Camshafts and timing and stuff

[Reinhoud]

Gents,

 

One hand just curious, other hand, what if?

I've got an Suzuki GS1000, 1245cc big bore, 119grind Webcams +1mm lift, 2 valve, cr 8:1, 15 psi boost

 

I've got a set of high performance cams, that much lift that the head needed to be modified, IIRC 284 degrees timing. These cams make the bike slower with stock pistons.

 

These cams, is that a no go already? Or would they have a positive result? Say, would they be beneficiary with my set up? Is it possible to change the timing so they have a positive result?

I assume that when you add lift, you change the timing?

 

 

Thanks for any information

 

 

[Gixer1460]

Big cams always come with large overlap numbers which is not what turbos want. No point making boost and blowing it straight out of the exhaust!

[Reinhoud]

17 minutes ago, Gixer1460 said:

Big cams always come with large overlap numbers which is not what turbos want. No point making boost and blowing it straight out of the exhaust!

2 valve heads have more lift then 4 valve heads?

 

With high lift automaticly comes more overlap? I guess?

 

Just thinking, sse a lot of modern bikes with turbos, more modern bikes have more lift and overlap then the oldies..

[Gixer1460]

They may have more lift as a big single valve will generally have less valve area compared to two smaller ones. You can achieve smaller overlaps but the ramp angles and valve acceleration become too extreme to control. It has always worked best to stick with 'std' cams with turbo installs unless you had specific cams ground to minimise overlap whilst having decent lift - mine were done by Kroll Cams in the US.

[Fredrik_Steen]

31 minutes ago, Reinhoud said:

2 valve heads have more lift then 4 valve heads?

 

With high lift automaticly comes more overlap? I guess?

 

Just thinking, sse a lot of modern bikes with turbos, more modern bikes have more lift and overlap then the oldies..

What works NA also works with boost.

There are plenty of test's out on Youtube on the topic.

 

I run this camshafts that has a lot of duration with good results 

Edited September 10, 2022 by Fredrik_Steen

[Gixer1460]

With respect, those aren't big numbers compared to a performance NA cam set - 256 deg is little more than std and they've spread the LCA - always advisable with boost to reduce overlap. As a comparison my Krol cam specs are 248 deg in / 245 deg ex, 9.3mm lift, with 111 deg in / 109 deg ex. I guess if (like you) you are intending to make huge boost, higher lift numbers are required, which by necessity / geometry, will increase duration. The cams i've quoted were designed for my engine spec - by people a damn sight brighter than me - so I trust they could deliver the ultimate target (which unfortunately is less than you've achieved LOL!) But generally the advice stands - shorter duration with less overlap and highest lift possible, will suit a boosted package that max's out at a lower rpm. 

[Reinhoud]

21 hours ago, Fredrik_Steen said:

What works NA also works with boost.

There are plenty of test's out on Youtube on the topic.

 

I run this camshafts that has a lot of duration with good results 

 

What CR do you have?

These are the cams I have in mine.

I also have another set of cams what has a mm extra lift, 2 mm extra lift over stock.

These cams need a higher CR, or else the bike becomes less powerful instead of more..

 

 

 

[Fredrik_Steen]

12 hours ago, Reinhoud said:

 

What CR do you have?

These are the cams I have in mine.

I also have another set of cams what has a mm extra lift, 2 mm extra lift over stock.

These cams need a higher CR, or else the bike becomes less powerful instead of more..

 

 

 

MTC advertise cr 10.0:1 for the pistons I use  But the cylinder and head has been resurfaced two times so probably i got a little bit CR

[Fredrik_Steen]

On 9/10/2022 at 12:09 PM, Gixer1460 said:

With respect, those aren't big numbers compared to a performance NA cam set - 256 deg is little more than std and they've spread the LCA - always advisable with boost to reduce overlap. As a comparison my Krol cam specs are 248 deg in / 245 deg ex, 9.3mm lift, with 111 deg in / 109 deg ex. I guess if (like you) you are intending to make huge boost, higher lift numbers are required, which by necessity / geometry, will increase duration. The cams i've quoted were designed for my engine spec - by people a damn sight brighter than me - so I trust they could deliver the ultimate target (which unfortunately is less than you've achieved LOL!) But generally the advice stands - shorter duration with less overlap and highest lift possible, will suit a boosted package that max's out at a lower rpm. 

I'm more interested in low boost and big HP numbers. Efficiency and a good base engine 

 

I also agree that high lift and shorter duration are the way too go if the NA engine likes it. But I don't believe that the boost will go straight into the exhaust if you have a little more duration.

 

The reason I have the specific camshafts are that they where on the shelf when I was going to buy and I didn't want to wait for other grinds to be manufactured. But they work great. 

[Arttu]

On 9/10/2022 at 12:30 PM, Fredrik_Steen said:

What works NA also works with boost.

I think this depends heavily on your turbo setup. If you have an efficient setup that has low exhaust back pressure, 1:1 with boost or lower, then the cams probably work pretty much like on NA engine. But if the exhaust pressure is high then short duration / overlap cams might give better results.

As far as I know blowing fresh mixture through during overlap isn't usually a problem. When you are at operating rpm range for the cams there isn't enough time for that. But pushing the exhaust gases back to inlet can be a real problem if the exhaust pressure is significantly higher than boost.

[94RF1146]

In my build, I used the high performance intake cam (.383" lift) set at 111* and used my stock exhaust cam (.332" lift) set at 110*. 

But have a 3mm oversize exhaust valve & seat for flow.

We'll see once I get the dyno results.

* Richard Holdener video influenced my build.

M.

Edited September 13, 2022 by 94RF1146

[Gixer1460]

Sean @ BigCC tried bigger exh valves years ago with the Kat engine and for whatever reason it gave no improvement, in fact it was worse in places, so wasn't pursued ever again. Hope it works for you.