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I'm rebuilding a NA8 engine - with some mods on the way. Acquired some parts, its a budget build so Im taking my time getting it sorted. Will be a street engine with hopefully a happy level of compromise between driveability and power.
Id appreciate any advice of the rebuild and choice of parts.


Ive already ground off the lettering off the cam cover, and will likely cut the face of the cover for access the cam gears. Unsure if I should paint or polish the cover, polish would look great but difficult to maintain. COPS mounting plate already made.

Headers are 4-1 stainless - not racingbeat but similar.

I bought the complete long engine a while ago -
The head was purchased separately, and has had backcut +1 oversized valves,porting and duel valve springs.




The block is original na8- with over 150000kms on it, slight ridge on top of bores.


Clutch and flywheel combo- flywheel is a lightweight chromoly one about 3.5kg and the clutch is a exedy with inorganic cushioned button plate.


2 X na8 exhaust cams (one wrapped up ready to send to regrinders) and a adjustable cam gear set. After regrinding both the exhaust cams, I'll do the ex inlet mod.



The valves are very long compared to standard at 117mm. Looks like the underside of the buckets have been machined to suit the valves and perhaps the previous owner ground the valve to get the correct length without using shims.
Testing with the standard 36mm base circle cam it seems the base circle would have to be reduced to 32-33mm for this to work.
Anyone know if I can grind/cut the the valve stem 2-4mm and use SUB shims? Do stainless valves have 'hardened' ends or is it ok to cut them?

I've been quoted $250 to get the block rebored, but was thinking about hunting around for a low kms block that doesn't need a rebore and only a hone.

Thoughts at the moment are to:
1 Get the cams reground to 270degree(220-230 at .050) with 10mm lift.
2 Shave head - it has marks in one cylinder that a shave would clean up.
3 Relap the valves. Fit cams with SUB shims- easier to write then do.
4 Use 10:1 pistons in a newer block or rebored this one.(hoping for 11-12:1 CR with head shave)
5 Maybe buy h beam conrods. Maybe buy new oil pump.
6 rebuild with new bearings seals gaskets water pump.
7 Get running with the na8 inlet manifold but replace it soon after with a handmade one with straight runners. Or a honda moded one. See the watercut flange plate already on the engine.

Lots of maybes like:
H beam rods, or are they only for turbo engines.
Is the standard front pulley ok for high revs
Is the std oil pump ok
Oil squirters, keep or remove.

Hooray for motor projects!

I'd go for 11:1 pistons. If 10:1 pistons is what you'd go for you could just find an NB8B bottom end and not have to build it. I think you might get close to 11:1 if you deck and shave with 10:1 but not really near 12:1. An oldie but a goodie...
http://solomiata.com/CheapHP.html


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Nice.

should be real sweet.

Nice one one the porting. Although i want to port patchy a little. I'm hesitant. Ive never attempted Porting work before.

Did You say $250 was for boring? Is honing less? in cost that is.

You want to get your compression from pistons not a head shave. If you ever need to shave the head again for a rebuild your in trouble.

Once you bore the lip out its not that much to just keep boring and put bigger pistons in for more capacity.


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Thoughts at the moment are to:
1 Get the cams reground to 270degree(220-230 at .050) with 10mm lift.
2 Shave head - it has marks in one cylinder that a shave would clean up.
3 Relap the valves. Fit cams with SUB shims- easier to write then do.
4 Use 10:1 pistons in a newer block or rebored this one.(hoping for 11-12:1 CR with head shave)
5 Maybe buy h beam conrods. Maybe buy new oil pump.
6 rebuild with new bearings seals gaskets water pump.
7 Get running with the na8 inlet manifold but replace it soon after with a handmade one with straight runners. Or a honda moded one. See the watercut flange plate already on the engine.

Given you have a solid lifter head, and your aiming at the Honda or similar manifold, I'm going to base my response that you want this thing to rev. It's N/A so you need to rpm to make it work...

