SVX gravel rally car...surely not? Absolutely... - Page 17

dynomatt · #**241** 06-21-2007, 05:36 PM

Bill...as to the timing, the issue is all about the valve events...nothing to do with the spark timing. Consequently, the Megasquirt can't do anything about it.

It's mechanical...and all about having the cams timed properly from the outset.

M

svxfiles · #**242** 06-21-2007, 06:38 PM

Quote:

Originally Posted by dynomatt

It's not 3 inch...it's probably got about 2 inch primaries (based on Bill's guess) and then about a 2 1/2 or 2 1/4" system for th rest with a resonator and a muffler.

M

Sorry,

my bad.
I got the idea you had a 3" exhaust mandral bent Ex from the dyno plot.
http://www.subaru-svx.net/forum/atta...9&d=1181993643

dynomatt · #**243** 06-21-2007, 06:39 PM

Yeah I realised that...no problems.

M

SVXRide · #**244** 06-21-2007, 07:21 PM

Matt,
Okay, looks like we're all straight on what exhaust system you're running

So, didn't you say somewhere along the way in this thread that you'd modified the cam gears to allow you to shift the static timing?

-Bill

dynomatt · #**245** 06-21-2007, 07:34 PM

Yep...sure have. So I've got the opportunity to adjust them...just not sure what to put them to.

Factory has inlet opening at 4* BTDC and exhaust opening at 55* BBDC. We timed the new cams to open approximately 2.5* BTDC. Retarding the cam timing pushes the power up the curve, with a resultant loss in bottom end.

benebob · #**246** 06-21-2007, 07:38 PM

Quote:

Originally Posted by svxfiles

The OD of the "secondary starts out at 1.91", and after the pre cats is 1.61"OD

on the US version.
I would have to agree with Bill, SVXRide that 3" exhaust is WAY to large for a NA 3.3.
And I've had several.

Come on Tom, you're showing your gray hairs now! 3" exhausts work perfect on a 1.6l honda!

svxfiles · #**247** 06-22-2007, 12:30 AM

Quote:

Originally Posted by benebob

Come on Tom, you're showing your gray hairs now! 3" exhausts work perfect on a 1.6l honda!

But ONLY if you compensate with extra vinyl, Dog.

dynomatt · #**248** 03-29-2008, 08:27 PM

Small update.

Pulled the engine out yesterday (down to 2 hours!!) ready to inspect the static cam timing.

Will have an update on this for you in a week I'd say.

After Rallybob's experience with exactly the same spec as me, I have renewed confidence that we were on the right track.

Time will tell.

Matt

IdeasMan · #**249** 03-31-2008, 03:39 PM

Are you using exhaust gas temperature sensors? If your still getting a big dropoff in torque at top end and the cam timing seems good, they may give you a clue as to what else could be wrong.
Other guesses for debate: valve float, head gasket leak, overtaxed or sticking fuel injectors (air/fuel ratio gauge would help here, too).
The size of your exhaust pipe and the location of your Y could also be messing with the resonance, but it shouldn't have that huge of an effect with the size you're running.

dynomatt · #**250** 03-31-2008, 03:42 PM

Thanks for the response.

Was not using an EGT, but did have a wideband lambda sensor in to do all of the tuning. Can't recall what AFR we picked, but it was safe, not wild.

It *shouldn't* be valve float, injectors or head gasket leak, but it certainly could be. I'm checking the timing tomorrow night, so will find out more then.

M

RallyBob · #**251** 03-31-2008, 03:53 PM

Interesting read here! I just went through all 17 pages, quite the buildup Matt, kudos to you! I love rallying in any form.

I do wonder if the lower-than-expected torque and the lower-than-expected peak power are caused by two non-complimentary facts. Retarded cam timing as you are well aware of, typically pushes the rpm band up higher. Yet the fact that you are retaining the standard exhaust manifolds and small-ish secondary tubes probably prevents the larger cams from being able to do what they do best, and that is to use the overlap to scavenge at higher rpms. I'm curious as to what sort of back pressure may be present?

RallyBob · #**252** 03-31-2008, 04:05 PM

Quote:

Originally Posted by dynomatt

Factory has inlet opening at 4* BTDC and exhaust opening at 55* BBDC. We timed the new cams to open approximately 2.5* BTDC. Retarding the cam timing pushes the power up the curve, with a resultant loss in bottom end.

Humor me for a moment please. Do you have the OEM cam specs and the new revised cam specs handy?

Are these opening numbers you've mentioned above measured at .00 lash, or at .002", .020", or .050" tappet rise? I think that given the increased duration, but only 1.5° change in inlet opening, you may well have the cams 17.5° or so retarded!

dynomatt · #**253** 03-31-2008, 04:14 PM

Which cam specs are you chasing? We graphed the factory cams and the new ones which I can provide the details around?

Matt

dynomatt · #**254** 03-31-2008, 04:18 PM

The figures in the post above are from the factory manual...I assume they are 0.00" lift.

We worked mostly off the "0.50 lift points for replicability.

Matt

RallyBob · #**255** 03-31-2008, 04:20 PM

Quote:

Originally Posted by dynomatt

Which cam specs are you chasing? We graphed the factory cams and the new ones which I can provide the details around?

Matt

Well, I'm looking for comparable opening and closing events at the same tappet rise.

Example: I recall the standard cams were *about* 196° @ .050" tappet rise. And I *think* you mentioned your new cams had 230° @ .050" duration on the inlet side, correct? Presuming the lobe separation angle remained the same, and the duration is now 34° (@ .050") more, then the new intake opening should occur at about 17° earlier than on the standard cams. Hope I'm making sense.