Head shave

[CWallace]

Hi all,
I'm up to rebuilding my 4.0p and while I'm at it a little hp increase would be nice. Is it worth the hassle shaving the head. If so, how much is sensible and safe with a stock engine. Plan is to get a light cam grind, head shave, extractors and a weber carb.
Any ideas or input would be much appreciated?
Cheers

[Esteban]

Talking only from experience. Years ago my brother and I had Patrols that were 2 years apart. He decided to shave the head of his by 1 mm (0.040"). I kept mine unchanged in every aspect, and was always faster than my brother's. We used to live at 9200 feet above sea level (2800 m) and it was less risky with the loss of compression at that height with what he did for the head. Specifically mine will always reach higher rpms. Torque at low rpms seemed better on his though. It's just an anecdotical case.

The light cam grid and the extractors, now that's a totally different case. No idea whatsoever in that department. Is your plan to increase rpms? The valve springs might become a limiting factor since they are on the soft side.

[CWallace]

I'm chasing a stronger low end torque rather than an increase in rpms. I live at 1000m elevation so not sure what makes a difference here. Thanks for your input. Did yours have any other differences such as air cleaner, exhaust etc?

[Esteban]

I mentioned the altitude, because you loose power with it. Increasing the compression does help a bit, but it might be risky when going to sea level again, with the possibility of blowing a gasket. That chance is very slim in a Patrol with its very low compression to begin with 7.6:1 if I'm not mistaken. Whatever increase you do by shaving the head probably won't cause any troubles.

Mine was always kept standard in every aspect. My brother began with the increase of compression with the shaving of the head. Later on he installed the complete intake and exhaust manifolds of a P40 engine, which is a direct fit, and also with it the two barrel carburetor of the 160 Patrol. There was definitely and improvement in fuel economy and overall smoothness in operation, but still on an incline that you barely could make it in 3rd gear, mine was always slightly better. I never drove myself his Patrol in the same circumstances, so probably had to do with the operator

I think many of us will want to follow your build, specially with the modification of the camshaft.

Have you consider a Marks transmission? Probably difficult to source one these days.

[CWallace]

I'll update on the build soon but need to know how to post pictures better as all mine are too high in resolution. I wasn't thinking of going too much on the head shave, probably .030. I do personally like the 3 speed for the old school factor so I havent considered a 5 speed conversion. Also I do not do many highway speed kms so not too concerned about it in that respect. In relation to valve springs, what rpm do they become an issue. I think that extractors will help it rev a little higher but I don't want to push the old girl too hard. The aim of the cam grind is to get a bit more fuel in at lower rpms to help with low and mid range torque.

[Esteban]

... In relation to valve springs, what rpm do they become an issue. I think that extractors will help it rev a little higher but I don't want to push the old girl too hard. The aim of the cam grind is to get a bit more fuel in at lower rpms to help with low and mid range torque.

I will say that 4000 rpm. Although the engine has its maximum power at 3800 rpm, years ago after rebuilding the head with new valves, valve guides, and springs, I was able to push in 2nd gear up to 4000 rpm. At that moment you could hear a strange noise coming from the valve train, as if the valves were rebounding. My take was that the springs were not able to close the valve fast enough, so a gap was created between the rocker arm and the valve producing the sound. This was done very briefly and only once. After that I've never been able to reach more than 3800 rpms, and nor that I try . Remember that the P engine and the P40 engines are ones of the most undersquare engines out there, so they don't like to be rev too high.

[Peter60]

My G60 came with a modified cam. I thing the PO used LPG and wanted better performance. It also has a Marks 5 speed.

I only now run petrol. It took me AGES to get the timing right. It wasn't till I found a little piece of paper from the PO that said set timing at 15 before TDC instead of 10. Once I found that it worked beautifully.

I do have another standard G60 (3 speed) and I can't tell much difference in power etc, but the Marks might disguise any benefit.

[CWallace]

Well I'm back again. It's been a long time coming but I've finally got my motor back together. One thing led to another and I ended up doing a lot of machine work to get things how I wanted them.
Block was decked 18 thou to get it flat
Block was bored to 60 over with pistons to suit
Mild cam regrind
Lifters were refaced
Head received new exhaust valves and seats while intakes were re seated
I flowed the head myself (lots of hours:))
Now for the surprising part. The engine shop that did my head shaved it 55 thou to yield a 9 to one compression, taking into account the larger bore size and the lower piston to deck clearance.
Chucked on a holley 350 and she started right up for a 20 minute break in. Can't wait to get the rest back together so I can enjoy the torque haha.
Does anyone know where to get extractors or should I fab some up?

[RiverPatrol]

Can't wait to see video!

[quentin.vds]

Gday blokes,

According to Michael Trinidad who raced A G60 in mud runs back in the day the secret is 3mm off the head, headers and springs from a chevy small block.
He also ran a holley 350 economaster. Hes since sent these parts to me and Ill hopefully make a post when the engine is up and running about its performance, but if its all Michael made it out to be it should outperform petrol v8s of the same era.

Cheers,