Cylinder pressure and advancing cam timing.

[hysteric]

You'd probabily also want to install that xs282 cam a bit further advanced from cam card. Say on 104 in c/l

I was thinking that too.

[twl]

If the cam events are correct for the engine, why mess that up to overcome a cylinder pressure matter which would be more properly addressed with a piston change?

[F-BIRD'88]

To know the real seat to seat timibg at lash point
You can:
Ask the cam designer/manufacturer

Measure in motor
Measure on a Cam Dr.

Get the data from someone who has already done
the measurement.

[David Redszus]

An advance in IVC of 5 deg would result in a compression pressure increase of about 12 psi.

What effect would that have on performance?

The change in IVC would also cause a change in compression temperature of about 20 deg, which might have a more significant impact on performance than an increase in pressure.

[hysteric]

If the cam events are correct for the engine, why mess that up to overcome a cylinder pressure matter which would be more properly addressed with a piston change?

There's no point its already at 70 over.

[hysteric]

An advance in IVC of 5 deg would result in a compression pressure increase of about 12 psi.

What effect would that have on performance?

The change in IVC would also cause a change in compression temperature of about 20 deg, which might have a more significant impact on performance than an increase in pressure.

It may just improve the combustion event enough to give me the performance I'm expecting?

[canada1]

Yes advancing the camshaft will lead to higher cranking pressure.
It will also open the exhaust valve earlier - what effect might that have?

[jeff swisher]

I have 2 friends that tried retarding their cams 4 degrees looking for more top end power.
Both lost cylinder pressures and did nothing but kill power everywhere and lost significant top end by retarding the cams.

First one was a 10.3 compression 357" with comp 292H 244@ .050 on a 110LSA.
Installed on the 106ICL it would rev strong to 7500rpm.
Retarded 4 degrees it was nosing over at 7200 and out of steam at 7000.
Went from 11.9 to 12.2 in the 1/4.

Second buddy was running basically the same same long block set up and a Solid flat tappet 252@ .050 and .571" lift on a 106 LSA with 1.6 rockers take .026" off that for lash.
He retarded his cam 4 degrees from the 102ICL and went from mid 11's to 12.20's.

I feel your 112LSA was a poor choice. I have no idea why you got that on a 112 LSA I think Crower offers those on a 105.

That is the path I would go if advancing the cam does not get you what you need.

[MadBill]

Historically, retarding a cam is significantly less likely to be a benefit than advancing it, but there are numerous exceptions and special circumstances.

An example of the latter from the mid-seventies would be my friend's open wheel Formula Ford 1600 cc racer. Permitted engine mods were very limited and did not encompass cam changes. For that engine's narrow operating range, the optimum cam indexing proved to be 8°retarded from factory spec!

From the 'exception' file, a nearby shop specializes in big Hemis and has a number of well-developed packages. A promising new cam from their usual supplier was installed in a ~ 950 HP 572" at the suggested 4° A and appeared to perform as expected, however progressively retarding it to 1°R added 20 HP peak and a substantial increase in area under the curve for the operating range.

[hysteric]

Just checked the timing on the camshaft at the valve and got 9 BTDC and 48 ABDC with a cold lash of .026

Cam card calls for 13.5 and 49.5 but i would imagine that is taken directly from the cam.

[Tuner]

How much base circle runout does it have?

Where is the equal lift point relative to TDC? The crossover point in the overlap, intake opening and exhaust closing, where both lobes are at the same lift.

[hysteric]

C'mon Tuner you're making my head hurt now.

[steve cowan]

I have 2 friends that tried retarding their cams 4 degrees looking for more top end power.
Both lost cylinder pressures and did nothing but kill power everywhere and lost significant top end by retarding the cams.

First one was a 10.3 compression 357" with comp 292H 244@ .050 on a 110LSA.
Installed on the 106ICL it would rev strong to 7500rpm.
Retarded 4 degrees it was nosing over at 7200 and out of steam at 7000.
Went from 11.9 to 12.2 in the 1/4.

Second buddy was running basically the same same long block set up and a Solid flat tappet 252@ .050 and .571" lift on a 106 LSA with 1.6 rockers take .026" off that for lash.
He retarded his cam 4 degrees from the 102ICL and went from mid 11's to 12.20's.

I feel your 112LSA was a poor choice. I have no idea why you got that on a 112 LSA I think Crower offers those on a 105.

That is the path I would go if advancing the cam does not get you what you need.

good information there Jeff,i am going to do the same testing myself over the next couple of months,i want to run lash loops,different spacers,ignition timing and fuel curves where possible,track tuning is tough due to so many variables.
and finding proper cam events for your own application is even harder.

Historically, retarding a cam is significantly less likely to be a benefit than advancing it, but there are numerous exceptions and special circumstances.

An example of the latter from the mid-seventies would be my friend's open wheel Formula Ford 1600 cc racer. Permitted engine mods were very limited and did not encompass cam changes. For that engine's narrow operating range, the optimum cam indexing proved to be 8°retarded from factory spec!

From the 'exception' file, a nearby shop specializes in big Hemis and has a number of well-developed packages. A promising new cam from their usual supplier was installed in a ~ 950 HP 572" at the suggested 4° A and appeared to perform as expected, however progressively retarding it to 1°R added 20 HP peak and a substantial increase in area under the curve for the operating range.

great post Bill,just shows that advancing cam timing is not the'' be all to end all''
those people who have access to a dyno will always have the advantage,and me thinks that 1 day on the dyno you will learn more than you would trying to track tune for a year.

[Stan Weiss]

Just checked the timing on the camshaft at the valve and got 9 BTDC and 48 ABDC with a cold lash of .026

Cam card calls for 13.5 and 49.5 but i would imagine that is taken directly from the cam.

So that is 243 @ 108 ICL, but does not help me. Where does the intake valve close? Also where does the intake valve close if you set the lash @ 0.030?

Stan

[Stan Weiss]

Just checked the timing on the camshaft at the valve and got 9 BTDC and 48 ABDC with a cold lash of .026

Cam card calls for 13.5 and 49.5 but i would imagine that is taken directly from the cam.

So that is 237 @ 109.5 ICL, but does not help me. Where does the intake valve close? Also where does the intake valve close if you set the lash @ 0.030?

Stan