The ultimate guide to engine choice
Feb 28, 2016 14:43:09 GMT
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Horney, atlex, and 3 more like this
Post by skuzzle on Feb 28, 2016 14:43:09 GMT
So we thought it about time to offer this advice up due to many misinformed nutzers offerings over the years. One time I did try to do this over there but got shot down hard so used that moment to ignore nutz there after.. So here goes.. And I think you guys will all make your own judgements, but this is completely unbiased as I've played with all the different engines over the years.
So I'll start with the good and bad points of each from 89 to 05
Short crank 1600
Cracking little engine when the crank is in good condition. Takes well to minor tweaks of ignition timing, fueling and breathing mods. Very easy to find the magic 115bhp it should have had from factory and with a light head skim and engine refresh regularly seeing 130bhp.
Known crank problem which certainly should put you off using high revs or supercharging.
Once crank starts to wobble cut your losses and drop in a long crank. Fixes don't often last long. You can, however fit a long crank into the short crank block but requires pulleys and oil pump from a long crank engine.
Long crank 1600
My preferred choice. It's lighter than the 1800 which makes it rev better. Same easy tweaks as mentioned above with the short crank engine.
No concern when supercharged and makes similar power when SC as the 1800. This is due to the chargers moving a set volume of air per revolution. Although it's not quite this simple, set air plus set fuel equals set amount of power. But the 1600 consumes less air per cycle than an 1800 so boost pressure increases raising the effective compression ratio. At sensible pulley ratios this can actually give more power than an 1800, but when boost level gets high enough control of the flame front is lost and ignition timing pulled allowing the 1800 to ever so slightly perform better.
90bhp 1600.
Now interestingly, this engine is my preferred choice for turbo builds. The cams seem to offer a faster spool and we are still limited on power by the conrods initially which is the same limit as all engines (but one for certain which I'll get to later)
Otherwise this engine is not desired. As an na engine it is soulless and gutless. A change of cams and ecu can liven it up again though.
Mk2 1600.
Pretty much just a mk1 engine with solid lifters and a slightly different cam profile to the mk1 (the lifters required this). Probably the hardest retrofit in a mk1 (matched only with the vvt engine) due to no slot I'm back of camshaft to install mk1 cam angle sensor. Still it has been done and with aftermarket ecu is a doddle.. Just not one for using all stock sensors and wiring. This engine does appear to offer a small amount of torque increase over the 115bhp mk1 engines but that seems to be its only positive as in the mk2 we have no easy control over fueling or ignition timing so we are left at factory settings (without mappable ECUs) meaning the mk1 will come out stronger with less effort.
Mk2 1800 99 engine
Now this one is a blinder. The cylinder head is very different to earlier engines with a better port angle. Much more desirable. It takes well to all na and fi tuning still limited by the con rods initially. Also an easy fit into a mk1 with the slot still available in the camshaft to take the mk1 cam sensor.
The sensible engine of choice for the power hungry, only rivaled on choice by the 115bhp long crank 1600 mk1 for those preferring a more responsive feel over max power.
Vvt or svt 1800
A sensible choice on paper. A poor choice in reality.
This engine in its natural state is the nicest of the bunch making the best power and torque. It is smooth to drive and really does offer the performance the mx5 should have had from day 1.
The bottom end also has different system for the oil baffle which is made from much thicker material than the earlier engines and is tied into the main caps offering a much stronger crank assembly which in theory should hold up to bigger power and/or higher revs than any of the earlier engines.
This makes it seem pretty obvious as the best starting point for big power but there are issues.
ECUs with vvt control are more expensive for a start. But this is the least of your problems. We are not sure of the exact year of change but the con rods in these engines (may be earlier too... Unconfirmed) are cast differently. At first glance they look identical but on closer inspection the casting marks and manufacturers markings are different. Even the colour of the casting appears slightly different to the earlier engines.
These rods bend and relatively low torque figures compared with the earlier rods but where as the earlier rods tend to just break and pop out of the side of the block, the rods in the vvt engine seem to distort over time and regularly give a warning knock long before popping out through the block and in all cases we have seen of this we are able to just replace the rods and the engine carries on good as gold with no other damage (result?)
