aklim

OTOH, with a 383 and the cam and heads set up, maybe that mid range might be OK

steven mack

When you go with the shorter runner intakes like the Mini Ram you trade torque for horse power.

pologreen1

loss of torque on short runner intake. Maybe?

Compare an LT1 c4 to and L98 c4 power specs.

Which one makes sense?

Which one is proven since TPIS came out with it and then GM did too?

aklim

Sure. Everything is a trade off. OTOH, low end torque doesn't do me much good if I am spinning the tires. Either get sticky tires or shift the band to middle to upper? At least that is my thought.

MatthewMiller

My engine is a 396 though. It's not that it didn't make the car faster - it did. It's just that this car's main purpose is autocrossing and road course events, as well as remaining useful on the street. So it wasn't the change the previous owner was looking for.

856SPEED

[i]Show me where my short runner miniram is losing torque....looks like a flat curve to me across the RPM range....you don't need a long runner intake for a 350 cube motor. I think we have covered this before. There is a common misconception that you have to spin a miniram intake to the moon to make power.....BS.....it also depends on the cam and heads you run. In this case, I run a short duration ZZ9 roller cam; actually the torque falls off in the higher RPM band with my miniram set up with the ZZ9 roller.

The only thing a TPI does for a 350+ SBC is look pretty.

steven mack

I call BS.Those numbers are with a stock tuned port set up.You put a First TPI on that motor the First will make way better horse power and it will make over 50 FT.LBS more torque than your Mini Ram.

MatthewMiller

Who cares? Torque at the crankshaft is not what determines how fast a car accelerates. Power is the all-important number...period. And the First intake will still make significantly less power than a MR and leave you stuck with a much narrower useful range of rpm.

Here is a good example. This is a 355 with AFR heads. The First intake made a lot more "torque," but of course at a much lower rpm. The poster thinks this is a great showing for the First intake, but what the chart actually shows is that the MR made at least 10 more horsepower. Note that they may have cut the test short before the MR engine peaked in power, so we don't actually know how much more power it made. But we know it made considerably more, and it's a much more flexible engine that actually takes advantage of the flow capacity of its aftermarket heads. On the street or race track, this will be the much nicer engine to drive vs the tractor motor created by the First intake (or any other TPI-based intake).

In terms of power, the First intake was still all-in by 5000rpm. That's the resonant issue that I wrote about earlier. You can't overcome that with porting. The resonant limitation it won't show up on a flow bench because a flow bench uses a steady stream of air (think d/c current). An actual engine uses pulses of air created by the valve opening/closing events (think a/c current), and that is what sets up resonance in any intake runner (also in exhaust primaries). If you set up a flow bench to have that kind of resonance, you'd see that the First intake hits a brick wall around 40Hz or so, which corresponds with ~5000rpm. At that point, the flow will drop off a cliff. The MR will flow much more air in a real-life situation such as this. You can't port your way around this fact.

cardo0

I think we eblaborated on intakes design on this forum before but it remains a hot topic. Well maybe I can add a few concepts w/o starting a new battle.

Like exhaust runner design the intake runner length determines RPM peak of the torque which is directly converted to HP. This is because of the pulse wave tuning as the intake valve shuts. The higher the RPM than at peak torque doesn't mean air stops flowing or won't increase but it just won't have the pulse wave to aid in cylinder filling.

What now limits the cylinder filling is the runner flow area. If this is to small, as in the stock TPI runner, torque and power fall greatly as RPM increases. But the trouble with huge area intake runners is the low RPM cylinder filling gets lazy due to low air flow velocity. I will stick my neck out here somewhat and say EFI has cured most low RPM air/fuel mixture distribution problems as evidenced by the batch fire controls. But it would seem to me the batch fire control would have problems with very large intake and head runners, more so than sequential fire controls but that's my expectation as I don't have proof to provide here. Take it leave it.

Looking at Edelbrock's Pro Flow Xt intake with stated 5.5" tapered runners seems to fall in range of Edelbrock Victor Jr. SP intake and a somewhat small step longer than the miniram or LT1 intakes. The FIRST intakes look to be same as stock TPI length. And the Lingenfelter Super Ram is a step shorter than stock TPI. But what they have in common is they all have larger runner flow area (diameters) than stock TPI.

Now exhaust manifold and restrictions can enhance or degrade any improvements to the intake as well as head, cam compression. But those are an entirely additional topics.

So what I'm saying is choose your intake with runner length to match your car (gearing, trans, cam, heads) and runner flow area (diameter) for your power requirements. And be thankful your C4 only requires hood modifications to fit taller intakes.

Good luck all.

