Camshafts and Compression

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Valman

Valman

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Hey guys, I’ve just joined & great to be on board.

A while back I put together a 410 stroker with some very good gear in it, it went together really well.
I got a lot of the parts from a well known builder, who also supplied me the camshaft. (Hyd.Flat Tappet).
The issue is, with 10.7:1 compression ratio, my cranking compression is up at 210-220psi!

After lots of number crunching, I’ve come to a point where I believe the camshaft doesn’t suit the engine combo.

The intake valve closes 42 degrees ABDC, which puts me at 9.8:1 dynamic CR. Way too much for pump fuel!

There’s a few problems I’ve noticed with this situation, but have any of you guys run a similar combo with a cam that’s really worked well? It seems to me that a cam that closes the intake valve around the 65-70 degrees ABDC mark would be a lot more suitable.

Appreciate any input, sorry if the post is a bit long!
 
I’d like to be around 180psi for pump fuel, 220 is more E85 territory.
It’s not that mild of a cam, 236* at 50, 108 LSA, 104 LCA. But only 23* of overlap?? Seems more like a speedway/oval track cam to me.
 
Valman said:
I’d like to be around 180psi for pump fuel, 220 is more E85 territory.
It’s not that mild of a cam, 236* at 50, 108 LSA, 104 LCA. But only 23* of overlap?? Seems more like a speedway/oval track cam to me.
Click to expand...
That's mild. I have a 10.5:1 slant 6 with a solid flat tappet .465/250@.050 on a 108. It gets driven daily quite regularly.
 
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That’s what I mean regarding the short overlap it has. For a cam at 236 duration, you’d expect more like 60-70 degrees, not 23.

Where does that cam in your slant close the intake valve? That should determine largely how much cranking compression it has.
 
Valman said:
Hey guys, I’ve just joined & great to be on board.

A while back I put together a 410 stroker with some very good gear in it, it went together really well.
I got a lot of the parts from a well known builder, who also supplied me the camshaft. (Hyd.Flat Tappet).
The issue is, with 10.7:1 compression ratio, my cranking compression is up at 210-220psi!

After lots of number crunching, I’ve come to a point where I believe the camshaft doesn’t suit the engine combo.

The intake valve closes 42 degrees ABDC, which puts me at 9.8:1 dynamic CR. Way too much for pump fuel!

There’s a few problems I’ve noticed with this situation, but have any of you guys run a similar combo with a cam that’s really worked well? It seems to me that a cam that closes the intake valve around the 65-70 degrees ABDC mark would be a lot more suitable.

Appreciate any input, sorry if the post is a bit long!
Click to expand...
I do not know it all but I do know what worked for me.
I don't think that you can "cam your way" out of high compression without some serious drawbacks.
ANY cam that has a later intake closing is going to build less cylinder pressure at low rpms but then REALLY make up for it at higher rpms.
That cam will make the engine lazy at low rpms too.
10.7 even with aluminum heads is not ideal. If your octane rating is not high enough, you'll have to restrict the ignition timing total and rate...That costs power too.
What I learned about 10-11 years ago is that less compression will allow you to run more spark timing which in itself, allows more power than the higher compression does.
I tried the Switch to a bigger cam advice with a 440/493 years ago. I was at 10.8 with aluminum heads and mine knocked at anything over half throttle. I had a MP 292/509 cam and was registering 190 psi cranking compression. I first tried slowing the ignition advance, I limited it to 31 degrees, I tried 1.6 rocker arms, then a bigger cam. Eventually I had to face that I simply had too high compression for the fuel sold at the pump. I slipped in thicker head gaskets which lowered the compression from 10.8 to 10.18. NO knocking but it wasn't a perfect setup. Years later I pulled the engine and swapped in dished pistons which dropped the ratio to 9.8 but now I had quench....THIS buys you some detonation resistance while making a bit of power.
Good luck to you.
 
The DCR is useless as a guide for CR. It takes NO ACCOUNT of how well the induction flow is [ the intake port, intake manifold & whatever is on top ]. You can have two engines with the same IVC but one packs more air into the cyl because of better flow. Yet both would give the same number with the DCR calculator.
 

