Turbo exhaust cams

[daedalusjc]

Hi guys just chasing some guidance/info on turbo exhaust cams and how they effect spool, boost, powerband etc.

current motor has mivec on the intake cam only and while it gives 40 degrees of positive overlap from base timing the stock exhaust cam remains static timing. From what i assume a cam design on a Naturally aspirated motor versus turbo would differ in overlap and possibly duration.

Would it be right to assume that an exhaust cam timed with too much duration would lead to higher overlap allowing pre turbo pressure to blow back into the cylinder and not scavenging correctly?

Has anyone got any previous experiences with turbo cams or advice and how its effected there setup.

[c.rusli]

im sorry if i missed something, what car is this applications for?

[daedalusjc]

Ah sorry bit retarded of me. its a mitsi colt with a 4G15T motor. almost identical setup to 4G63 evo series.

Current mods are td04, custom steampipe manifold and dump, 2 1/2 exhaust, manual throttle body conversion and a few other misc boltons. engine remains untouched but rods and studs are on there way. mainly chasing spool and wondering if cams mainly exhaust is going to be of any help.

[PAGZ]

showcase plz, Used to have one of these as my dailys and it wasnt slow!

[daedalusjc]

umm yeah will put something up somewhere. theyve come a long way since the early days. up to 190fwkw and 330nm atw these days. 12.2 has been the quickest pass haha. but i wish i could get faster spool. 21psi @ 3500 is a touch late

[ED40]

12.2 1/4 mile with only 190fwkw.. fuck me haha

[daedalusjc]

yeh they dun weigh much. strippd out to i think 1090kg, fat front tyres. qld bloke though. i found it unbelievable but time slips either well edited or real.

anyway back to cams,

anyone have any insight

[joshg123]

As a general rule of thumb, turbos want alot less overlap than a N/A. Duration is dependant on exhuast backpressure, the larger the turbo and manifold setup, and the better the exhuast from there back. The more duration you can run.

I havent had any personal experience with that motor, but cams can be very hit and miss if your flying blind. Perhaps a regrind to a common profile might be worthwile, but unless something is availible off the shelf i wouldnt go reinventing the wheel. Also, if you did make a cam, is there a way to dial teh cam in without massive exersize. Ie timing covers have to come off every time you want to change etc..... if it runs a chain that is.

[Lonewolf]

good think about having mivec is that you can control the overlap
e.g. have small overlap down low for fuel economy, idle and spool up, then change it for big overlap at high RPM for power.

you are correct in that most turbo cams have less duration and overlap, but more lift than their n/a counterparts.