If you do not want to read all of this, the best bits, the dyno results are at the end.
1.0tr Micra Rebuild M98MJM.
The plan was to rebuild an engine to the Junior F1000 spec and pop it into the Micra I had picked up for my daughter to use in the under 17 car club. The engine was completely stripped including the head and everything was thoroughly degreased and all the old carbon removed from the pistons etc, everything now liked like new.
There were some corrosion marks on the head and block so between the two we removed a total of 0.025” to get a totally clean and flat surface, which is the total amount allowed to be removed under the Junior F1000 rules. The cylinder bores were honed to give the new piston rings a chance to bed in correctly. Finally we painted the block with some new heat resistant paint I wanted to try out.
The crankshaft was checked, but not balanced. You are not allowed to balance the bottom ends in the Junior F1000 series and to be honest the Micra bottom end is very good in standard form. New bearings were fitted and the crankshaft checked to make sure the crankshaft rotated nice and freely. New piston rings were being fitted, but first we had to check the ring gaps in the bores and adjust as necessary. The rings were fitted taking care to position the ring gaps in the correct place as per the manual. These were then but into the block and everything torque up making sure everything still rotated nicely.
Attention was now being turned to the cylinder head and apart from re facing the head 0.025” and having the valves and valve seats re cut no other work is allowed. At this point things start to waver from the Junior F1000 rules and the temptation to have a little play with the die grinder got the better of me. That little devil in the back of your mind saying go on, who’s to know, you know you have those 1.3 cams sitting around doing nothing and before you realise what you have done the die grind is out and you are carefully blending the valve seats into the ports and reshaping the turn from the port onto the valve head. The other side of you is saying do you know what you’re doing? You could so easily be making things worse and not better. The thing is, if you don’t try some of these things how are supposed to learn.
The valve seats were blended nicely into the port and the turn from the port to the area under the valve head was rounded and slightly enlarged. Use a finger to gauge each opening, a bit cawed I know but more accurate than just guessing. The valve stems are slightly thicker just above the valve head so these get carefully thinned down to the same size as the rest of the valve stem. This is easily done by having the valve rotating in an electric drill and using the die grinder on the stem. The valve heads are also polished in the same way making sure the inlet valve has a nice radius at the edge of the valve head and the exhaust has a square edge on the valve head. The radius on the inlet valve aids flow into the cylinder and the square edge reduces back flow of exhaust gases, well that’s the theory. Once all the head work had been done the valves and seats had a 3 angel cut and lapped in.
An easy way to lap in the valves is with a cordless drill with variable speed and a length of vacuum pipe large enough to go over and grip the valve stem. Put the vacuum hose in the drill and lub up the valve stem and add the cutting past. Put the valve into the guide and push the vacuum pipe onto the end of the valve stem. Carefully operate the drill and apply slight pressure with your finger to the valve head. It does not take long to lap the valves in and a lot easier on the arms.
Once the valves have been fitted and the collets checked they are correctly seated the 1.3 cams are fitted and shimmed up, setting the clearances as tight as possible within the valve clearance spec, this will ensure maximum lift.
With the head and cams fully rebuild the head was fitted to the block and new timing chains, tensioners and guides fitted. The block and head were treated to special high temperature paint and all the other parts like front cover/oil pump and sump were fitted. We also treated the rocker cover to some high temperature paint just to finish off the overall appearance.
We wanted to keep the standard exhaust manifold so this to was treated to a session with the die grinder. We matched up the manifold to the head ports and then enlarged the exhaust manifold to create a set effect as the exhaust gases leave the head. The idea here is to reduce any back flow of gases as the pressure builds around the tight bends on the standard manifold. I was quite surprised how much of the manifold could be clean up with a die grinder and some flexible abrasive paper. We also blanked off the lambda sensor and moved this onto the competition front pipe by the gear box at the back of the engine. The exhaust manifold and front pipe, which does away with the front car was wrapped with a special heat resistant wrap to reduce under bonnet temperature. The remaining exhaust system consists of cat replacement box and a 1.75” system.
We had the flywheel refaced and a new uprated clutch fitted and with the gear box checked and mounted onto the engine everything was put back into the car. The standard air box was modified with a larger intake pipe; Green Cotton panel filter and a cold air pick up and feed into the air box. We also connected up a 1.3 ecru, but this was more to do with the 1.0 ecu having an intermittent misfire which was cured when the replacement ecu.