My advice:
1 sounds good... or go for more duration. 282 degree
2 I'd try and get most of your target compression with pistons. Then deck the head to suit. Make sure you check valve clearances... they will be close and may require machining the valve reliefs.
3 Be careful lapping the valves by hand, don't work them too much. Fitting the SUBs isn't that hard. My head runs two shims, one on the lifter, one on the valve so you could always do something similar if you need to. I found it was fairly easy to take a few thou off a shim with 800 wet and dry using oil. One day I'll make up a portable shim pack that can be shipped around Aus. User pays for shipping and replacement shims.
4/5 ... if you want to rev it go straight for forged rods and higher compression pistons. Wiseco are nice and their rings are the best. It's worth spending the $1000 on rods and pistons, otherwise you'll be back in the motor, or picking parts off the road.
5. If you are aiming for revs, block off the oil pressure relief valve in the stock oil pump and run an external Peterson one. This will fix the oil pump issues and it's nice to be able to adjust oil pressure remotely. I don't run the Boundary Engineering pump and everyone who has an external relief valve has no problems with exploding oil pumps... You also need to run an oil cooler too.
6. Yup new seals all round
7. A handmade intake would be awesome. It's going to be hard to fit in a straight runners without a brake booster delete so you might need to curve them or aim them forwards etc. The Honda manifold works well however it still requires a high reving engine to match... eg 9000 rpm.

Other tips:
1. A high reving N/A engine will put very high tensile loads on the rods vs a high power turbo car which puts compression loads. I beam is suited to N/A because it's lighter, H beam for turbo because they are stronger in compression, but basically any forged rod that is lighter than stock is fine for a N/A engine. I was looking at the K1 rods from Summit. They are lighter than the ebay H beams but cost 50% more. I'm sure the ebay H-beam ones would work.
2. No squirters required if you go for forged pistons. Block them off with cap screws, copper washers and loctite
3. I'd add a sump baffle if you plan on tracking it. I added one to mine and it's easy enough to do. PM me for the template.
4. I run a cut down stock damper. It's been machined to just a single pulley... so no PS or Aircon Maybe not for a street car though.
5. You should run a MBSP if you are reving the engine. It helps stop the crank moving around and helps with windage. Try and find a wrecked later model engine that you can grab the sump and MBSP, or buy a new one. It will fit into your NA8 sump but will need a bit of persuasion (aka grinding)

building a N/A engine is hard work... so many things to get right! It's definitely worth all the work though, but you can see why people just slap on a turbo!

Plus 1 to that entire post.

madjak post of the year!

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GREAT POST MADJAK!!!!.

Thanks guy for your inputs - esp Madjak for that detailed post.

I do want it too rev, but its a budget street build that shouldn't stretch for $1000 rods/pistons and a $200 oil reg but those petty thoughts may change. Would standard rods and 2002 pistons be ok for 7500rpm? ie if I buy a 2002 short block and put my head on it.

I did find china H beam rods for $240 a set but I would have to buy 5 sets to get them at this price. Group buy anyone?

Re: the cam duration - I do want use this on the street but im ok with some poor engine manners. Lack of power in the low rpm range is ok, but hopefully not low throttle bucking. Anyone have 280 cams in a street car, thoughts?

The compression ratio - I was going to do like Quinns car- ie 2002 pistons and shave about 2mm off the head. But this head has had some work done to it, so Im probably are better off using pistons to increase the CR.

Lapping / shims- thanks for the advice, its been 20 years since ive done this.
Im thinking that when I get the cams reground to 33mm(36 standard) the clearance to the buckets will be so close that i may have to grind/cut the valve stems and then use shims.

Home made inlet manifold - yeah, its hard to estimate how long the runners could be at the moment as the 1.6 engine is still in the car.
Using some online calcs the runner length should be 250mm for peak at 7000-7500rpm. If using a 100mm pipe for the plenum and if I relocate the brake bias block and tubes, this should be 'just' doable.

I and H rod - thats interesting re the weight., Ive seen the I beams for sale but never seen anyone use them - probably because of mx5 turbos out numbering non boost builds.

re: Damper/pulley. Thats a great idea! By cut down, how you do it? Turned down on a lathe?

