How far can you push a forged 2.5?
 

Hi,

Having read through as many old posts that I can find on SN. I have come to the conclusion that a forged correctly built 2.5 makes a great road car with plenty of low down torque. However the engine shouldn't really be pushed to 500/500 as this is where the engine becomes unreliable and a host of problems start to occur.

I currently have a 2.5 converted WR1 producing 438bhp and 485ft lb on an SC46 on 1.7 bar. Don't get me wrong it's amazing on the roads and bloody quick. I have no intention on using it on a track day. Now question is could I up the turbo to an SC50? pushing 500? however keep the boost on say 1.5 - 1.6 bar? Or will that just be asking for trouble?

The car is used every weekend and 90% of the time i drive it like a granny.

Thanks,

Loz.

On one hand I have seen builders push these things to well over 500bhp and claim no issues.

Someone I rate very highly says you can get a reliable 500/500 with proper maintenance, good mapping and sensible use.

However I have seen some suggest that the blocks on these cars fail as low as 1.2 bar, regardless of the internals.

Just add some meth, or peg the block with 14mm head stud conversion. Personally I would use 20% meth

Sod the bhp, How much lb/ft would a forged 2.5 make with a billet SC50???

Just to add the block has been pegged and has ARP head stud conversion.

I couldn't imagine the torque on an SC50, be interesting to know.

I know someone who ran 650bhp in a pegged 2.5 block.
Don't know how much torque it was putting out mind.

ozne....
how you got 485 of torque from a 2 litre??? im only getting 350 with a md321t billet!!!

Sounds like he has the 2.5 fitted and asking how far he can push it?? Thats how I think it sounded anyway!!:thumb:

I think you maybe right mate. hopefully lol

Hope so too!!:thumb: if not im changing my 2.5 to a 2litre!!:norty:

Sorry! Yes I have a 2.5! I was only getting 340 on my old 2.0 on a SC42!

phew!!!

I have wondered the same... I have a 2.5 with CDB insert 14mm head stud conversion fully forged with ported headers etc and a VF48 Billet. It's getting mapped on 3rd of April but I'm already looking at what is needed for 500/500 as I think this is an achievable figure for a reliable daily driver.

Hardy172, exactly the same as me. I'm looking for the 500/500 but I won't risk it if its unreliable.

Same for me lads' I've got a MD321V going on and I'll be looking for 500/500. Sticking to the 11mm Cosworth bolts unless the ARPs deliver the same performance?

mine sat at 550/525 running 1.9barfor a couple of years then it with a bit more power up to 2.1bar and the liners cracked :D

Good effort that Steve, that was odb right?

Nice Steve! Got a bit greedy though! ;)

Closed deck 2.5ltr.

Here is a graph of the car at 1.9 bar but it was only on ported sti5 heads, I changed the heads to my avcs heads and upped the boost and that's when the block cracked as the power and the way the car pulled just totally transformed :)

http://img.photobucket.com/albums/10...bt01032009.jpg

I wouldn't fancy running 500 on 11mm head studs. Think you might end up seeing a few head gasket problems.

I've sourced a re-worked 321V that ran over 500 on v power. Just need to find the funds as still suffering the kick in the wallet from the rebuild :)

It's not the BHP , it's the Bar
1.7 on 11mm any more takes your chances :)
Liners are thin & weak
Darton dry liners are a solution , but I don't want to get into a debate as there not everyone's choice
470-480 is a good number for reliable strong build for everyday use
Torque is the goal

On the road the sc50 wouldnt be as usefull as the sc46, ive a 46 and the spools pretty good for a larger turbo, I was told by my builder that 450/450 is ideal and once you go over that you get issues

11mm Cosworths will be fine, they are the UHP ones. Was just wondering if anyone rated the higher rated ARPs but it appears the cossie bolts are 1mm thicker as well.

I've run 11mm ARP at 570/570 on a 2.35, no issues

Anymore views on this?

I'm upping the turbo to a SC50 sometime in the future, Pegged block with 12 mm ARP Head Stud conversion.

Personally, I'd leave well alone unless you going to get a CDB and 14mm headstuds

2.5 and SC46 makes for a great combination not just because of the headline figures but because of the response, boost threshold and lack of lag.

The danger is that the compromises you make in the above respects will not be offset by any power gains (i.e. you could significantly compromise drive-ability for a fairly nominal gain in power) and the process will cost you a lot to do safely! You're at the stage where there is a real law of diminishing returns operating!

Suggest you talk to your engine builder.

Ns04

No disrespect Loz as it sounds like your car is a monster already :) but why would you want to push your car to 500, if you only use it every other weekend and never on a track plus you drive like a granny :wonder:

True :) after considering it I'll opt with what I have. The driveability is amazing and plenty of power :).

Thanks guys.

im thinking of going 2.5 forge in my 05 sti. want torque more than anything so dont think s 2.1 would satisfy my needs. all I want is 450/450 road car. any one know whos best to use to build? timewise? cost? would I be able to sell any of my engine to fund the project?? cheers all