Critique My Set Up

[MrStabby]

i have a 3in exhaust and make 350rwkw.

I would be interesting to see what it would make if you dropped the cat back. The consensus here appears to be that people find they can get good gains at that power level by going bigger than 3in. Nismoid posted;

300kw = 3in

350kw = 3.5in

400kw = 4in

recently as a rough guideline/rule of thumb on what is the sweet spot for exhaust sizing. No doubt he'll slap me if i've misunderstood his post.

[R31Nismoid]

^ and that's the thing. You can make power on a 3" exhaust.

However as many have seen before, a simply upgrade to 3.5" or 4" gives them better power overall, more timing, same boost.

Not unknown for a car to take an extra 2-4 degree's of timing, make 10-20rwkw more and not have an increase in boost what so ever just from exhaust changes like that.

On E85 / -5s / built motor = over 400rwkw

But as i said about the OP's exhaust, the CAT is 100% a problem. No doubt about it. 4" CAT as a min.

Just have a look down one, it can't possibly not pose a restriction hence a nice big mofo is needed, bigger than the exhaust itself.

[GT-R32]

Jez, I haven't run this one down the 1/4. I haven't ran a car for 3 years! I actually changed it to this cat as the one it had previously looked old. This cat looked exactly the same as the previous one. It's probably not crash hot, a 3" 400 cell.

I saw that too, Adam. So thanks for clarifying Ash. I will go 4" to save upgrading again later. Does any one do a bolt in 4"? I know X-Force do a 3.5" bolt in, but would ideally be after a 4".

[DVS JEZ]

get the 4inch that Ash recomended but try a decat aswell. or if youve still got the old cat punch the guts out and bolt it back in for a quick test

[R31Nismoid]

Just drop the exhaust from before the CAT for the time being - see what gains you get first up

[DVS JEZ]

^^^^ that will keep the neighbours happy

[Deano 1]

Just drop the exhaust from before the CAT for the time being - see what gains you get first up

i like this idea... take it to the closest peace of straight road and see if it makes a diffrence......take a video cam with you too so we all can here it... lol

ahh yea and thats a private straight road if anyone asks too.....

[R31Nismoid]

^^^^ that will keep the neighbours happy

lol i meant on the dyno

[Ziller]

I have a built forged engine running standard cams with Tomei cam gears, standard head, air box and running -5s at around 20 psi on a safe tune.

The exhaust is 3.5" with a matrix 3.5" cat, this reduces down to a 3" exhaust about 600mm past the cat which includes two 3" elbows and a 3"muffler.

The cars at the workshop now and they are changing it to a full 3.5" system with a dyno run for minor adjustments to suit, its currently pulling 338Kws, this is a genuine back to back dyno run with an exhaust upgrade so it will be interesting to see what and if there is any differance in the power levels running the same psi and safe tune, results next week, Cheers.

[GT-R32]

Thanks Nick. It will be interesting to see your results.

[Ziller]

Thanks Nick. It will be interesting to see your results.

My old workshop said it will make no difference, the new one said it will.

will post results soon as I get them, Cheers

[choyda]

I went through the same predicament as you a few months back - trying to get better results out of -5's.

Any chance your intercooler is a restriction? I changed mine to a thicker core and got better response and top end power.

[GT-R32]

Thanks for that Damien, that'll be next round of mods if I don't get much out of this lot.

Only after 10% at this stage (hopefully enough boost to wake up the -5s) which I think is probably realistic.

[NSNPWR]

^ and that's the thing. You can make power on a 3" exhaust.

However as many have seen before, a simply upgrade to 3.5" or 4" gives them better power overall, more timing, same boost.

Not unknown for a car to take an extra 2-4 degree's of timing, make 10-20rwkw more and not have an increase in boost what so ever just from exhaust changes like that.

But as i said about the OP's exhaust, the CAT is 100% a problem. No doubt about it. 4" CAT as a min.

Just have a look down one, it can't possibly not pose a restriction hence a nice big mofo is needed, bigger than the exhaust itself.

