big boost engine rebuild or not

[dub-disaster]

hi all,
  i am going big boost soon i have a bvh to put on and intend on running 21-23 psi ish from a ko3 setup my engine has been putting out around 150 bhp with a charger and has done around 100k miles is it worth the cash to go 1341cc or shall i just replace the parts in my engine and keep the same pistons ??
  I intend on eventauly driving the car daily, including long motorway drives to to london and back (about 2 n a Half hours) so i want a realiable useable 200bhp really is it worth going 1341cc with a 9:1 compression ratio for better of boost driving or could i just run alot more boost with the wossner 8:1's is it all really worth the extra cash remebering that im putting a bvh on ??
   Just peoples opinions as i know some of you are running these setups and wondered how you find them
Thanks again for putting up with my constant questioning 

[Varley]

If you plan on running 200bhp i'd want forged pistons, and if you're paying for them you may as well spend the bit extra and go for 1341cc, can't think of a reason why not.

Big boost:lower compression imo - go for the wossners.

[dub-disaster]

thanks for your poinion , any one else wanna add there 2 pence??

[Tommo]

23psi still dosent sound like a right lot to me. I ran 18-19psi on 1.3 SPi pistons at 9.5:1 compression for 5K miles, and when I took it apart there were no det marks at all. Although I did run it quite rich and without much advance.

I see a lot of people on here who have worked out their compression ratio and its over 9.0:1 and they dont seem to have too much bother. But I can understand the safety of 8:1, especially for long motorway boosts  .

Ive just machined my pistons for 8.7:1 and am hoping to run over 20psi, but I will be monitoring detonation very closely and it will run on premium fuel all the time. I suppose if I was spending that much money on forged pistons etc I would want to make sure it wasnt going to self destruct.

As for the 1341 its a no brainer for me, no replacement for displacement.

200bhp is approaching the far edge of the compressor map for a K03 though, it wont be very efficient and will run in choke causing thrust wear. Somthing that flows a bit more might be more suitable especially with the 1341.

[Andy]

21psi doesn't trouble a K03 on a small block Polo lump - the 20v guys push them much much harder. Plus they're cheap enough to treat as a service item anyway!

When mapping Robin's car (9:1CR 1341cc, stock head) it was apparent that much more than 21psi needed lots of ignition advance taking out the map, and the car didn't really feel any quicker. 15psi to 21psi is a noticeable difference, but if 21psi doesn't give you the power you want, you need a bigger turbo. Robin made 193bhp with that spec.

Yoof's car makes 10bhp more than this thanks to a BV head, which if you must have 200bhp is a worthwhile investment. On the road, they're both bloody quick cars with nicely sized turbo/cam combinations that give decent spool-up characteristics.

On this basis, if you're sticking with a K03 and want 200bhp or so I'd build the motor using 9:1CR pistons, and whack a BV head on there.

Reason I suggest using the higher CR pistons is that whilst Robin's and Hayesey's K03 turbo'd G40s make the same power, Robin's makes 10bhp and 10lb/ft more than Hayesey's low-down/off-boost thanks to 1341cc 9:1 pistons over Hayesey's 1272cc 8:1 jobbies. If you think you'll stick a bigger turbo on there and run lots of boost from that, then go for the lower compression pistons - but K03/1341cc/9:1 is a proven combination that works very well.

[dub-disaster]

thanks for the very informative responses
guys thinking of going forged 1341cc with the 9.1 cr then for a ko3 , just outta intrest whats the next sorta step up from k03 i assume a k04 will bolt straight in place and will prduce a fair bit more boost but do they take alot long to spool how much longer would i be looking at  ?? i will definantly be investing in a bvh got on on the way hopefully i also have got a ko3 turbo spec psd newman cam at the moment
  In the way of other turbo's that could boost around the 25-30 psi mark what turbos is there around that wont take ages to spool up, i know id have to change the cams for a bigger turbo just wondered about a ko4 because if i get bored with ko3 power i could always go to ko4 but wanna build my engine so i dont have to change pistons for cr lowing if i go ko4.
  Also with a ko3 setup bvh 1341cc engine boosted to about 20psi ish will this be useable power for road use or is it a bit savage i will mainly just be blasting country lanes and down to the coast and such like maybe some motorway juants to shows and that just wondered what these setups are like for that ??

