Cam retarding?

Swifty1638 · 02-08-2009

I was looking into more and more (after talking with andrew) aout retarding my exhaust cam a few degrees, to try and help spool up. After talking to Lampi on the topic, i find even more that people do it often as a way to spool because it allows the exhaust valves to open during the burn, and therefor, the hottest gasses escape to the turbo helping spool. But, it also causes motor damage to valves and such. I was going to just turn the exhaust cam gear a few notches, but does anyone really see a big difference in degreeing theirs? Anyone else do this? How much did it really help spool or not?

-A. Swift

Swifty1638 · 02-10-2009

So the ways to increase spool speed so far mentioned:

-Ball and spring MBC
-Retard exhaust cam or advance intake cam by one tooth
-Open/better flowing exhaust (cutout)
-Retard the timing and richen the fuel : I've had decent results actually leaning out because it makes then exhaust gases hotter. I don't want to make a primative antilag effect, I jsut want to make a little faster spool, since Work done by the turbine = Massflow X Cp X (Temp exhaust manifold - Temp down pipe)
-True cold air intake
-Tubular exhaust manifold
-higher spring preload on the wastegate

-A. Swift

**asshanson** · 02-10-2009

One tooth? Isn't that like 6*? I was thinking more like 3* or so, 6 is quite a bit, and probably the ghetto way to do it for those who don't have adjustable gears.

Swifty1638 · 02-10-2009

yea, i copied and pasted that from talk. I gotta double check my gears too, as one I think has 0* at the valley of a tooth, and the other is at the top of a tooth..I forget which is which though..eek.

I have a cutout on the way, and am trying to figure out how else I'll spool quicker.

-A. Swift

Swifty1638 · 02-10-2009

I'm thinking 1* advanced on the intake cam, and 3* retarded on the exhaust cam..could this be the sweet spot?

-A. Swift

Matt D. · 02-10-2009

Wouldn't you want to advance the exhaust cam so when it opens the air-fuel mixture is still burning? If you retard the exhaust cam it will open later when the burn is further progressed and more of the energy is already spent, leaving less for the turbo. Retarding the timing is the same thing, the burn starts later allowing more energy to be fed into the exhaust and less contained in the combustion chamber.

Ask me how I know... I had a Ford 302 once and the vacuum advance fell apart on the distributor when I was on the highway. By the time I was able to pull off without getting ran over I was greeted with glowing exhaust manifolds under the hood.

Swifty1638 · 02-10-2009

I just know that every site I've seen for dsms, this is how they do it..perhaps that's due to the fact you only had 1 cam? (I know nothing of ford motors)

-A. Swift

**Shane@DBPerformance** · 02-10-2009

Most of the things you do with adjustable cam gears to help spoolup can hurt topend power a lot. That's the beauty of systems like MIVEC where you can change the cam advance/retard vs rpm/load.

Most of the the things you listed above could very slightly improve spool up, but maybe not enough to notice, unless your exhaust is really restrictive of something. A tubular manifold usually adds a decent amount of lag. An OEM or FP style cast exhaust manifold will normally drastically outspool a tubular, longer runners, bigger runner manifold. Your best options are to get smaller turbo, get a bigger motor, use nitrous, or just rev higher.

FattyBoomBatty · 02-10-2009

Yeah, get a stroker kit, that'll help spool.

Swifty1638 · 02-10-2009

I'm really considering throwing a bigger motor in this car. Revving higher only means it'll be harder to shift..arg.

Shane, should I try anything with the cam gears at all, or just leave them at 0? I have a 3" cutout on the way, and a dual spring WG too.

-A. Swift

**asshanson** · 02-11-2009

How about on a stroker, does it hurt top end as much, seeing as there isn't much above 6500rpm as it is? Maybe I won't install those gears...

Pushit2.0 · 02-11-2009

I would degree the cams.

wheelhop · 02-11-2009

I had my exhaust cam retarded by 1 tooth on my stock cams a long time ago. The boost cam on all at once, it hit earlier and it fizzled out up top a little more. It spooled my small 16g a little faster.

There is no general sweet spot. Every build is different, with different demands and different backpressures.

Hotter gases definately increase spool speed. But in the case of exhaust cam retard, valve overlap is the cause for the increase in spool speed, not hotter exhaust gases. As a check you can advance the intake cam and see a similar increase in spool speed. At lower demands on the turbine, the compressed air actually helps drive the turbine as you blow aircharge right through the combustion chamber and into the exhaust manifold. The exhaust pulse ends for the cylinder but pressure directed to the turbine from that exhaust runner lingers.

This is why the cam timing "sweet spot" is different with different setups. When do the exhaust pulse pressures end? When does there develop more back pressure than manifold pressure, reversing the flow back to the intake valve? Etc.?

Cam duration and cam timing is velocity dependent not rpm dependent. To be exact, cam timing and duration takes advantage of momentum of the individual particles. Momentum = mass X velocity. A stroker has a higher intake air velocity at a lower rpm, hense why strokers and v8s get away with more duration and overlap with out idle issues. If you degrade topend VE with cam timing for a 2.0L stroke, then you will degrade the VE of a stroker at the same air velocity, which occurs at a lower RPM. The stroker motor piston speed at 7300rpms is as fast as the piston speed of a 2.0L at 8000rpms. Piston speed and air velocity are nearly directly proportional. So if you kill VE from 6500rpms to 8000rpms with cam timing or a particular duration on a 2.0L, then you will kill VE with a stroker from about 5900rpms to 7300rpms [(6500/8000) X 7300)].

Swifty1638 · 02-11-2009

so that's why i was thinking 3 deg advance on the intake, and 1 retarded on the exhuast..happy medium?

-A. Swift

**Shane@DBPerformance** · 02-11-2009

There is no happy medium. Every setup is different. How milled your head and block are will effect it. Exactly how your exact set of cams are ground will effect it. The backpressure in your exhaust housing will effect it. Most of these cam companies are not perfect at setting up their cams. Some might have some advance/retard built into them on purpose or on accident. If you do play with your intake cam gear, it will also change your ignition timing.

wheelhop · 02-11-2009

I was editing my post while you posted

^^^^^YEP! You have to test and see. It depends on the cam duration, initial cam centerline angles, turbine, intake manifold design, even exhaust manifold design, displacement. There's SO many variables. The factory cams have a certain cam timing for the stock setup and intented results with such a setup. The same goes with aftermarket cams. They are setup for the most common range of upgrades. I would use a dyno or trapspeeds to dial them in.

niterydr · 02-12-2009

Quote:

Originally Posted by Pushit2.0

I would degree the cams.

Could you maybe check that when you are assembling his wiring/piping?

Swifty1638 · 02-12-2009

he is

-A. Swift

Cammaxon · 03-01-2009

im not retardingggg

turbotalon1g · 03-01-2009

I'm a little retarded?
I tried this on my car and I didn't like the top end drop off i got. Mess with the tune for spool if you are still not happy do one of the many things shane said.

I know a guy selling a dp nitrous kit for dirt.