Cam advice sought for petrol XN1 504 engine please

Trent172

Trent172

Member
Fellow Frogger
Tadpole
Tadpole
Joined
Nov 29, 2020
Messages
158
Location
Adelaide
Hi all, I’m looking at 2 options.
First option is a 505 SLI cam - anyone have the cam specs for this one?
Second is a wade (Clive Cams) 112 cam.

Engine will have square port head, big bore exhaust and Weber 32/36.

what would be the better option for smoothness, power, torque and overall driveability?
 
I found this snippet of info in my collection.
valve timing.png
 
I suspect the XN6 (SLi) cam would be pretty tame. The K-Jet system didn't like pulsing airflow at idle, so they usually had very gentle cam profiles to maintain smooth airflow at idle and low RPMs to have any chance of coming close to passing emission requirements. The injected XN6 produced the same power but less torque than it's contemporary carburettored equivalent XN1.
 
Haven't used it personally, but have heard good things. I feel that a little more compression and mapped ignition would really bring an XN to life. Do you have any other details of your build?
 
Btw, I think you may have done some work on my old 72 504 about 15 yrs ago when you were living in Adel. It was a brown manual. What Im planning at this stage is cam, recond square port head (done) big bore exhaust and 2 inch system, new m48 ducellier dizzy. Thinking of a new fuel and oil pump and a new coil and leads. Nothing radical.
 
I vaguely remember that!

See if you can find an electronic ignition system from a 505 SR. It is just better in every way, one of the best investments you can make to a standard-ish XN1 motor.
 
The 112 is good, the 240 may squeeze a little more performance out of your XN1 with the big bore and square port. Do you know what the compression ratio is or how much the head has been skimmed? I agree with Scott about the 505 SR dizzy; not sure that you can convert the M48 to the same ignition curve, reprofiling it is pretty complicated.
 
Thanos will the 240 maintain a smooth idle? Do you know what the difference is between both cams?
 
Trent172 said:
Thanos will the 240 maintain a smooth idle? Do you know what the difference is between both cams?
Click to expand...
The 240 will maintain a smooth idle at 900-1000 rpm. The 240 is a fairly mild cam: 280 degree duration, 0.352 valve lift, 61 degree overlap. The 112 specs are 266 degree duration, 0.356 valve lift, 46 degree overlap.
 
Yes. Do you know the current thickness ?

And BTW, I suggest you take a really, really close look at the thread in the rear exhaust-side head bolt hole in the block. They are known to degrade due to heat. Being in the rear and next to the exhaust, it gets hotter. If not perfect, helicoil. Often people only discover this when they are tightening down the head.

And what torque are you going to do the head bolts up to ?
 
Last edited:
No I’m sorry I don’t know the thickness. What torque should be applied to the head bolts? I’m not doing the rebuild someone else is but I will discuss the head bolt hole issue with them. Thanks for the tip Beano.
 
Those blocks ain't getting any younger.
We have previously had debate on this forum about head bolt torque, with some saying that the angle tightening method is best. That is to say, doing it up to a certain middling torque, then turning the bolt a certain number of degrees.

From memory, the infallible :LOL::rolleyes: Haynes manual says 55 ft/lbs torque, which of course is absurd. A local Pug mechanic here used to regularly do them up to 60 or 65, and said that there was no problem doing them up to 70 ft/lbs. And that is what I used to do.

If too much is shaved off the head, the engine is then prone to ping, which is irritating as it sounds metallic. I think that heads started out as 92.5 mm thick and you could take them down to 90 before pinging started, but don't quote me on this. Please somebody correct me if I'm wrong.

Heads can be shaved further but then either an aluminium shim (shaped like a head gasket) is needed (or else two head gaskets, with more torque added, but that's not ideal) . So you are better off with a shim, plus liberal Hylomar squirted on all mating surfaces.
 
Beano said:
Haynes manual says 55 ft/lbs torque, which of course is absurd. A local Pug mechanic here used to regularly do them up to 60 or 65, and said that there was no problem doing them up to 70 ft/lbs. And that is what I used to do.

If too much is shaved off the head, the engine is then prone to ping, which is irritating as it sounds metallic. I think that heads started out as 92.5 mm thick and you could take them down to 90 before pinging started, but don't quote me on this. Please somebody correct me if I'm wrong.

Heads can be shaved further but then either an aluminium shim (shaped like a head gasket) is needed (or else two head gaskets, with more torque added, but that's not ideal) . So you are better off with a shim, plus liberal Hylomar squirted on all mating surfaces.
Click to expand...
I think 70 ft.lbs is a good number, we use 80 routinely on the rally engines with copper gaskets and o-ringed liners.
Pinging is lethal to engines, yet another reason to go with a bigger ham than stock. If your head has been skimmed to 90.8 to 92.0 mm the compression ratio will be 9.5:1 at the most, and the 240 can easily handle that without the need for a shim or two gaskets.
 
Demannu said:
I suspect the XN6 (SLi) cam would be pretty tame. The K-Jet system didn't like pulsing airflow at idle, so they usually had very gentle cam profiles to maintain smooth airflow at idle and low RPMs to have any chance of coming close to passing emission requirements. The injected XN6 produced the same power but less torque than it's contemporary carburettored equivalent XN1.
Click to expand...
Yes, I built an 1800 with this cam and it was very tame. Best 1600 I built had the XM7 cam and it went very well as did the brand new 73 model 404 that I drove as a rental car in Noumea. This is supposed to be the detuned version of the 1600 but the cam specs look Ok in the table.
 
Demannu said:
I vaguely remember that!

See if you can find an electronic ignition system from a 505 SR. It is just better in every way, one of the best investments you can make to a standard-ish XN1 motor.
Click to expand...
I've never found an SR dissy which wasn't worn out, they all performed poorly. 123 ignition full solid state with only the rotor as a moving part are around $550.
 
You must log in or register to reply here.
Top