[Mk2] [Turbo] Do uprated cams help reduce turbo lag?

[dellams]

Hi Guys,

Sorry if im sounding a bit of a noob but I heard from somewhere that uprating the cams can help reduce turbo lag? Is this true? And if so how much of a difference does it make?

Cheers.

[RyanRs]

It depends on the cam spec.

Generally the answer is no.

A 272 10mm lift cam will be laggier than stock cams.

The purpose of different profile cams is to optimize VE between a certain rev range. Ie, CT26 will be out of steam by 5.5k rpm, So theres no point using a cam designed to work optimally between 3k ~ 10k rpm, you would pick one thats between 1.5k ~ 6k.

However, using a cam thats optimal between 1.5~6k with something like a GT4088 would mean the cams come out of sing just as the turbo reaches full chat.

there is more to it than that, but in simple terms, thats what happens.

[dellams]

Going to continue sounding like a noobie, but whats VE?

How about with the turbo I have now which is rated to 420. Thing its fully spooled by around 4k. Problem is I normally change up by about 5k!

Cheers.

p.s. Is there anything else you can do to help reduce lag? Heard something about keep the turbo spooled all the time even when idle but doesnt sound very safe to me and will prob reduce the life of the turbo quite drastically!

Also thinking about a NOS progressive controller!

[mattcambs]

Volumetric Effeciency. Basically how effeciently the engine can pump air. The more air the engine can pump, the more torque is made.

If you want less lag you might want to consider a V6 conversion You'll never get a 3S-GTE to be as lag free as the modern 4 pot turbos like in the Megane and Golf. They have the benefit of direct fuel injection and variable cam timing.

You could have Anti-lag setup on an aftermarket ECU. This changes the cam timing so that at low engine speeds the combustion exits the exhaust ports and keeps the turbo spinning. It's what rally cars do. It's not advisable in a road car

[dellams]

Right, cos it causes more wear on the turbo?

Is there anyway of upgrading the 3sgte to work with variable valve timing and direct port injection?

[Century Motorsport]

You could have Anti-lag setup on an aftermarket ECU. This changes the cam timing so that at low engine speeds the combustion exits the exhaust ports and keeps the turbo spinning. It's what rally cars do. It's not advisable in a road car

Thats not correct, anti-lag infact alters the ign timing not the cam. It also requires an air valve on the manifold to bypass the throttle when its closed to enable the anti-lag to work.

And yes post chamber combustion will destroy a turbo pretty quick.

Nathan

[Century Motorsport]

Also, if you got some real high lift cams with short duration that could infact bring the lag down - you are infact allowing the engine to shift more air so would spool the turbo up quicker. Its duration that kills the bottom end.

Nathan

[dellams]

Which cams would do this then? And any idea how much they are roughly?

Cheers.

[Century Motorsport]

Well, as far as i know there aren't any on the market that reatin a short duration.

I would give piper a call - they can grind you a cam from blanks, although expect to pay £500 for them. If you go really agressive on the lift you will need dual valve springs as you cant get a valve spring strong enough without coil binding at high lift. Just so you know piper do a set of dual valve springs that they claim will fit straight in - the is NOT true, infact it couldn't be further fron the truth as its a mamouth job to get them fitted which requires extensive machining work on the head.

Another thing to consider is the ramp angle of the lobe, you cant have it too high, esp as our followers aren't so big - but piper can go through all this if you speak to them. All they will need to know are your requirements and the bucket size (which is 31mm).

Lastly, for this mod you will need either under bucket shim or solid lifters as the extra lift of the cam can swipe the shims clean out the bucket causing destruction of the head and pretty much anything else under the rocker cover.

Nathan

[mattcambs]

You could have Anti-lag setup on an aftermarket ECU. This changes the cam timing so that at low engine speeds the combustion exits the exhaust ports and keeps the turbo spinning. It's what rally cars do. It's not advisable in a road car

Thats not correct, anti-lag infact alters the ign timing not the cam. It also requires an air valve on the manifold to bypass the throttle when its closed to enable the anti-lag to work.

And yes post chamber combustion will destroy a turbo pretty quick.

