Max dynamic compression on 93 octane?

[Caprimaniac]

I know this is an old thread, but the question asked is relevenat....

This is a race- only engine. DCR 9.56:1 on Wallace calculator w/ 0.05" closing point.

SBF with Victor heads and 4.125 bore 3.47 stroke.0.040" quench.

Inlet close 65 deg ABC @0.05". Seat duration is 328 degree, 276 @0.050.

Assuming the cam is symmetrical (it's a Jones solid roller), will that give a closing inlet valve at 65 + (328-276)/2= 91 degrees ABC? And DCR at 7.1:1?
I do not currently have the carnk in, so I have no way to meassure.


I would have no fear starting and running enginge w/o load- but I am a bit worried to race on 93- should I go to 110 octane? Since I'm EFI, I can make up a map for both. Even have injector size to go meth, but then I'm missing 3 points in compression....

[Nut124]

Hello Maniac,

Applyind DCR to an all out race engine seems a bit off to me. The big cam is there not to lower DCR but to maximize VE and peak HP at race rpm, right? What is your static CR?

[Stan Weiss]

I know this is an old thread, but the question asked is relevenat....

This is a race- only engine. DCR 9.56:1 on Wallace calculator w/ 0.05" closing point.

SBF with Victor heads and 4.125 bore 3.47 stroke.0.040" quench.

Inlet close 65 deg ABC @0.05". Seat duration is 328 degree, 276 @0.050.

Assuming the cam is symmetrical (it's a Jones solid roller), will that give a closing inlet valve at 65 + (328-276)/2= 91 degrees ABC? And DCR at 7.1:1?
I do not currently have the carnk in, so I have no way to meassure.


I would have no fear starting and running enginge w/o load- but I am a bit worried to race on 93- should I go to 110 octane? Since I'm EFI, I can make up a map for both. Even have injector size to go meth, but then I'm missing 3 points in compression....

What is your rod length?

Using a 5.7" rod, IVC 91 ABDC and 7.1:1 DCR I get 11.7:1 SCR

Using a 5.7" rod, IVC 91 ABDC and 9.56:1 DCR I get 16.:1 SCR

Stan

[skinny z]

This is a race- only engine. DCR 9.56:1 on Wallace calculator w/ 0.05" closing point.
Inlet close 65 deg ABC @0.05". Seat duration is 328 degree, 276 @0.050.
Assuming the cam is symmetrical (it's a Jones solid roller), will that give a closing inlet valve at 65 + (328-276)/2= 91 degrees ABC? And DCR at 7.1:1?

You would have to use the advertised duration value for the IVC and input for a DCR calculation. Better still is if the cam card offers the IVC at .006". You can then use a calculator like Pat Kelly's (which uses adv. numbers plus LSA and ICL ) and compares the calculated number vs the actual number.

[Caprimaniac]

I know this is an old thread, but the question asked is relevenat....

This is a race- only engine. DCR 9.56:1 on Wallace calculator w/ 0.05" closing point.

SBF with Victor heads and 4.125 bore 3.47 stroke.0.040" quench.

Inlet close 65 deg ABC @0.05". Seat duration is 328 degree, 276 @0.050.

Assuming the cam is symmetrical (it's a Jones solid roller), will that give a closing inlet valve at 65 + (328-276)/2= 91 degrees ABC? And DCR at 7.1:1?
I do not currently have the carnk in, so I have no way to meassure.


I would have no fear starting and running enginge w/o load- but I am a bit worried to race on 93- should I go to 110 octane? Since I'm EFI, I can make up a map for both. Even have injector size to go meth, but then I'm missing 3 points in compression....

What is your rod length?

Using a 5.7" rod, IVC 91 ABDC and 7.1:1 DCR I get 11.7:1 SCR

Using a 5.7" rod, IVC 91 ABDC and 9.56:1 DCR I get 16.:1 SCR

Stan

So, Stan- you agree on my math on converting from 0.050- numbers to actual seat timing?

I have 5.400 rods and static is 12:1 (or vety close to. Like 12.01 or so).

Yes- I figured I had to use actual timing, intake valve closinh @. But lacking that number, convert numbers from .05 to adrevertised...

[Stan Weiss]

Is 328 seat-to-seat duration at the valve with lash set?

328 seat-to-seat duration installed on a 107 ICl is IVO 57 BTDC and IVC 91 ABDC.

I get 7.3:1 DCR with 12:1 SCR and 5.4" rod.

Is the engine together? If so have you done a cranking compression test?

Stan

[Caprimaniac]

Hi, Stan. No; crank is at the shop getting balanced. Has taken close to a year...

Yes- I thought the lash had to be calculated in just after I posted the last answer.

