VR6 over fuelling at high revs

[Fanjita 1]

Hi all,

 

I'm really hoping someone can shed some light on this issue before i spend money on the wrong fix.

 

Basically I've done some serious work to my VR these are as follows;

 

Reconditioned head fitted - skimmed, ported and polished

Fitted a racetech 6 branch manifold

Fitted a decat purchased from the same seller (belgian ebay company)

 

As you may agree, i was hoping for gains of about 15bhp

 

I had it on the rollers yesterday, and it was producing a not great 188.5bhp(& 165.8 lb/ft), not bad if it were standard, but unfortunately it isnt.

 

The problem is, 2 years ago, a previous owner had it on the rollers too, and, having only been chipped, it was producing 198bhp (have the graph to show it). my initial expectation was roughly 215bhp and i would be chuffed, but unfortunately i didnt even come close. I was told by the roller operator that he suggested my engine was mechanically sound, despite the high mileage (134k) and that the chip i had installed could be holding it back.

 

there are also fuel ratio plots and it does seem to raise after about 5000 revs, and it looks like the torque plot has a bit of a trough and then increases again.

 

please could anyone suggest what i should do? I was thinking of reinstating the original chip, and getting a new map done, problem is this company would want £450 for a piggyback ECU!!!

 

i'd be very grateful for any help you can offer,

Jim

[dr_mat 0]

Basically I've done some serious work to my VR these are as follows;

 

Reconditioned head fitted - skimmed, ported and polished

Fitted a racetech 6 branch manifold

Fitted a decat purchased from the same seller (belgian ebay company)

 

As you may agree, i was hoping for gains of about 15bhp

 

I had it on the rollers yesterday, and it was producing a not great 188.5bhp(& 165.8 lb/ft), not bad if it were standard, but unfortunately it isnt.

 

Well overfuelling wouldn't help, ultimately, if that's what it's doing, but don't forget different rollers give different results for point number 1 and for number 2 I wouldn't expect 15 bhp from just a decat and 6-branch on a naturally aspirated VR6.

 

Piggyback ECUs are not that great either, they tend to perform fine on the rolling road but out in the real world they're not quick enough to respond to throttle changes. I'd go for a in-ECU rechip if that's the route you're going.

 

And finally, the stock ECU chip should be perfectly adept at extracting pretty much all the performance available on those simple modifications, and getting the best from your nice shiny top end ..

 

So if it were my money I'd go back to the stock ECU and see where we go from there.

[Fanjita 1]

hi mat,

 

I totally agree, it might be simply that the chip is meant to work with a totally standard vr, to be totally honest i think it was one of those ebay plug and play cheap jobbies anyway.

 

i didn't realise that even with all the work i put into it that 15bhp would be an ambitious gain expectation! I know you can't believe what you see, but the belgian site i bought the Mani from suggested 10% gains!!!

 

I could safely say the decat would free up a few horses though right? In any case, what kind of power would you expect from this sort of setup? 210bhp maybe? (id still be happy with that!)

 

Just slightly changing the subject, is the loss of power through the gearbox normally this high? on the dyno it was 139.8 at the wheels!! a loss of 50bhp?

[dr_mat 0]

I think more likely the chip is just a bit rubbish then! Get rid! :)

 

I'm not an expert on modifying cars, but from experience with other people's stories on here, you'd rarely expect to see more than a few bhp either way with just exhaust mods (even a decat - the standard cat is pretty free flowing). This is around the same difference you'll see between good fuel and cheap shite, or the difference between performance on a cold day and in the height of summer.

 

Unfortunately, naturally aspirated cars rarely release big numbers from simple mods..

 

If you want 15-20bhp gains you need to be thinking cams..

 

As for the drive train losses (it's not just the gearbox..), 50bhp doesn't sound too unusual.

 

BTW you might also find that you've got a dodgy camshaft sensor. Might be worth getting the ECU scanned for faults.

[Fanjita 1]

no probs, thanks very much for ur help mat, ill let u know how i get on..

 

1 quick question, whats the best way to get the ecu checked?

 

Can get the necessary equipment quite cheaply and do it myself or is it a mechanic jobby?

[dr_mat 0]

If you have a laptop you can get a cable off ebay and the VAGCOM software for free - fine for just reading/resetting codes.

Go to http://www.ross-tech.com for more details.

 

Otherwise there's a whole thread filled with people who have this setup and will scan your codes for ya!