jonbill

I've had the RT mount for few years and used 3 or 4 diffs over that time. The diff is squashed between the RT mount and the Nissan mount. I have no noises unloading the diff (with any of the diffs) , but on the first diff and the current one I could get the clunk on loading it. The one that had no clunk ever did develop a serious whine and on checking, the pinion is worn. My conclusion is that the clunk in my case is down to the clearance between pinion and crown wheel, and I'm happy to live with a clunk occasionally if It means I'm not killing the diff!

are '73 style' pistons flat top? If so, it'll be pretty close I think. I'd mock it up with plasticine and check how much clearance there is.

Is your question about clearance between valve and rocker or valve and pistons?

I suppose you might get lucky and only have to take material off the new cap. maybe you could weld the new cap in prep. But I'd think just buying a complete l28 block would be easier and cheaper.

Here's an unmodified P90 (I think it's unmodified anyway!) So yours has been filled in quite a lot on the left side, and maybe also around the spark plug boss (but that also could just be a big skim maybe?) I'm surprised there's not more of a chamfer on that infill - isn't 'unshrouding' the valves part of head porting 101?

quite a lot I'd think, its a good start for a 300 bhp engine.

Yes! welding and grinding by someone talented, not me 😊

Yes, agree p79 also very good. Being pedantic, you don't *have* to skim it and shim it. There are better (if more expensive) alternatives.

Os giken TC24 is that sort of money. P90 is a great head. My one is anyway 🙂

what I read was that manifold pressure tends to atmospheric long before full throttle, so you get relatively poor resolution at higher throttle openings. I expect its less of a problem with smaller choke sizes and clearly many people have joined TBs and MAP etc working fine. I don't know microsquirt, I'm using Speeduino. If Microsquirt is MAP only, you might not have a choice.

I think there are downsides to joining the TBs, and limitations to using MAP for load. on my engine, I've only got the brake booster on #6 vacuum tap. I'l use TPS for load and my regulator is a constant 46psi. dunno about AC tho!

at the bottom end, there isn't a difference between compression stroke or exhaust stroke. theres just pistons going up and down. the cam timing determines whether a piston up stroke is compression or exhaust. so if the piston #1 is at TDC (determined by your screwdriver) and the cam dowel is correctly engaged with the cam pulley and the marks line up on the cam pulley and the thrust plate, then #1 is at TDC on compression stroke. Then if the distributor drive spindle is aligned 11:25 with the tang offset to the correct side (which side? can't remember!) then the spark timing is in the right ball park and the engine should attempt to run if you have sparks and fuel.

I agree, think that timing cover is going to have to come out to remove the debris and straighten the key.

The woodruff key is present on the crank, so the crank pulley can only go on in one position. And if the engine is at TDC then the crank pulley is in the right position and maybe the pointer is in the wrong position. on earlier engines, the pointer on the timing cover and the pulley marks are on the left (10 oclock) at TDC and on later engines, they're on the right (3 oclock). so it sounds like you've got an early pulley with later timiny cover/timing marks.

that seal doesn't look right to me - is it the same size as the timing cover hole?

I'm afraid I don't know your setup and how its adjusted, but yes, I'd be trying to get it at least to mid 13s.

well, depends on your gearing of course, but typically 2500 to 3500 rpm. But you do need to measure it on the road - it's not valid if the engine has no load. (just checking!)

I would yes, unless you've got to get through a strict emission test, in which case aim for 14.7 at idle. Modern OEMs run leanest at cruise - lots of ignition advance and a little leaner than 14.7.

TBH those values look pretty good. I wouldn't go leaner than low 14s at idle. Mid 14s at cruise, no need to go leaner unless you're doing big mileage and want to save a few pennies.

What sensor can you put in the inlet tract to measure the air/fuel ratio?

thats too far in, should sit flush with the outside face of the timing cover. I think thats in danger of falling in!

Thats partly true. as I said, if you don't have a high enough energy coil discharge, the spark won't be able to jump a 1.1mm gap. so you could buy - 11 plugs for that or regap any other plug. The heat rating of the plug (5,6,7 etc) is dependent on combustion pressure and temperature, not so much the ignition system.

In the same way that taking your temperature is a reliable indication of whether you have an infection.

The residual oxygen in the exhaust is a reliable indicator of the ratio of fuel and air at the inlet. This is true given a working and reasonable ignition and cam timing. Engine Management systems do work on this basis. I mean, as well as that being an assumption they make, they actually do work well in optimising fuel mixtures.

I think its mainly a function of the coil and the voltage. points running at only 8v, there's not enough energy to jump the gap at peak cylinder pressure. start at 1.1mm, and if you don't misfire anywhere in the rpm range, leave it there and be happy. if you misfire around peak torque, close the gap a bit until the misfire goes away, then leave it and be happy.