With the vvt engine we also have a known issue with the cam position trigger which is press fitted on to the back of the camshaft and when put through a lot of heat cycles and overly thinned oil (superheated track use usually) it can slip which causes cam sensor fault errors and failure of the engine to start. We have yet to test pegging the trigger wheel in place but this would be our suggested pre-emptive fix.
I think that will do for now and I'll add info as I get time.
So I'll start with the good and bad points of each from 89 to 05
Short crank 1600
Cracking little engine when the crank is in good condition. Takes well to minor tweaks of ignition timing, fueling and breathing mods. Very easy to find the magic 115bhp it should have had from factory and with a light head skim and engine refresh regularly seeing 130bhp.
Known crank problem which certainly should put you off using high revs or supercharging.
Once crank starts to wobble cut your losses and drop in a long crank. Fixes don't often last long. You can, however fit a long crank into the short crank block but requires pulleys and oil pump from a long crank engine.
Long crank 1600
My preferred choice. It's lighter than the 1800 which makes it rev better. Same easy tweaks as mentioned above with the short crank engine.
No concern when supercharged and makes similar power when SC as the 1800. This is due to the chargers moving a set volume of air per revolution. Although it's not quite this simple, set air plus set fuel equals set amount of power. But the 1600 consumes less air per cycle than an 1800 so boost pressure increases raising the effective compression ratio. At sensible pulley ratios this can actually give more power than an 1800, but when boost level gets high enough control of the flame front is lost and ignition timing pulled allowing the 1800 to ever so slightly perform better.
90bhp 1600.
Now interestingly, this engine is my preferred choice for turbo builds. The cams seem to offer a faster spool and we are still limited on power by the conrods initially which is the same limit as all engines (but one for certain which I'll get to later)
Otherwise this engine is not desired. As an na engine it is soulless and gutless. A change of cams and ecu can liven it up again though.
Mk2 1600.
Pretty much just a mk1 engine with solid lifters and a slightly different cam profile to the mk1 (the lifters required this). Probably the hardest retrofit in a mk1 (matched only with the vvt engine) due to no slot I'm back of camshaft to install mk1 cam angle sensor. Still it has been done and with aftermarket ecu is a doddle.. Just not one for using all stock sensors and wiring. This engine does appear to offer a small amount of torque increase over the 115bhp mk1 engines but that seems to be its only positive as in the mk2 we have no easy control over fueling or ignition timing so we are left at factory settings (without mappable ECUs) meaning the mk1 will come out stronger with less effort.
Mk2 1800 99 engine
Now this one is a blinder. The cylinder head is very different to earlier engines with a better port angle. Much more desirable. It takes well to all na and fi tuning still limited by the con rods initially. Also an easy fit into a mk1 with the slot still available in the camshaft to take the mk1 cam sensor.
The sensible engine of choice for the power hungry, only rivaled on choice by the 115bhp long crank 1600 mk1 for those preferring a more responsive feel over max power.
Vvt or svt 1800
A sensible choice on paper. A poor choice in reality.
This engine in its natural state is the nicest of the bunch making the best power and torque. It is smooth to drive and really does offer the performance the mx5 should have had from day 1.
The bottom end also has different system for the oil baffle which is made from much thicker material than the earlier engines and is tied into the main caps offering a much stronger crank assembly which in theory should hold up to bigger power and/or higher revs than any of the earlier engines.
This makes it seem pretty obvious as the best starting point for big power but there are issues.
ECUs with vvt control are more expensive for a start. But this is the least of your problems. We are not sure of the exact year of change but the con rods in these engines (may be earlier too... Unconfirmed) are cast differently. At first glance they look identical but on closer inspection the casting marks and manufacturers markings are different. Even the colour of the casting appears slightly different to the earlier engines.
These rods bend and relatively low torque figures compared with the earlier rods but where as the earlier rods tend to just break and pop out of the side of the block, the rods in the vvt engine seem to distort over time and regularly give a warning knock long before popping out through the block and in all cases we have seen of this we are able to just replace the rods and the engine carries on good as gold with no other damage (result?)
With the vvt engine we also have a known issue with the cam position trigger which is press fitted on to the back of the camshaft and when put through a lot of heat cycles and overly thinned oil (superheated track use usually) it can slip which causes cam sensor fault errors and failure of the engine to start. We have yet to test pegging the trigger wheel in place but this would be our suggested pre-emptive fix.
I think that will do for now and I'll add info as I get time.
le sigh