GREGGPENN

I've been reading and reading. I've seen the products and the testimonials for what new bases/runners/ported plenums can do -- even with stock cam and heads.

I have an '89 (113 heads) and a stock cam.

Here is a basic example of what's tickin me off....
48mm TB is big enough -- even for a modded motor and a factory 502. 4 cycle motors turn twice to fire. At 6000 rpms, a 350CID motor requires 607cfm. That means a 48mm TB at 650CFM is big enough. Fine....

Vader's website lists stock flow rates for the base and runners at 199cfm each. 607 cfm for the WHOLE motor means 76cfm for each cylinder!!! 199cfm is way over that!!!! Though I can't find cfm for the plenum, I'm guessing it's fine too.

Why does anyone here say the TPI sucks??? How can anyone say it needs to be better? Sumbeech motor has worse VE as it goes faster (due to air friction, etc) so the cfm requirements are even lower, right?

But, hey, exhaust scavenging and port velocity can make a cylinder appear BIGGER than it really is.... Of course, there's pulse waves and on and on.

O.K. I'm convinced there's a real need for bookoo bucks on motor research. But 199cfm vs 76 cfm seems too friggin easy for math.

Why does any of this BS work? Moreover, if it works, why say it doesn't? Why quote simple math alone -- if it's not sufficient to answer a real question?

Something's rotten in Denmark!!!!!!!!!!!
gp

89onlyZ51

Another provocative greggpenn post! OK, I'll bite and throw this out for discussion:

At the air filter and TB, you can pretty much look at cfm flow and determine your needs. When you get close to the cylinder, cfm is important, but you can't only looking at cfm flow. Without getting into pulses and wave theory (which I don't know much about), I'll try to explain how I think about it.

With each intake stroke (1/2 of engine rpm), you're starting and stopping the column of air in your head port and up your intake runner. Since air does have mass, it has inertia and will bounce off objects and do all those things that you can see solids or liquids doing. "Tuning" a runner just means that you're sizing it to take advantage of those properties at a certain rpm range (i.e. so that air stack is timed to be bouncing back toward the intake port when the intake valve is open). Plenums act as a reserve volume of air for the motor which ensures your total runner length doesn't extend all the way to your air filter.

Put another way, a 2 inch dia tube that's 1 inch long will flow the same as a 2 inch dia tube that's 10 inches long, but they would behave very differently as intake runners. (OK, so the 10 inch long tube will flow marginally, probably immeasurably, less because there will be some additional friction of the air moving down its longer walls).

Now my head hurts...

cv67

Beats the hell out of a thermostat thread

95PoloVert

You probably realize this already, but:

a. That 199cfm flow rate is at some nominal (and static) pressure differential that bears little or no resemblance to actual operating conditions.

b. That 76cfm will move in 3000 short staccato bursts, not some ideal smooth, even flow. Check out the IVO/IVC events for your cam to determine how much of that minute the valve is even off its seat.

c. Finally, you have flow losses due to factors such as inertia, friction, & other fluid dynamics characteristics (already covered so well by 89onlyZ51) that prevent the runner from achieving the same flow that it would in an environment with a static pressure differential.

rodj

"48mm TB is big enough -- even for a modded motor and a factory 502. 4 cycle motors turn twice to fire. At 6000 rpms, a 350CID motor requires 607cfm. That means a 48mm TB at 650CFM is big enough."

That's what the numbers say;
so why do racers run 750 / 850 even 1050 cfm carbs on their 350 engines

"Why does anyone here say the TPI sucks??? How can anyone say it needs to be better?"

The TPI is a great manifold ; it is just that due to the runner length it does not flow up top.
Great bottom end , awresome torque but no rev capability.
Conversely a short runner manifold will lose power (relatively) down low but give great top end.
Horses for courses

runner140*

[QUOTE=cuisinartvette;1561970835]Beats the hell out of a thermostat thread

QuickGlass

The 650 CFM at the throttle body is enough, because all the cylinders are not drawing in air at once.
You can't just take the 607cfm / 8 and get 76 cfm each.
That would be true only if all the cylinders were drawing in air at once.

steven mack

There are restricted class racers making 500 horse power useing 500 cfm carburators.

Demonic85

From my personal driving experience, carbed engines seem to have a wider power band than FI engines. Yes the maximum power is usually up high (4000-5000) but theres plenty of torque down low.

Tuned port is all low end in terms of torque and horsepower and after 4500 rpms you aint making jack, cant suck enough air in. The LT1 makes power up high and torque about midrange, so all you would need to do is get some lower gears for the rear end to make it faster than the TPI, which is why we've got it so bad. TPI can only hold its ground upwards of 350-400HP. Anything higher isnt worth keeping the TPI.

Yes its way more complicated, i'm just trying to make it sound a little simpler.

