Ph4 Cams

[Mochachino]

Posted this on a few forums but theyre not overly busy.

Basically whats required to work Ph4 cams with a JP4 head on a J4 bottom end? Or would it make more sense to rework the J4 head?

Already got JP4 head and Jenvey bodies. ARP bolts, standard rods, forged pocketed pistons (which ones), J4 valve springs are on the list - what else if JP4 head is the way forward? If not then whats needed with the J4 head?

[jsdvtr]

Well running ph4 cams would need either high comp pistons or standards pocketed.

With the jp4 head i think say if running ph3/708 you would have to be careful with the cams hitting the pistons but this would be a problem unless using a thicker head gasket but that would lower the compression but with ph4 and high comps this would be a problem. Im looking at buying a jp4 head and putting j4 internals in.

Im not all 100% on this but im sure someone would know if this is correct or not.

[Mochachino]

Well running ph4 cams would need either high comp pistons or standards pocketed.

With the jp4 head i think say if running ph3/708 you would have to be careful with the cams hitting the pistons but this would be a problem unless using a thicker head gasket but that would lower the compression but with ph4 and high comps this would be a problem. Im looking at buying a jp4 head and putting j4 internals in.

Im not all 100% on this but im sure someone would know if this is correct or not.

Yeh I know about the pistons, but the problem will be the compression. What was toads setup?

The results were total lift of 2.80mm inlet and 3.05mm exhaust, with the standard JP4 gasket and an un-skimmed head.

Personally I'm not happy to have less than 1.5mm inlet and 1.8mm exhaust valve to piston clearance at TDC, so subtracting that, leaves you 1.3mm inlet and 1.25mm exhaust lift available. Somewhat less than the Catcam 1321708 spec timing of 1.55mm inlet and 2.00mm exhaust.

If you backed off both cams enough to have safe clearance, you'd be looking at peak angles of 114 degrees inlet and 116 degrees exhaust, which isn't great for getting a decent spread of power and lively performance.

:S

[Mochachino]

Finally found toads spec list:

Fully re-built TU5JP4 lump
Low friction big ends
Re-bored to 80mm
80mm Wossner Hi-Comp pistons (running 12.3:1 cr)
Forged conrods and ARP rod bolts
Modified head to accept bigger valves
Newman uprated valve springs

so going from this, would it be wise to get the whole JP4 engine? Or can you put the J4 rods in a JP4 bottom end so that theyre stronger than JP4 but not costly as forged would be?

Or with a J4 engine same spec without the forged conrods?

[benkelsall]

Id have thought PH4s, Hi-Comp Pistons, JP4 head, and JP4 rods with a J4 bottom end would work fine.
To be on the safe side though I'd want to try and get forged rods too.
JP4 head be better id say as already got bigger valves unless you use a J4 head and get headwork done by Sandy or who ever.

Want the same engine spec as toad then but without forged rods just standard ones.

Or to save money something like this would be good, just fit the bodies and its done.
http://www.106owners.co.uk/forums/showthread.php?172085-ricky-p-built-high-comp-gti-engine-180bhp-possible&highlight=

[AlexB]

If you get a jp4 head j4 pistons wont work as per dave origonal e gine that went pop on the rollers the piston cutouts arent large enough to clear the jp4 valve

[jsdvtr]

If you get a jp4 head j4 pistons wont work as per dave origonal e gine that went pop on the rollers the piston cutouts arent large enough to clear the jp4 valve

Would you not fit the j4 valves into it though? Just fit all the j4 stuff into the jp4 head.

[dannygti]

Would you not fit the j4 valves into it though? Just fit all the j4 stuff into the jp4 head.

not the valves lol, thats the only advantage of that head. you would change the valve springs/retainers etc though

[raunchz]

if going for ph4s, Id just stick with a j4 engine.

To get the most out of them you'd ideally get some headwork, so would be an ideal time to spec up a head to make the most of the setup, a dry build would highlight any potential piston/valve incompatibility.

the jp4 rods have a different small end size to the j4 rods, so if using jp4 rods, you'd need the matching jp4 hi comps which you'd hope would match the bigger inlet valves of the jp4 head and make the compression ratio around the right figure.

[jsdvtr]

not the valves lol, thats the only advantage of that head. you would change the valve springs/retainers etc though

Are the exhaust and inlet parts slightly bigger too? letting more in and out?

[raunchz]

Are the exhaust and inlet parts slightly bigger too? letting more in and out?

inlet bigger, exhaust the same size

[jsdvtr]

inlet bigger, exhaust the same size

Do you think you would see much of a gain over a j4 head bhp wise?

[raunchz]

Do you think you would see much of a gain over a j4 head bhp wise?

It's hard to say as I don't remember reading any definitive proof over the benefits of jp4 over j4.

Other than bigger inlet valves, but is bigger always better?

[adamskiTNR]

Only if matched to cylinder capacity, cam profile and inlet size

[jsdvtr]

if going for ph4s, Id just stick with a j4 engine.

To get the most out of them you'd ideally get some headwork, so would be an ideal time to spec up a head to make the most of the setup, a dry build would highlight any potential piston/valve incompatibility.


What sort of headwork would get the best out of them? I dont know much other than just a port and polish as tbh not many people get headwork done other than high spec cars so its quite unheard of on sites like this.