Kern Dog said:
I do not know it all but I do know what worked for me.
I don't think that you can "cam your way" out of high compression without some serious drawbacks.
ANY cam that has a later intake closing is going to build less cylinder pressure at low rpms but then REALLY make up for it at higher rpms.
That cam will make the engine lazy at low rpms too.
10.7 even with aluminum heads is not ideal. If your octane rating is not high enough, you'll have to restrict the ignition timing total and rate...That costs power too.
What I learned about 10-11 years ago is that less compression will allow you to run more spark timing which in itself, allows more power than the higher compression does.
I tried the Switch to a bigger cam advice with a 440/493 years ago. I was at 10.8 with aluminum heads and mine knocked at anything over half throttle. I had a MP 292/509 cam and was registering 190 psi cranking compression. I first tried slowing the ignition advance, I limited it to 31 degrees, I tried 1.6 rocker arms, then a bigger cam. Eventually I had to face that I simply had too high compression for the fuel sold at the pump. I slipped in thicker head gaskets which lowered the compression from 10.8 to 10.18. NO knocking but it wasn't a perfect setup. Years later I pulled the engine and swapped in dished pistons which dropped the ratio to 9.8 but now I had quench....THIS buys you some detonation resistance while making a bit of power.
Good luck to you.
Click to expand...
Yeah, your experience there sounds about where I’m at now. I have C.N.C. ported aluminium heads with 0.036’’ squish/quench clearance. I hand polished the chambers & equalised the volume.
I’ve taken the advice of the ‘experts’, however I think a lot of them tend to have more of a racing mindset, even when it comes to giving advice on street engines.
I have got the ignition timing at 30*, at 32* it would occasionally pre-ignite. It sometimes feels the engine is ‘working against the compression’ when over about 4000rpm. Hope that makes sense.
Maybe with the long 4.00’’ stroke, the CR should be under 10:1 for pump fuel. With the long stroke, the piston is at TDC for more degrees plus a tight quench, there’s more than enough compression?? Thanks man
 
Bewy said:
The DCR is useless as a guide for CR. It takes NO ACCOUNT of how well the induction flow is [ the intake port, intake manifold & whatever is on top ]. You can have two engines with the same IVC but one packs more air into the cyl because of better flow. Yet both would give the same number with the DCR calculator.
Click to expand...
Yes, I understand what you’re saying. A better induction ‘system’ will give you better flow, V.E etc therefore more cylinder pressure.
I understand you can’t just take static measurements as a final word. But we still need to know them to roadmap where we need to go.
 
Valman said:
I’d like to be around 180psi for pump fuel, 220 is more E85 territory.
It’s not that mild of a cam, 236* at 50, 108 LSA, 104 LCA. But only 23* of overlap?? Seems more like a speedway/oval track cam to me.
Click to expand...
Those specs should be about 50-54 overlap. What are you using to calculate this?
 
MV8 said:
Those specs should be about 50-54 overlap. What are you using to calculate this?
Click to expand...
Exhaust Closing + Intake Opening. I tried the other method of adding the duration together and then dividing, got the same results.

Int.Open 14 btdc
Exh.Close 9 atdc
Int.Close 42 abdc
Exh.Open 53 bbdc
236* intake 242* exhaust @0.050
 
Valman said:
Hey guys, I’ve just joined & great to be on board.

A while back I put together a 410 stroker with some very good gear in it, it went together really well.
I got a lot of the parts from a well known builder, who also supplied me the camshaft. (Hyd.Flat Tappet).
The issue is, with 10.7:1 compression ratio, my cranking compression is up at 210-220psi!

After lots of number crunching, I’ve come to a point where I believe the camshaft doesn’t suit the engine combo.

The intake valve closes 42 degrees ABDC, which puts me at 9.8:1 dynamic CR. Way too much for pump fuel!

There’s a few problems I’ve noticed with this situation, but have any of you guys run a similar combo with a cam that’s really worked well? It seems to me that a cam that closes the intake valve around the 65-70 degrees ABDC mark would be a lot more suitable.

Appreciate any input, sorry if the post is a bit long!
Click to expand...
How many pumps on the pressure gauge?

If you want an easy solution just retard it.
 
On a Crower cam I moved around it would pick up 10 psi with 2 degrees forward. Move it around and see what you get
 

What's your octane rating and how do you have your advance curve set? That's not nearly enough cam for optimum performance for a 410 stroker with CNC heads. Also, if it's an automatic, what converter? What is it in (weight) and what's the rear axle ratio?
 
Valman said:
Exhaust Closing + Intake Opening. I tried the other method of adding the duration together and then dividing, got the same results.

Int.Open 14 btdc
Exh.Close 9 atdc
Int.Close 42 abdc
Exh.Open 53 bbdc
236* intake 242* exhaust @0.050
Click to expand...
About your cam specs being odd, a third of the cams in Eric's cam comparison test had the same or less overlap. Most had an ivc in the 40s with the latest being one cam at 55.5 and 37.5 overlap at 50. Based on ranking for avg tq, #2 had specs very similar yours.