Red Tornado

number and stats, dynos and slips. magazines and mouths, it's all pie in the sky.

the tpi SUCKS because the party is over in the RPM world far too soon -- a true kill-joy, the technology is obsolete and been walked on many times over. it's anemic all thru the gears, if my butt says so then that's where the day counts regardless of some slip of paper that might say otherwise; my hobby ain't in braggin' for i surely despise that, it's in simple to-myself livin'.

you're looking for every reason in the world to justify leaving it stock; if that's your bag there's nothing wrong with that.

to over-analyze time & time again is to help ensure that will happen.

C6/Z06 (not base C6), mildly modified (another must), 5-7 years used by then, will be my next steak on the corvette plate. i'm a very patient person when it comes to plans and execution of plans.

F1Fan

I bet thats still gonna be easily a $40,000+ car in five years, for an '05 even,
That car won't take the usual depreciation route due to it's extra low numbers and high demand and collectibility. My plan is similiar, but I'll "settle" for a base model with the Z51 package

Red Tornado

Greg, for a daily driver I would get the Superram, Trickflow heads (and sell your stock heads), LT headers, an LPE 219/219 cam or GM 218/228 H.O.T. cam (although you won't need exhaust runners with such split duration, the Trickflows have very good E/I ratio across the lift range), or a custom cam in that realm.

Tried, proven a million times, and no joke. It will whack you back, I guarantee it -- and that's where the rubber meets the road.

I know its the "all" route. I don't operate in any other mode

I love my setup, but the C4 platform has been walked on thru time and technology, the world has moved on in severalty and its only a matter of time till mine's sold (albeit a couple years away at this point -- saving for that C6/Z, with easy very mild bolt-ons).

95PoloVert

Based on what? 199 > 76?

Demonic85

I'm still using the stock TPI on top with bolt ons and it throws me back in the seat pretty good. I bet adding that SR would be killer.

cv67

Dont need every component to flow 300 cfm in order to have a fun street car, they cant all be dragsters. Research is good but dont let too many internet charts, dyno sheets threads make your decisions for you, just a guide at best.... THen separate the cream from the which it sounds like youre capable of and build it.

GREGGPENN

Well yeah....

When someone jumps in and says a 48mm will work on a 502 because the flow numbers show it's big enough, why not throw them out there myself.... DANGIT!!!!!!!

GREGGPENN

From Vader's website:
======================================== ============
What fuel pressure setting will give me the best performance?

A: The stock setting is 42 PSI. Much track testing has showed that any type of increase will greatly benefit both horse power and torque. Here's some dyno testing on a stock 350 motor which substantiates those claims:

42 PSI (stock) 46 PSI 50 PSI
RPM Torq HP Torq/diff HP/diff Torq/diff HP/diff
------------------------------------------------------------------------
2250 237.7 101.8 254.9/17.2 109.2/ 7.4 275.0/37.3 117.8/16.0
2500 241.7 115.1 262.1/20.4 124.8/ 9.7 283.3/41.6 134.9/19.8
2750 241.5 126.5 275.2/33.7 144.1/17.6 297.0/55.5 155.5/29.0
3000 237.1 135.4 278.2/41.1 158.9/23.5 305.5/68.4 174.5/39.1
3250 233.8 144.7 278.9/45.1 172.6/27.9 311.3/77.5 192.6/47.9
3500 241.0 160.6 278.2/37.2 185.4/24.8 309.5/68.5 206.3/45.7
3750 246.6 176.1 283.4/36.8 202.4/26.8 303.3/56.7 216.6/40.5
4000 250.4 190.7 278.3/27.9 212.0/21.3 298.0/47.6 227.0/36.3
4250 251.6 203.6 272.5/20.9 220.5/16.9 289.1/37.5 233.9/30.3
4500 253.5 217.2 257.3/ 4.2 220.5/ 3.3 277.0/23.5 237.3/20.1
4750 245.0 221.6 242.1/-2.9 219.0/-2.6 266.4/21.4 240.9/19.3
5000 227.6 216.7 225.0/-1.4 214.2/-2.5 237.8/10.2 226.4/ 9.7

It shows that by increasing the fuel pressure to 50 PSI, results in maximum torque increase of 58 ft-lbs (along with a much flatter torque curve) and a maximum horse power increase of 19 HP over stock. 46 PSI also provides a noticable increase which should work well for day-to-day street driving. An adjustable fuel pressure regulator (see Chap 5.2) is required to increase the fuel pressure.
======================================== ============

