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If you like experimenting with your B3 like I do then you may want to investigate an adjustable cam pulley. Adjusting the camshaft timing can alter the power band of the little B3 to fit your driving needs.
I offer this simple writeup for folks interested in tuning, however I cannot confirm any benefits because my application is too different to compare data. My car (Miata) is slightly heavier and has completely different gear ratios in the transmission. Overall my results may differ than yours.
This project has the same difficulty as changing the timing belt... and while your at it... you should change the timing belt.
Unfortunately the only pulley that will fit is from a DOHC Mazda engine and you have to buy two units. The CorkSport pulleys look nice but others are available. Figure anything for a 90-97 Mazda Miata DOHC 1.6 - 1.8 will work. Other years may be ok.
Before you begin, you should get out the timing light and set the base ignition timing. Connect the STI connector to ground and adjust the ignition to 10* BTDC.
The CorkSport cam sprockets are identified by E for exhaust & I for intake. The timing marks on the intake sprocket are in the correct position however the exhaust sprocket has the marks in the wrong spot. I chose to use the exhaust sprocket because it is harder to sell ( I have a buyer interested in other one).
Anyway, setting the base ignition timing was a way to confirm the cam timing was also correct when the engine was running again. This is an excellent way to confirm all is well before you start changing the cam timing.
The Corksport pulleys were never meant to be installed on a B3 and I have no idea how they fit on a DOHC engine, but I did find that the pulley did not automatically center on the B3 camshaft. There is about a 015 (fifteen thousandths) slop between the cam bolt and the pulley. Perhaps a genuine Miata cam bolt is different and take up this slop, but a Festiva cam bolt will not center the sprocket well enough.
I carefully cut some aluminum tape about 1/4 inch wide and wrapped the cam bolt to make up the slop and perfectly center the pulley on the camshaft. (See picture) I also use a larger washer.
The pulley installs and centers perfectly. You need to apply the correct torque to the bolt and may need to remove the cam cover to gain access to the hex shaped segment on the camshaft use to provide counterforce. Using the belt for counterforce may not be enough.
Once the cam sprocket is installed, start the engine and confirm the ignition timing is correct... if not.. then check your work.
You are now ready to change the cam timing. Remember, everytime you adjust the cam timing you need to set the base ignition timing. Advancing or retarding the cam also changes the ignition timing so keep that in mind.
I'm currently running an Aspire roller cam from an engine originally equipped with an automatic transmission. I found that 4.5 - 5.5 degrees advance has improved fuel economy slightly. My Megasquirt remaps the fuel trim for a perfect tune and I'm not sure if a stock ECU can handle this amount of change.
In the near future I'm going to put the non roller cam back in the B3 and experiment with the timing. The final results are pending.
This is the exhaust pulley, its the one with the wrong timing marks. install it with the slot up (red dot).
The intake pulley has the correct marks and installs normally.
Also note the cam bolt has been modified by wrapping aluminum tape around the shank to make up for some slight slop. The larger washer should be used to distribute the pressure correctly.
B3 with an adjustable cam pulley.
Have fun!
Jim
I offer this simple writeup for folks interested in tuning, however I cannot confirm any benefits because my application is too different to compare data. My car (Miata) is slightly heavier and has completely different gear ratios in the transmission. Overall my results may differ than yours.
This project has the same difficulty as changing the timing belt... and while your at it... you should change the timing belt.
Unfortunately the only pulley that will fit is from a DOHC Mazda engine and you have to buy two units. The CorkSport pulleys look nice but others are available. Figure anything for a 90-97 Mazda Miata DOHC 1.6 - 1.8 will work. Other years may be ok.
Before you begin, you should get out the timing light and set the base ignition timing. Connect the STI connector to ground and adjust the ignition to 10* BTDC.
The CorkSport cam sprockets are identified by E for exhaust & I for intake. The timing marks on the intake sprocket are in the correct position however the exhaust sprocket has the marks in the wrong spot. I chose to use the exhaust sprocket because it is harder to sell ( I have a buyer interested in other one).
Anyway, setting the base ignition timing was a way to confirm the cam timing was also correct when the engine was running again. This is an excellent way to confirm all is well before you start changing the cam timing.
The Corksport pulleys were never meant to be installed on a B3 and I have no idea how they fit on a DOHC engine, but I did find that the pulley did not automatically center on the B3 camshaft. There is about a 015 (fifteen thousandths) slop between the cam bolt and the pulley. Perhaps a genuine Miata cam bolt is different and take up this slop, but a Festiva cam bolt will not center the sprocket well enough.
I carefully cut some aluminum tape about 1/4 inch wide and wrapped the cam bolt to make up the slop and perfectly center the pulley on the camshaft. (See picture) I also use a larger washer.
The pulley installs and centers perfectly. You need to apply the correct torque to the bolt and may need to remove the cam cover to gain access to the hex shaped segment on the camshaft use to provide counterforce. Using the belt for counterforce may not be enough.
Once the cam sprocket is installed, start the engine and confirm the ignition timing is correct... if not.. then check your work.
You are now ready to change the cam timing. Remember, everytime you adjust the cam timing you need to set the base ignition timing. Advancing or retarding the cam also changes the ignition timing so keep that in mind.
I'm currently running an Aspire roller cam from an engine originally equipped with an automatic transmission. I found that 4.5 - 5.5 degrees advance has improved fuel economy slightly. My Megasquirt remaps the fuel trim for a perfect tune and I'm not sure if a stock ECU can handle this amount of change.
In the near future I'm going to put the non roller cam back in the B3 and experiment with the timing. The final results are pending.
This is the exhaust pulley, its the one with the wrong timing marks. install it with the slot up (red dot).
The intake pulley has the correct marks and installs normally.
Also note the cam bolt has been modified by wrapping aluminum tape around the shank to make up for some slight slop. The larger washer should be used to distribute the pressure correctly.
B3 with an adjustable cam pulley.
Have fun!
Jim
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