MatthewMiller

I don't think air stops flowing entirely: obviously the engine continues to run! But pulse wave tuning is a function that both giveth and taketh away. There is an rpm (frequency) where the resonant wave is working for you, in the sense that it adds to the pressure differential across the intake valve which is causing the intake air to fill the cylinder (if there is no pressure at all, the air stagnates and goes nowhere). There are several forces creating this differential, including the air's inertia, the cylinder scavenging, etc. At the tuned rpm, the wave tuning in the intake is another one of those forces, and it increases the air entering the cylinder.

But that automatically tells us there is another frequency that is 180* out of phase with the desire tuning frequency, at which the wave subtracts from the sum of all forces pushing the air into the cylinder. At this frequency, the wave is decreasing power compared to an intake that had neither tuning effect at all. It can't overcome the other forces, so some air still flows - but it is hurting power at that frequency. I think the rpm in question would be 150% of the rpm at which best cylinder packing occurs.

All of the above will happen regardless of the cross-sectional area of the runner. The larger cross section will reduce runner velocity for a given flow rate, which as you say improves high rpm flow but may hurt low-rpm flow, due to the lower inertia of the intake charge. But as the numbers I linked show, it is inescapable that an intake with runners as long as a TPI setup will hurt high-rpm power and severely limit the useful powerband of an engine, as compared to an intake that effectively avoids useful resonant tuning altogether. As I noted, if you could compare the TPI and MR on a flow bench that actually set up a pulse wave instead of using constant flow, you would see that the TPI (regardless of runner area) would flow much, much less air at the out-of-phase resonant frequency.

steven mack

There is an Sticky article over at third gen.org.Super Chevy did a Dyno comparison Of several intakes.TPI to Mini Ram.Your choice of intakes would depend on what range you spend most of your driving.1/4 mile or road course.

MatthewMiller

Are you talking about this sticky, where a MR on a 383 made 41hp more than the best TPI (the ASM siamesed-runner intake) and 95hp more than a stock TPI? Really, whether you drive your car on the street, a road course, and autocross course, or drag strip, the MR or similar intake is always going to be the better choice for any kind of aftermarket engine.

The original L98 had such a small cam that the TPI's rpm limitations didn't matter as much. If you're sticking to an all-stock L98, then maybe - maybe - there is an argument to made for sticking with TPI. Or if you're building an engine for a pickup that will tow frequently, maybe. The OP is building a 383 with aftermarket cam for his C4. There is absolutely no argument for limiting it to 5000rpm with any form of TPI. That engine will be hobbled if he does that, and he will pay a hefty price for the privilege ($1050 for the basic First intake!). That's just plain silly.

856SPEED

i post my dyno sheet with my mods and your're still convinced the ACTUAL numbers in this dyno are false??

You are referring to things you READ. Give me your real life experiences like I have. Those who don't like the miniram have either not ran it or cannot afford it. My so called hi flo Edelbrock TPI intake on the same motor provided 296 horsepower mex...at 4800 RPM with 379 max. ft pounds at 3800 RPM before dropping like a brick after 4000 RPM....if you want a diesel like motor go for what you want to believe. I don't auto cross, but I can tell you Matt Miller has and I rode in his LT1 car....he was quicker in the auto cross that day than any TPI car...quicker than just about everyone actually! Now his car is amazing!!!

856SPEED

lets see the dyno on those ....you are throwing numbers out and you have no clue to back up your claims....show me the dyno comparisons! Are you saying my dyno sheet was from a stock TPI intake????

I wish it was....would have saved me quite a bit of cash!

cardo0

That's a very good point in that there more likely is an RPM where the pulse wave pulls the wrong way instead of pushes. But as a whole I think you are overestimating the effect. What I'm trying to say is the restriction of a small flow area runner has a much greater effect deminishing cylinder filling that a negative harmonic of the pulse wave.

Most your stock auto engines have a VE near 80% and most street enthusiasts are lucky to get anywhere near 90% VE with their performance mods. A highly tuned professional effort may get over 100% VE but that is with the whole engine package complimenting each part.

So what I'm trying to say is yes you can get gains and loses from manifold length tuning but the result is much less than a restricted runner. A restricted flow runner flows continually less air as RPM increases due to greater mismatch in piston speed and runner velocity. The larger pressure loss overshadows the negative pulse wave effects. Now I don't have any data to show what a negative pulse wave harmonic can do in magnitude but you would have to agree the effect will deminish as RPM moves even higher yet. But as whole the negative effects of the opposing harmonic wave is not in proportion to a restricted runner. And can be offset by exhaust manifolding length tuning.

Whew, that's enough for me.

pologreen1

lol, these same conversations happened before this forum was established and before the c5 came out.

The real research was done by shops and die hard car guys doing mods. Now it's all documented, but yet ignored.

rklessdriver

LOL... Can't you read. It says so right on the internetz.... he read it on TURD GEN. Just bolt a FIRST TPI on your car and...... instant +50TQ.

