dhirocz

iTrader: (2)

While I was studying info about tuned ports to decide on a runner diameter for my 427 I found quite a bit of info some of you might be interested in. Figured I might share some.

TPI engines are a balance of runner diameter and runner length. This is what gives the 'tuned' effect. Too much or not enough of one or the other ruins the whole purpose of running a TPI style intake.

Its impossible to have a 275cfm+ TPI intake and still have a stock type powerband. The more the intake flows, the more it can support cylinder filling at higher RPM/HP and the higher the torque peak goes. If it goes too high, you wind up in territory better suited to other intakes. TPI is best suited for 3400 RPM torque peaks and below. Superrams work best at around a 4000 RPM torque peak. In between, what you use depends on what you want that is more important to you...tq or hp...I would say a siamesed runner should work in that area just fine.

If you are looking to increase torque, you need to have a different approach then for increasing HP. For torque, look towards increasing flow efficiency WITHOUT increasing diameter. This means port matching, smooth transitions, clean up the casting...lessening the chance through the intake for frictional flow loss. For HP, you are looking for the same, plus increasing the CFM needed to support power in the upper RPM ranges. This means increasing the diameter. How much you increase the diameter will pinpoint where in the powerband the intake will be best suited to make peak power, so bigger isnt always better.

Theoretically, an edelbrock base can be ported to 1.7 inches ID.
Mathematically, a stock 350 TPI has a port velocity of 511 fps at 4400 RPM. A stock 305 TPI which redlines at 4000 only has 406 fps. Makes it easy to see why the 305 has such a tiny cam and is less responsive to the same mods.
Theoretically, a 427 could use an edelbrock ported base with a 1.660 ported base and AS&M or extrude honed accel LTR's and still make max power at 4600 RPM, meaning a torque peak in the 3400 RPM range. This is a 2.16" cross section.

It makes no sense to upgrade only portions of a TPI system, since the system will only flow as much as the weakest flowing piece. Now that my point has been made...

A stock 350 TPI has a port velocity of just under 400 fps at it's torque peak. This is when everything is sized just right where the intake can fill the cylinder best, in other words, peak volumetric efficiency. It drops to 345 fps (assuming the same size in the base) when used with a 1.615" runner/base combo (same size as an accel unported runner). Equipped as such, it returns to 395 fps at 4115 RPM, which just happens to be where a 350 so equipped makes peak torque. Meaning at right about 395fps is where your LTR intake will make peak torque. At that RPM, you are best suited for a superram...or stroke it to 383ci and bring the RPMS back down and the torque up more.

CSA on most TPI bases is always larger where it meets the head than in the other side where the runner bolts up. Meaning, port work on the head side should be limited to port matching and creating a better entry angle. Dont touch the floor, if anything, raise it with some welding. Do some math, and create a runner diameter in the base that is at least the same ID as your runners. Keep in mind air flows along the roof of the port. Try to aid flow and reduce turbulence without increasing ID more than necessary, but keep in mind, too small a cross section in the base lowers the power peaks.

With all this information, I've determined that a 427 with a set of accel runners and a base just cleaned up to 1.625" (2.07" cross section) would have a velocity of 395fps at 3400 RPM, all things being equal. At 4400 RPM (stock 350 power peak) the engine would have a 510fps velocity, just under stock. Again, this means a stock type powerband. If the intake is cleaned up to flow well with minimal restrictions to flow other than the expected frictional and thermal flow loss, and the rest of the engine is built to spec, this type of engine should make gobs of torque, though little HP. If built to perform/flow higher in the powerband, it would have a flat torque curve, but wouldnt be nearly as peaky.

Since TPI isnt designed for HP, cfm measurements should be used mainly for evaluating resistance to flow, not HP potential, as in other engines. Even a well built 350 TPI only makes 350 RWHP, roughly 400 FWHP. It doesnt take much cfm to do this, so dont put much stock into CFM numbers unless you are feeding a huge motor (like me )

I will add to this as I discover more. I am currently looking into the frictional losses from the plenum to the base as the air travels through the curvature of the runners.

Remember, it's a TUNED port. Runner diameter, port velocity, your cam selection, torque peak, size and everything plays a role, so if you are going to spend the money, spend it well. It's a tuned intake, unlike a carb or LT1 intake which is not tuned, meaning only select parts of certain specs will work well, and they have to work together. For the most part, this mean using proven combos. LT1's are antituned intakes, like carbed engines, and can work well with a wider variety of cams, heads, etc...

Also keep in mind that there are variances here, such as OEM restrictions in the plenum, MAF screens, exhaust, and other variables that can affect this. I wish I had a dyno chart of a well built 350 TPI with a stock portmatched only intake and stock cam; it would help me nail this down more to a T. I'm also thinking that perhaps the flow has a secondary function to carry the torque longer after the torque peak...I'm also still trying to nail the relationship of port velocity to the torque band.

johndinu

wow interesting info, thanks for sharing.
my car ia a 89 350 gta, stock with the exception of a high flowing cat and catback
just replacing the injectors with bosch gen III. since I have the runners and the plenum in my hands decided to clean up the casting a little bit.
I am wondering what role does the egr ridge just behind the tb openings has, and also why the tb openings are chamfered in the sense of reducing the diameter...
looking at the runner openings in the plenum, they are radiused like a velocity stack would be, so why put a chamfer behind the tb when they could have used the same thing?
is there a runner length/diameter calculator anywhere?
for now I'll just clean up the castings the best I can... I hope maybe to build up a cfd model for this ...someday...

BlackTopKing

iTrader: (1)

This was interesting indeed and infact refreshing point of view comparing actual flow ablities to inpacts of the actual TPI design. Seemingly, in a way seems over looked but the TPI proves to be more flexible the its reputation.

cuisinartvette

Ive found that the siamesing bit/giant gaping holes gains you nothing
Portmatching similar result.

Dyno Don

iTrader: (7)

Really....
My base is welded and ported to 2.3 sq.in. flows 310 CFM
My runners:

cuisinartvette

I shoulda added application dependent.
(lets say the basic 350 tpi with a cam)
Obviously with a welded base your runners needed all the help they could get

Just wrapping up a long term superram project (350) flowedeverything backwards and forwards etc. There was hardly any difference between a stock runner and what I wound up with. Almost 2x2 square entry, rest taken to the hilt of the casting. Perhaps your longer runners/rpm need more
Finishing the heads tonight then off to valve job then reflow again.
Ill put up ALL the #s before and after might dispell a few myths