retarding the cam from 4 degrees to straight up

[JC565Ford]

Every combo is different & the only way to know how the cam timing affects power is to dyno the engine & change the cam timing....

A very true statement. It did the classic teeter-totter in the shift of the power:

When the 565 was on the dyno back in Sept '22:


We put the Danny Bee to use and advanced the cam in just few minutes. Can't wait to do it again when the engine is fresh this year. Goal is 1,000+ at 7,200.

[rfoll]

Give me the stroke length, rod length, static CR, and intake valve closing ABDC in nominal degrees (not .050").
I wrote an Excel app that can (roughly) calculate CCP in psi as well as running CP @ 1,000 RPM, then try alternate IVC closing points.

I will check that stuff out tomorrow.

[travis]

My opinion, fwiw...

I think you are going to have problems on pump gas. If you had some 72-76cc chambered aluminum heads with the fast burn style chambers, I wouldn't think twice about running it. But you don't...you have an iron head with a conventional style open chamber, with a slightly more detonation prone bigger bore block, in a car that is known to have cooling airflow issues, with a cam that is going to generate some strong cylinder pressure. The gears, converter, and weight will certainly help here. If the tune is spot on, and you can keep it really cool...you might have a fighting chance.

I do tend to be more conservative though, especially when it comes to someone else's vehicle. And I don't like redoing a job if it doesn't work out

[Monza355]

What fuel are you going to run ? What octane rating ?

[rfoll]

My opinion, fwiw...

I think you are going to have problems on pump gas. If you had some 72-76cc chambered aluminum heads with the fast burn style chambers, I wouldn't think twice about running it. But you don't...you have an iron head with a conventional style open chamber, with a slightly more detonation prone bigger bore block, in a car that is known to have cooling airflow issues, with a cam that is going to generate some strong cylinder pressure. The gears, converter, and weight will certainly help here. If the tune is spot on, and you can keep it really cool...you might have a fighting chance.

I do tend to be more conservative though, especially when it comes to someone else's vehicle. And I don't like redoing a job if it doesn't work out

I haven't seen the heads yet, but the pictures I have seen show what appears to be a standard heart shaped Dart chamber, albeit a deep one. It bears no resemblance to a 70s smog chamber. He has an air dam installed on the car to help cooling issues, and it does work. I have never had a problem with cooling on my 400 based engines, but I never had one in a Corvette.

[rfoll]

Give me the stroke length, rod length, static CR, and intake valve closing ABDC in nominal degrees (not .050").
I wrote an Excel app that can (roughly) calculate CCP in psi as well as running CP @ 1,000 RPM, then try alternate IVC closing points.

The engine is a 4.185 bore, 3.75 stroke, and 5.7 rod. The static compression is 10.2:1, I measured it twice, assuming the actual chamber size. The cam card says intake closing is 64 degrees @.006, I measured 63 degrees. I'm getting ready for the s..t storm from everyone for running a .060 over 400, but this engine has been successfully run in it's previous life. Hopefully this info will answer my initial question as to whether pulling timing back from 4 degrees advanced to straight up will have any effect at all.

[Stan Weiss]

Give me the stroke length, rod length, static CR, and intake valve closing ABDC in nominal degrees (not .050").
I wrote an Excel app that can (roughly) calculate CCP in psi as well as running CP @ 1,000 RPM, then try alternate IVC closing points.

The engine is a 4.185 bore, 3.75 stroke, and 5.7 rod. The static compression is 10.2:1, I measured it twice, assuming the actual chamber size. The cam card says intake closing is 64 degrees @.006, I measured 63 degrees. I'm getting ready for the s..t storm from everyone for running a .060 over 400, but this engine has been successfully run in it's previous life. Hopefully this info will answer my initial question as to whether pulling timing back from 4 degrees advanced to straight up will have any effect at all.

Retarding the cam 4 degrees from 64 to 68 will reduce your cranking compression about 8.5 psi.

Stan

[skinny z]

I've run the following successfully on the street and track for tens of thousands of miles.

355: 4.030” x 3.48”
5 cc piston
Elgin rods
.014” deck
670 Holley
RPM Air Gap
RHS Pro Torker Vortec heads. 64 cc
Custom cam. 274/282, 224/230, .574”/ .569”, 110 LSA, 106 ICL, 63 ABDC IVC (COMP XFI lobes)
Victor Reinz 5746 head gasket .026” x 4.120”
.040" quench.
Mid length headers
10.37 SCR / 8.4 DCR
Cranking pressure: 200+ 600’ elevation

3600 lb 3rd gen Camaro. 3.73 gear, 700R4 with ~3000 stall lockup converter.
Simple timing curve with 18 initial and another 16 mechanical. All in by 3000-3200.
The converter worked well as it allowed the engine to get through the lower RPMs quickly with no lugging.