[hayesey]

20psi with a k03 is pretty savage as it is.  Forget putting your foot down if it's even damp.  The track day I did on friday started off with a damp (not wet or raining at the time) track and I couldn't put the power down with a subframe, LSD and 15" wheels until it dried out.  And that's on a proper track with pristine tarmac. 

I'd imagine 30psi would make lots of power on a dyno but be totally undriveable on the road unless you fit a 4wd system, or convert to rwd at least.

Plus boost isn't everything, you might find at 25-30psi that you're having to back off ignition so much that you're not making much more power than 22-23psi.  It would probably require a more efficient head like a 16v one.

[dub-disaster]

ok cheers mate i think i was just looking for figures but shouldn't should think of more driavability.
   jst a couple of more questions , got a bvh on the way do i really need foreged 1341cc bottom end?? will it be much better and worth the extra cash?? i suppose it would be more reliable beause i want a really reliable setup that i can rant all day long ant not worry to much about busting anything would the cr matter if im doing motorway driving with it is 9:1 safe? i dont mind running aqua mist if i have to.the 1341cc bottom end doesnt actualy add any power other than increasing the cr if i want to wich from what andy wa saying sound like a good idea for all round drivablility wich is wat i want from my motor .
    from what every ones told me think ill go 1341cc bottom end  bvh and ko3 with a nice map from andy  just outta intrest how much am i looking at roughly for a 1341cc forged bottom end and how much is a the custom mapping from andy ??
    Aswell robin what brakes do you run as ive bought a 256mm upgrade but wanna run the ats classics or cups do they fit , or do you have to stick with the standard items??
Cheers guys

[hayesey]

a 1341cc bottom end will give you approx 10bhp more power throughout the rev range.  Mine & robins cars made the same peak power but only because his doesn't have a BVH so ran out of breath higher up the rev range.  If he had a BVH then he'd probably have made about 203/204 bhp (which is what yoof's made with 1341 & BVH) which would be 10bhp more than my peak power, so it all adds up.

Plus the 1341cc extra compression means the car is a bit nicer to drive off boost which would be the main issue I'd have thought if you're planning on using it daily.  

As for money for a 1341cc bottom end, I think pistons are about £450-£500.  It'll prob cost somewhere between £800-£1000 all in for the bottom end work depending on how much work you do yourself and how much work you pay someone to do.  

I've got 256mm discs with wilwood four pots on mine but they are overkill for on the road (but great on track).  I'm not sure why you are asking Robin things as he's not even posting in this thread!  The usual 256mm audi brakes should be fine but if you're thinking of fitting them under 13" ats classics then there's not a cat in hells chance!  I think you have to use spacers to fit them over standard g40 239mm brakes.

[dub-disaster]

thanks for all the help , its really cleared things up for me , sorry i got confused with a different post !! think im going to go 1341cc forged bottom end along with bvh and k03 should be nice Will try and do as much of the bottom end myself as possible to save on labour, but ive never built a engine before i do some mechanical fitting at work but never undertaken anything like this before, ive got a haynes manual and that seems really help ful and i understand the basics but in your opinoin is there anything i should get done by a professional or anything that i may find too hard to do myself also any other little tips / books to read or anything that will help me in removing and rebuilding the engine ??
Thanks for all the help guys been really good

[Tommo]

You can always open the diffuser gap up on the K03 to allow it to flow more air. No wonder the aqua mist works well on these cars as a K03 will be blowing pretty damn hot air at that sort of power.

[dub-disaster]

What Kinda turbo would you suggest then for that amount of boost? one of those Saab gt17 jobbies, or a ko4? Wich saabs had these fitted? Wouldn't a ko4 or larger turbo have lag problems? I under stand what you mean though about it runningn hot but you can't have a turbo that spools up as early as a ko3 and produces 21-23psi of boost can you to
mo? That's like having your cake and eating it.

[hayesey]

a k03 will make 21-23psi of boost. I've got mine set to 21psi at the moment and yoof ran his at 23psi.

[dub-disaster]

I just thought that it decreased the turbos life as it was operating at the edge of it's limits? Any how I am thinking of running two ecus that I can switch between so I can have a 15psi for daily driving and better fe economy and a high boost one for when I feel like ragging it a bit more

[hayesey]

k03s are £50 from scrapyards so if it even does reduce life slightly, who cares.  You dont need to have 2 ecus for that.  Just use a bleed valve or adjust the wastegate actuator to switch between boost levels.