Important! : Cylinder Head?

3rd May 2010, 15:32

Right, just gathering information.

Im after some headwork but was wondering what would be best?

Big valves or standard valves? Jp4 head?

I have saxo cams/springs/retainers and followers, do these all fit a jp4 head ok?

Anything to watch out for when mating a jp4 head to a j4 block like piston to valve contact?

Or shall I stick with the j4 head and get that re-worked to a top spec?

Any advice = awesomeness

3rd May 2010, 17:09

I've recently had to do some fairly quick learning on this subject but have yet to complete but I'll try to help.
I know that if you are planning to run a JP4 head on a standard J4 bottom end you won't be able to safely run more than standard J4 cams in it as the valve-piston clearance isn't enough.
So you may have to get your pistons pocketed or maybe some high comps if you want to run some decent cams
There are also problems with the inlet manifold not lining up and the inlet manifold stud pattern being different.
This is a very useful thread although its on moaners

http://www.106owners.co.uk/forums/sh...d.php?t=125703

The inlet valves are much bigger on the JP4 head but as far as I'm aware the J4 springs are better, and the exhaust valves are the same

Hope this helps

Moo

3rd May 2010, 17:28

If you're going for headwork (including some larger inlet valves) then I'd stick with a j4 head for the following reasons:

- the j4 head has inlet studs already
- you already have a j4 head
- j4 cams fit perfectly offset wise
- j4 head had breather in the side of the head to join with sump breather
- you know the compression ratio with j4 head/highcomps

I know a lot of the above can be overcome, but with the j4 you can just remove it, send it off for headwork/valvework, get it back, measure clearances, assemble and start engine!!

Just my 2p

3rd May 2010, 17:41

Quote:

Originally Posted by raunchz

If you're going for headwork (including some larger inlet valves) then I'd stick with a j4 head for the following reasons:

- the j4 head has inlet studs already
- you already have a j4 head
- j4 cams fit perfectly offset wise
- j4 head had breather in the side of the head to join with sump breather
- you know the compression ratio with j4 head/highcomps

I know a lot of the above can be overcome, but with the j4 you can just remove it, send it off for headwork/valvework, get it back, measure clearances, assemble and start engine!!

Just my 2p

Pretty much spot on, half the reason why i want to stick with J4 head.

Has anyone fitted JP4 inlet valves to a J4 head?

3rd May 2010, 17:43

dont you usually fit the internals out of the j4 head in to the jp4 head then use a specific headgasket to overcome the valves hitting the pistons?

3rd May 2010, 18:26

Quote:

Originally Posted by Drago

Pretty much spot on, half the reason why i want to stick with J4 head.

Has anyone fitted JP4 inlet valves to a J4 head?

I'm not sure the size of the valves that companies like QEP fit in their 'big valve heads (not their full on hardcore heads) - as they might fit the jp4 inlet valves? Also I'm not 100% about the amount of valve seat area on the j4 head for the larger valve to seat against? Whether or not you can just regrind the valve seat to suit the jp4 inlet valve, get the ports sorted and away you go?

I've not got a jp4 valve and j4 head to hand to have a look

Quote:

Originally Posted by jeffchiz

dont you usually fit the internals out of the j4 head in to the jp4 head then use a specific headgasket to overcome the valves hitting the pistons?

Ja, the standard thing to do is fit all the J4 valvetrain with jp4 valves.

You risk compromising the compression ratio, so when you're spending all the money etc. playing about with it you don't really want a compromise.

GMC do a valve set without domes in them so you could gain some compression back by fitting them, a slightly thicker hg and then the jp4 head and I bet your very close to oem compression ratio?

I've not measured it all up so am just shooting off the top of my head from reading on here. If you were seriously planning on doing it, it might be worth measuring it all up and calculating the compression ratio changes and clearances just to make sure the switch to a jp4 head is actually worth the hassle !

3rd May 2010, 18:35

imo i dont think it would be worth the hassle I'd stick to tried and tested methods by just sending you j4 head off and making that as good as it can be also you dont have to go to the expense of buying a new cylinder head

if some one has done it and can tell you exactly what to do and what to buy then yea it could be worth it but i can see you trying different methods and wasting some money, id have a look through people progress threads as its definitely been done before and PM them would be much easier as most of us are just second guessing at what you need to do

3rd May 2010, 18:36

Colin - it might be worth speaking to Sandy/QEP about the valve sizes and work to be done to the head vs your budget and what sort of figures you're looking for.

They'll be able to give you good information and know first hand about whether larger exhaust valves are needed, the size of inlet valves (got to be careful as I think Toad had his uber larger inlet valves hit the cut-outs in pistons before) etc.

3rd May 2010, 18:57

Thanks very very much for everyones input, its all very appreciated. Its all brilliant stuff.

Its my thoughts too initially, hanging onto the J4 heads as the point Raunchz stated are what i had in mind. Sounds like the JP4 head is alot of hassle!

I have spoke to QEP and they do 31mm inlet valves and 26mm exhaust iirc, is there any actual advantage to bigger valves? I know more air in = more power out but Sandy has had some brilliant results on standard valves!

3rd May 2010, 19:04

Yeh I think Sandy is all for keeping oem sized exhaust valves I think based on some good results he's had with them.

Good article on exhaust valve sizes:
http://www.pumaracing.co.uk/Exvalve.htm

another coupld of good reads by the same man:
http://www.pumaracing.co.uk/PP03.htm

http://www.pumaracing.co.uk/PP02.htm

3rd May 2010, 19:49

Quote:

Originally Posted by raunchz

Yeh I think Sandy is all for keeping oem sized exhaust valves I think based on some good results he's had with them.

Good article on exhaust valve sizes:
http://www.pumaracing.co.uk/Exvalve.htm

another coupld of good reads by the same man:
http://www.pumaracing.co.uk/PP03.htm

http://www.pumaracing.co.uk/PP02.htm

Fantastic as ever Ross! Ill have a read.

I spoke to Sandy a good few months ago, and he said for Rallying he would keep standard valves!

5th May 2010, 07:28

Looking at it simplistically, the valve sizes ultimately dictate maximum flow at a steady state, but the inlet does not flow in a steady state. The standard J4 valves are relatively small for the capactiy, but the with the right port design makes better use of that available area over a wider operating range than with bigger valves on medium spec engines. It's all relative to the cam profiles, inlet tuning and a number of other factors, but a well modified J4 head generally I find to make a more driveable engine than JP4 head, for little or no peak power difference. Maximising a single aspect of the engine, such as valve sizes, results in other aspects becoming more sensitive to the overall result; moderating each aspect makes for a more rounded package and 9 times out of 10 a better engine.
This is tuning, which is slightly different to just making stuff bigger

5th May 2010, 08:31

very good info there, i am running standard size valve just got the head p+p.

i dnt know the gains, but i see what see does once mapped,

6th May 2010, 09:57

Bang on Sandy, thanks for the input. And I like the last statement! Very true...

Will be in contact