J4 vs JP4 Tuning

7th April 2014, 09:41

Which engine is easier to tune?
Would be looking to get around 150 bhp as cheap as possible with either engine

7th April 2014, 10:24

JP4 has larger valves, so that would give more room for cheap power over the J4

7th April 2014, 13:00

yeah, cheers! ive heard cams are the best option for starters with either engine, is this correct?

7th April 2014, 13:39

can't go wrong with cams. Make sure you use cams specific to the engine though.

7th April 2014, 14:21

big debate this, some people will say that j4 with cams and breathing mods mapped will give you 150bhp, jeffchiz had jenveys, cams and exhaust and made 155... sexy_gt i believe was disapointed with the initial mapping of his one but i think in the end it made 162 (maybe that was a calculated one) but up to 171bhp has been seen on std pistons, i believe that was tom5910 that saw that... i dont know what mine is not had it near the rollers, id estimate somewhere about the 165-168 mark just from what i know i can keep with and come up against a few other saxo's that have a dyno print out of 150-152 (cammed and mapped with breathing mods) and i just laughed my way past them in a straight line...

thats about as much info as i can give on the subject, jp4 you have to worry about piston to valve clearances, kam racing do some catcams that are specifically designed to fit the jp4 head on the j4 bottom end, but the valve lift is compremised by the larger valves...

someone did say to me that not all jp4's have the larger valves, again might just be shite ive heard from somewhere...

7th April 2014, 19:52

I'm running a j4 engine ( 151.4bhp )

Mods :

Mild head work
Stock cams
Stock ecu mapping
Cold air feed
Hiflow air filter
3.5fpr
Rebuilt bottom end
Janspeed manifold with wrapping
2" exhaust system

7th April 2014, 21:25

thanks for the info guys, hmm, jp4 is supposed to be freer down the rev range and more economical but the j4 is supposed to have a better to end, choices choices haha

15th April 2014, 11:58

When you say "stock cams" do you mean JP4 or J4?

I've just got a JP4 for my Rallye. I'm going strip and swap lifters over and put the standard J4 cams in it. I also have some Kent PT50 cams in my current J4, has anyone used this set up in a JP4? I know they are only very slightly harsher than standard J4 ones but I'm obviously worried about the the valve to piston contact?

I was also wondering how people got around running harsh cams in a JP4? Do they notch the pistons etc?

Or use cams specially for the JP4 engine?

Another thing that crossed my mind was using a set of TU5JP4S cams? Surely someone has gone down this route also?

Thanks Dan

15th April 2014, 15:06

either engine with cams should give 150 no problem assuming no cat and decent manifld =ex system --you only begin to notice the lareger valves hwne you go a lot more --when flow becomes an issue --not at that level though

15th April 2014, 21:48

In my case it's not a case wanting it for the bigger valves it's just a fresher low mileage engine.

15th April 2014, 22:30

Quote:

Originally Posted by dan_87

When you say "stock cams" do you mean JP4 or J4?

I've just got a JP4 for my Rallye. I'm going strip and swap lifters over and put the standard J4 cams in it. I also have some Kent PT50 cams in my current J4, has anyone used this set up in a JP4? I know they are only very slightly harsher than standard J4 ones but I'm obviously worried about the the valve to piston contact?

I was also wondering how people got around running harsh cams in a JP4? Do they notch the pistons etc?

Or use cams specially for the JP4 engine?

Another thing that crossed my mind was using a set of TU5JP4S cams? Surely someone has gone down this route also?

Thanks Dan

I have J4 Kent PT50 cams in my JP4 engine, they fit without problem, i've done already 6-7000miles.

18th April 2014, 09:43

Ahhh excellent cheers