Originally posted by bret:
ok... well let me put it to you this way... mark had some people at his work crunch some numbers on the optimal size for a 2.5L duratec engine with the vortech supercharger. They said optimal size would be 73mm. You are telling me the only differene between the optimal size for a forced induction engine and a n/a engine is 3mm? I highly doubt that.
Never compare natural aspiration to forced induction.
All i am saying is that i am sure roush did not just pick 60mm out of a hat, or the parts bin for that matter.
Is that your opinion? Let us look at the facts:
1) A 15% power increase was needed over the standard 170hp Duratec
2) Airflow was increased else ware in the engine, so more incoming air was needed
3) They already had a larger TB casting available from the 3L Duratec
Now let?s go back to Economics 101. If you already have a larger TB, would it be practical to design and manufacture a larger TB solely for the use in 10,000 SVT Contours? They already were spending enough money on proprietary cams, as well as extrude honed intakes and higher compression pistons. This was a simple case of ?what we already have at our disposal is good enough for stock?.
Just like nearly every other part designed for the svt contour research was done... all i have heard from the people that have done this mod is "it feels faster" no before and after dyno plots, not real information to back it up. i am not saying this is 100% not going to make an improvement, but the smart money is on something more like 63 or 65mm tb, even then i would have to see before/after plots before i was convinced. If someone is willing to send me the 70mm/65mm/63mm tb (any or all) i will glady have them put on the dyno and then return them.
Wait a minute! Weren?t you just saying in a previous post that the 63mm TB used on the SHOShop?s project car, which uses a maxed out
3L, will
loose power as compared to the 60mm TB!? Pick on stance and stick with it!
For the sake of argument, let us go over this one more time.
Disclaimer: The following is strictly ?in optimal conditions? and does not necessarily reflect real world circumstancesFacts:
- low end torque is determined by air velocity and fuel atomization as a result of said velocity
- high end hp is determined by overall air volume
Hmm, that said, let us look at how a 2 valve per cylinder, single runner per cylinder, pushrod V8 would work.
If this engine were to use a set of short, wide diameter intake runners, then it would be allowed to breath well at higher rpms (given that the cam/heads were setup accordingly, of course), giving it better high end HP. Well, that?s fine, but what about the low-end? Well, with that intake, low-speed air velocity would suck (pun intended). It leads back to your McDonalds straw analogy. OMG! You?ve actually said something correct! Wait a minute, you were referring to the TB, and I?m referring to the IR?s! Anyways, air velocity wouldn?t be that great, and fuel atomization would be poor at best.
Now let?s give this same engine an intake comprised of long, smaller diameter runners. Well, now we have tremendous air velocity during low speed operation, giving us excellent low end torque. Uh oh, now the engine is starved for air higher up, limiting high rpms power. I wonder if there were a way to combine both of these principles??
Duh, let?s look at the Duratec now:
4 valves per cylinder, on short and one long runner on the intake side per cylinder
During low-speed operation we have the single, long runner being used. Like I said before, it is already matched to give us optimum (for our displacement) torque down low. Increase TB size and what do we have? More disposable air for the cylinder to draw air from. If the runners were significantly wider, then there would be the possibility of lower air velocity, but that isn?t the case here.
High speed operation. The secondary (short) intake runners open up. Air flows in the path of least restriction, which is the shorter runners, since they have a shorter distance to travel to the intake valves. This means the secondary runners are doing the job that the primaries were before. If the engine needs more air than the secondary runners can supply, then the primary runners will still flow additional air. Now we have the engine breathing in as much as possible. What holds it back from breathing better is?.the TB!
Hmm, so here we have a setup that will still benefit from a larger TB, despite whether the engine is stock or not. On a stock SVT a 63mm TB would be ideal. Open it up with an intake and headers, and go for 65mm. On a 3L with 34/35 runners, bolt on a 70mm.
Is there the possibility of decreased low-end torque with a larger primary runner? Yes. That has already been demonstrated. Look at the dynos of a stock SVT vs. a stock SE. The larger primary runners combined with the longer duration cams on the SVT dropped low-end torque a very slight amount. Going by that, there is the possibility that the 98 and 98.5?s have 1 or 2 more ft. lbs. than the 99+?s due to the extrude honing of the primaries that the 99+?s have. Then again, that was responsible for the 5hp increase up top.
Also unless you have some knowledge of flow dynamics (or whatever is necessary to full understand the effects of adding a larger tb) i really don't want to argue about this because neither one of us will be able to provide any solid proof regaurding this.
Do I have formal training on this subject matter? No. Do I have first hand experience with all the aforementioned? Hell yes. Even if I didn?t, there?s plenty of legitimate sources of tech at the local Borders or Barns and Noble. Your tech on the other hand seems to be based off of what you read in Motortrend or MM&FF. Your little disclaimer in your .sig isn?t an excuse to go touting your opinion as fact when you have nothing to base your ill-formed findings on.
also you keep saying $$$ is the bottom line... well wouldn't it be cheaper not to offer an svt vehicle at all or any model variations? why even offer options... money is not ALWAYS the bottom line, but it is definatly a pretty big factor.
That is a lame argument. If you want to know why SVT exists, go read their mission statement or something.
i just don't see why roush would do some of the things it did (more costly then a larger tb) that yeilded small returns... ( < 5 hp at the crank )
Yeah, because Roush knows all, right? Roush does good in NASCAR, and they did a decent job with the Contour, while the ?00 Cobra R will be described as ?interesting? by me, but you won?t see me leg humping their production cars. Regarding the TB comment. Like I said, why start from scratch if you can get ?almost as good? at 0% of the cost of a new product.
I?m done with the thread. The tech in here was otherwise good until you started running your mouth. You don?t like it? Then STFU.
