The V8 Owners Forum -

Hi,
I'm starting to build a 4.6 to go in my Thor p38, I have bought a top hat liner-ed engine that has previously been back dated to fit in a Range Rover classic, it was built by RPI but has early heads, ERC 0216 Stage one prepped.

The question is which heads to use? should I just skim and rebuild the proper 4.6 heads or skim down the early stage one heads to get the compression ratio back? I think I'm right in thinking the 4.6 heads have bigger valves? Also they have the smaller cc chambers so which way should I go? Also is it actually acceptable to skim down early heads to suit?

I suppose I really need to take the early heads off to check the valve sizes before being able to make a final decision.

I'm not after every ounce of power but dont want too waste any either!!

Steve

Steve,

No real difference in the early later heads apart from combustion chamber size and the mounting holes for ancillarys, the valves are the same size but the later heads have the push on stem seals but they can come adrift.

The early heads have an extra outer row of bolt holes which can be ignored

The late heads have 28cc chambers for use with composite gaskets which are thicker, if you have or use the thinner tin gaskets with the early heads you end up with the same compression of approx 9.35/1

Can you see what head gaskets you have?

Kevin.

Thanks for that Kevin,

Nice reply looks like all in my favour to use the stage one heads, I will be taking them off just for inspection anyway so even if they used comp gaskets on the last build then I can still use steel this time, I will get them checked for flatness as well before putting them back on, I guess if they need skimming the best option will be to get them skimmed enough to use the comp gaskets to get the best of both worlds?

Glad I checked as I had in my head that the newer heads had bigger valves as well as the smaller chambers.

Thanks again!

Steve

Steve,

If your going to have the heads skimmed then approx 30thou. with tin gaskets will get you close to 10/1 which will be beneficial on LPG.

Don't forget that skimming the heads will effect the lifter preload, anything between 20-60 thou is ok and if you do not rev the engine very high you can get away with using shims under the rocker pillars to reduce the preload.

A 30 thou. skim will increase the preload by 48 thou. ie 30 x 1.6 (Rocker ratio)

Do check out the timing issues on gas as you can find a lot of power by optimising the timing for gas, on the basis that the engine is only started on petrol and not put on load and wont incur detonation because of the increased advance.

Having just reread your first post it would be wise to check the combustion chamber size before doing any skimming as they may have had a skim anyway, look for shims under the rocker pillars this may be a sign that they have had a skim.

Is it a standard cam?

Kevin.

Hi
I would go for the stage 1s, I would check the guides as if they have been used with a higher lift can they may have worn a bit more, but apart from that they should be better you can skim them down to match the later gasket, then you won't have to use shims under the rocker shaft pillers.
Best regards
Mike

Use the later heads, refitting all the front end twirly bits will be a real PITA with the early head bolt pattern, for very little gain headwise IMHO.

Assuming it has the P38 dizzyless front end & serp brackets....

spend wrote:Use the later heads, refitting all the front end twirly bits will be a real PITA with the early head bolt pattern, for very little gain headwise IMHO.

Assuming it has the P38 dizzyless front end & serp brackets....

Just when I thought I had an answer some one else had to throw this in the mix

I was wondering about the bolt holes for all the front end bits, I had looked at them the other day to see if they would work, I assume you are on about the 3 bolt holes on each end of the heads to bolt the alternator, power steering pump etc onto? I checked that they were the same pattern but without taking any measurements just a visual check I thought they looked ok, are you thinking they are different layout or spacing?

As I think Kevin has said I would be leaving out the outer row of head bolts, as I have done in the past with other 3.5's. Kevin I see you seem happy that they are the same bolt pattern.

Yes, it is the serp front end using the later Thor set up, 1999 p38 not yet on lpg but may be later in life if I ever get around to it!!

Kevin, I think I'm right, but not 100% sure, that the Thor setup will look after the timing through the sensors etc? Will it continue the same on LPG?