I am glad you posted your dyno sheets..... they are a good example of how well a mild short runner combo works.

I so wanted to post all those LTX and L98 builds with single planes or mini rams I have done for members on CF over the years... but I don't like to seem like a know it all. It's difficult to hold back because there is a lot of mis-information posted here all the time by people with clearly no real serious engine building experience.

Will

steven mack

Yeah I'm talking about that article where the Mini Ram made 63 FT Lb's less Torque Than TPI.Oh yeah an how much does the Mini Ram cost ?Over $1,000 dollars. The winner in that shoot out was the Stealth ram.It's cost $500.

MatthewMiller

Torque is irrelevant in car performance. If my C4 makes 300lb/ft of torque, then how fast does it go? You can't tell me. How much torque or tractive effort is being made at the tires (you know, the force that actually does determine how hard the car accelerates)? You can't tell me. Because torque is meaningless. Power is all that matters. It's what determines how much torque is available at the tires. The car that generates more power over any given distance accelerates harder every. single. time. In that test, the MR makes for a faster car, every time. Oh, and the First TPI intake that you are recommending to the OP starts at over $1000, too. The Stealth Ram is a great intake, but apparently it doesn't fit under a C4 hood. So that makes it a non-starter for a lot of C4 owners.

It seems we agree on what's happening in there. We might differ on the magnitude of the factors. I have a couple thoughts. First, the "giveth and taketh" aspect of resonant tuning is of equal magnitude. That is, however much the wave tuning adds to the power at its peak frequency, it takes away that same amount when it's exactly out of phase. So if it isn't reducing power that much when its out of phase, then it also isn't adding very much at its in-phase peak. If that's true, then it basically means all the mystique about TPI wave tuning is overblown.

OTOH, there is some fairly compelling evidence that says the resonance is a fairly powerful effect. One piece of that evidence is the fact that, even with the much larger TPI runners of some aftermarket intakes - to the point that they flow similarly to a MR on a flowbench - they still don't make nearly as much power although they still do make higher peak torque at a lower rpm. If not for resonance effects, intakes that flow the same should make the same power at that same pressure drop on an engine. But they don't. So there must be something going on beyond steady-state flow numbers.

Another bit of evidence is to be found in loudspeaker designs that have ports (usually for their low-frequency driver). If you look at the graph of just the single ported driver output (as opposed to all the drivers combined outputs), laid over the graph of the port's output, you'll usually find a "minimum motion frequency." This is the frequency where the port's output is maximized, and the speaker cone is actually held completely still by the resonance of the port. In order for that to happen, the resonant force must be at least as strong as the magnet motor driving the cone.

What I would really like to see is a controlled test where the same engine gets a really large-bore TPI intake that flows identically to a MR or LT1 intake or whatever short-runner intake you want to choose. Then bolt each one to the engine and dyno them. The differences in power would then be due only to resonance effects in the TPI-style intake. I am not aware of such a test having ever been run, but it would be interesting. On edit: This test could be run on an engine dyno more directly by just using eight straight, vertical intake runner with a common plenum and TB on top (think old-school Hillborn injector manifold without the eight individual throttle blades). You could sub in various lengths of runner tubes easily enough, retaining the same diameter, and run each configuration to see how the lengths change power at various rpm.

Also on edit: I think the harmful resonance effect from a long-runner intake will be a lot more marked with a cam that has longer duration and more overlap. Remember that the TPI system was created to work with a teeny factory cam on a 305. In the early 80s when it was developed, it was a big step forward in creating some sense of power while still hitting emissions goals. It's no coincidence that they disappeared from factory engines as we got better at managing emissions and other aspects of an engine's performance. On an aftermarket build, and especially with a decent-sized cam, it will hurt power potential quite a bit.

Last addendum for the night! Google "intake experiment variable runner length resonance" and you'll find some interesting reading material. For example, read Analysis Of Change In Intake Manifold Length And Development Of Variable Intake System. This is exactly the sort of test I was interested in. Changing nothing but runner length from 200mm-300mm, their test engine moved its torque peak from 10000rpm to 8200rpm. At 12000rpm the 200mm engine was still producing around 18Nm and power was still climbing at around 24hp (Fig. 5). But with a 300mm runner (and no other changes) it was down to around 14Nm and falling fast, with power having peaked at 10000rpm and about 20hp. That's a really big difference, and the only variable was intake runner length!

856SPEED

I tend to listen to others who have done the engine building/racing, etc. and my personal experiences with my own car since I have made intake swaps on the same motor/heads/cam; with very different ACTUAL results.

I have to say this though-I once used your avatar pic to send to my brother and his son (my nephew). I said, my Vette ran real well at the track last night- almost got away with it since I have a white C4- ALMOST; in that case I was called out on BS! I don't have that much torque!

Nice shot!