What head gaskets and pistons were used? I know someone that has similar psi, runs pump gas, but has zero initial (and probably not much of a curve). You probably don't care about mpg but may care about range. I'd keep the cam and change the pistons, also for easier starting and less heat to get rid of.
 
Valman said:
That’s what I mean regarding the short overlap it has. For a cam at 236 duration, you’d expect more like 60-70 degrees, not 23.

Where does that cam in your slant close the intake valve? That should determine largely how much cranking compression it has.
Click to expand...
You're probably reading the .050" figure, I'm sure. Mine has an IVCE of 71 degrees ABDC.
 
MV8 said:
About your cam specs being odd, a third of the cams in Eric's cam comparison test had the same or less overlap. Most had an ivc in the 40s with the latest being one cam at 55.5 and 37.5 overlap at 50. Based on ranking for avg tq, #2 had specs very similar yours.

What head gaskets and pistons were used? I know someone that has similar psi, runs pump gas, but has zero initial (and probably not much of a curve). You probably don't care about mpg but may care about range. I'd keep the cam and change the pistons, also for easier starting and less heat to get rid of.
Click to expand...
Pistons are Icon forged flat tops with the valve reliefs.
Head gasket is Felpro composite, 0.039’’ thickness.
The starter motor does struggle when the engine is warmed up. Starts well when cooled down.
I’ve noticed it idles perfectly with the initial at around 22*, of course this much initial doesn’t help with starting it hot. ATM the timing is all in by 2700.
I have a good cooling system, a flow cooler pump (with a vane impeller) good radiator, etc. I overdrive the pump at around 1.2:1.
 
Int.Open 14 btdc
Exh.Close 9 atdc
Int.Close 42 abdc
Exh.Open 53 bbdc
236* intake 242* exhaust @0.050
Click to expand...

Overlap and dynamic compression calculations are done using seat-to-seat(advertised) timing numbers…… not the numbers at .050”.
However, having the correct timing numbers won’t change what the compression gauge reads.

For a more realistic dynamic compression calculation, try adding about 15deg to your int closing point of 42abdc.
EDIT: I should have said “add 22-24deg”, not 15(236@.050 should be close to 280-284@.006).

If you’re running lifters with a fast-ish bleed rate, they’re bled down some during the cranking pressure test, which will inflate those numbers a bit.

To test for that, with the lifter on the base circle of the cam, back the adjusters for one cylinder off, insert a .010” feeler gauge between the valve and rocker, then slowly tighten the adjuster screw until the lifter plunger is bottomed out.
Remove the feeler gauge, do the other valve the same way.
Retest the cranking pressure on that cylinder.
If your lifters were bled down before, the new test with the bottomed lifters will show lower numbers.
If the numbers are about the same as before, the lifters weren’t bled down on the previous test.

Obviously, after the test, reset the lifters to desired preload.
 
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Garrett Ellison said:
What's your octane rating and how do you have your advance curve set? That's not nearly enough cam for optimum performance for a 410 stroker with CNC heads. Also, if it's an automatic, what converter? What is it in (weight) and what's the rear axle ratio?
Click to expand...
I took the advice from the gurus who recommended that cam. That was back in 2016-17. I tend to think they got it wrong.
We have 98 RON fuel here, about equivalent or slightly better than your 93 MON fuel. We could get 100 RON a few years ago.
It has a good shift kitted TF, 3000 stall that I had specially made, 3.55:1 gears ATM.
 
PRH said:
Overlap and dynamic compression calculations are done using seat-to-seat(advertised) timing numbers…… not the numbers at .050”.
However, having the correct timing numbers won’t change what the compression gauge reads.
Click to expand...
Cam card only has numbers at 0.050’’. The calculator I have used in the past does ask for duration numbers at 0.050’’, funny enough, it did predict the cylinder pressure accurately. But there’s probably better calculators around.

The gauge doesn’t lie, 210-220psi. Too much for pump fuel.
 
210-220 is not too much for pump fuel. I have a turbo Honda v6 in my falcon and it pumps 225, run boost, and it does it on California 91 octane. You need to put a better curve in your distributor. All in by 2700 is too early and you should delay the curve a bit around peak torque and add it in as the engine rpms. That’s not to say that you might be able to cut a camshaft more suited to your build, but you should be able to tune around the detonation with a proper curve that allows you to make the same power.
 
Here’s the results from the Wallace site, using the 42abdc closing point.
Notice the instructions at the top of the page.

Changing the closing point to 65abdc(282deg advertised) lowers the DCR number over 1 point and the cranking pressure by 30psi.

IMG_3791.png
 
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