Best example. Leading edge of an airplane wing... ;)

 

I was looking at some of the pics on the links you've
provided and obviously you're intake is getting a much different
air signal at idle as well as throughout the RPM band.
How ever at idle the computer isn't going to offer as much
variation in the injector cycle. Once you're off idle, you're
gonna have more available fuel curve, and the lean situation
is taken care of.
Just tryin' to offer an idea.Good luck with that set up.
Bob.

 

luckily though, idle fuel mixture is controlable in the chip, so ill look into that some more later. im off to grind away on my spark plugs now. :seeya

 

By the way,
how did your torque at low RPM get effected?
I don't have the TPI experience that some of you guys have, but
I always thought that when you punch up the top end, it's gonna cost you in the bottom.

 

if i punch it from a stand still with no brake, it will smoke the tires through second gear easy. doesnt feel like it lost anything on the bottom end pull.

 

Here's a link to a posting on the Camaro/Bird forum on a couple guys doing this to their base. I was curious if this really worked or not. http://www.thirdgen.org/messgboard/F...ML/001492.html

Thanks,

Carl :chevy

 

here are some pics, looks like i found my next mod :D :D

 

also note, that dyno on the after siamese mod had to be shut down at around 4900rpm because he heard a rocker arm come loose and start making a lot of noise. the engine was still pulling strong. you can see at ~4800rpm on the stock tpi, the hp peaks and starts to take a nose dive, with the siamesed base, its still climbing steady.


[Modified by 88L98, 2:14 PM 9/24/2001]

 

Yep, definitely on the "gotta do" list.

 

That dyno comparison is flat amazing. I am surprised it put our more torque across the board.

This mod appears to be worth about 30 hp. Wow. Good bye miniram and superram. I wonder what the performance on a stroker motor looks like.

Gentlemen, Start your grinders.


[Modified by AquaMetallic94LT1, 2:55 PM 9/24/2001]

 

like i said before, there is no noticeable loss in low end, it feels like it is pulling harder, granted i dont have a dyno of my car yet, i bet mine is around the same. i cant wait to get mine done to see what rpm the HP is going to peak at. id love to see what this thing would flow like now if i got it extrude honed. if i did that, i bet we are talking ~300 flywheel horsepower. LT-WHAT?

 

ok......sorry but Iam one of the biggest skeptics......ya know the old fashioned...if its too good to be true...than it usually isn't......

please tell me the downsides here....I have a stock L-98....and an extra 30hp.....for free!!!.....only thing is I don't have any extra runners or intakes...so I screw it up...well....ouch....

pretty much why I probably gonna stay away from doing this......right now anyway....

just curious why GM never caught onto doing this....surely something is a downside....otherwise I would think it would have been done already....

Please prove me wrong......

Jeff

 

Well as someone mentioned earlier, cylinders 5 & 7 fire in succession. Since each of 8 cylinders fires every 720 deg of crank rotation, then #7 lags $5 in phase by only 90 deg. This means that there is overlap in the intake valve open phases between these two adjacent cylinders. Whereas the other pairs differ in phase by 270 deg.

Lets assume the siamesed base and an intake valve dwell of say 212 deg (at .050"), then #5 can only draw from both tubes for the first 61 deg of crank rotation and #7 can only draw from both tubes for the last 61 deg of crank rotation. For 122 deg of crank rotation these two will be both pulling air through the intake runners, though at different phases of the intake cycle. But this is only a simplistic view because cylinder filling is a matter of fluid dynamics in the intake system, after all it is a "tuned port" system.

Now will this cause these two cylindes to run slightly richer than the other six and will that in turn cause the right bank to run a little leaner (O2 sensor in the left bank)??
Also if the other pairs of cylinders are building more power will the imbalance in power stroke impulse have any detremental effects??
It may be possible for this mod to provide a net power increase in the motor with these two detremental factors at work.
If so, is this imbalance of any significant magnitude?? Or does it simply just detract a little from the power that would otherwise be provided??

Why wouldn't the General do this; actually why would they chose this path when there are simpler ones available. They don't always chose the path to maximum HP/torque do they. And, as has been mentioned elsewhere, this mod should work best on a motor that is experiencing a need for more air. So, it may prove rather ineffective on a bone stock motor.

There are some unanswered questions here but I still plan to pick up a used intake base and try out this mod. Maybe I'll install a new set of spark plugs along with this mod and monitor their condition over say a half-year or so.

BTW, if anyone sees any flaws in the above please jump in with comments and/or corrections.