So; cam data gives timing figures with lash included @ 050 but then- seat timing is given at the lifter; no lash included. What that mean is you have to meassure actual seat timing at the valve with correct lash.

But the numbers you leave are identical to what I found on Wallace. You prob use the more advanxed calc.

[David Redszus]

My DCR numbers match those of Stan's.

If a cam card is missing, one way to determine IVC is by use of a Compression Leak Tester.
Simply pressurize the chamber (any low pressure) and rotate the engine until the pressure
jumps. That would be the IVC seat angle.

More important. Just what does DCR tell you? What can be made of the DCR number?

[rustbucket79]

Race engine with 12:1 static and a 274 @ .050 cam, unless you’re running a restrictor plate or the heads are junk, the engine is going to exceed 100% volumetric efficiency for a good part of the powerband. Other than the initial fire up and light load, this is a race gas only race engine.

[midnightbluS10]

Hi, Stan. No; crank is at the shop getting balanced. Has taken close to a year...

Yes- I thought the lash had to be calculated in just after I posted the last answer.

So; cam data gives timing figures with lash included @ 050 but then- seat timing is given at the lifter; no lash included. What that mean is you have to meassure actual seat timing at the valve with correct lash.

But the numbers you leave are identical to what I found on Wallace. You prob use the more advanxed calc.

Close to a year to balance the crank? Are you serious?

[skinny z]

More important. Just what does DCR tell you? What can be made of the DCR number?

For me, it's another tool in the toolbox however this tool, I would say, is very platform or even engine specific.
Similar to original 10 year old question, I've got an idea of what an effective DCR might be for an iron headed, 230-ish @ .050", Gen 1 350 SBC.
I can't say how that would translate to a BBC or even a Gen 2 SBC. But I know what to shoot for with what I've got (and even then I'm not so sure).

[David Redszus]

More important. Just what does DCR tell you? What can be made of the DCR number?

For me, it's another tool in the toolbox however this tool, I would say, is very platform or even engine specific.
Similar to original 10 year old question, I've got an idea of what an effective DCR might be for an iron headed, 230-ish @ .050", Gen 1 350 SBC.
I can't say how that would translate to a BBC or even a Gen 2 SBC. But I know what to shoot for with what I've got (and even then I'm not so sure).

Any non-numeric comparison would be correlative and not causative. DCR values are mere ratios and cannot be
compared since they lack actual measurement of pressure and temperature.

DCR values must be converted to actual compression temps and press by using initial conditions.

[skinny z]

More important. Just what does DCR tell you? What can be made of the DCR number?

For me, it's another tool in the toolbox however this tool, I would say, is very platform or even engine specific.
Similar to original 10 year old question, I've got an idea of what an effective DCR might be for an iron headed, 230-ish @ .050", Gen 1 350 SBC.
I can't say how that would translate to a BBC or even a Gen 2 SBC. But I know what to shoot for with what I've got (and even then I'm not so sure).

Any non-numeric comparison would be correlative and not causative. DCR values are mere ratios and cannot be
compared since they lack actual measurement of pressure and temperature.

DCR values must be converted to actual compression temps and press by using initial conditions.

Would it not be reasonable, despite the absence of measured data, to say that from one iron headed Gen 1 SBC to another that the emperical results can be transferred?
That is to say, if my calculated DCR was "x" for engine 1, and "x" was difficult to manage, then the same engine or similar would be even more difficult with a value greater than x.

[David Redszus]

For me, it's another tool in the toolbox however this tool, I would say, is very platform or even engine specific.
Similar to original 10 year old question, I've got an idea of what an effective DCR might be for an iron headed, 230-ish @ .050", Gen 1 350 SBC.
I can't say how that would translate to a BBC or even a Gen 2 SBC. But I know what to shoot for with what I've got (and even then I'm not so sure).

Any non-numeric comparison would be correlative and not causative. DCR values are mere ratios and cannot be
compared since they lack actual measurement of pressure and temperature.

DCR values must be converted to actual compression temps and press by using initial conditions.

Would it not be reasonable, despite the absence of measured data, to say that from one iron headed Gen 1 SBC to another that the emperical results can be transferred?
That is to say, if my calculated DCR was "x" for engine 1, and "x" was difficult to manage, then the same engine or similar would be even more difficult with a value greater than x.

No.

[F-BIRD'88]

My DCR numbers match those of Stan's.

If a cam card is missing, one way to determine IVC is by use of a Compression Leak Tester.
Simply pressurize the chamber (any low pressure) and rotate the engine until the pressure
jumps. That would be the IVC seat angle.

More important. Just what does DCR tell you? What can be made of the DCR number?

Especially when Cam card duration valve events are rarely
actual seat to seat specs.

If it is 12:1 compression put good gas in it.

If all it took was a late closing in valve there would be no market for race gas.