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The 128 drama!

Moderator: David Vizard

skinny z
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Re: The 128 drama!

Post by skinny z »

Hi Gary (think it's been a while)
Here's a spec lifted directly from the T&L's small-block 383 crate stroker article Mr V wrote about 13 years ago.
https://www.hotrod.com/articles/0703phr ... ine-build/
I found it very intriguing and this one cam spec really stood out. Not to mention that there's one portion of the build that mirrored the parts I have (and will have).
This cam spec in particular.
"284/288 of seat duration and 240/244 @ 0.050 on a 106 degree LCA. Lift on this cam was .541 on the intake and .503 for the exhaust."
That's a flat tappet grind. I'd like to know how that translates into a roller profile. Also, there's no mention of the ICL (which I suppose is a fine tuning point seeing as that it's adjustable). The split duration is a bit of a departure from what I've read to be DV's usual style of single pattern cams. I'd like to direct this spec to an open header application.
I've a few bits of software that I'd like this and other recommendations to run through but in the meantime I'm gathering as much info as I can before I finalize any further engine details. At this point all I really have are the heads, valvetrain and shortblock architecture (Gen 1 SBC fitted for a roller cam).
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Re: The 128 drama!

Post by skinny z »

David Vizard wrote:
"If so, I could now start trying to convince doubters of the value of my 'so called' port energy.
DV"

If I understand correctly, this was precisely the point of the small headed 383 built in the article I've reference earlier. Or at the very least why the small port volume does have a certain advantage when feeding a CID generally considered outside of their range.
And also the reason why I'd to fine tune the cam specs to suit.
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Stan Weiss
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Re: The 128 drama!

Post by Stan Weiss »

If we look at this article we can see that this engine had a 108 LSA and the article also lists the other cam specs
https://www.hotrod.com/articles/hrdp-12 ... -be-small/

Hopefully I have gotten all of the specs from the article entered correctly. Using TMC which uses 128 you can see what it says.

Stan
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skinny z
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Re: The 128 drama!

Post by skinny z »

Thanks for that Stan.
And using the Torque Master program too. (That's right isn't it?)
What is see though are a couple of departures from the 128 rule as directed by DV. One is the CR of 10.5:1 vs 11.7:1. The other is what is considered to be a typical discharge coefficient from a 23 degree SBC head with a 2.02 valve vs the 2.055. More compression and a better CD both serve to broaden the LSA. Even with the increased CID to 400+, the 128 rule would be modified to suit the CR and valve size. That's from what I'm getting from DV's papers on the 128 rule and his other writings anyway. Based on 128 a 406 would see a 104 under the guidelines.
For what it's worth, using what software I have available and inputting my data, which is slightly off the standard spec for 383 CID, DV's Lunati grind of 290 single pattern, 106 LSA, 102 ICL is producing the best theoretical results. That's against a few sought after recommendations and some of the other usual suspects. What my software can't determine is port velocity rather than flow. This is based on the premise on which the small headed 383 is built based on DV's paper that you posted (and I've followed) earlier. Port velocity makes up for the low end losses that would otherwise be seen by an over-cammed engine. Bigger might be better in this regard.
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Re: The 128 drama!

Post by Stan Weiss »

Yes that was done using TMC / Torque Master which does use 128 for SBC. I believe David did at one time post up how to adjust for a CR other than 10.5:1. Anything else about the formulas would need to come from David.

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Re: The 128 drama!

Post by RevTheory »

I had a detailed post that I apparently miscued so here's the dirty recap:

An 11.5:1 402 with 2.055 intake valves gets "128" plus .5 for the full point of compression increase from 10.5:1 and +.21 for the rocker increase over 1.5:1. At the Chaska seminar, David said +.6 for every .1 increase over 1.5 so a 1.85 would be +.21

128 with the adjustments applied to Stan's example would equal 106.46 and I'd round up to a 107 in that example because no one is going to grind you a cam on a 106.5. I probably shouldn't say "no one" but it's not common. I'm not sure why Torque Master is a point and a half greater than that, though. Maybe a 1.7 rocker on the exhaust influences it beyond a simple calculation.
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