Camshafts and Compression

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PRH said:
Here’s the results from the Wallace site, using the 42abdc closing point.
Notice the instructions at the top of the page.

Changing the closing point to 65abdc(282deg advertised) lowers the DCR number over 1 point and the cranking pressure by 30psi.

View attachment 1716360666
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Yep, got those exact same results myself.

I did the ‘Vizard’ calc’s as well and got,
240* @ 0.050 intake
106* LCA
That calc doesn’t account for compression though? I did do it a while ago.
The Comp XE 20-225-4 seems quite close ‘visually’.

240/246* at 0.050’
0.541 / 0.544’’ - 1.6 rockers.
106 LCA
110 LSA
70* overlap
68 ABDC IVC
 
TT5.9mag said:
210-220 is not too much for pump fuel. I have a turbo Honda v6 in my falcon and it pumps 225, run boost, and it does it on California 91 octane. You need to put a better curve in your distributor. All in by 2700 is too early and you should delay the curve a bit around peak torque and add it in as the engine rpms. That’s not to say that you might be able to cut a camshaft more suited to your build, but you should be able to tune around the detonation with a proper curve that allows you to make the same power.
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Could that have to do with having a smaller cylinder volume though? Lots of motorcycles crank over 200psi with no issues, but with only 250-300cc per cylinder. We have 840cc per cylinder here at 220!

Good call on delaying the ignition timing, it’s probably too quick.
 
Valman said:
Pistons are Icon forged flat tops with the valve reliefs.
Head gasket is Felpro composite, 0.039’’ thickness.
The starter motor does struggle when the engine is warmed up. Starts well when cooled down.
I’ve noticed it idles perfectly with the initial at around 22*, of course this much initial doesn’t help with starting it hot. ATM the timing is all in by 2700.
I have a good cooling system, a flow cooler pump (with a vane impeller) good radiator, etc. I overdrive the pump at around 1.2:1.
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I can tell you right now there is no way, no way you can have 20 initial and have full timing at 2700 and not have it rattle.

I don’t know what full timing is, but I’m betting you might and I mean might need 24 total at peak torque.

I’m going to assume from limited information that peak torque is going to be nearer to 3500-3800 if not a bit higher.

Running those pressures your coolant temperature should be no higher ever than 180F and 160F would be even better.

If your cooling system won’t keep it that cool, update it so it will.
 
Valman said:
Could that have to do with having a smaller cylinder volume though? Lots of motorcycles crank over 200psi with no issues, but with only 250-300cc per cylinder. We have 840cc per cylinder here at 220!

Good call on delaying the ignition timing, it’s probably too quick.
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It absolutely can have something to do with volume, efficiency, electronic timing control, and a host of other variables. The point is the same. Working on the curve and delaying the timing when VE is highest (peak torque) is what you need to do. You can add the timing back in later as rpm increases and VE goes away. You’ll probably find that it makes more torque with less timing at those points as well.
 
A guy in WA Bruce Robertson said he had no issues running 240 psi on pump fuel.

Greg from Carby Tuning techniques told me he has run up to 12.5 to 1 on pump fuel. He's also from WA as well.
 
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Newbomb Turk said:
I can tell you right now there is no way, no way you can have 20 initial and have full timing at 2700 and not have it rattle.

I don’t know what full timing is, but I’m betting you might and I mean might need 24 total at peak torque.

I’m going to assume from limited information that peak torque is going to be nearer to 3500-3800 if not a bit higher.

Running those pressures your coolant temperature should be no higher ever than 180F and 160F would be even better.

If your cooling system won’t keep it that cool, update it so it will.
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I have no overheating issues, it won’t go over 185f on a hot day. Usually runs around 160-175f. Cooling system MUST be good in Australia.

The mechanical advance in the distributor is 5deg, so 10deg at the crank. 22 initial, 32 total ATM.
 
Has the obvious question been asked about is it actually detonating and how have you verified it?
 
Valman said:
I have no overheating issues, it won’t go over 185f on a hot day. Usually runs around 160-175f. Cooling system MUST be good in Australia.

The mechanical advance in the distributor is 5deg, so 10deg at the crank. 22 initial, 32 total ATM.
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That’s basically (in at 2700 with any converter at all) locked timing. There’s lots to tune there before giving up on that cam.
 
Valman said:
it would occasionally pre-ignite. It sometimes feels the engine is ‘working against the compression’ when over about 4000rpm. Hope that makes sense.
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This? What do the spark plugs look like?
 
Hysteric said:
This? What do the spark plugs look like?
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Plugs are mid grey, the ground strap has the annealed mark right around the bend. Maybe a bit closer to the threads.
No white, peppery marks on the plug or anything like that which would indicate detonating. But it does ping occasionally, as I pointed out.
It has NGK ‘7’ range plugs in it ATM.
 
Valman said:
Plugs are mid grey, the ground strap has the annealed mark right around the bend. Maybe a bit closer to the threads.
No white, peppery marks on the plug or anything like that which would indicate detonating. But it does ping occasionally, as I pointed out.
It has NGK ‘7’ range plugs in it ATM.
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You need to post a picture.

I’m deferring to Hysteric to read it because I don’t read plugs with your fuel. He does.

You could be rich, you could be lean. You fuel is different from our fuel and the plug reads differently.
 
The detonation will look the same though. It will pepper the porcelain the same on any fuel.
 
Newbomb Turk said:
You need to post a picture.

I’m deferring to Hysteric to read it because I don’t read plugs with your fuel. He does.

You could be rich, you could be lean. You fuel is different from our fuel and the plug reads differently.
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Thanks. I can read plugs, I won’t say I’m a guru at it though. I know the fundamental stuff well enough. It’s probably a bit lean. I’ll grab a plug.
 
Newbomb Turk said:
I’m deferring to Hysteric to read it because I don’t read plugs with your fuel. He does.
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Its the same. Plugs tan in America like they do in Australia. Grey is usually the plug working in exhaust gas residual, ie the chamber doesn't exhaust very well and the left over exhaust hangs around and is present at the next ignition event so leaves a grey colour.

Bruce discussed this with Mattax about his engine a long time ago. If you don't evacuate the cylinder what is left over becomes part of the next cycles AFR.

1738446139609.png


What are you using for headers and exhaust Valman?
 
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