I also employed a lean cruise and with the vacuum advance pulled at 2500 RPM highway cruise advance approached 45. AFR's were thinned out to 16:1. As mentioned, this is where it was most sensitive to rattling and could be heard faintly if up against the guardrail.
Always, premium fuel 94 octane.

I still have that cam and am very much considering using it again. The new 357 will also see 10.2:1 with the iron heads. Possibly tighter quench at .034" but basically the same build with refinements.

[rfoll]

Give me the stroke length, rod length, static CR, and intake valve closing ABDC in nominal degrees (not .050").
I wrote an Excel app that can (roughly) calculate CCP in psi as well as running CP @ 1,000 RPM, then try alternate IVC closing points.

The engine is a 4.185 bore, 3.75 stroke, and 5.7 rod. The static compression is 10.2:1, I measured it twice, assuming the actual chamber size. The cam card says intake closing is 64 degrees @.006, I measured 63 degrees. I'm getting ready for the s..t storm from everyone for running a .060 over 400, but this engine has been successfully run in it's previous life. Hopefully this info will answer my initial question as to whether pulling timing back from 4 degrees advanced to straight up will have any effect at all.

Retarding the cam 4 degrees from 64 to 68 will reduce your cranking compression about 8.5 psi.

Stan

Is that enough to make it less sensitive to pinging?

[Bigchief632]

The engine is a 4.185 bore, 3.75 stroke, and 5.7 rod. The static compression is 10.2:1, I measured it twice, assuming the actual chamber size. The cam card says intake closing is 64 degrees @.006, I measured 63 degrees. I'm getting ready for the s..t storm from everyone for running a .060 over 400, but this engine has been successfully run in it's previous life. Hopefully this info will answer my initial question as to whether pulling timing back from 4 degrees advanced to straight up will have any effect at all.

Retarding the cam 4 degrees from 64 to 68 will reduce your cranking compression about 8.5 psi.

Stan

Is that enough to make it less sensitive to pinging?

I'd run a .051thick gasket. That will work better, I promise. It actually works the opposite of what most believe. What elevation are you at in Oregon?

[travis]

https://www.castheads.com/cylinder-head ... ent-heads/

If you indeed have the S/R heads, which afaik are the only ones with 76cc chambers, then the above link will show you what you've got.

[rfoll]

https://www.castheads.com/cylinder-head ... ent-heads/

If you indeed have the S/R heads, which afaik are the only ones with 76cc chambers, then the above link will show you what you've got.

Those are World products heads. We have Dart SS.

[travis]

https://www.castheads.com/cylinder-head ... ent-heads/

If you indeed have the S/R heads, which afaik are the only ones with 76cc chambers, then the above link will show you what you've got.

Those are World products heads. We have Dart SS.

My mistake. I seen 76cc and immediately tunnel visioned right to the WP heads

[rfoll]

Retarding the cam 4 degrees from 64 to 68 will reduce your cranking compression about 8.5 psi.

Stan

Is that enough to make it less sensitive to pinging?

I'd run a .051thick gasket. That will work better, I promise. It actually works the opposite of what most believe. What elevation are you at in Oregon?

We already have the 1014 .039" gasket. Purchased a long time ago. I gave some thought to the 1044/.050" gasket, but I debated the extra .010" of quench. It would drop the static from 10.2 to 10.0. The CR might change when I get my hands on the heads. Publishes volumes can be different from reality. I plan on polishing the chambers some to reflect some heat. We are under 100' in most of the surrounding area. The drag strip is about 30'. "It actually works the opposite of what most believe". Would you care to explain?

[panic]

With IVC @ 63° the DCR is 8.3:1, about 192 CCP gauge psi, volume/pressure index is 457 (input is CCP × reduced stroke length, etc.). Guessing ratio of heats @ 1.25...
Retarding it to 67° gives DCR is 8.05:1, about 185 CCP gauge psi, volume/pressure index is 420. Combustion pressure is down about 8%.
Another retard to 71° gives DCR is 7.79:1, about 177 CCP gauge psi, volume/pressure index is 383. Combustion pressure is down about 16% from original.