Saaaaweeet!!! I like it!! But, wait... Look at Plemon's website:
======================================== ============
Adjustable Fuel Pressure Regulator - One of my personal favorites on the useless items list is the adjustable fuel pressure regulator. The concept behind this modification is pretty sad. The claim on this mod is that by increasing the fuel pressure you can effectively tune your engine to take advantage of your other modifications. The problem with this theory is that such changes are global, meaning that if you increase the fuel pressure you will make your injectors flow more fuel at every given point in the RPM band. This might work if your A/F ratio is globally lean or globally rich, but I can tell you from experience that this is rarely the case. At part throttle the increase in fuel pressure will make the injectors flow more fuel than they were intended to. The computer will see this as a rich condition as detected by the O2 sensors but it will not know why. The computer will reduce the injector pulse width to compensate, this messes up the fuel trim tables and in the case of the Corvette fools the computer into thinking it is getting better gas mileage than it really is. This modification makes the computer have to constantly adjust the fuel trims which is not a good idea. For best performance the computer needs to know exactly what is going on, it should not be fooled. As long as an engine is running stock fuel injectors and is not running nitrous or forced induction there is no reason to ever mess with the fuel pressure. If a modification requires serious changes to the A/F ratio these changes need to be done in the computer to be truly effective. You might correct your A/F ratio at one RPM with the adjustable fuel pressure regulator but in the process mess it up in another part. This is a terribly inaccurate way to tune a car.
======================================== ===========

Note the part I highlighted....

Now, I never thought of Nathan as a guy to spout BS, but the numbers above don't seem to lie either. Sure, the numbers on top are for a L98, but the operating principles of the two aren't that different.

JAKE

In stock form, not all intake runners are capable of flowing the same amount of air, too. There can be close to as much as 100 cfm difference between one port and another on the same manifold.

I recently came across a mag article where a few intake manifolds - none were TPI though - were flowed out of the box. I was amazed at the difference between one port and another on the SAME intake manifold.

Even after porting, the runners did not all flow the same. The gap was narrowed, but there was still significant differences between one port and another.

I recall the BB Chevys had this particular problem and GM stagger jetted the carbs to address the unequal flow. One of GM's intakes actually had the carb mounting location turned on an angle in an effort to better equalize the airflow through the intake.

Just something else to muddy the waters.

Jake

Blownfuel1

Gregg, there's a series of books you need to read, that will explain this to you, mine are in storage, or I would just copy the pertinent info hear for you. All of them are by David Vizzard, he's an old Chevrolet Engineer (worked on the Can Am cars amongst others), and he runs a no B.S., straight shooting, automotive testing & consulting business now, and also does the ocasional article for Popular Hot Rodding. His book's are How to Build Horsepower Vol's I (covers basic bolt on's) & II ( covers Intakes and Carb's, with a real good section on air flow theory), and then there are " How to Build and Modify Chevrolet Small-Block V-8 Cylinder Heads (this one's for the layman), Theory and Practice of Cylinder Head Modification (this ones for the pro's, it's a $95.00 hardback), How to Build & Modify Chevrolet Small-Block V-8 Pistons, Rods & Crankshafts, How to Build Max Performance Chevy Small Blocks on a Budget, Nitrous Oxide Injection, etc....but I've blown his horn enough. I specifically suggest you pick up How to Build Horsepower Vol's I & II. In How to Build Horsepower Vol. II (I think) he explains exactly why your math doesn't work (but using a carb'ed 350 as an example). The short version is the equations your using are based on maximum volumetric efficiency, not maximum horsepower output. It takes more CFM to produce maximum horsepower than maximum volumetric efficiency. I wish I had the books handy so I could give you a more detailed explanation, but I don't, and I don't want to put out something incorrect due to my fuzzy memory. I did a search on Amazon.com, and one of the used book sellers has How to Build Horsepower Vol's II up for $8.00, and Amazon has it new for $15.00.

GREGGPENN

Well I certainly understood, in some of my reading, how VE decreases as RPMs increase. This might explain if a bigger TB than 48mm is useful, but I'm skeptical that it will explain how a 200cfm runner isn't sufficient to supply a 76cfm cylinder. (My "pressure" theory below might though).

The books sounds interesting but I'm not sure I'm looking for more than the short answer so I can figure out my next move.

------------------------------------

I understand that feeding a cylinder (thru a valve) is like opening the door to a room and letting air flow in. I look at the air routing in the manifold as a hallway leading up to the door. If the doorway has a funnel-shaped border, it will help smooth/speed delivery. That's why valve passage porting is helpful. I also understand that a bigger door or a longer opening door lets more air in (e.g., bigger valve or increased cam lobe).

I can see that changing the cam/head would help but I'm not so crazy about dumping the money in that. Not now anyway.

So I'm left looking at the "hallway". If it's bigger at the opening, then gets gradually smaller, the hallway becomes it's own funnel too. It's that 90degree bend from the TB into the runners I don't like. THAT'S GOTTA HURT! (That's probably why minirams/single plane manifolds are less restrictive).

In my case, I like the idea of porting the plenum, increasing the runners, and maybe swapping manifolds/TB. And yeah, I get that the door (valve) is still the same size and opens the same duration. It does seem like the more pressure potential behind the door (bigger intake) should help get the air in, but the whole aspect is poorly documented here. At least in recent posts (of a year or less). Websites and marketing don't seem more convincing.

I've also looked into SChargers but think the pricing is too high for an "air pump".

I'm getting discouraged. But, I also don't want to end up P.O.'d that money spent didn't seem worth it.

gp