ok this is about porting the base
i have the stock runners and stock plenum (ported) and right now the stock base. i am going to port the base no matter what but i have a theory and would like someone to back me up or say it can't hurt or to slam me down if it would totally mess up everything.
i would like to siamese (spelling) the base from the runners to about halfway to the intake side of the heads. so that each intake stroke could pull from 2 runners. i will go ahead and open up the rest of the intake (from halfway to the intake side of the head) quite a bit.
now i know this will hurt my low end torque but it should help my top end hp a bunch shouldn't it?
i am going to mildly port my heads and get some 1.6 rocker arms and new valvesprings. another question whats the stock valve spring seat #pressure? what would be a good upgrade 10-15 more #s maybe?
my mods so far are in my sig. i do have a msd blaster coil on the way to help out with the top end spark as well.
thanks a ton guys
Andrew

------------------
Andrew Peery
1987 IROC, 305 TPI, T5
Hooker Competition Ceramic Coated Headers, Flowmaster, Ported Plenum
All smog equipment gone and no cat
before headers
192hp and 265tq
15.20 @ 92.5 mph 2.4 60ft
After Headers
14.480 @ 95.01mph 2.194 60ft

 

anyone?

 

You're into uncharter territory here, i don't think anyone has tried a siamesed base on an LB9 yet. Keep us posted as to how it works out, i know i am curious. You might need a cam swap to really take advantage of the enhanced breathing though. The big question will be how bad does it hurt you off the bottom.
...ed

 

Would someone mind telling me EXACTLY WHY things like this hurt bottom end?

Why doesn't more breathing = more power period

why does lower end like less air?

I DONT GET IT!#$!

------------------
-------------------
1985 IROC-Z, nuff said :P

 

because the longer the tube the more air velocity is created and more low end torque.
more breathing and more room to breath slows the air velocity down but allows more air to breath from. so better top end
anyone correct me if i'm wrong
Andrew

 

Nice theory!

I understabnd the velocity on the exhaust side........


But intake.... who knows but sounds great! :P

So tell me, how would you make torque like you have with tpi, with a carb? high rise manifold?

------------------
-------------------
1985 IROC-Z, nuff said :P

 

I actually had the siamese base I have on the 350 in the Grand Prix in the TA first, which was an 86 LB9 engine with a mild cam. It ran .5/3-5mph (cant rememeber the exact number) faster on my g-tech with the siamese base rather than the stock unported base, whatever that might mean. I never did take it to a dyno or the track with the siamese base on the TA however.

This is what it does on a 350 from my experimentation:
https://www.thirdgen.org/messgboard/...ML/001492.html

 

Really, i didn't know you had ran it successfully on a 305 first. How'd it feel, any noticeable drop in low end?

 

highrise maybe if that is what its called i was thinking of tunnel ram? the ones where the carbs sit up fairly high and it looks like lt1 runners going from the carb side of the intake down to the intake openings on the heads. but i think with a carb its different cuz those style intakes do well at high rpms i think.
don't quote me though i'm no expert
someone that knows please post so we can be sure
thanks a ton guys i'm gonna go ahead and siamese the base i can't wait
Andrew

 

Successfully.. hmmm...

Well it did lose some low end for sure I know, it definitely pulls harder now with the stock base in the lower RPM's than it did before with the siamese SOTP. However, I think it was more than able to overcome that loss by running through the RPM's faster after about 3500, at least thats how it felt. The 4500 wall was totally gone, I pulled that poor engine up to 6400 the last run in which I ran the best time with it, no telling what would happen if I would have gone for more RPM's... although from my past experiences thats the very last thing you want to do on a stock 305 bottom end, so it may not be the best idea for many of us.

I do want to do some more experimentation, the results were what I wanted out of it, and I like the results very much. The torque now with the stock manifold sure is nice, but its nice to pull serious RPM's in a TPI too.

What I have now is a stock 91 engine that I think is about where I was before, in the 15.3-15.5 range. I am having thoughts of tuning it correctly, dyno run, and then make another siamese manifold, tuning it again, and see what it does from there.

[This message has been edited by madmax (edited July 16, 2001).]

 

Hmmmm... unfortunately for now i can't afford to lose a single drop of bottom end, i already come off the line like a slug as is. But some 3.73s and a siamesed base sounds like a nice idea. I'll have to see how yours goes.
...ed

 

Friendly warning:

DONT DO 3.73's!!!!!