Nathan

Sorry for the mis-info Thanks for correcting, Nathan

Dellams, what about a smaller turbo or a roller bearing type? Head work is going to be uber expensive

[RobCrezz]

Easyest solution would be a faster spooling turbo. Garret roller bearing GT series turbos have really good spool for the power range.

[cantfindausername]

If you're changing by 5k RPM how about trading the MR in for a diesel.

Don't be shy on using the other 2,000+ RPM the engine can deliver.

[jimGTS]

rolling bearing turbos, anyone know if the apexi IHI is one?? as my turbo still spins round even when the engine is off. i can here it spooling down....

i beleive i got 272 cams on, cam overlap is a pita in traffic, thats all ill say.

but when at wot, are amazing.

if you change gear at 5k, then there is no point at all in going for a big build when most large turbos are only fully spooled by 4-5k rpm....

[cantfindausername]

Some links showing ball bearings in turbos...

http://uk.youtube.com/watch?v=H1MryAt1dw8&NR=1

http://uk.youtube.com/watch?v=-Jkwt79Ax ... re=related

http://uk.youtube.com/watch?v=6YSDyI6sh ... re=related

http://uk.youtube.com/watch?v=E2ung98bu ... re=related

http://uk.youtube.com/watch?v=GZcJMRXR6 ... re=related

[Marf]

if you change gear at 5k, then there is no point at all in going for a big build when most large turbos are only fully spooled by 4-5k rpm....

Agreed, he'd be better of fitting something like a GT2860RS and having a great midrange and spool.

[JJ]

i beleive i got 272 cams on, cam overlap is a pita in traffic, thats all ill say.

Hey jim,

whats sort of characteristics have you got ??! I run 272s with a 10.4mm lift... and its quite steady at 1000 - 1100 rpm.. barr a little hunting that goes on sometimes !

[jimGTS]

i beleive i got 272 cams on, cam overlap is a pita in traffic, thats all ill say.

Hey jim,

whats sort of characteristics have you got ??! I run 272s with a 10.4mm lift... and its quite steady at 1000 - 1100 rpm.. barr a little hunting that goes on sometimes !

basically, partial throttle, between 2-3rpm, when slowing down, or partial throttle when speeding up (2-3rpm), the car can stutters/kangaroos...
ive had ryan at 2bar on the case, but he mentioned the overlap on the cams are huge, and difficult to smooth out.
if im at wot at 2k rpm, totally fine, or enough gas to start spooling up the turbo, its fine.
just sometimes in traffic is annoying. as sticking in 2nd at 20-30mph can be annoying. (be nice to change into 3rd without having to worry about dipping into 2nd again, lol)
my idle is set to 1400....

[jimGTS]

Some links showing ball bearings in turbos...

http://uk.youtube.com/watch?v=H1MryAt1dw8&NR=1

http://uk.youtube.com/watch?v=-Jkwt79Ax ... re=related

http://uk.youtube.com/watch?v=6YSDyI6sh ... re=related

http://uk.youtube.com/watch?v=E2ung98bu ... re=related

http://uk.youtube.com/watch?v=GZcJMRXR6 ... re=related

prob not far off of the last vid you posted...tho id need the intake pipe off to see exactly.

[RyanRs]

If your car runs lumpy with 272s then its been set up poorly.

I do believe it was proven on the usa boards that Cams Do not cause bad tickover!! unless they are not timed up correctly.

its the use of very large injectors that causes lumpy idle. Imagine trying to fill a kitchen sink with a fire engine hose!? well thats the same principle as trying to hold a 800rpm tickover with 1600cc injectors.

About your turbo, if it spins for ages after you shut off the engine, then yes it is a BB turbo.

[jimGTS]

If your car runs lumpy with 272s then its been set up poorly.

I do believe it was proven on the usa boards that Cams Do not cause bad tickover!!

its the use of very large injectors that does it. Imagine trying to fill a kitchen sink with a fire engine hose!? well thats the same principle as trying to hold a 800rpm tickover with 1600cc injectors.

About your turbo, if it spins for ages after you shut off the engine, then yes it is a BB turbo.

it doesnt run lumpy at idle or anything. doesnt hunt either.
very smotoh sound, but idle is at 1400.
run 850s (i believe), uprated pump, and possible uprated PP rail