Lets talk about cams

[speed]

Not sure if I should be offended by that comment. Was just passing on the word of an experienced race engine builder and thought relevant to this thread.

[NitroDann]

Aimed at him not you.

[RS2000]

Just for interest sake.... porting & polishing is not always the thing to do.

It's a well known fact, that with the old Ford SOHC (Escort 2L, CI head, carbies), inlet porting & polishing is the best way to lose power.
The factory inlet port is already too large, & increasing port size slows down gas speed & causes fuel to drop out of suspension.
Also polishing allows the dropped out fuel to stay liquid on the surface, whereas the rough cast surface is more likely to reintroduce fuel back into the air stream.

But probably totally irrelevant to the more modern MX5 engine

[StanTheMan]

I think for us mere mortals it sounds like removing big uneven scarring and perhaps matching the gaskets to the ports can reap some benefits if it's particularly bad.

[manga_blue]

RS2000, inlet ports should never be polished for those very reasons, including on MX5s. Rough finishing with 80 or 120 grit is the best way to leave them. Exhaust ports do benefit from fine polishing but they clag up so quickly with crud that the benefits are pretty short lived.

[datfreak]

I think the Honda manifold is really only a sensible option if you have a ported head with big cams.....Over a stock NA8 intake I picked up over to 40hp in parts of the dyno curve but also made the power curve more cyclic.... so the NA8 intake was restricting the flow a lot but was also far more consistant....
The car wants to get into a leaping cadence so I tend to back off and coast for sections then power up to speed and repeat rather than sitting at part throttle.

This is the problem with cam choice... you really need to know your target usage and rev range before buying anything over 272 degrees.

Also, I think you need to be in the over 170whp category for the Honda manifold to work well and then I think ITBs might be a better choice for anything but the most extreme track car targetting high revs like mine.

Thanks for your thoughts.
I have a oversized valve head that has been ported coming. It also has SUBS, so I can use reground cams with a smaller base circle.
The plan was get my spare na8 cams (I'll use x 2 exhaust ones as they have more meat) reground to about 270 deg/10mm , shave the head 1.5mm, use 2001+ pistons (second hand if i can find some).
So copying Quinn's setup except using oversized valves/porting.
This is a street car which I'm willing to except a medium level of compromise of drivability. I've owned cammy street cars before, and know the character and fun they have isn't as special when I'm tired.

A decision is which intake manifold - ive got a na8 one for now. The gains you got from yours, really show how much extra power that can be had.
Obvious in a street setup like mine the gain would not be that awesome, but def something to look into - maybe making a manifold from scratch but using a longer length/smaller ID runner to bring the power band under 8k.

[StanTheMan]

Cams were installed a few weeks ago.
Was surprised at how stock like it runs on zero
Installed adjustable cam gears today.

Theory was to dial in some lumpyness by increasing the overlap or decrease the LSA.
I also wanted slightly more response at the top like over 5000 rpm but not loose too much torque below 5000 rpm

I figured I would advance the intake a bit. & regatard the ex. This should theoretically get slightly more torque Down low. Retarding the ex. Would increase the overlap , give me a lumpy idle & go hard at the top without hopefully loosing too much down low
Started with in +2 ex--2
What happened.
Idle was lumpy
Idle was all over the place. Very erratic
Take off .....like a bitch backfire drivability below 2k was crap plenty of power though & very lively at the top
Sound was awesome at various speeds. I could certainly live with the sound. But not the characteristics of below 3000 rpm

I mucked around with settings a bit. Until I figured......How much overlap can it handle? Standard ECU & standard CR?
It turns I'm unable to dial in any extra overlap to what is already preset in the cams. Which I think is like 12 deg @ 0.050
Or the LSA is at 107

So I'm now back to standard LSA but retarding both in & ex the same amount. This has taken away some torque down low but added extra response up the top.
Drivability idle & take off are now back to stock like behavour

Keep in mind. Patchy is not going to a Dyno until CR has been upped. And eventually will have a stand alone ECU.

