Noway to compare Prostock to nextel cup considering one is a BB and the other a SB,intake resonance is alot different, not to mention cam profiles used. The combo itself will pretty much tell the tale..prime ex. was my setup last year I was steadily stacking spacers on the intake ( 4 1/2" in fact)and was still picking up low end, which is pretty much a given intake plenum volume was not enuff or cross sectional area in the runners could be enlarged... There again alot of testing to really figure out what combo wants, no tricks, no mathmatical equations, can beat real world testing and making notes for reference..Sometimes a combination will want something totally opposite than what you think...

 

There was a guy on thirdgen.org that added to the stock upper plenum on his 350 TPI and added 10hp across the board, if I remember right. I am going to have to do some looking, as my friend showed me the thread, but both of us were suprised that the motor gained hp from the added volume. We came to the conclusion that since he opened up the area behind the TB, it gave the air a smoother flow to the front 2 runners and that is proabably were the power increase came from.

 

Got to thinking of a design I dont think Ive ever seen before, not to say it doesnt exist, but wouldnt this make sense.

Have a box plenum sitting on top of angled runners, by angled I mean that they start out forward towards the TB, and angle back and down into the ports so that the air has a more direct path into the heads, I think that LT1 runners are kind of like this but a very very small degree off of 90, I am thinking more like 75* or more.

I drew up a picture in word of what Im thinking.

http://www.geocities.com/jonaddis842003/intake.jpg.JPG

 

I just did some rough measuring of my 3rd Gen TPI plenum and came up with 146 cubic inches. Thats about 42% of a 350 engine. I have heavily modified my SLP runners to give at least an extra 25 cubic inches of plenum to each side for a total of 50. Again a rough measurement. This rounds out to about 200 cubic inches of plenum volume which is 57% of a 350. I will post the results of my dyno run with the modified plenum and runners.

The modification has also smoothed out the airflow from the plenum to the runners quite abit. There are no sharp right turns into the runners from the plenum as on the stock design. I also smoothed out the entry into the plenum from the throttle body so this will also help. This issue was addressed in the above post. So it will not be a cut and dry situation as in just increasing the plenum volume alone.

One more thing, from my already modified SLP TPI runners I have a dyno chart that looks like it could have come from an LS1 engine with an auto versus a TPI L98 engine. My torque graph is virtually flat at 311 ft/lbs. By the way my last time out my 1989 GTA with a 350 ran 13.30 and 103.59 at the track. Looking to break into the 12's next time out with these mods and fine tuning the fuel air mixture. Allen

 

You hit the nail right on the head. Give it your best guess and then test it to see how it works and what works best.

That's why Pro Stock grinds several cams for their individual engines. Can't beat the real stuff. Not even with a slide ruler.

 

My guess is that folks doing ProStock or Cup engine development use all available resources including simulation as well as dyno and tracktesting. Because they are looking for fractions of a % improvements they order and test literally hundreds of cams. "Let's add 4 degrees to the intake and increase the LSA by 1.5 degrees. I'll want that cam this afternoon, if you please. My airplane is on the way to pick it up."

Fortunately, with today's CNC cam grinders or other dedicated machinery, a new cam is only a few hours away for these guys. It helps to have DEEP pockets, and great sponsorship.

FWIW, 1 day lead time on a custom grind is doable, if the core is in stock, even for us lower budget guys.

If my eyes didn't deceive me, all but one of the Cup cars ar Daytona had the cam company sticker ( and cams) of one manufacturer. Anyone notice who the "lone wolf" is? Nope, not Jarrett or Johnson.

 

as far as all the testing.. i just asked opinioins because if i wanted to spend 1500 bucks on trying stuff i would just go proram and be done.. but i like to make my own stuff.. and try to get it as close as possible to right the first time around.. next let me say holy ****.. i didnt realize joe o was responding to one of my posts.. damn.. a living legend..lol.. all jokes aside congrats.. you have accomplished an awesome task.. so back to the topic.. everyone agree to just try to make the plenum the same ci as the motor?

 

i think the only flaw in the design is that the whole purpose of a plenum is to slow down the movement of the air and make it more dense.. if you gave it more or lest a straight shot.. youre really defeating the purpose of slowing the air down to help it become more dense.. make sense?

ive exhausted most resources now and have a billion different opinions.. any real life expiriences out there..

 

Interesting thread.

What about adding an elbow or an adaptor like this?:



Can you add plenum volume like this, or would it "count" different since there is a turn involved before the runners?

Ryan

 

Nope that volume counts too. It's not as effective, but it does count.

Those elbows take some work to get them around the rest of the stuff in there.

Bret

 

I see. So, in theory, what would too much plenum volume give you vs. what too little plenum volume would leave you with?

Ryan

 

Don't know if there is too much in this situation. Too much makes a car not recover on shifts as well, but too little will hurt power.

Bret

 

Interesting. Just trying to grasp what the characteristics of each might be .

Ryan

 

Ryan,

Right along with what Joe and Bret have said....

If you were to keep adding 1/2" spacers to an engine on a dyno, you'd likely see gains in hp with each addition. At some point you'll put the engine in a car, attach a trans to it and take it to the track where you'll find that, what made the most hp on the dyno doesn't necessarily produce the quickest ET's. You'll usually settle on something 1.0-2.5" tall on a carb intake but what's "optimal" is always a matter of trial and error. Car weight, tranny type, gearing, converter and a host of other variables will determine what ends up working best. That's why the guys with all the $$ try lots of intake designs on both sides of the "theoretically optimum" to find the best fit. Walk into a race teams shop and you'll see alot of used sheetmetal intakes sitting on the shelves. I personally went through 3 different intake setups (induction-wise) and 4 revisions of the final configuration on my old top sportsman race car. It's just money right?

-Mindgame

 

Interesting point, MG. When Bret mentioned a car not recovering on shifts as well my mind immediately started thinking auto vs. manual (same engine) and why some cars like different things (dyno vs. track). You really can't even make a blanket statement for the same engine and different transmissions - too specific - can you? Too many variables to account and pack into a single formula, it seems.

On a side note, I notced the first 7-8 of Reher Morrison's (single carb) engines come with a single 1" spacer. Maybe that is a starting point for their customers? I've seen a few RM cars at Houston Raceway before. Now I have something to talk to them about .

With our small LT1 engines and different intake options (or lack thereof), these adaptors add quite a bit more volume than a single spacer. Makes it hard (well, expensive ) to fine tune the plenum volume. I guess one could always add spacers to an adaptor setup and see what happens. If you added one and went slower, well, I I guess you could assume the engine wants you to keep chopping it down a little until you get slower .

Edit: Going back to the first two pages again. Runner length can't be forgotten either. Unfortunately, this would probably be much more expensive to experiment with than plenum volume. Oh well...let's just maximize what we can and add some tricks when possible .

Ryan