133.5 Cam # & Edelbrock’s Supposedly Lame BBC ‘E’ Heads

[Wolfplace]

I did add on .045 to .9 deg LSA (for compression ratio above 10.5:1) to the result of the math in brackets subtracted from 133.5

To get 105.16 LSA to 105.6 LSA recomended.

it is very interesting what DV is doing here with this. But I'm not yet convinced it is absolute......

But interesting...I hot rod little cheap $$$ motors. Its seems to work pretty well with the SBC if what you are after is a very hot torque curve....

Ok
I am going to go back to this one more time
What am I missing in the formula as written in the first post
THERE IS NO .9 MULTIPLIER AS WRITTEN UNLESS MY ENGLISH IS COMPLETELY FUBARED UP,,,,,,,,,,,

Doing the math as shown & I still come up with 102.35 for a 11.0 582
The formula as written
For a 10.5/1 motor the required LCA will be LCA = 133.5 - (CID of one cylinder/Intake Valve dia Inches).
For each whole ratio above 10.5 the LCA needs to be spread by 0.9 of a degree.
Now maybe it is just me but I read that line is saying add .9° per point of compression so:
582/8/2.3=31.63
133.5-31.63=101.87
101.87+.45 for 1/2 point of compression=102.35

The example as written is
500 inches so one cylinder is 62.5 cubes. That number divided by 2.55 for an intake valve gives us 24.5.
Subtract that from 133.5 and you have a base line LCA of 109 degrees.
But our Pro Stocker is going to be a 16.5/1 CR motor not 10.5 so we need to correct it for that.
This means we have to add the six extra ratio’s x 0.9 (6 x 0.9 =5.4) onto our base 109 and that gives us a LCA of 114.4

[F-BIRD'88]

If the formula is based around 10.5:1, how do you adapt it to a very low CR engine (say 8:1 like a typical stock mid-70s truck 454)?

Clairification: when I sold the 454 motor to my friend it was 8.5:1cr. The plan was to rebuild it and hot rod it.
The pistons were changed. The new cr was 12.5:1, Then it got the Crower 107deg LSA solid cam.
We had tried the tunnel ram briefly on the low cr build first just to show him the potential. Thats when he got the bug.
So I told him what to do to finish the combo for the tunnel ram. The cam was in the same duration I said to use , ( I'd already done this before) but the Crower cam was was on a unusual 107LSA... seemed odd me. But we tried it any way as it was free and new ..It worked GREAT!. It was much better than my previous cam (which was very good)

Remember I had already done this combo before but not with a 107LSA cam like this. My previous 454 version was very good. This one was CLEARLY BETTER with the 107LSA cam in it. It worked great and DV's math predicts/recommends a 107LSA cam for just this combo. Like I said this thing was punching way above its weight, with that camshaft.

The old 8.2:1cr 454 version was a older sleeper nitrous build. it was getting long in the tooth and my friend wanted it...
I still have the Trophies from racing that Nitrous motor combo. (Another tale) That thing was pretty much untouchable...
"sleeper" would be an under statement. (cast intake and exhaust manifolds and all.)
That same 454 motor went thru may variations over the years.

Just saying....


To adapt to the low 8:1cr correct the LSA by .9 x the difference from 10.50:1 (10.50-8='s 2.5)

10.50 CR is The base default cr ratio . So reduce the LSA by 2.25 Degrees LESS LSA.

133.5- (CID/8/In valve size x.91) + or - (.9x each whole ratio change) +/- from 10.50:1 cr ='s DV cam LSA

Old OEM BBC heads use 131

[F-BIRD'88]

I did add on .045 to .9 deg LSA (for compression ratio above 10.5:1) to the result of the math in brackets subtracted from 133.5

To get 105.16 LSA to 105.6 LSA recomended.

it is very interesting what DV is doing here with this. But I'm not yet convinced it is absolute......

But interesting...I hot rod little cheap $$$ motors. Its seems to work pretty well with the SBC if what you are after is a very hot torque curve....

Ok
I am going to go back to this one more time
What am I missing in the formula as written in the first post
THERE IS NO .9 MULTIPLIER AS WRITTEN UNLESS MY ENGLISH IS COMPLETELY FUBARED UP,,,,,,,,,,,

Doing the math as shown & I still come up with 102.35 for a 11.0 582
The formula as written
For a 10.5/1 motor the required LCA will be LCA = 133.5 - (CID of one cylinder/Intake Valve dia Inches).
For each whole ratio above 10.5 the LCA needs to be spread by 0.9 of a degree.
Now maybe it is just me but I read that line is saying add .9° per point of compression so:
582/8/2.3=31.63
133.5-31.63=101.87
101.87+.45 for 1/2 point of compression=102.35

The example as written is
500 inches so one cylinder is 62.5 cubes. That number divided by 2.55 for an intake valve gives us 24.5.
Subtract that from 133.5 and you have a base line LCA of 109 degrees.
But our Pro Stocker is going to be a 16.5/1 CR motor not 10.5 so we need to correct it for that.
This means we have to add the six extra ratio’s x 0.9 (6 x 0.9 =5.4) onto our base 109 and that gives us a LCA of 114.4

You are missing the x .91 part of the formula the formula is 133.5 -(CID/8 /in valve dia X.91) result.. THEN correct that result for compression ratio over 10.50:1 @ add +.9 per ratio over 10.50:1 equals DV's cam LSA

Someone wrote the formula wrong. 133.5-(CID/8 /in valve size x .91) + .9 degrees LSA added on per 1 ratio above the 10.50:1 base cr ratio

[Wolfplace]

Well,, I am guessing that someone would be David
Look at the first post, I did not miss it is not there & is also missing in the example given which is also in the first post of this thread
Makes things a little hard to follow with missing pieces.