The car started first turn and everything seemed okay so a good long road test was required. The engine certainly felt very good and showed good signs, but you could tell it was lacking a bit of fuel or more ignition or both. This left only one option and that was to contact Ed and get a Nistune board fitted so we could see the true potential of the new engine. I am sure a lot us have a section of road which we use to test any improvements, two points which are used to see how fast or quick the car gets from ‘A’ to ‘B’ and I’m no different. I have a section of road with several key points to indicate how well a car is performing and having driven lots of Micra’s and other cars down the same stretch of road it was easy to see how well are new engine was performing without having Ed’s magical touch. It was certainly a lot quicker than the standard 1.0 Micra, knocking several seconds off the 0 – 60 in fact it was as quick as a standard 1.3 or possibly slightly quicker.
Once Ed had received the Nistune board I could not resist the temptation to spend a day with Ed testing some different set ups on the rolling road and with the new engine I was confident we could up the rev limit with it effecting the reliability so a day was booked and the following tests carried out.
I had changed the standard exhaust manifold to a Janspeed 4 branch system as this would be easier to remove and change back to the standard manifold later in the day. The first test was carried out with the Janspeed Manifold and one of our Group A induction kits. Ed spent a bit of time setting the fuelling and the ignition timing for this set up as we have some customers running very similar engine specs in an overall / grass track racing series and we wanted to get the best set up possible as they are unable to get their cars to a rolling road. The final figure end up at 84.1 just over 7000 rpm and 68Ft/Lb of torque at 3250rpm, this set up also gave the best torque figures between 5500 and 6500 at around 66Ft/Lb.
We then tested the following induction kits with the Janspeed manifold and got the following results
1. Standard air box with a new standard Nissan air filter 78 bhp
2. Standard air box with a Green Cotton Comp Filter 78.7 bhp
So the Green Cotton filters do give slightly more power over a standard filter when new, what I should have tried was a used standard filter to see how much power is lost with a filter that had done 6000 miles. I’m sure the Green Cotton filter would perform much better when this has done 6000 miles.
3. Standard air box but no filter 83.2 bhp
I would not want to run my engine without an air filter; it takes too long and too expensive to keep rebuilding engines.
4. Green Cotton Nano Induction Kit 84.3 bhp
Although this had the most power it was down on torque mid range and only peaked better than the Group A air box at just under 7000rpm. Max power is not always the most important thing. Still a good induction kit
5. Green Cotton Twister Induction Kit 83.4 bhp
Same as above but slightly better, still a good Induction kit
6. Just a pipe going straight onto the air flow meter 83.2 bhp
But no mid range torque at all
7. Simota racing sports filter Induction Kit 84.1 bhp
But no mid range torque at all
8. Standard modified Air Box + Green Cotton filter 82.8 bhp
Similar torque curves as the Group A air box. Where the Group A Air Box would perform a little bitter than the others would be when the car is on the move and the air is being rammed in.
You also have to remember this is a small low powered car with limited modifications. If we fitted some better cams etc then the air box would really start to help to add power.
We then put the standard exhaust manifold back on an tested the following
9. Group A Air Box 79.6 bhp
Interesting to see the Janspeed manifold only gives another 4 – 5 bhp but again this might be more when fitted to a 1.3 Micra.
10. Green Cotton Nano Filter 80 bhp
11. Standard Modified Air Box + Green Cotton Filter 78.5 bhp
This is the final set up we have on the Micra and it now feels very good to drive. With the standard gear box final drive of 4.4:1 and some 185/60R13 tyres the engine seems to live between 3000 and 5000 rpm and will happily red line in 4th gear (Okay with a tail wind) The car feels very nice to drive and does not seem to use an excessive amount of fuel, it’s possibly on different to a standard Micra if you don’t push the car, which is kind of difficult when you have to travel home on country roads which open out nicely in places. Acceleration, I would say the 0 – 60 is definitely quicker than a 1.3.
I will let you draw your own conclusion from the tests and you comments welcome.
Matthew
PS. Sorry if this is a bit long winded.
