Building A Tu5Jp4 Engine. Cam Advice?

[johnnyboy666 195 1 Cars]

Hello,

 

I intend to build a Tu5JP4 engine to replace the Tu5J4 I currently have in my GT, but I'm just after a few ideas from anybody who has tried and tested these engines and knows the best combinatation of parts.

 

As it stands my idea is as follows

 

-Tu5jp4 block and head

-J4 sump

-J4 inlet/throttle body (I'm aware there is an extra few holes to be drilled/tapped in the head for this)

-J4 4-2-1 exhaust manifold

- J4 loom and sensors and ECU (currently mated into my 205)

- J4 valve springs (Jp4 ones are much softer i believe)

 

I'm aware that the J4 cam is a bit hotter, so was wondering whether I would be better off using that, or using an aftermarket one for a little more oomph?

If I do use an aftermarket one, is there a tried and tested one that works well on standard management with this setup? I don't mind getting a remap if its worth the effort.

 

Its worth noting that I don't want something that's all top end and no bottom and mid range, in fact I'd prefer a bit more low down grunt if such I thing is achievable.

 

and last question; is it all worth it, or would I be better off just pinching the TU5JP4 bare head and slap it on the J4 with J4 cams and everything else?

 

Cheers!

[Sandy 189]

The valve to piston room in the JP4 is very tight and obviously gets worse if you skim the head as many do. You can't safely run more than about 1.25mm lift at TDC, which pretty much limits you to std J4 cams or very mild aftermarket. Lots of people run 708s/PH3s etc, but in most cases are touching and they don't realise until it fails.

[calvinhorse 870]

Can the pistons be pocketed sandy?

[johnnyboy666 195 1 Cars]

Thanks sandy, you've saved me making a potentially expensive mistake! I guess budget wise then I might just use the J4 cams to start off and go from there. I probably won't split the jp4 head from yhr block before fitting as its a very low mileage engine so *should* be ok. I can then look at other avenues at the next time it needs to come apart.

Do you think I'm likely to get noticeable gains from doing this? I've read that the jp4 feels a bit more powerful lower down in the revs, which appeals to me

[Sandy 189]

J4 cams will be better yes, but you need the springs too and that's a head apart job. The pistons can be pocketed, but needs to be done accurately and judiciously!

[johnnyboy666 195 1 Cars]

Oh yes good point! Good job I've just bought an engine stand, might as well do it right the first time