..... It sounds to me like your easy-to-stall L98 vette is sick and needs some mechanical help or tuning and maybe no mods at all ... and , keep in mind that the L98 is rated around 240hp while the LT1 in an F-body is probably 280 or so ... 40 hp and a more rpm friendly intake will obviously be felt in the seat of your pants ... if your L98 is sick then the hp difference is just that much greater .....

 

Dude....the guy has a TPI. Ain't NO dual plane intake on this planet, that has longer or even 1/2 as long runners as the TPI. So...while the runners of a dual plane are longer than those of a single plane, they're way, WAY shorter than the TPI's....so no way is he going to gain low RPM tq from a dual plane. No way.

Second, the runners in a dual plane aren't even tuned! They're different lengths! Although they're longER than a typical single plane, they're not long enough to effectively use a harmonic frequency in most peoples' RPM ranges. No, a dual plane intake on a MPFI engine is not good advice. It won't help (down low) over most stock MPFI intakes, and it won't help up high compared to most decent MPFI intakes either.

 

The LT1 did what you're looking for; increased low end tq and increased/extended high RPM power, compared to the L98. It did this with slightly more compression than the L98 and the short runner intake...but essentially the same cam. They're different, but the LT1 doesn't have "more cam" in a meaningful way, IMO.

Make sure when comparing your Firebird to the 'Vette that you're considering gear ratios too.

 

Late L98s and LT1s are essentially the same motor with the exception of the intake manifold. Take a MR and slap it on the L98, tune the chip for it, and it'll basically make the same power and have similar characteristics. Cam and head differences are small and evolutional, not revolutional. Exhaust manifold on LT1 is better but not hugely better.

But the different characteristics of the intake tuning does bring rear gear ratio (and TC for Automatics) into play and these have to be considered if you want to have the car feel different to drive.

 

TBH I did forget about the gear difference. The LT has a T56 going to a 3.73 rear where the L98 is mated to the ZF6 on 3.33. On paper the T56 and ZF should be equal but I'm sure there is a variable I am over looking. I just now ran the numbers to see that there is a 10% higher gear advantage with the 3.73 and that alone could be the answer to my issue.

I will have to look up the cam profiles of a 94 F-body LT1 cam and the 90 L98 corvette cam. I have a spare stock LT1 cam sitting here but I'm not sure if it is enough of a difference to be worth the swap.

 

Why do I need to repeat myself as I said before I wasn't to match or improve his bottom end performance. You need to re-read my post.

As for unequal length runners you are incorrect in assuming they diminish the runner pulse wave as it still exists but now at different RPM for each cylinder and broadening the power band - something the OP is looking for. And the OP now explains this so I don't know how you are not seeing it. The trend in many racing classes is now unequal length runners of both intake and exhaust to broaden/spread the power band. If you do want one huge torque peak then run equal length runners for both intake and exhaust designed for the same RPM - that's your choice. But the dual plane has proven it's self for street applications for over half a century and I believe the newer LS intakes incorporate features to broaden the power band though I will admit I don't fully understand them.

 

Do I?

I guess you didn't say "low RPM"....you said, "Lower the powerband". Still, a dual plane is not the way to do that; a mid length runner "single plane" intake would be the right way to do it -like an HSR or Pro Flow.


Here is why I'm not seeing it:
1. It's a poor solution
2. I never said anything about diminished pulse wave. What I DID say was:
they're not long enough to effectively use a harmonic frequency in most peoples' RPM ranges
3. They're different lengths...the length determined by the packaging limitations of any given engine. That ain't "tuned". It's a by product of where ever they could fit the runners on a Ford/Chev/Dodge. Tuned means that the runners were made a certain length for a certain RPM range. Dual plane intakes runner lengths are determined by packaging...not tuning.



Yeah....under a CARBURETOR. OP don't have a carburetor. Tell us: Why did GM go from dual plane carb intakes to a single plane when they went to MPFI? They didn't just do it on the L98 either; ALL the "V" engines went from dual plane with carb to single plane MPFI. Why did tq jump something like 40 lb-ft (on V8's) at the same time (with similar or same short blocks)? Why are all EFI intakes still single plane? Why haven't they gone back to dual plane, "tork monster" EFI intakes? Because it don't work that way with EFI.

