another issue to consider from the point of view of head gasket integrity/clamp down, although some have had good results at 400+ BHP from open deck blocks most would opt for a closed deck block if possible.
If you fit a 2.5 crank to an EJ20 you end up with IIRC a 2.12 not a 2.2.
2.2 in the 22b is I gather entirely from the bore. Stroke this with a 2.5 crank and you end up with about 2 1/3 litres.
If you start from the 2.5 end you can liner down to 2.4 for extra strength, but you have an open deck block unless you get it closed which has issues of expense, coming from US or Aus, although Pavlo is working on something.
I am sure I will be swiftly corrected if I've got the measurements wrong
[Edited by john banks - 4/16/2003 2:23:08 PM]
Potentially all other things being equal (and I am conveniently ignoring some confounding factors that I am aware of and no doubt some I am not) you would gain 10% power/torque across the range. The main attraction is that you can run 9% less absolute manifold pressure for roughly the same charge. You could get a wider power band for the same power, and potentially run on lower octane by turning the boost down. Increasing the compression ratio can be done in various ways, but can improve off boost performance, but also increases octane requirements for the same on boost timing. As always a compromise.
Stroker engines at the same RPM will have higher forces on the rotating assemblies, which if keeping the strength the same would advise a lower rev limit. But then most people uprate the rotating assembly - particularly the conrods and keep the piston weights down.
You will benefit from forged lightweight aftermarket pistons by having stronger ring lands and crowns which are more resistant to high temperature and detonation damage, but for high specific outputs you still have to be almost paranoid about detonation to make the engine last.
Closed vs open deck block is another issue to consider from the point of view of head gasket integrity/clamp down, although some have had good results at 400+ BHP from open deck blocks most would opt for a closed deck block if possible.
If you fit a 2.5 crank to an EJ20 you end up with IIRC a 2.12 not a 2.2.
2.2 in the 22b is I gather entirely from the bore. Stroke this with a 2.5 crank and you end up with about 2 1/3 litres.
If you start from the 2.5 end you can liner down to 2.4 for extra strength, but you have an open deck block unless you get it closed which has issues of expense, coming from US or Aus, although Pavlo is working on something.
I am sure I will be swiftly corrected if I've got the measurements wrong
[Edited by john banks - 4/16/2003 2:23:08 PM]
16 April 2003, 05:26 PM
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sounds good to me, also need to consider standard 2.5 rods are 1mm longer in an attempt to maintain similar rod/stroke ratio. As it is a longer stroke will mean greater side loading on the piston. At higher rpm and torque this is more lilely to result in walking of the cylinder bores and so a closed deck block will be of more benefit with a stroked engine.
You can offset grind the 79mm stroke to yield a 83mm stroke if you really want to, but personally I would rather have 52mm big end journals seeing as the bearing and oil film area will be that much bigger.
You can offset grind the 79mm stroke to yield a 83mm stroke if you really want to, but personally I would rather have 52mm big end journals seeing as the bearing and oil film area will be that much bigger.
16 April 2003, 10:31 PM
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Closed deck block is a "phase one". The EJ25 phase one crank has 48mm big end journal.
Realistically, you can only offset grind an EJ25 "phase two" crank, but then you'd need to use the STi7 block if you want a semi closed deck block(easiest option).
Mark.
Realistically, you can only offset grind an EJ25 "phase two" crank, but then you'd need to use the STi7 block if you want a semi closed deck block(easiest option).
Mark.
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