------------------
-------------------
1985 IROC-Z, nuff said :P

 

just thought I would try to explain some stuff that people have asked about above as best as I know how.

the effect that you are messing with if you siamese your intake on the TPI is called RAM TUNEING (sp)

a long time ago I think it was chrysler that did alot of experimentation with this and they found that when the intake valve closes (after the intake stroke) it causes a pressure wave to travel back up the intake runner. now when this wave reaches a large difference in the tube diameter (ie the plenum) it is partially reflected back down the intake tract twoard the intake valve again.
now if you are still with me, the guys at chrysler realized that if you waited for this wave to come back down to the intake valve and opened the valve at that moment it would help the engine breathe better (positive pressure at the valve).
technically this is called tuning for the third harmonic.

now, depending on how long the runners are, the waves will take different amounts of time to reach the intake valve again. therefore by changing this length you can "tune" for this pressure assist by finding the right length so that this happens at the RPM you want it to.

there is a formula somewhere online that will give you runner length and the corresponding RPM that the boost will occur at.
I strongly suggest finding this formula (the one corrected for temp too) before deciding on just how short you want to make your runners.
there should be a tech article on this soon (maybe ill write something) so that all these people thinking about this mod at least have something to work from.

------------------
88 WS6 T/A 305 TPI--
K&N,Air foil,hypertech chip, thermostat+fanswitch
free mods, dynomax catback, urethane motor+trans mounts,
SSM SFCs, Bilsteins
very trick homemade ramair, Accel 300+ ignition system.
Planning: hedman 1-5/8 longtubes, NOS 150 plate, world 305 heads, replace the "peanut"! and other susp. mods.
check it out at:
http://www.geocities.com/transam617

 

wow i never even thought about using harmonics to aid in air flow.
that would be nice but it will just happen at certain rpm's 1st 2nd 3rd etc harmonic. what i want is the ability to have more air to breath from. this should accomplish that as well.
keep me posted on whether or not you find that formula or not. if you get it before i finish up i'm gonna go ahead and use it.
thanks
Andrew

 

just do a search online for "ram tuning" and you should come up with the formula.

 

Wait till you calculate the ideal runner length and diameter

Throw the book out, thats what I did.

 

I have the Hot Rod article typed out. If anyone wants it, email me.

BTW it was in the 1950's when research was done.

------------------
86 T/A 5.0 A4 & 2.77 gear
15.62 @ 86 mph
93 Civic 1.6L
13.5 @ 100 mph

 

Well, here is some more info on the topic that I have picked up in my reading. There are actually two distinct phenomenon occurring in the intake system of your TPI motor. One is considered an inertial effect and the second is a wave tuning effect. In the case of inertial effects, when your intake valve opens, the suction created by the cylinder moving down causes air to flow through the intake tract. This column of air that is now moving has a mass and velocity and thus has inertia and kinetic energy. When your piston reaches BDC, you are no longer "pulling" any air through the intake valve, but since this column of air is moving, it will tend to keep moving and effectively packing more air into the cylinder, even though the piston is now on its way up. This is also called "ram charging" or inertial supercharging. Since inertia is proportional to the square of velocity, you can see how important the velocity is to the inertial effect. The downside to velocity is increased pressure loss thru the passage at higher airflow rates. These small passages which serve to enhance velocity at low rpm, become very restrictive when you try to rev the motor. As with most things in life, you cant have it all!! No intake design will work optimally well at all rpm ranges. The stock TPI does a wonderful job when it is operated where it was designed to perform.
The wave tuning effect is an acoustical effect that arises due to addition and subtraction of pressure waves traveling in the intake passages. These pressure waves propagate at much higher speeds than the mean velocity of the air through the passage. Both the opening and closing of the intake valve causes rapid changes in pressure which sets pressure pulses moving back up the intake runner. When these pressure fronts reach a discontinuity in their path(ie the plenum), reflections occur and the pressure wave begins to travel back down the runner. If the timing is right, this wave front will create an additional pressure at the intake valve when it opens for the next intake cycle. This same principal applies to the pipe organ, a 2-stroke engine, and a ported speaker enclosure. The important point with all these systems is that they are all only effective at a point near their "resonance" frequency. This frequency where the effect is maximized is called the "tuned" frequency and is where the "tuned" port EFI gets its name. This tuned frequency is determined by the length of the runner and the propagation velocity , which is close to the speed of sound. In general terms, porting the passages to make them larger will reduce cylinder filling at low rpm and enhance it at high rpm, but has very little effect on the "tuned" effect. If you shorten the runners you will raise the resonant rpm point and reduce the flow losses which both improve high end HP and hurt midrange torque. The equations that define the flow thru a pipe or tube clearly show that the pressure drop encountered when air passes thru the tube, is directly proportional to its length, and inversely proportional to the square of the cross sectional area. Ray Bohacz wrote an excellent article covering this subject in a past issue of GM High Tech Performance magazine if you want to do some reading on your own.

