Wnts2Go10O

iTrader: (12)

any builders have more insight on this?
http://www.youtube.com/watch?v=wNZig...ature=youtu.be

Mell00

Nothing new in the racing world. Common for single carb racing engines.
The cams are for just what the young lady says...engines that have different intake runner lengths from inboard to outboard cylinders.

This type of cam config does not apply to engines with intake runners the same length.

Nothing trick about it as typically you use 2 different intake lobes and 2 different exhaust lobes that are a couple degrees shorter or longer in duration between the inner and outer cylinders. Lift may change as well a few thousandths. Any good racing cam grinder will do this as requested or they can recommend a combonation of lobes as well. Crane Cams, Comp Cams and any other major cam company has done this for years. Comp seems to be the first one to be advertising it though.

Sales@Tick

iTrader: (3)

This, it's been a "secret" for a while, but it's nothing new.

I have a friend with one, it has two different Lobe separation angles. One for the shorter runners, one for the longer runners.

Wnts2Go10O

iTrader: (12)

in an ls style intake: while the runners are equal length, doesnt the position of the runners in relation to the tb affect them in a way that manipulation similar to how this sort of cam works get the same sort of results? ie slightly different specs on the back half than the front half or even cylinder to cylinder. or does the positioning of the runners in an intake not matter when they are equal length?

on top of that have you or anyone else measured airflow/airmass for each separate cylinder on the LS series to get a sort of avg discrepancy?

Sales@Tick

iTrader: (3)

IMO not enough to make a difference.

When I'm reading plugs on my race car and I'm spraying more than 200-250hp worth of jet or when I had my previous car which was turbo charged in the neighborhood of 725-750rwhp was the only time I saw irregularities in cylinder to cylinder distribution with a stock style intake.

A N/A motor IMO wouldn't have these problems, or at least to anywhere near the extent a nitrous or F/I motor would.

427

iTrader: (3)

It was developed for NA engines in Nascar. It is helpful when rules dictate problems, but not many have the testing ability to use it effectively.

Kurt

SSCamaro99_3

iTrader: (1)

Just thinking out loud. Is this because the plenum "fills" and then the runners are equal length, unlike the carb style which fuills the plenum and then has different length runners. I am guessing once the system is "full" the only thing that would change with rpm would be rate through the system. With unequal length runners, you have efectively a variable rate through the system between short and long runners.

Plate motors, and turbulent airflow past the plate, lean conditions due to the plate, something else my dumbass is missing?

Mell00

The "rule" is a signle 4v carb, or now-a-days, the same damn intake manifold with a FI system integrated with a throttle body.

427

iTrader: (3)

The carb being in the middle forces certain cylinders to be different lengths than others. Length has a tuning effect as the pressure wave when the valve shuts goes up the port backwards, opening the valve when the pressure is higher behind it causes better cylinder filling, this happens based on rpm and runner length. If you can't control runner length on all cylinders, but your rpm band is constant, you can run lobes that are the best at every runner at the control rpm.

Kurt

Wnts2Go10O

iTrader: (12)

hence why prostocks use the split twin dominator setup?

how does the size/shape of the plenum affect that pulse on an equal length runner vs something like a single 4bbl intake?

427

iTrader: (3)

The PS guys tune for a very narrow band, the split Dominator helps them get a great "line of sight" port so the air does min direction change for max cylinder filling.
Generally larger plenum will show power gains, but may slow a car down. If the plenum is smaller the engine will respond better to the rpm drop on a gear change, when the air stalls and must re accelerate down the port. This is the thing that give computer engine/cam simulators the most trouble as the variables are many. You will see many internet high hp cars that will not run numbers that make sense, the engine is just lazy although it makes good dyno numbers.


Kurt

Wnts2Go10O

iTrader: (12)

in reality you want the smallest plenum that will make the power you need is what im getting from that. a plenum that isnt just a box but one with the best velocity recovery with gear changes or changes in load is best. sounds like there would be a physics model to determine not just how much and how quickly the plenum is filled but how quickly the air inside is accelerated based on load, runner size and shape, and head runner size and shape.

it seems like the same issue cars have with intake runners that are way too big: they flow well but the air is moving too slowly to be useful.

how would you, as a builder, manipulate the pulse in the plenum (speed it up/slow it down) based on cam specs? if you could do such a thing..

427

iTrader: (3)

The cam can change the tune length of the runner. Generally as the intake lobe gets longer in duration the runner will get shorter to match up the anticipated power band.
Sometimes for street or road race type cars you will pair a longer runner with more duration and get a wider tq area that makes the car faster over a broader range. This will not get you the "hero" internet hp numbers, but you can drive this type of engine to work on Monday comfortably and turn good dragstrip et's and nice lap times on road course or autocross.


Kurt

Wnts2Go10O

iTrader: (12)

so the cam can change the frequency of the pulse (changing the tune length)? concerning the long runner, long duration combination: is that because the longer the duration, the longer the recovery time but on a long runner long duration theres a sort of "leftover" or even slight reversion?

if you took a short runner long duration combination then added to the length of the runner to effectively double its volume at the same taper and shape on that same cam; would you essentially drop the peak but gain in avg power?

427

iTrader: (3)

The stall in the port starts when the valve closes, so the cam timing can change it. Both things matching your needs will work best, but you can shift bands around with either the runner or the cam. If you maximize one rpm you can become the internet hp hero, but your car may not race well.


Kurt

SSCamaro99_3

iTrader: (1)

Great posts. I love learning.

Wnts2Go10O

iTrader: (12)

i get that numbers dont matter, results do and that working towards your requirements also dictate where you go.

with my last questions, i was trying to understand in more detail how the longer runners can work more efficiently (efficiency not necessarily leading to better power number on paper). i think the term i wanted to use was "harmonic resonance." if you lengthened the runner, would you lengthen it to the next harmonic resonance to take advantage of the pulse wave youve created with the camshaft? or is that what GM did with teh tuned port injection system that was very good at one spot then dropped off?

427

iTrader: (3)

Not sure I get what you are saying, but as the runner gets longer the torque peak will happen sooner and rpm higher will suffer as a rule. The factory LS intake is very good at producing broad power while still making nice upper rpm hp, but the LS1 intake was improved upon immediately after release. If you can find pictures of the engine in the GM concept truck called the SST, that intake rocked at 5000rpm and above for a stock concept part. It had a bit more plenum than the LS1 and shorter/straighter runners with less bend than the candy cane type.

Kurt

Wnts2Go10O

iTrader: (12)

trying to break down long vs short runner on equal duration to a more primal piece of the puzzle. while a long runner wouldnt produce as much peak power, it is more efficient over a broader section of the band than the shorter runner. that being because it caters to the harmonic resonance of the pulse wave but on a different level or a wider range than the short runner and whether or not the old GM TPI runners were so bad (overall performance wise) because they matched the resonance of the intake pulse wave too well at a single point. think... church organ pipes.

trying to pick your brain on the physics of it is all

427

iTrader: (3)

I wish my brain could understand! No secrets involved, the pressure wave will happen, the length of the runner will change when the ram effect will be most helpful. No cheating can really be done, but you can make something more drivable or different at the cost of other areas. If you can break down what you are doing to a very narrow band, then the choice of length is simple. In wider bands it is compromised by needs of the driver.

Kurt