 

65Z01, I see your point in terms of running into a lean condition in the motor. I guess an easy fix would be to weld in a bung on the right exhaust manifold to relocate the O2 sensor and plug up the one one the left exhaust manifold. Or, you can install an O2 sensor to monitor the fuel/air mixture on a seperate device as oppose to just plugging up the bung on the left exhaust manifold. I think MSD makes a air/fuel monitor if I'm not mistaken. I can see all of us, including me are going to make a mad dash for a spare intake manifold. I think the idea of a siamesed intake manifold makes good sense. I wonder, how far should you mill the walls of the intake manifold. Is 3 inches a good start?

 

If we are looking at 20-30hp gain on a midified L98, that's like a 5-10% power boost. So I wouldn't expect an imbalance (lean/rich) condition to be any worse than say 5% from one side to the other. Plus the knock sensor should tell us if it gets too lean in either cylinder. Then we could just put the O2 in the right side and run those two a little rich.

I think I've seen depths of anywhere from about 1.5" to 3" with some cutting into the runner base; I have no clue on that aspect yet except I think to keep the opening as far upstream as possible to maintain velocity. I'm thinking that this mod may use a sort of Ventouri effect with high velocity air down one runner sucking air from the other. In that case it wouldn't take much of an opening to help top end breathing.

 

i look at it this way, theres pretty much no possible way that its going to run lean. and if it somehow, someway, ran rich, it would be a very slight difference. about the power imbalance, what about a single turbo on a v6 or a v8. perfect example 84-89 300ZX turbo, v6 single turbo. wouldnt the extra back pressure cause the drivers side manifold with a restriction to make less hp than the free flowing passenger side cylinders with no restriction? thats where the marvel of the modern engine comes to play. sure these things might have an adverse affect on the engine if they were to be a long lasting condition, but the engine inhales and exhales air so quickly that it really doesnt hurt anything. plus thats what a harmonic balancer and a flywheel are for. these are good points though. and on the 5 & 7 cylinders being on their intake stroke right after each other did kinda make me leary of doing this at first. (i looked into this alot before i actually did it, i did it on my only manifold) air, just like water, will flow at the easiest path it can take. once the number 5 intake valve closes and cylinder 5 begins its compression stroke, the intake valve 7 starts to open and the injector fires for a few milliseconds. WHILE (the key here is while) the injector is firing air is already starting to rush past the firing injector from the easiest point of flow, and that would be from the two runners it now has to suck air though. the intake valve is closed on 5 so the fuel that is fired from injector 5 will stay stationary due to the fact that there is still a large seperated "tuned" runner, and there is nowhere from behind the fuel to suck air from, therefore that mist of fuel stays in the #5 runner. air is NOT going to go all the way into the number 5 runner, mix with the fuel, then back upstream then into the 7 runner and downstream past the intake valve. there simply just isnt enough time. another thing it already has going for it is the air is already in the runners moving downwards, it just simply shifts directions with the suction of the different cylinders.


[Modified by 88L98, 12:17 AM 9/25/2001]

 

:crazy:


[Modified by vettenuts, 5:03 AM 9/25/2001]

 

I have been thinking about this mod since my previous posts.

Theres another way to look at this mod. You get a short runner single plane intake plenum for each of the two cylinders with tuning from the runners going into the plenum. The interaction between 5 and 7 is going to be more significant than in a single plane intake because the plenum is smaller. The interaction will be more of a problem at higher vacuum conditions. I wonder how the idle is affected by this mod.

There is another way to increase the topend. Get some a set of the aftermarket runners that are siamesed together like the edelbrock set. Cut the divider down on the plenum side on each one. The deeper the cut, the higher the power band moves up the rpm range. The downside to this mod is that you will lose the plenum before the two cylinders that the other mod provides.

 

if you do both, like you said with the runners, and like i have done with the manifold, i bet you would *might* be able to pull 5500+rpms. now i havent verified this YET, but im going to do it with some SLP semi-siamesed runners sooner or later, and after studying about it and looking at how the air flows, im figuring a pretty high rpm powerband.

 

65Z01...since your up on firing order physics here...did you now that all production V8's have the identical firing order? ( Fords just labels their cylinders differently and there was that one cam designed to reduce 5-7 scavenging by changing firing order, ford used it back in the early 70's)

It's also the same problem single plenum carb intakes have. If anything it makes one of the two cylinders run a little richer than the other cylinders...but not by enough to measure. It's really worse with carbs than with TPI ( air flowing is much more forgiving than air+Fuel mixture flowing in a carb setup).

I think it's definitely worth it...besides, when someone looks under the hood and see a visibly "stock" motor...you can then have a little fun :D

BTW: All domestic 6 cylinders have the same firing order too ( 6,5,4,3,2,1 ) just remember ford numbers their cylinders differently :D