Turbo engine build question.

2nd November 2015, 09:32

Hi all i have a few questions for my build.

First, I have a jp4 in my car right now and i have a broken j4 at my garage is it better to just upgrade the jp4 or to take and fix the j4.

Second, the jp4 has granny style cams should i change them to j4 cams or just keep them because they will now make that much of a diffrence.

Btw, I am aiming for around 200hp and its a budget build. Sould i just make a adaptor for a jp4 mani or save a bit more and get a propper turbo mani?

Thanks.
Laurynas

2nd November 2015, 11:38

What is wrong with the J4? I suppose a decision hinges on that. What inlet are you using on the JP4?

You could build up the J4 out of the car with your turbo bits and then when done, drop it in (depending on what is wrong with it). The jp4 cams are offset by other benefits of using that head, so if you have the skills and time a j4 cam and running gear swap could be slightly beneficial.

I probably wouldn't bother, especially if you're on a budget. You've answered your own question about the turbo manifold as well. If its budget, why bother - just use a cast adaptation manifold.

2nd November 2015, 12:03

also the question of the cams --what rpm you want to use --cos the jp4 cams make max power at a lower rpm that j4 --which with turbo might be just what you want
people will race to say that the j4 makes 10bhp more than a jp4 --but at 1000rpm higher --so if you compare power at same rpm -you will find the jp4 is not a bad a choice as you may think --most turbos don,t make max power at the 7k +anyway and if using a cast adaptor idoubt the extra rpm will do much due to possible rstriction of cast manifold --your choice

2nd November 2015, 13:20

My j4 has a timing belt broken and all of the valves are bent so if i would do that i would have to refurb.

And one more maybe somebody can answer.
Does the jp4s have better cams than the jp4 and are they a strait fit?

3rd November 2015, 07:39

try reading and understanding what i said in first post --your answer is there

unless you want to quantify the word "better"
if you change to j4 cams then you need to swop over valve springs +caps as well for higher rpm range

3rd February 2016, 16:54

Either J4 or JP4 cams will do an adequate job, and as John says the JP4 is probably better suited to a turbo application; you don't want anything more than stock cams though.

If you're on a budget the turbo and exhaust manifold from the 207 GT/Gti/DS3 etc can be fitted with some fettling. There's just, only just, enough room between the rad and the turbo with the heat shields fitted, which I strongly recommend.

I have just done this to a C2 (with the JP4 engine) and the results were very good, making 180 bhp at just 0.4 bar boost on stock compression with boost picking up straight from the off building smoothly from 1000 rpm to full boost at 2000 rpm. The engine also wants to rev beyond where it did as a stock motor. I have used the stock ECU with bigger injectors and a different MAP sensor to read the boost. This keeps the standard knock control in place which is there to protect the engine against det, and also saves a lot of money.

Obviously, 99 octane fuel is used exclusively given the 11:1 compression (10.8 in J4) plus boost.

The same can be done with the Saxo/106 that uses the Marelli ECU, single or three-plug, (the C2 uses a Bosch ECU) but all versions have knock control, which only the better aftermarket (standalone) ECUs have that are typically £1000+ to buy. Basic systems like Emerald, DTA, Omex etc don't have the same engine protection unfortunately.