FYI, "LS" (Gen III^) engines in NO WAY use the theories that you're trying to peddle. They too, use a "single plane" intake with tuned, equal length runners...same philosophy as TPI -just different runner lengths for a different RPM range.

Where did anyone say that the OP should "run equal length runners for both intake and exhaust designed for the same RPM" I'm sure that I didn't say that. He already has that philosophy with his stock TPI.


.

 

Me - pull intake and swap to Tunnel Ram like the TPIS. greg

 

somehow I get the feeling anyone bringing up the idea of intakes and cams opens a can of worms and everyone wants to prove they know more. Tom you are very correct about the majority of EFI engines use a uniform runner length, There are uses for a multi length systems as I believe Mazda is using now. To be honest single plane or dual plane carb setups send to have unequal length runners no matter what the setup if running a single carb so the point is mute. A tuned Intake is about as useful as a tuned set of headers, they only benefit a very short RPM band and are best used for racing.

 

Wishes do come true, don't they? I am glad to see that others can safely inquire about interesting engine modifications without dealing with so much scrutiny compared to others.

 

An LT1 or Miniram has runner so short they aren't tuned to any RPM. They're all the same...so they work well with the same cam, same heads etc...but the tuned frequency on those, with the intake port factored in is something like 9000 RPM -a place where you will never get to. What that means is the nice, broad tq curve that you've mentioned that you are looking for.

 

Dont pay too much attention to the back and forth, Tom just likes to argue. You gotta take the replies for what they are, just suggestions.

Like mentioned before, if you're having to slip the clutch from take off there might be something wrong with your car. When I had the stock tpi I could let the clutch out with no throttle and it wouldn't stall, not slipping much either. Check for codes, check compression, ignition system, fuel system, vacuum, etc., The usual stuff.

Your best bet might be to use the search function for threads on intake manifolds. There is a ton of information on the site, all you have to do is search for it.

 

Thanks Thurman, I am still within the first 500 mines of owning this car. Had to replace the entire fuel system and spark system due to it sitting with the last owner. It feels fine, runs smooth, I am kinda feeling like its just a combo of maybe a worn clutch causing it to bight late and very abrupt and the gear ratio differences like Tom mentioned. I will probably revisit the idea in the near future when all the little bugs are worked out and I'm ready to play a little harder.

 

HSR and ProFlow would be in tunnel ram category and hardly anything like a single plane.

GM transitioned to the TPI independent runner to start with but built it for a 305" displacement instead of 350" or more and becomes to restrictive for larger engines at higher RPM. So the next evolution was the low restrictive LT1 intake which followed what TPIS already had on the market and it fit great under the cowl of engine setback camaros. At the same time the LT5 was produced and that did have dual runners as a mechanical way of feeding quad valve cylinders. A good example of how flow velocity and flow limiting restrictions play out. Big intake ports/holes make for lazy airflow trying to fill the cylinder.

So this is where experience comes to play as there are many compromises and choosing the best combination that compliments the part to work together. Heck even a roots blower need a matching cam, cylinder chamber and compression to be optimized or it can even make you slow down.

 

What is the "entire fuel system and spark system" consist of? What was wrong with them?

If it were me, I take the attitude that "If it flows, it goes.". All fluids. Clean the entire TB and IAC housing, etc.

 

Actually Tom likes accurate info. Watch what's next, as an example...



Yeah? "lol"?? Why don't you tell us how many planes exist in a tunnel ram's plenum? I'll help you out here: ONE. It's a single plane intake, pard.

EDIT: I guess it's time for "manifold skool for dummies" so we know the facts about what intakes are what.

A dual plane intake groups 4, even firing cylinders together into one common "box" (called a plenum), which draws from one side of a pair of throttle systems. One of these 4 cylinders draws from the "box", every 180˚ of crank revolution. There are 4 other cylinders, however (3 others, in a V6). Those cylinders draw from a second box and a second throttle system. SECOND. There are two boxes and two throttle systems...TWO. Since the two box and runner systems would intersect w/each other, designers ensure that doesn't happen by situating them at different elevations Like two airplanes on the same path, flying at different altitudes so they don't collide. One box and set of 4 runners is above the other box and set of 4 runners. They are on...(get ready, folks). TWO DIFFERENT PLANES! That is where the term "DUAL plane" came from.

