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Working out the req'd compression ratio on turbo build
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206gt160

Posted: Sat Mar 15, 2014 3:46 am

Joined: Apr 16, 2013
Posts: 676
Trade Rating: +1
Location: Blackburn

Right I've come on here to see if any of you guys can point me in the correct direction, I'm going to be doing my turbo build soon and I need to know how I will work out the correct compression ratio to go for with my build. I know you can change compression ratios with the head gaskets and piston and cams etc, the thing I want to know is should I go high boost with low compression or low boost with high compression and a higher grade fuel?? I'm only thinking of running 240-260hp so high boost isn't really needed, I wouldn't have thought anyway. One of the factors is obviously efficiency, the higher compression turbo build's seem to be more efficient, Just not as good performance wise due to running lower psi. I suppose if I wanted more power I could eventually switch to a low comp set up.

I know I will have to get the bores sleeved and run a higher octane to cope with the higher temperatures in the combustion chambers this isn't, as such, a problem

Now I know some of the people on here won't have heard about high comp piston turbo builds but if you google it will tell you everything you red to know. It's not all about low comp unless your looking at high boost.

Hopefully someone will know more on the subject than I currently do.

macj

Posted: Sat Mar 15, 2014 6:58 am

Joined: Feb 07, 2010
Posts: 3085
Trade Rating: +12
Location: Essex

Low comp/high boost is fine with most applications. There are several theories about high comp/low boost which relate to lag and the use of anti-lag to keep the motor on the boil...... but that's getting into race applications which I am sure is not in your project ....

206gt160

Posted: Sat Mar 15, 2014 7:32 am

Joined: Apr 16, 2013
Posts: 676
Trade Rating: +1
Location: Blackburn

Thanks for that macj.. my overall goal is to track day it really so nothing serious as of yet.. ill have a read up on the lag, I was under the same impression as people with high vomp turbo setups usually use bigger turbos with lower boost (or at least this is what I have read from a few people that have done so) the anti-lag is that when they have the injection system set up to add extra fuel into the exhaust side of the turbo before it enters the turbo.. as they did in the stage b rally cars etc? Or is there a different method?


	1999 206 Gt... Gti180 inlet, Gti180 exhaust manifold, Gti180 injectors, Gti-6 throttle body, Custom Adapter pipe to mate the throttle body to intake, Gti180 alternator, Gti-6 ICV, Straight through stainless exhaust system, cat cams (apparently), Avo coilovers, short shift gear stick, stripped out with fixed back bucket seat and harness, flocked dash, momo steering wheel and D2 solid boss, real carbon cold air intake, Gti-6 front calipers and 288mm disks, rear drilled and grooved disks, morette headlights, sp bonnet grill 71,456 miles 2008 Audi A3 2.0 Tdi 170

Edward

Posted: Sat Mar 15, 2014 12:46 pm

Joined: Feb 08, 2010
Posts: 7045
Trade Rating: +5
Location: In the garage

I'd go for a low boost set up initially. Get it all screwed together and working. Iron out all the problems then move onto the different internals with higher boost.


	2001 GTi 138, Bilstein Sprint dampers, H&R springs, 21mm Peugeot Sport torsion bars, 22mm rear ARB, Peugeot Sport Group A wishbones, 283mm discs, Goodridge stainless hoses, Maniflow 304 grade 4-2-1 2.5" manifold and system, 200 cell cat, Richard Longman head, 45mm Jenvey throttle bodies, 9.5mm TB spacers, 90mm air horns, Jenvey throttle linkage, Jenvey fuel rail, Aeromotive and Goodridge fuel fittings and braided hose, ITG sausage filter, Radtec custom radiator, Piper Ultimate Road cams, Piper vernier pulleys, Omex 600 ECU. Saxo electric PAS pump, Vibra Technics engine mounts. Samco coolant hoses, TTV steel flywheel, 4.76 final drive ratio, 307 CC 180 ratios. 2019 BMW 530i. 2017 Mercedes C300 convertible.

206gt160

Posted: Sat Mar 15, 2014 2:57 pm

Joined: Apr 16, 2013
Posts: 676
Trade Rating: +1
Location: Blackburn

I will need to get forged high comp pistons to do this still but would I need a high comp gasket? Or just use my standard gasket. Not looked that up yet.


	1999 206 Gt... Gti180 inlet, Gti180 exhaust manifold, Gti180 injectors, Gti-6 throttle body, Custom Adapter pipe to mate the throttle body to intake, Gti180 alternator, Gti-6 ICV, Straight through stainless exhaust system, cat cams (apparently), Avo coilovers, short shift gear stick, stripped out with fixed back bucket seat and harness, flocked dash, momo steering wheel and D2 solid boss, real carbon cold air intake, Gti-6 front calipers and 288mm disks, rear drilled and grooved disks, morette headlights, sp bonnet grill 71,456 miles 2008 Audi A3 2.0 Tdi 170

macj

Posted: Sat Mar 15, 2014 6:52 pm

Joined: Feb 07, 2010
Posts: 3085
Trade Rating: +12
Location: Essex

206gt160 wrote:

I will need to get forged high comp pistons to do this still but would I need a high comp gasket? Or just use my standard gasket. Not looked that up yet.

A set of forged pistons would be good, but I suggest not going for a H/C set as these are usually 12.5:1
I would get a set of forged pistons with a slightly lower CR which is probably standard CR the lower CR being around the 10 mark. This would be better for track day applications as it wont need such a complex map..... worth reading up on first to get it straight in your head.

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