PorKen

In hopes of getting over 300rwhp/tq (standard correction ) I retarded the '86 valve timing by 4° crank, approx. 3° more than the best run at -1°. With nothing else changed, it showed a leaner mixture at the tailpipe, and I lost 20ish hp/tq. From a nice 13ish, to a 15ish AFR.

I suppose the exhaust could be scavenging too much, pulling the air/fuel out, but there isn't any overlap on 928 cams, right?

Looking at it another way, if I dump more fuel in to compensate, would I make more power?

atb

Maybe not so much "pulling air/fuel out" but just allowing more air to pass through the cylinder (without atomized fuel) yielding a leaner reading at the O2 sensor?

The overlap measurements aren't taken at zero lift Ken. No overlap at the spec lift that the overlap measurement is taken, but not zero overlap absolute. Maybe there is enough overlap where it does become an issue when making major came timing adjustments.

Lizard928

So Ken, how about 316.3 RW TQ (standard correction) shoot high.

PorKen

Adam,

Hmmmn... I getcha.

...

Colin,

A 200K mile, '86 32V, barely tuned, sputtering, engine with 5 speed pulling 283/316 RW STD on the dyno? Pull the other one, mate!

(I can always do some trickery with the % loss with the auto, to make up the difference. )

FlyingDog

So... retarding cams gets more power on the top end and goes leaner? Sounds like what my car needs. How would your ignition timing advancing resister play into this?

Adam, due to the batch injection if the air is coming through the intake it has atomized fuel. The injectors on fire once or twice per combustion cycle (or revolution?).

edit = typo

PorKen

Matt,

I dunno. FWIU, the 4 valve is more sensitive to adjustment than the 2. In theory, retarding should raise the HP, but I may have gone too far, or it needs more fuel. I lost power with the WOT fueling I have. I tried both the clone, and the factory chips, and they were both lean.

The EZ-F full throttle switch disconnect tweak should fill in the curve, but not effect the fuel delivery, or top end?

I suppose it could be ignition advance/retard related, not enough or too little advance for the cam timing.

mark kibort

i dont think retarding should change AFR's. 15 is near 14.7 and thats where bad things happen.
Im running 2mm on the cam settings on both cams. (slightly advanced to the stock spec and matching both sides, vs the 1.8 /1.6mm spec) ive been at 320rwhp for years now. with the stock set up, (ie no headers and stock exhuast, sans the cat) it ran 290rwhp with no tuning at all.

MK

PorKen

Mark,

I'm curious to see what the 2.0 spec measures out to. If I loaned you my 32V'r (or maybe someone in SoCal has a V2 you could use), would you check it out?

If you set the cams to the same lift with the engine cold, then the right (pass) cam may be advanced 1-2° crank vs. the left, when the engine is hot.

PorKen

Is it possible that the intake valve is closing too late, and some of the mixture is being pushed back out on the compression stroke? I was reading about reducing pumping losses for higher MPG, and how Honda uses variable valve timing to keep the intake valve open longer while cruising, reducing dynamic compression, and vacuum levels.

BTW: I checked, and the full load/WOT switch input is getting to the ECUs. Anyhu, I ended up resetting back to zero, and the power is back up.

The 32V does seem to be much more sensitive to cam timing than the 16V, or perhaps the amount of lift is a factor. All this makes me hot to start working on a properly engineered PKVVT for my 86.



One stumbling block is the length of the timing belt, and keeping enough belt wrapped around the crank gear. There's no other belt with the tooth pitch and dimensions of the 928's, so I may have to make an electric water pump next, as Louie refuses to develop one.

RyanPerrella

Ken,

Lastnight I finally got to use your 32vr timing tool to get my engine in time before installing it. I found it to be invaluable in getting everything back together.
(assuming of course its accurate )

Thanks again

PorKen

Ryan,

You should check it again when you retension, as it may change.

I'm going to add to the 32V'r manual a couple of tips I've found after setting my cams so many times: When changing the timing, set one side at a time, starting with the left. Take out the fuel pump fuse, and crank the engine for a few seconds to settle the belt after each adjustment. Verify that the damper mark is aligned every time.

I've found that belt stretch while just turning the engine over by hand can change the timing by a degree at certain points, so it needs to be evened out. This would apply with the 32V'r or using a dial indicator. I also found that the engine likes to move by itself!

RyanPerrella

Ken,

I checked and repositioned the sprocket and cams a number of times before i was happy with it. I have maybe 20 crank revolutions on the belt now so i know it will continue to stretch more.

One thing i noticed was that after positioning the cyl 1-4 cam it would move a couple degrees always after i rotated the crank, so what i ended up doing to get 1 deg retard was set it to 1 advance and after i tightened it it moved into the 1 retard position. The 5-8 side was easier to set.

PorKen

I found the same problem with the 1-4 side, when measured at TDC #1. The valve train is under maximum loading at that point, and the belt is stretching. It's takes >50ftlbs to turn the gear, using the bolt, at that point!

I found it more predictable and easier to set the timing at -45° #1, then recheck at TDC #1.

RyanPerrella

Ken,

How accurate is the damper for finding true TDC. I was going off the pointer on the water pump as opposed to the one on the timing belt cover. I found them to be off about a degree.

Even a degree diff is still only 1/2 degree for the cams so i am sure its fine. Ideally you measure TDC with a dial indicator, thats something i didnt end up doing though

mark kibort

im curious too.

is it easy to install the devices? maybe i should do it when its time to change the timing belt.

Mk