A single plane intake groups all 8 cylinders and runners together into one common "box" (called a plenum), Each of the 8 cylinder/runners is able too draw through all throttle body options. One of these 8 cylinders draws from the "box", every 90˚ of crank revolution.
In the single plane, it doesn't matter if the box is down low, up high, way off to the side, or encompasses all of the runners w/in it (like a cross ram). All runners are drawing from one single box. SINGLE. The single box is on "one plane" (b/c it's...you know...ONE box), so it's understandably called a "SINGLE plane".

But don't believe me....here are some sources that are WAY more credible than I am. Let's see what they have to say....
ENGINE LABS -"A dual-plane manifold has a split opening in the plenum area directly below the carburetor mounting pad. Each side of the opening feeds four cylinders on a V8 engine. Single-plane manifolds have a single intake opening into the plenum and feeds all 8 cylinders directly. "


SO...as I stated before, virtually all EFI intakes are single plane intake systems, since all 8 cylinders are drawing from a single "box". Only EFI intakes that I can think of right off that are NOT single plane are the '88-'95 Chevy TBI 4.3, 5.0, 5.7 and 7.4 engines, which are adaptations of carbed intakes to a TBI EFI systems....and the late '80's to early '90's Ford 302 and 351w in trucks. All TPI, HSR, CFI, Pro Flow, Super Ram, Miniram, LS1,2,3,6,7,8,9, and on and on, are all single plane intakes.



Not sure what that mixture of fact and fiction has to do with anything that we were or are talking about.
1. I'd like someone to cite a legitimate source for the claim that "Tpi was designed for 305's". I've NEVER read that...and I've read a lot of **** about SBC's.
2. The cross section of the TPI intake isn't an "RPM killer" (as in, if it had been designed for the 305). It's the length. The LENGTH is the RPM killer on the TPI, for both the 305 and the 350.
3. The LT1 was restrictive? On a 300 hp engine??

Not that any of ^this^ has anything to do with anything in this thread....



Now this is a paragraph that with. Very true...but kind of opposite of multi length runner intakes, case.


I hope some folks appreciated some facts.

 

entire system means that I replaced the tank, pump strainer, filter, 8 injectors and the FPR for the fuel side, spark got plugs wires and a cap and rotor. The coil is putting out strong consistent spark so I didnt go for it. Reason for this was the car seat for more than 5 years. As a result the multec injectors where bad and the tank had about 2 inches of debris and what smelled like turpentine. The throttlebody and upper intake along with all attached parts where removed and cleaned when the injectors came out.

I decided to take the corvette to work and it couldn't have been happier on the 45 mile drive. It seems my complaints on the lower end are all tied to the clutch and just getting used to the car.

 

Thx for the video. I like how they call the dual plane a torque monster and it adds mid-range torque from 3500 RPM and up. So you must now be agreeing with me the dual plane increases torque.

Well that box you refer to is actually a plenum. Calling a tunnel ram a single plane is as bad as calling a stroker small block a big block. I'd say your "school on intakes" would never achieve accreditation. That plenum on a tunnel ram is huge in volume capacity compared to any carbed single plane intake and it acts as infinite volume to reduce reversion where the reflected intake charge has a nearly 180 degree turn to enter the wrong runner. Not so with the diametrically opposed single plane plenum runners. Tunnel rams have several advantages that the single don't share and I think you should look them up rather than have me explain them to you. The HSR shares many tunnel ram features even though it runners are shorter than most tunnel rams. The problem is the HSR still requires more clearance than a stock intake and that's my justification for the dual plane conversion. It does reduce reversion and increases mid-range torque while adding flow potential. Using a dual plane with EFI now has the advantage over a carbed dual plane as almost none of fuel charge has to make the tight turns of the dual plane - mostly air only. If you can't see this I can't help you.

