Ph4 Cams - Page 2 - Saxperience

AndySAXO^p · 14th November 2010, 22:59

Also it not always about bigger valves too.

Pm sandy for prices

mark1311 · 14th November 2010, 23:14

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

LeeM · 5th December 2010, 21:47

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

AndySAXO^p · 5th December 2010, 21:49

Quote:

Originally Posted by LeeM

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 · 5th December 2010, 22:01

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 · 5th December 2010, 22:15

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^p · 6th December 2010, 09:08

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 · 6th December 2010, 09:30

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 · 6th December 2010, 17:39

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 · 2nd January 2011, 17:42

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 · 2nd January 2011, 18:00

jp4 rods use a 18mm pins from memory,

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

JoshB · 2nd January 2011, 18:04

So how could you get round the issue?

mark1311 · 2nd January 2011, 18:06

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 · 2nd January 2011, 18:15

Quote:

Originally Posted by JoshB

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 · 2nd January 2011, 21:31

Quote:

Originally Posted by 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,...

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.

Quote:

Originally Posted by raunchz

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?