The fact that I can't dial any additional overlap may have something to do with CR or that it's too much for the standard ECU to handle And/or bit of both.

I'll keep you updated.

[StanTheMan]

So I did manage to dial in some overlap.
I just couldn't do it by advancing the intake.

Advancing the intake caused issues with the ram effect? Crappy idle & backfiring on takeoff. But very nice high rpm characteristics. Low rpm characteristics simply not tolerable.

Currently I'm on -2/-7
idle is slightly lumpy
Idles on about 950 give or take a bit
Power comes on from about 4500
Low rpm characteristic is stock-like
High rpm appears to be livelier than before but I haven't dríven it much yet

I'll keep it like this for a while. Probably will not be able to do much else until it gets on a Dyno

[Alex 2550]

Thanks heaps for the update Stan, sounds like you have got it pretty right there and will have some more in it when you get the computer. shame we can't catch up at the monkey on the weekend (hope you have a good one) but hopefully one day down the track.
i really appreciate the updates as im still thinking ill go the same type cam as yours but i have decided to go SUB's and aftermarket springs of some sought. with everything going on at the moment (building stables, wedding, cape york trip and possibly a new turbo on Patrol) i don't have the time to take the head off and don't want it to be one of those never ending projects due to time so will put the install off for probably 12 months.
Still buying all the parts now as they come up but i want to clean the ports up and match them, un-shroud the valves and have the head re-conditioned and take my time to enjoy the process not rush it. i will also do the timing belt ect while there and the coolant reroute while head is off purely for the ease of access.
hoping to get to WTAC in October and see Magpie in action so maybe we will get a chance to catch up then.

[StanTheMan]

Just incase you misses it from the Fawlty Towers Risk management thread

So I managed to hit the limitations on the ECU with the cams.
The cams are 272/264 10/9 mm lift 106/108 lobe 52 deg overlap all advertised specs

To say that these cams can just bolt in is pehaps misleading. The head on my NA6 has had the lifter guides shaved to make room for aggressive lifts in a previous build. So it's not entirely just a bolt in.
I don't intend on going very far over 7500 rpm. I've left the springs untouched for now. Previous build had the engine reving at around 8000 rpm but I'm unable to say the springs are OEM or replacements.

The cams installed on centre are fine. Decent midrange torque & generally more perky all round.more free reving at top too.

I introduced extra 7 deg of overlap with adjustable cams gears . Sprited driving put a massive smile on my dial.on that set up.
But I've hit the limitations on the OEM ECU. It is bucking when coasting at 1500 rpm in peak hr traffic. Even playing around with the AFM Spring would move that rpm around a bit but not sort it out the bucking altogether.

Standard compression doesn't seem to want to cope with any more advance on the intake. It is on zero. This is nothing to do with the ECU though. It's more to do with standard compression currently. I think.

This is where I'll leave it for the moment until I get the compression ratio upped. Then I will look at the stand alone ECU.
The ECU scares the sh*t out of me. Yes I want it a little more hectic at the top. I want drivability with more go. Will consider having 2 maps, one for 98 another for E85. If that's possible at all.
Wouldn't it be great to press a button & just have the right map? Rather than uploading a map via laptop. When the time comes ?. I'll go & see the man up north when it comes to the ECU.

So now it's back to the more mundane stuff like crinkle paint on the cam cover & getting that crappy paint job a bit better.
I'm loving this journey. Bit by bit , learning in the process . My previous journey was like. Bolt it all in...... Then realise ....fark what have I done..... In over my head.

[hks_kansei]

Curious.

If the base circle remains the same as stock, are the factory lifters (shim over bucket) ok to use? or do you still need to go shim-under to stop it spitting a shim?

(Of course, whatever option you'll need to change shims to keep tolerances right, but the retention of shim-over would mean saving the few hundred to convert to shim-under)



I've considered a mild set on the OEM ecu for ages, but when I looked the cost/power was too much for the 5-10kw gain you'd probably get.
$400ish for cams
$300ish for shim under
plus some ancilliaries.


And yeah, doing bigger cams with ECU etc is well beyond the budget.