So wouldnt some bigger aftermarket dump pipes tie in with this concept? The same logic of being able to run more timing surely applies, factory dumps are shocking lookin things with all their castings and restrictions. Im not sure why'd you do the cat and not the dumps...not stirring just sayin, you cant look at the cat and the factory dumps and say one poses more of restriction than the other, all the heat is in the first foot or so of the exhaust.

[GT-R32]

I didn't do the dumps because I had often seen 380+kW seen being made by R33 and R34 dump pipes. I am yet to see a 3" Catco (not metal) do that kind of power?

I've bought a 5" Cat, 550cc injectors, plugs and APEXi pods (second hand - just in case my tuner really, really wants to fit them... I'd prefer to stay with the air box I went to an effort of sourcing and fitting).

Still got to buy cam gears, coil packs and 100k service kit.

[GT-R32]

OK, I've questioned whether the injectors I bought are big enough... They aren't 550cc but Blitz 534cc. How much power can these handle? (I don't know the specs of delivery for calculations. )

Would these be better?

http://cgi.ebay.com/ebaymotors/RB26DETT-7MGE-7MGTE-4ME-5ME-rb26-680cc-Fuel-Injectors-_W0QQcmdZViewItemQQhashZitem27b8a9b421QQitemZ170601853985QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories

More than happy to listen to recommendations for new ones if mine are too small...

[MrStabby]

OK, I've questioned whether the injectors I bought are big enough... They aren't 550cc but Blitz 534cc. How much power can these handle?

The rule of thumb is 1hp at the flywheel for each 1cc of injector with pump 98 - so the 550/534 size suits -7s or -9s. If you're going to keep the boost down to keep the unbuilt motor safe (ie the 330kw you mentioned) you should be ok. If injector duty gets tight you can just pull the boost down a little further.

It seems to me there's two clear options - Which of these are you aiming for?

1. Cheap - unbuilt motor, -7s/-9s, 550cc, 3 or 3.5 inch exhaust

2. $$$$$ - built motor, -5s, 700cc, 3.5 or 4 inch exhaust, aftermarket gear set to stop third from stripping

Of course if you go with option 1 with -5s you don't have the most responsive turbos, but since its expensive to change, maybe you can just live with it.

[Brezza]

I went through the same predicament as you a few months back - trying to get better results out of -5's.

Any chance your intercooler is a restriction? I changed mine to a thicker core and got better response and top end power.

At what level did you run out of puff with the std GTR intercooler?

I had mine tuned on e85 and gained bugger all top end, only 5rwkw, and that was pumping more boost into it.

Granted it was tuned on a bloody hot day, 35+ degrees. the intake temps were quite high. and the tuner gave the car long breaks inbetween runs. the midrange is wild now and it pulls over 500nm of toque. so its fairly punchy.

I'm going to take it back someday and get it tuned again on a cooler day just so he can tidy up the tune as he left the top end a little rich just incase it was a cold night and the mixtures leaned out too much. rather be safe than sorry.

I've been looking around for a FMIC but finding one that will flow 400kw is quite $$$

I'm not too keen on getting a cheapie like cooling pro and finding that its no good and i've wasted my money by getting one that doesnt flow aswell or has a severe pressure drop.

It becomes a very expensive task to get a 2.6L motor over the 350rwkw mark.

i've been told that the big gains are to be made in the midrange on e85 rather than top end, is that correct?

[GT-R32]

Thanks Adam, I figured the 20% additional flow should be able to cope at this stage. Seems like I was right, I just saw Nismoid mention minimum 700cc in another thread and started to wonder...

I'm at Option 1, with Option 2 around the corner. I'm not fussed about the higher boost threshold with the -5s... I have a 440ci V8 in my Challenger for when I want 'response' LOL

[R31Nismoid]

At what level did you run out of puff with the std GTR intercooler?

See Snowman was running a 96mm Trust core.

He swapped back to stock item - didnt lose one iota of power or response on -5s

Swapping was to remove the airflow restriction the larger cooler was creating on the radiator etc.