Re the damper... yeah just cut / lathe the outer pulley off. Saves lots of weight and still provides dampening.

If you aren't too stressed about pushing the revs then yeah you can stick to stock pistons / rods. The oil pump isn't much of an issue either then. Also no point going any larger on the cam. So I think 7800 would be fine but maybe others can comment on that. Just don't money shift and over-rev it... not that you can do that on a built engine either.

I'd also run acl race bearings especially on the big ends and oil with zinc if you don't run a cat (though you should if its a street car). That will give you a bit more safety on thr revs.

The only major issue with decking the head a lot is getting a loose timing belt and requiring some correction to the timing. Plus you can't go back and if you ever damage it you can't remachine it. Still it's a good way to up the compression without the cost.

Amayama sells the later model 10:1 pistons, plus some of the oversized ones too. $350 for a set from memory. There is really nothing wrong with them except they aren't forged so they are a bit heavier and don't give you the safety factor. Still for a mild n/a build they are a good option.

I could be persuaded to pick up a set of china rods... at those prices why not?

My car runs Carillio I beams.

datfreak if you are down Ipswich way give me a shout and I can give you a drive in mine so you can see how streetable large duration (288­, +11 lift, base circle reduced and ramp angles softened) cams are. Actually it has most of what Madjak, well apart from the sump baffle and the Honda intake.

Runner length will depend on the characteristics that you want from the engine, have a read of this thread http://mx5cartalk.com/forum/viewtopic.php?p=825891#p825891. The thread never did solve the question

$ 250 Seems a little steep ,I think I paid bore/hone around $150 [ Engine Engineering ] From memory Eagle I rods and Supertech 10:6 [ b6 engine } together around US $ 600 . but it was a while back ! and after a lot of price searching .

madjak wrote:Re the damper... yeah just cut / lathe the outer pulley off. Saves lots of weight and still provides dampening.

I could be persuaded to pick up a set of china rods... at those prices why not?

I'll try hacksawing the out side pulley off, leaving it a bit wide and grinding it even on the belt linisher.

Here is the picture of the rods the china supplier sent me- minimum order quantity is 5 sets. Price was for the H beams(left). They also sell rod bolts cheaply at about $50 a set but I've read the china bolts arn't great and I'd prefer paying for ARP ones.


Thanks for the advise - keeping it under 7800 probably is a good idea on a dd roadcar.

Magpie wrote:datfreak if you are down Ipswich way give me a shout and I can give you a drive in mine so you can see how streetable large duration (288­, +11 lift, base circle reduced and ramp angles softened) cams are. Actually it has most of what Madjak, well apart from the sump baffle and the Honda intake.

Runner length will depend on the characteristics that you want from the engine, have a read of this thread http://mx5cartalk.com/forum/viewtopic.php?p=825891#p825891. The thread never did solve the question

Thanks for the offer Magpie, if im down your way I'll take you up on that. Could you use it as a daily car or do you think its cammy bad manners would be too annoying?

That is a good read re: runners. Lots of conflicting info out there, might be a trial and test thing which is easier with ITBs.
I found this site for inlet runner calc- im unsure which data it uses to make its assumptions.
http://www.exx.se/techinfo/runners/runners.html

a222133 wrote:$ 250 Seems a little steep ,I think I paid bore/hone around $150 [ Engine Engineering ] From memory Eagle I rods and Supertech 10:6 [ b6 engine } together around US $ 600 . but it was a while back ! and after a lot of price searching .

I'll ring around some more. The place that quoted me $250 also quoted $60 for a head shave which sounded very good value, maybe they out source the boring hence the price.
If I dont use 2002 mazda pistons I was thinking about the supertechs in 11:1. Might be a price overkill for a street car tho

The MX5 is fine as a daily, however its fuel consumption does not encourage it to be used that way. Remember it is tuned for track and not economy, it does not use target AFR when being dríven.

The consensus with respect to runner length is that do the maths for a starting point but the final length will be trial and error (heaps of dyno time).

The limiting factor in my build is the exhaust side and there is gains to be had from playing on the hot side, however not on the agenda )just yet).