Applying the DV 128 formula on a Supercharged engine

[F-BIRD'88]

How would you adjust -modify the LSA of the 128 formula when applying to a supercharged engine.
Eg: Roots supercharged (non intercooled)
Lowered compression for pump gas operation.

X? amount of added LSA per lb of boost?
Y? amount of subtracted LSA per full 1 compression ratio reduction?
Or???

Example engine: Typical 350 cid Sbc 23 deg head
2.02" intake valve.. 7.5:1 cr
5 psi boost....... 10 psi boost 15 psi boost.

What would the 128 formula LSA recommendation be for these boosted example engines be?

[SchmidtMotorWorks]

Use 129, that will be perfect.

[superpursuit]

I find it amazing how quickly some people will respond with sarcasm.

F-bird. I don't know the answer to your question but have you tried posting it on DV's forum on this board? You may get a reply from David directly this way.

I would imagine it gets a little complicated as your boost actually translates as a higher compression to the engine.

Allan.

[Orr89rocz]

Thats an na formula from na dyno tests. I wouldnt use it that way and try to compensate with an adder

Just pick some thing in the 112-114 lsa range and generally you’ll be fine with a low boost street deal.

Or if the 128 typically ends up around 105-108 lsa for sbc’s, add 6-7

[RevTheory]

I wouldn't go trying to stuff that formula into a box it doesn't belong in. You may be able to get a little something out of it because I doubt that a 327 with a 2.02 valve and a 421 with a 2.055 valve will need the same standard-issue 112 but you'd really just be guessing.

[piston guy]

"I" would simply ask Mike what to run.

[Stan Weiss]

David's TMC program for SBC which uses a enhanced / modified version of the 128 formula limits CR input from 8.5:1 to 13.5:1.

Stan

[F-BIRD'88]

The idea is to apply a enhanced version of the DV 128 formula to make a better camshaft selection choice than get a 112-114 LSA you'll be fine.
Anybody can do that.
If a flow coefficient value can be applied to a valve size /CID at ambient air pressure (absolute pressure) Than a increase in absolute pressure (supercharged) then a model can be
created calculatedd to predict the new mass air flow.

If the 128 formula is usefull than a new formula can be usefull on a supercharged engine.
If test data analysis supports the 128 formula method as usable, minimum new testing of similar supercharged engine examples will support and allow adjusting this new formula as trends will show in this new data.
Mathmatics should be able to predict this before hand.

One factor is may be the difference in tuned length vs non tuned length of a typical sbc n/a intake manifold vs a typical blower manifold.

The purpose is to get a usable midrange torque advantage.
Street stuff.

[GARY C]

The issue I see here is that you would need thousands of supercharged dyno test to develop the needed data to develop a formula with.

In the discussions I have had with David in regards to boosted and nitrous cams as well as the discussions here there seems to be little if any testing done with cams and power adders and those that do it don't share their results.

[falcongeorge]

FWIW, the current trend that I see with with those that are actually doing a lot of testing with crank driven superchargers is away from the traditional 112-114 LSA's and towards 108-110, or to phrase it another way, I see a trend towards increased overlap in blown applications.
I really don't see how you can rationally "fudge" the "128" formula to make it work with blown motors. I guess if you have a pre-concieved idea of what number you want to generate, you can modify it to fit with your projections, but I don't really see that as a valid approach.

[F-BIRD'88]

Why not? The biggest difference between a N/a engine and a supercharged engine is absolute air pressure applied to the induction side. A change in Absolute pressure results in a predictable calculatable change in mass air flow thru a discribed flow orrifice..

[GARY C]

FWIW, the current trend that I see with with those that are actually doing a lot of testing with crank driven superchargers is away from the traditional 112-114 LSA's and towards 108-110, or to phrase it another way, I see a trend towards increased overlap in blown applications.
I really don't see how you can rationally "fudge" the "128" formula to make it work with blown motors. I guess if you have a pre-concieved idea of what number you want to generate, you can modify it to fit with your projections, but I don't really see that as a valid approach.

Yes on a power adder engine it seems that overlap and exhaust duration play a big part and neither one of these can be derived from a formula like 128.

Or at least as far as I know.

[falcongeorge]

Why not? The biggest difference between a N/a engine and a supercharged engine is absolute air pressure applied to the induction side. A change in Absolute pressure results in a predictable calculatable change in mass air flow thru a discribed flow orrifice..

I actually just came back to delete the post. Don't let me stop you. Figure out what number you want your formula to generate, and add a "fudge factor" that generates that number. Hell it was good enough for Albert Einstein, who am I to argue?

[ProPower engines]

Why not? The biggest difference between a N/a engine and a supercharged engine is absolute air pressure applied to the induction side. A change in Absolute pressure results in a predictable calculatable change in mass air flow thru a discribed flow orrifice..

I really don't see how you can rationally "fudge" the "128" formula to make it work with blown motors. I guess if you have a pre-concieved idea of what number you want to generate, you can modify it to fit with your projections, but I don't really see that as a valid approach.
It seems to me if you are willing to do the testing to develop an optional formula then have at it.
There is some that say it can't be done but they said cars would never get over 200 mph either.

If it works for what your doing and the results are positive then why not if it proves it works a different way then we all
learned something.

[F-BIRD'88]

"ctually doing a lot of testing with crank driven superchargers is away from the traditional 112-114 LSA's and towards 108-110, or to phrase it another way, I see a trend towards increased overlap in blown applications"

In my brief limited experience I have noticed this trend on the street stuff I have done. Noticable difference in usable street car acceleration.

These are low compression ratio engines with relative modest cylinder heads.