Would be good to read up on some cars with sandy built engines to get abit more knowledge about it.

[raunchz]

What sort of headwork would get the best out of them? I dont know much other than just a port and polish as tbh not many people get headwork done other than high spec cars so its quite unheard of on sites like this.

Would be good to read up on some cars with sandy built engines to get abit more knowledge about it.

Well it's all to do with the shape of the ports, texture of walls, size on inlet, the intake itself etc.

a 'port and polish' doesn't mean much as you could 'port and polish' the inlet ports and actually make them worse than if you'd not have touched them at all.

Bigger valves doesn't necessarily mean more power - the ports themselves need to suit the larger valves, and the cams need to match etc. The intake needs to compliment the bigger valves, I think it's all to do with air speed and the quality of the air mixing with the injected fuel.

It's a big topic, that IMO is all based on experience, tests and people experimenting to see what's best in terms of power, usable power etc.

[raunchz]

It is worth remembering that the jp4 combustion chambers are a different shape than the j4 head - whether it's a better thing or not then who knows.

I think also, that the J4 engine was like a 'test' engine before PSA introduced a lot of cars with the JP4 engine, so I'd like to think the spec of the J4 head was changed to the jp4 head to try and increase a bit more low down torque and maybe meet some of the increasing emission regulations?

I'm just speculating here, the proof is in getting a jp4 head and j4 head with the same spec and seeing how the results differ.

[Mochachino]

Thanks for all the input here, sounds like ph4 are back on the plan now but with a J4 full engine and therefore sell the jp4 head now.

So to sumerise:

J4 engine
Forged pocketed pistons
ARP bolts
Will keep standard rods as it wont be revved over 8k and should be ok right?
Get some headwork done

Thats all right?

Also the port and polishing thing isnt as simple as gettin your dremel out on a head, get a flow bench in the kitchen instead lol

[AndySAXO]

Yer standard rods will be ok for the engine not revving over 8k

Maybe worth new con rod bolts and all new bearings get some acl race ones, which are the same as toad engine has.

Talk to some one like sandy about the head work if you send him the head and cams he can do the head work to match the cams profiles.

Depends on the money

[Mochachino]

Thanks mate!

Any ideas on how much headwork will cost? I guess under a grand?

[AndySAXO]

Also it not always about bigger valves too.

Pm sandy for prices

[mark1311]

i no alot of u hate hi flow head but there sites quite good for rough idea on prices ect

[LeeM]

youll need hi comp pocketed pistons, pockets to deal with increased lift and hi comp to compensate for the increased overlap

[AndySAXO]

youll need hi comp pocketed pistons, pockets to deal with increased lift and hi comp to compensate for the increased overlap

no you dnt you will to get the full benifits but can be ran on standard pistons but again to get the full benifit out of ph4 you will need pocket pistons

[LeeM]

i see, i was under the impression the increased overlap gives less time for the fuel and air to be compressed, so the high comps will make up for that. still learning though

[Colin]

Overlap means inlet and exhaust valves are open at the same time. This creates the scavenging effect and gets the next cycle of gases out quicker (exhaust) or brings them in faster (induction)

So using high compression pistons do help this effect.

P.s I dont mean to sound like a cock!

[AndySAXO]

Yer the hi comps will help yes, but to the answer I gave it was just that you can use them on standard pistons but by no means say it the best way to go, they will have to be timing to match ph3 cams in term of lift.

[Colin]

Agreed Andy, yeah coz you can only run a certain amount of lift and duration on standard pistons without ptv. Ph4 on stds would be backed right off and run bad

[Olly]

My simple way of explaining it is,
high comps dont increase the compression they maintain the same dynamic compression but with a higher overlap. This is obviously not the law.

[JoshB]

So if I were to purchase Hi-Comp pistons to put in my J4 bottom end, I should get ones designed to fit the JP4 bottom end so the inlet valve cut-out matches?

[raunchz]

jp4 rods use a 18mm pins from memory,

so you couldn't use jp4 pistons with j4 rods.

[JoshB]

So how could you get round the issue?

[mark1311]

why are you wonting to mix and match the engines? i would stick with he engine you have tbh mate as its a reali good engine with low milage ect, for all hassle of mixing matching heads and bottom end i would just stick with your orginal engine and rebuild tht mate,...

[raunchz]

So how could you get round the issue?

I presume you want to fit a jp4 head to the j4 bottom end?

In that case I'd do one of 2 things, stick with a j4 head, and get some headwork done on it byt keep standard valve sizes.

OR

Go all out and get some jp4 forged rods etc.

[JoshB]

why are you wonting to mix and match the engines? i would stick with he engine you have tbh mate as its a reali good engine with low milage ect, for all hassle of mixing matching heads and bottom end i would just stick with your orginal engine and rebuild tht mate,...

After I'd bought the car I found out the cambelt had snapped. The engine did run rough and stalled everytime it idled. I'm guessing that theres a few bent valves in there. I did get a set of new valves but read about JP4 heads and got one cheap off ebay, thats the only reason.

I presume you want to fit a jp4 head to the j4 bottom end?

In that case I'd do one of 2 things, stick with a j4 head, and get some headwork done on it byt keep standard valve sizes.

OR

Go all out and get some jp4 forged rods etc.

So I could still put JP4 rods and pistons in a J4 bottom end?