[F-BIRD'88]

Well,, I am guessing that someone would be David
Look at the first post, I did not miss it is not there & is also missing in the example given which is also in the first post of this thread
Makes things a little hard to follow with missing pieces.

Ahhh I know...Got to cut him some slack... You'll wish you were still that pretty at his age ....HHAH HA .


But for these Big CID BBC's I have no reference for how this will work.

[Wolfplace]

Well,, I am guessing that someone would be David
Look at the first post, I did not miss it is not there & is also missing in the example given which is also in the first post of this thread
Makes things a little hard to follow with missing pieces.

Ahhh I know...Got to cut him some slack... You'll wish you were still that pretty at his age ....HHAH HA .


But for these Big CID BBC's I have no reference for how this will work.

LOL,,, I am his age, might even have to add a multiplier for wear
Thing is we ain't actually all that old, just very well seasoned

[Geoff2]

In DVs first post using the 133.5 rule, the 0.91 multiplier is not used; it IS used with the 128 rule. Whether this was an omission, I do not know, DV would need to clarify.

There is also the 0.9 multiplier for CR, so maybe some folks are confusing the two..

[bigfoot584]

But our Pro Stocker is going to be a 16.5/1 CR motor not 10.5 so we need to correct it for that.
This means we have to add the six extra ratio’s x 0.9 (6 x 0.9 =5.4) onto our base 109 and that gives us a LCA of 114.4 degrees.

David - does this work in reverse? What if someone has a 8:1 engine and they are trying to find the right cam? Would you do (2.5 x .9 = 2.25), and subtract 2.5 from the LCA you find with the "133.5" formula?

Thanks,
John

This seems to be a legit question, why no response ?

[MadBill]

Hard to imagine it would be otherwise; 10.5:1 would be just a logical reference for a hot street engine...

[David Vizard]

David,

I just noticed there's no "x .91" in this equation like there was in the 128 deal. Was that a typo or omitted by design? Also, any adjustments for rocker ratios above 1.7?


Rev

Mr. Rev sir,
Not a typo it's just a plain 133.5.
No there is not a correction in this simplified formula for rockers over 1.7 on the intake. But for each 0.1 of a ratio above spread the LCA by about 0.4 of a degree.

Of note here is that anyone who has read my books on BBC will know that the advertised ratio of rockers varies hugely from the advertised ratio. The real ratio's are in the book and as can be seen some rockers are as much as 0.4 under ratio and some are as much as 0.2 ratio higher. Knowing which is a power bonus.

If you are looking for max output from your BBC this is stuff you need to know as you could be throwing 30 hp out of the window.
DV

DV

[David Vizard]

But our Pro Stocker is going to be a 16.5/1 CR motor not 10.5 so we need to correct it for that.
This means we have to add the six extra ratio’s x 0.9 (6 x 0.9 =5.4) onto our base 109 and that gives us a LCA of 114.4 degrees.

David - does this work in reverse? What if someone has a 8:1 engine and they are trying to find the right cam? Would you do (2.5 x .9 = 2.25), and subtract 2.5 from the LCA you find with the "133.5" formula?

Thanks,
John

This seems to be a legit question, why no response ?

Only just got to it!! the answer is YES.

[MadBill]

Presumably the critical portion of the rocker ratio is that below say 0.200" of valve lift. David's chart shows large variations in same, even for rockers with similar max lift ratios...

[RevTheory]

Thanks, David. Just making sure I'm not out in the weeds here.

[F-BIRD'88]

No there is not a correction in this simplified formula for rockers over 1.7 on the intake.


Now you got me confused... Why does the SBC head "128" equation have a .91 multiplier and the BBC 24deg head "133.5" formula does not have this .91 multiplier What does the .91 in the equation represent?


133.5 - (CID/8/In valve dia)

128 - (CID/8 /In valve dia x .91)
131-(CID/8 /In valve Dia x .91)

Is the .91 dropped? Why is it dropped from the equation? ??


Also
Outlining a rough LSA +/- qualifier for Roots supercharging..Need data. (Besides my own)

[RevTheory]

Let's not get carried away. This isn't supposed to be used for supercharged engines and as is stated in his book, the 128 deal is for your normal aftermarket heads that we're all subject to. Not tricked-out, 18 degree heads or LS engines or Hemis...