mx5cartalk.com

I don't give a rats anus about the BP so lets leave it out of this thread.
I don't have the funds to go turbo. I know turbo is the most sensible way.
This needs to be gradual. Under the radar. Drivable in the mean time. I also need to make the best with what I currently have.

Breathing is pretty much open as I can get it. The only real restriction I have is the standard 1.6 AFM & the head itself.
The AFM will probably eventually go when an ECU will get installed.Patchy is currently got a full mania intake 4-2-1 headers with a 2.25 inch exhaust all the way to the back.

I've had this set up before. I just want to make it better this time around.
This is purely hypothetical at this stage

Cams 272 duration Advertised
Compression. 10.5:1?
Stand alone ECU

I loved it above 5000 rpm it recited poetry. The torque was insane from 4000 up. Below 4000 it was great too with the stand alone ECU.
with the standard ECU was a bit on the garden path type performance below 4000.
The compression increase should help this along while it's running on the standard ECU. This should also reap benefits once the stand alone ECU gets installed & tuned.

One thing a cant get my head around. Is the lift. Billet vs regrind.
I understand when regrinding a cam the duration would increase , which increases the time the valve stays open. However the actual physical lift is the same as stock?
So when you get a billet cam and it has 10mm lift, a regrind would then have 8mm of lift? Or whatever stock lift is
Does the physical lift make a difference? Or in my case where the head flow will pretty much stay standard, is the 10mm lift going to make any difference? Compared to getting a regrind.

How much of a head shave is required for a 10.5:1 ratio? Is 10.5:1 sensible?

Current timing is set at 15 deg BTDC
Will this have to be adjusted once the compression ratio gets increased And while it is running on the OEM ECU & cams?

Hi Stan,
I would think a regrind would get built up with weld first, and then ground down to what the chosen specs are.
Lift increases would be reducing restriction (like opening your hot tap in the basin that bit more, say 45deg-90deg) of the valve, by getting it out of the flow path.

Go as high as you can with the compression... 11.5:1 pistons and a bit of a head shave for great justice, and it will still be fine to run on 98.
You may need to take that timing out at that point but I am no expert, not sure if you can wait til you put the cams in it.

Did you keep all the hot toys from when you had them before, or are you really having to start over?

High compression Pistons are not happening. I would need to rehone cylinder walls and that would bring it up to Turbo cost.
aim is to make it more fun without too much cost.
Head shave is like $200? plus Head gasket. maybe 1 week out of action?

I sold all the hot bits to get a pushbike which has kept me very fit for the last 6 years I regret selling the cams

Ah yes sorry I equated your mention of compression ratio with new pistons... no worries.

No way you will get to 10.5 with a head shave. A head shave is good for 0.2 extra compression.

Considering you ain't aiming for big power and want a cheap as chip build. I would just go itbs, cams, ecu.

Head shave can go MORE than 10.5 actually.

OPs idea wont work though I am sorry. If you want cheap port it yourself, get it shaved, rebuild it without replacing any parts at all, add used cams and run it on methanol.

Dann

Reground cams can be made to whatever specs you desire.

Some they weld to the cam to add material and then grind it to the wanted spec (then hardening etc)

And some they simply grind out around the base of the lobes reducing the minimum diameter (thus allowing more than standard lift)
Usually with this method you'll use much thicker than standard shims to keep the lash in check. Since the NA6 head uses HLA it's less of an issue, but check with the cam grinder to make sure you wont be goign outside of what the HLA can cope with.


Billet cams are simply brand new cams ground from a fresh billet of metal, basically scratchbuilt rather than adjust and existing cam.

StanTheMan wrote:Cams 272 duration Advertised
Compression. 10.5:1?
Stand alone ECU
...snip...
Is 10.5:1 sensible?

You need to match your fuel to your CR and your intake valve opening point, which more or less means your cam duration. And then adjust your ignition timing to ensure there is no knock/pinging.

For a 272 cam on 98 fuel you will need more than 10.5 to get the best from the engine. For a 10.5 CR you will need less cam than 274 so that it doesn't run like a pig down low. Although if you want to run on 91 fuel this combination (274/10.5) might be acceptable.

FYI, I have 11.7 to 11.8 CR (depending on the cylinder) with a 280 intake cam. It did ping on 98 at about 3500rpm, so I had to back off the timing and forgo some torque/power at this engine speed, but other wise it is all good.

This concerns B6 mods.

For those considering high lift cams. In particular Normally Aspirated.

Mine are 272/264 @advertised

lift is 10mm/9mm

this is getting aggressive. you do need to be clear abut clearance when increasing CR.

while its most probably fine on a standard gasket when you start shaving the head to maximum you need to tread carefully if you reduce the width of the head gasket as well.

I'm extremely lucky.

I got the head shaved by 0.75mm and got a 0.7mm head gasket to increase the compression a little more.

that's a total of 1.3mm reduction with big valve lift. So with big lifts, Ive passed the safe zone. I don't know if or how much the head was shaved before I owned the car.

at this stage I don't know the extend of the damage but from about 3500-4000 rpm the pistons started started touching the valves. Ive given the intake a bit of extra clearance by retarding the cams via adjustable cam sprocket. On the surface it seems to be running fine but the head will come off to change the thickness of he head gasket and I will get a closer look. having HLA's may have just saved me from total destruction.

If you are decking a head, plus running larger lift cams you really need to check for valve to piston clearances when building any engine. If you have adjustable cam wheels, mark on the wheels the maximum rotation either way before the tolerances get too tight. It's common for a tuner to adjust the timing of the cam 3-4 degrees plus or minus to see what effect it has on power. If you don't know where the limit is each way then it could all end badly.

For a rough idea you should have around 80 thou (2mm) clearance on intake and slightly more on exhaust, around 100 thou (2.5mm). You can go less if you know what you are doing... but then you wouldn't be reading a forum like this!

If the valves and pistons have been touching, then you need to decide if you will run the valves again. Most likely they will have fatigue stress cracks around the head and there is a chance they will fail in the future. I wouldn't run them in my engine unless I knew the contact was extremely minor. The typical failure is the head of the valve falls off, bounces around in the combustion chamber, jams up against the head and leaves big divots in the head and piston. It's pretty much a destroyed engine if that happens.

The typical failure is the head of the valve falls off, bounces around in the combustion chamber, jams up against the head and leaves big divots in the head and piston. It's pretty much a destroyed engine if that happens.

Don't I know it!...
http://mx5cartalk.com/forum/viewtopic.php?f=29&t=73473

yes i saw that.......

It's also just happened to a mates race car. Timing skipped a tooth and the piston was hitting the exhaust valve, but only at high revs. The head of the valve fell off just as it was heading into the pits and locked the engine up. In this case the head has been welded up and remachined with new pistons and valves.

If you take a photo of the top of the piston, it will tell you how bad the interference is. if it's just a circle then it was only just touching. If there is a decent indent it's bad.

edit: You can also have the same issue if you are floating a valve at high revs if you have tight tolerances.