anyone care to explain this?

why does an intake manifolds runner length/shape effect powerband?

why do TPI guys say the LT1 intake manifold is "too much" for a stock L98 due to its low end powerband? how can getting too much air hurt performance?

someone please explain

 

"why do TPI guys say the LT1 intake manifold is "too much" for a stock L98 due to its low end powerband? how can getting too much air hurt performance?"

That's a good one. The TPI is about the most useless intake i've seen on a performance engine, now for a truck, maybe.

Start here: http://www.mercurycapri.com/technica...intake/pt.html

As Chuck Riddeck always says there is alot to learn if you just look for it. (that was paraphrased some, well alot)

Bret

 

I just read the link. It's enough to make my head spin. Does this mean that there needs to be a balance between the runner length of the intake and the length of the tubes in the header? Is this why long tube headers provide better performance than shorties?

Curt Sr

 

TPI's are built for torque, and heavy street cars like torque, its my 392 ft lbs of bottom end torque (2700rpm) that allows me to leave everyone standing at every traffic light without going over 3000rpm - now if you're talking racing, then bottom end is irrelivent, my Z has a 4600 stall torque converter and about zero bottom end torque, but its a race car, so the only street its gonna see is to and from the track and to n from car shows. Its all about your requirements, but using something like a Holley Stealth Ram on a TPI car really wakes it up since its a high-rpm weiand tunnel ram cut down with a plenum thrown on top.

However, people starting out with a TBI or Carb, and "upgrading to TPI"... THAT, sir, I shall never understand! But if the car came with TPI, by all means use it.

 

Ok, very generally speaking, you need to match all the components of the engine for the desired application. Intake, exhaust, cam, etc., etc.

So, generally, torque will be produced higher in the rpm range with shorter intake runners and exhaust primaries & collectors. Torque will be produced lower in the rpm range with longer intake runners and exhaust.

Most street cars are heavy and need low end torque to move them off the line. So they have longer intake runners and exhaust. The TPI on the L98 is a classic example. It produced most the it's power and torque between 2500 to 4500 rpm.

I ran a SBC dragster in the 70's. It red lined at 9000 rpm and had Enderlie(sic) injection and 8 individual exhaust tubes. The total distance from the top of the velocity stack to the valve was around 6", the exhaust tube were only about 18" long. It produced it's peek torque at around 7200 rpm.

I've heard a lot of people say that the "LT's" are better than the "shorties", this is of course incorrect! They are only better for the specific application (heavy street driven Camaros).

 

Heh, Ok, in that case I’ll disagree with a few people here.

Measure the runner sizes on a TPI, and you’ll find that the harmonic tuning points that you have a chance of hitting on a small block with one are in the mid 3K rpm and mid 5K rpm range. That’s not really a useful tuning point for most real trucks/4x4’s which people actually use (My full size rarely goes much over 2-2500rpm, it would need much steeper gears to really take advantage of a TPI).

That being said, they could be a very decent ‘street performance’ intake under 400hp on a 350 or smaller, and with large runners and base for slightly larger engines. You just have to remember that you’re basically building an engine that should be entirely optimized for 3000-5600rpm, and ditch the crappy stock heads. With long tube headers this could be a brutal, fun combination on the street (of course, you guys running 700+ hp would laugh at it).

WRT to the original question, there is no good reason to say that. LT1 intakes will flatten out the torque curve some, so it will feel more tame then with a TPI in the 3000-5500rpm range (or to about 4600rpm if you’re running stock heads), but above that the LT1 intake will ‘feel’ much better, and it will feel about the same below 3K. Since most TPI guys are running cams better matched to something like the LT1 intake I don’t really see a problem, and with the stock cam and better heads it would be very similar to an LT1. I’d bet that the typical TPI guy that’s stuck something like an LT4 Hot cam in his car would be happier with an LT1 intake.

 

Well any intake which almost forces a truck cammed 350 to a HP peak of 4600 to me is good for a truck. The long runners on that intake are PERFECT for a truck. Not only is is going to cause a extremely low TQ peak, but it is also going to cause alot of tuning pressure at low RPM. Using the 3K TQ peak with that intake it's also going to greatly increase the TQ below that point better than about any other SBC EFI intake. So it would in fact make a great truck motor.

Long small runners are going to make alot of TQ down low, there is no way around that.

Bret

 

WS6 T/A...
Are you saing The L98 makes power at 5600??
Every one I have ever dynoed without major mods fell on its face after 4600. 18 inch curved intake runners are great for for a heavy musclecar, just not for a true race application.

Trey.... What you have got to understand is Air speed determins torque, Basicly it determines when you max out voloumetric efficiency. Intake runner length, port sizing, and plenum area are some of the major factors in changing where this takes place.
In a N/A with proper tuning you can achieve over 100% volumetric efficiency with everything tuned properly. Believe it or not some pro-stock guys get 120%. Alot of that has to do with what they call pulse reversion tuning. When the intake valve shuts it sends a pressure wave back through the runner.
When Incoming air collides with this pressure wave they call this Inertial ram effect pressure in the intake runner increases dramaticly. If you can time it so this occurs right as your intake valve opens you will send higher than atmospheric pressure into the combustion chamber. Having high air speed for the inertial ram effect is critical in raising the runner pressure. The longer runners increase Air speed, however they restrict air Flow at high RPMs. The Lt-1 runners make up for their 3 inch runner with a venturi which allows for Better flow at high RPM with minimal loss of torque....

 

Dave,

Actually the Intake Pulse Tuning Effect is the highest at intake valve closing. One reason why intake valve closing point is so super critical.

Bret

 

you are right... so you can push air for a few degrees in while the piston is moving up. Most cams for street cars will close the intake fairly soon after BDC though. But is also important to scavange the cylander better during overlap by having a higher pressure differential between intake and exhaust to reduce pumping losses...