j4/jp4/jp4s heads also some pugsport cams

20th October 2013, 20:41

Right of the above heads in terms of "flow" which as standard is supposedly better? I remember years ago an argument about the crossover J4 heads on a single plug ecu with the 2 prongs for the air pump (that the 3 plugers had) had a slightly better flowing head? also some associated blurb at the time that these crossover engines had 130bhp? I just remember massive arguments across here 106moaners and ssc before it died

Been years since I've read into this, anyway pugsport cams anyway of identifying them at all from normal j4 items?

20th October 2013, 23:36

I remember a guy called Stuart digged into this and found that the jp4 head flowed a lot better than the j4 if u do a search I'm sure it will be somewhere , unfortunately he died in a car crash can't member his name on here maybe someone will know ? He had a supercharged vtr and was in the middle of supercharging a vts lump

21st October 2013, 00:16

J4 (120bhp) is the same regardless of age/prongs etc. myth that they had more power.
Jp4 (110bhp) has larger inlet valves (1mm) only, but milder cams as stock (which is why you see the suggestion to fit j4 cams/springs in a jp4). Jp4s (125bhp) also with the 1mm larger inlet valves, has similar cams to vts, and with different (alloy) inlet makes a little extra over the j4 with a wider torque curve.

If you start swapping cams about, they're all much of a muchness.

For boost, the j4 head is marginally better until you go power hunting as the jp4 adds a little lag (fractionally). Once you want head work, jp4(or jp4s) is the better option as you're already starting with larger valves.

21st October 2013, 06:20

Is the jp4 head with j4 cams not the way to go as you also get much better fuel economy.

I've seen folks claiming as much as 45mpg when taking it easy........

Them sort of figures appeal to me as I'm currently undecided about this j4 engine I have for a rebuild with port and polished head.

Does the jp4 head bolt straight onto the j4 block??

21st October 2013, 09:28

I can't comment on the economy as I don't know. I can't imagine it making any real difference personally but... :/

Yes - the jp4 head is a direct fit in the j4 block.

21st October 2013, 10:10

Jp4 - larger valves, milder cams, not as good valve springs

J4 - smaller valves, wilder cams, better valve springs

You can't (or shouldn't) swap cams as they are different spacing

21st October 2013, 10:13

Quote:

Originally Posted by Ross

I can't comment on the economy as I don't know. I can't imagine it making any real difference personally but... :/

Yes - the jp4 head is a direct fit in the j4 block.

But, the inlet manifold has different hole spacing, you have to tap some holes or use jp4s alloy manifold (which is very good but difficult(expensive) to find).

21st October 2013, 10:46

Quote:

Originally Posted by jpsaxo

You can't (or should) swap cams as they are different spacing

Agreed - but you'll often "get away with it" - the castings aren't great and frequently they will fit without issues, but yeah, I've also seen issues with the j4 cams catching on the jp4 head casting.

Quote:

Originally Posted by Kwik-Nick

But, the inlet manifold has different hole spacing, you have to tap some holes or use jp4s alloy manifold (which is very good but difficult(expensive) to find).

Agreed. But that wasn't the question

21st October 2013, 23:06

Quote:

Originally Posted by Ross

Agreed - but you'll often "get away with it" - the castings aren't great and frequently they will fit without issues, but yeah, I've also seen issues with the j4 cams catching on the jp4 head casting.

Agreed. But that wasn't the question

Just wanted to make it clear.

cheers

21st October 2013, 23:31

I wouldn,t say the 130bhp was a myth as such as those cars had the 3 plug ecu with squential injection + different mapping,
but i wouldn,t neccessarliy agree they were ALL 10 bhp better than ALL earlier type cars--the ecu was the big difference not the head
they did seem to always have the edge on earlier engines though as std

21st October 2013, 23:35

Well I have one lol. I was not in any way noticeably different to a pre-2000 engined gti I drove, but I guess its subjective.

Foe sure wasn't 10bhp more, agreed!

22nd October 2013, 22:10

Kyle, Stuart Band you were thinking of. He died in a crash in my old Saxo

If I remember correctly someone tested a few of each type (old and revised) j4 heads and there was about a 7% better flow across each of them, fairly consistent results. Id imagine that, with a better ECU, would make a fair bit of a power difference over the earlier setup.

That said, the VTS engine in my AX seems to be very good - it puts out great figures for a near standard engine (and feels it). Probably helps that Ive owned it since less than 20k on the clock, and its had a looked-after but testing life lol

22nd October 2013, 23:14

Quote:

Originally Posted by axsaxoman

I wouldn,t say the 130bhp was a myth as such as those cars had the 3 plug ecu with squential injection + different mapping,
but i wouldn,t neccessarliy agree they were ALL 10 bhp better than ALL earlier type cars--the ecu was the big difference not the head
they did seem to always have the edge on earlier engines though as std

Quote:

Originally Posted by Ross

Well I have one lol. I was not in any way noticeably different to a pre-2000 engined gti I drove, but I guess its subjective.

Foe sure wasn't 10bhp more, agreed!

The mrs car is a 2003 vts 3 plug ecu job.

Standard car with cheap open ind kit and a decat pipe only.... made 137bhp.

Same rollers same day 20minutes later my black bodied vts made 151 on same rollers (708, 330cc pred ecu and at bodies).

28th October 2013, 13:46

Correct me if im wrong but 151 seems low for 708's, 330cc injectors, at bodies and predator ecu.... Asuming a stock 120 thats 31 increase from what is mildly wild tuning... Malcyt on 106 moaners has a jp4 engine with j4 cams and springs and made 150ish on the rollers (agreed not the same ones on the same day...)

28th October 2013, 15:51

what injectors it has makes no odds to a point, as long as they flow enough and its mapped properly

but its well known that AT bodies don't perform as well as a properly designed inlet like a satchell gsxr setup.

28th October 2013, 17:42

Quote:

Originally Posted by greyjasper51

Correct me if im wrong but 151 seems low for 708's, 330cc injectors, at bodies and predator ecu.... Asuming a stock 120 thats 31 increase from what is mildly wild tuning... Malcyt on 106 moaners has a jp4 engine with j4 cams and springs and made 150ish on the rollers (agreed not the same ones on the same day...)

axsaxoman said there was something wrong with sexy_gt engine

29th October 2013, 15:34

Quote:

Originally Posted by welshpug

what injectors it has makes no odds to a point, as long as they flow enough and its mapped properly

but its well known that AT bodies don't perform as well as a properly designed inlet like a satchell gsxr setup.

well known by whom ?
we have made 210@flywith these bodies --so you can,t say the AT bodies don,t work on a decent engine spec.
sexy gt was a good case in point of some gremlin in the engine set-up that was not allowing everything to work as it should
his graph ,from memory went flat across the last 1000rpm + it didn,t make the max power where it should have done anyway --so there was some other factors involved that were limiting the engine .

29th October 2013, 23:30

My point was my other near stock vts 03 reg made 137 on rollers. Brought the cammed vts into it to suggest rollers were not "happy" rollers.

30th October 2013, 00:50

Stick your cock down the inlets gav, the one with the most "slack" will flow better