DCR and SFT valve lash

[blackford]

I have a 331 SBF with a Comp 282S and 1.7 rockers. Engine has ported DOOE Ford iron and it makes about 420HP@6500.

With this combination, I am seeing 1 point of change in DCR depending on whether lash is set tight or loose. With lash set to .015, DCR is in the 6.9s. With lash set to .025, DCR is almost 7.8. This is based on analysis using EA Pro 3.9. HP doesn't really change all that much though...maybe 5-7 HP at peak.

Less than 7 DCR just strikes me as being pretty low and lazy. The engine runs on pump gas and I have SCR of about 9.7. I've read that a DCR of 8, especially with aluminum heads, can be OK with pump gas. I've routinely run this cam with tight lash, but a difference of almost 1 pt in DCR depending on lash was as surprise to me (assuming EA Pro is correct) and now i'm wondering if I ought to run a looser lash of say .020 where DCR was around 7.4.

I am seriously considering switching heads soon from ported Ford iron DOOEs to something aluminum. I wonder if I ought to also have the new heads milled to get SCR up around 10.5 and then this would allow me to get DCR up around 8 with lash set to .020 (currently i'd have to run lash looser than .025 to get DCR of 8...too loose). If I get detonation, then I can tighten lash and/or adjust timing as required.

Does this sound like a reasonable approach? Other recommendations?

[HQM383]

I have a 331 SBF with a Comp 282S and 1.7 rockers. Engine has ported DOOE Ford iron and it makes about 420HP@6500.

With this combination, I am seeing 1 point of change in DCR depending on whether lash is set tight or loose. With lash set to .015, DCR is in the 6.9s. With lash set to .025, DCR is almost 7.8. This is based on analysis using EA Pro 3.9. HP doesn't really change all that much though...maybe 5-7 HP at peak.

Less than 7 DCR just strikes me as being pretty low and lazy. The engine runs on pump gas and I have SCR of about 9.7. I've read that a DCR of 8, especially with aluminum heads, can be OK with pump gas. I've routinely run this cam with tight lash, but a difference of almost 1 pt in DCR depending on lash was as surprise to me (assuming EA Pro is correct) and now i'm wondering if I ought to run a looser lash of say .020 where DCR was around 7.4.

I am seriously considering switching heads soon from ported Ford iron DOOEs to something aluminum. I wonder if I ought to also have the new heads milled to get SCR up around 10.5 and then this would allow me to get DCR up around 8 with lash set to .020 (currently i'd have to run lash looser than .025 to get DCR of 8...too loose). If I get detonation, then I can tighten lash and/or adjust timing as required.

Does this sound like a reasonable approach? Other recommendations?

Make wholesale changes to up static comp or go a smaller duration cam. It depends on end goal.

[1980RS]

I have a 331 SBF with a Comp 282S and 1.7 rockers. Engine has ported DOOE Ford iron and it makes about 420HP@6500.

With this combination, I am seeing 1 point of change in DCR depending on whether lash is set tight or loose. With lash set to .015, DCR is in the 6.9s. With lash set to .025, DCR is almost 7.8. This is based on analysis using EA Pro 3.9. HP doesn't really change all that much though...maybe 5-7 HP at peak.

Less than 7 DCR just strikes me as being pretty low and lazy. The engine runs on pump gas and I have SCR of about 9.7. I've read that a DCR of 8, especially with aluminum heads, can be OK with pump gas. I've routinely run this cam with tight lash, but a difference of almost 1 pt in DCR depending on lash was as surprise to me (assuming EA Pro is correct) and now i'm wondering if I ought to run a looser lash of say .020 where DCR was around 7.4.

I am seriously considering switching heads soon from ported Ford iron DOOEs to something aluminum. I wonder if I ought to also have the new heads milled to get SCR up around 10.5 and then this would allow me to get DCR up around 8 with lash set to .020 (currently i'd have to run lash looser than .025 to get DCR of 8...too loose). If I get detonation, then I can tighten lash and/or adjust timing as required.

Does this sound like a reasonable approach? Other recommendations?

Has anyone ever told you about the secret of the Magnum solid cams, Scooter Brothers told me one day. It was quite an eye opener.

[Geoff2]

These cams have a 0.015" - 0.030" lash adjustment range which gives a change of 20* in adv duration.

[blackford]

These cams have a 0.015" - 0.030" lash adjustment range which gives a change of 20* in adv duration.

Yes, i've seen that. I'm on the tight end of things with lash set to .015 cold for an iron headed iron block engine. I did check the cranking compression and it was 185 psi (engine hot) at a cranking speed of 200 rpm and the throttle wide open. That was encouraging as I was expecting a lower result given that EA Pro had calculated a DCR of less than 7 and cranking compression quite a bit lower than 185. I'm going to have to check my inputs used to calculate ramp rating...something seems off. Maybe my DCR at this lash setting isn't so bad after all.