While runner length does add to restriction that's not the case with the TPI. As most intake runner lengths are chosen to create a 1/4 wave length for the Helmholtz reflected pulse. And a full wave length Helmholtz runner would be restrictive let alone difficult to fit under the hood. Again there are compromises. But the larger TPI intake runners from FIRST, ACCEL, Eldebrock all extend the power band RPM range. Here's a nice dyno comparison of a large runner TPI (Edelbrock) to a HSR. Yes the the HSR made more power and at higher RPM but look at the hp curve of the larger runner TPI. https://www.eecis.udel.edu/~davis/z2...age021105.html It was flat all the way to the HSR peak while torque peak was larger and lower than the HSR. Open the TPI runners more to a FIRST intake size and you have a race on your hands for the HSR. Sorry but I gave up looking for a FIRST intake dyno result.

Say what you want, calling plenums boxes and tunnel rams single planes. The science speaks for its self.

 

I wouldnt get too freaked out over equal runner length. Head and intake ports can measure the same but flow differently, if anything it helps give a broaer powerband. Much ado about nothing. Buy what fits, you can afford aand motor on.

 

I agree when you're talking carb induction. I hope that you're smart enough to realize the "tork monster" comment was relative to the single plane intake...and that is using carburetors. Right? you DO "get that"...I hope. The OP has TPI which is also a "tork monster" @ about 3200 RPM. The OP was asking about increasing LOW RPM torque...which "3500 RPM and up" isn't that. Low RPM torque on a 0-6000 RPM motor would be in the idle to ~2500 RPM range, or so. "3500 and up" is squarely in the "mid range" on a typical street motor.



Indeed it is. You are stating the obvious and that which I already knew. You can tell I knew that, if you read my post. Here is one excerpt that is a clue that I know what I Plenum is:
"into one common "box" (called a plenum)"

Reading helps....try it. Using the term "box", I was just trying to keep it simple for folk who don't know what kind of intake is what. You know...guys like you.



HOLY COW, that was a load of horse ****. You know just enough to throw out "terms" and convince yourself that you know...something...but ya don't know. My school might not get accredited. You're right; but you wouldn't get a passing grade, at a "school on intakes". A dual plane intake has two planes, 4 even firing cylinders/plenum, and 180˚ intake events in each plenum.

A single plane has one plenum, 90˚ intake events, and each cylinder can draw from all TB options. Did you actually watch the video? Read the links? Read my post? Doesn't seem like it.

Here is a much better analogy than your failed attempt to use a stroker and a big block: A stroker small block and and a big block are both engines. They are different types of engines, but they're both engines. You can tell that they're that they're both "engines", because they meet the definition of an "engine". An HSR, Super ram, miniram, tunnel ram, T-Ram, Ramjet, you-name-it-ram...TPI, CFI, LT1, LS1, FAST, FIRST,....they're all single planes. They are different types and/or configurations of single planes, but they are all fundamentally single plane intakes. You can tell that they're a single plane design because they meet the definition of a single plane intake. Let's have a look shall we? Right from that Engine Labs article that you didn't read, 4th paragraph down:
"Single-plane manifolds have a single intake opening into the plenum and feeds all 8 cylinders directly."
Huh. Does the HSR have "a single intake opening into the plenum and feeds all 8 cylinders directly? Indeed, it does. Single plane. Small blocks and big blocks are both engines.

There is no need to pontificate about...well, all the irrelevant, diarrhea that you shared with us, above. If you think dual planes are the "hot setup" on MPFI engines, you'll have to start pointing out all the dual plane, MPFI winning combos that are running around terrorizing the rest of the intakes (that are a single plane). Right? 'Cause MPFI dual planes are just dominating the engine building scene right now!



The science? Can you not see the diff between two boxes and one box? This thread is embarrassing for you.

Really though...not one whit of this matters. You recommended a dual plane intake for the OP's MPFI engine, and that is terrible advice. It won't give "low RPM torque", and it won't help on a MPFI engine. A dual plane is for, and helps on a carb'ed engine. We aren't talking about carb'ed engines in this thread.


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