Cam.........
Now that was going to be the next thread question, but being as it has been brought up now here we go!!

The stage one engine has a Piper RP4 cam with J & P timing set in at the moment, I have the rpi Build sheet which states this unless it has since been changed!, problem is I have to change the cam and followers etc as I will be using the serp front end not the early front so I am let to believe that the drive will be wrong so may as well go for a bigger cam while I'm in there!!

So what cam do you all suggest?

Car will be used mostly for round town and long distances, a fair amount of towing, and usually when towing it will be working hard well and truly loaded to the max or even above! a bit of off road but not any huge amount, the towing is the main reason for having the thing in the 1st place...that and I just like Range Rovers, I have 5 in various states!! As you can see the use will be quite varied so cam choice needs a bit of thought or possibly just stick with standard, but I do like more performance!!

STEVE

The Real Steel blower cam is a nice set up for a good torquey engine and won't run out of steam too early. Don't be mislead by the name, it is a really good all round profile.

Alan

[I was wondering about the bolt holes for all the front end bits, I had looked at them the other day to see if they would work, I assume you are on about the 3 bolt holes on each end of the heads to bolt the alternator, power steering pump etc onto? I checked that they were the same pattern but without taking any measurements just a visual check I thought they looked ok, are you thinking they are different layout or spacing?

STEVE[/quote]

My later heads have 4 bolt holes at one end and one of the threads at the other end is a larger diameter ???

Denis

I've had a chance to have another look at the engine, I've taken the heads and sump off, all looks nice and clean so far no nasty surprises so far!

I've done a bit of a check and the heads measure up at 35cc's they have been punch stamped 35cc on the front ends as well!

The pistons seem deeper than the ones on the engine in the car, the trouble is the heads are back on in the car so I cannot compare them! I did a bit of a check and the dish in them seems to measure up at 34 to 35 cc's I've taken a couple of pics hopefully I can post them on here.








The piston at tdc seems to stick slightly proud of the block, again as the other heads are back together on the engine in the car I can't compare them.

So any one shed any light on what the pistons are? will they give me enough compression?

Steve[/img]

Just been looking at the real steel blower cam, I see they say that I will need to use double springs and different caps, this will add another £130 or so, I'm on a bit of a budget but if it really makes that much difference I won't cut corners.

But I have been considering the Piper 285 which seems to work without any thing else required, I am happy that I will have to check and set up the preloaad whichever cam I use.

I will obviously be using new followers and chain etc with whichever cam I use so only the cost of the actual cam that makes any difference to me.
Also I assume that the blower cam is available for the serp front end with pulley for the Thor setup?

Steve

gulf blue rsr wrote:Just been looking at the real steel blower cam, I see they say that I will need to use double springs and different caps, this will add another £130 or so, I'm on a bit of a budget but if it really makes that much difference I won't cut corners.

Steve

There is a point of view out there that forced induction pressure will tend to keep the valves off their seat, hence the desire for double valve springs. I don't agree with this as I believe there is increased pressure on both sides of the valve head.

Denis

"There is a point of view out there that forced induction pressure will tend to keep the valves off their seat,"
And a fly hitting the windscreen of a truck at 70 slightly reduces the speed of the truck! but not enough to be worth considering. if it were a millercycle engine running 30+ lbs boost I might consider it but not with an atmosphere of boost and normal cam timing.
best regards
Mike

From those last 2 replies then I guess it is just the cam I require then and forget the springs and caps......which is nice!!

So then are we all agreed that the Real Steel Blower cam is the prefered option over the Piper 285?


Steve

Ohh and forgot to ask any ideas on the pistons?

I'm thinking perhaps the best option with the heads/pistons will perhaps be wait till I have the proper late 4.6 heads off when I'm taking the engine back out so I can compare everything then make the decision, only thing is I was hoping to built as much as possible before stripping the car and making it a 2 ton lump that I can't move around!

Steve