Mista: Could I get a copy of your article?? Always trying to learn more!! Thank you

 

hey yelofvr.......I GOT A HEADACHE READING YOUR POST!!

 

if you want to repost what I said you should just cut and paste. much easier than rewriting.

Madmax - do you still have the old formula, I cant seem to find it anymore.
I know what you mean about throwing the book out. this kind of tuning works well on a single cylinder basis but starts to get muddled when 8 are involved.
I worked for formula SAE when I was still in school and we made our own variable runner intake that changed runner length with RPM. it was wild but we found the old formula to work pretty well....

of course it was an f3 600 cycle motor but the airflow numbers seemed to like the old formula...

 

88305tpiT/A: I was trying to show the distinction between "ram effects" and "tuned" effects. Many people confuse them(or lump them together) and I saw nothing in your post regarding the inertial effects of the intake system. They are very important in understanding what goes on. I felt I had to explain both effects in order to show the difference. I did NOT mean to offend you or discount what you said in ANY way. Your comments were right on regarding what you covered.

 

cool man - nice to see some other people that want to take this board up a notch or two intelectually.

no flame intended here either.

I reread what you wrote and you are right on.

I just didnt think that inertial effects were needed here because they are present in all intake designs whereas ram tuning is not.

we still need the formula so we can do some calculations and get madmax to tell us what he thinks of the formula
James

 

AND you always have inertial effects in ANY engine that has at least some runner length, but the longer the ISOLATED the runner is, the more the effect.

and hence the name of the team that took great use of it in the 1950s: the Ram Chargers.

oops. You were doing great, and I mean really great until that one. Inertia is forcelike, that is that it has units of force: mass*accel

accel(eration) is d/dt (velocity), and more precisely inertia is d/dt (mass*velocity) which is just d/dt (momentum).

So there is no square of velocity involved in inertia. btw, d/dt is a derivative (change mathematically) with respect to time for anyone not familiar with it.

I don't think that's entirely right. The wall friction forms a boundary layer, and the viscous stress within that layers slows the motion of the flow even though the pressure gradient is still working to try to, ahem, suck air&fuel into the engine.

I think you had the idea right, but you got too liberal with the wording.

Agreed.

Exactly.

True.

Long Aside: The acoustic (sound) waves travel at around 1100 ft/sec at normal outside air temps and pressures, and faster for warmer temps. The same is true in the exhaust but the wave speeds are higher due to the higher exh temps. BTW at WOT and for any 260 hp engine, the airflow requirement is around 388 cfm. That's like 6.5 cubic feet/sec airflow. For a intake cross section (a 3" diam MAF, just for the sake of a good example) of .049 sq ft, the flow speed is 132 ft/sec. That's at WOT for a L31/LT1 350... so the mean flow speed, on average and feeding the plenum leading to the eight cylinders, so the mean airflow speed is 0.1 the speed of the acoustic wave.

as well as at the back of the valve,

It works similarly on the exhaust, except that you want the rarefaction half cycle to reach the exhaust valve when it opens (or duing some part of the exh open event) to help withdraw the combustion products from the chamber.

..good correct stuff snipped...


I'll add that the math allows more that one resonance-tuned rpm; so you could have one at 2000 rpm and another one at 6000 rpm (odd multiples). IMS you also have a second set of equations applicable to the exhaust runners, but the waves speeds are higher (from the hot gas) and the tuning lengths are different because you want scavenging and not filling.

Most auto manufacturer's DON'T use resonance tuning from pipes anymore because the runners are just too damn long.

Instead they use much shorter runners with the mass within the air plenum to act as a Helmholtz resonator. This allows them to make all parts of the intake smaller in size, and it's a lesson they borrowed from the loudspeaker industry. The good setups involve using one, two or three different sized chambers within the intake plenum, and doors which open and close to add or seal off the chambers, so that the Helmhltz tuned intake can resonate at a progressively increasing frequency, and in so doing match the increasing rpms during a WOT event.

Good post Yelofvr. - Ken

 

Good, revisited, how about the smart guys help me out a bit, eh?


https://www.thirdgen.org/messgboard/...ML/005696.html

------------------
"Question with boldness even the existence of a God; because, if there be one, he must more approve of the homage of reason, than that of blind-folded fear."

-Thomas Jefferson

 

I really dont want to start anything because I know we all took these classes but are we going to get some usefull formulas for runner length soon out of these
I agree with your analysis
replys??

oh and by the way
quote kdrolt:

oops. You were doing great, and I mean really great until that one. Inertia is forcelike, that is that it has units of force: mass*accel

accel(eration) is d/dt (velocity), and more precisely inertia is d/dt (mass*velocity) which is just d/dt (momentum).
"

actually you said it yourself----
inertia is the derivative of momentum which is one half M V squared!

James

 

Just a clip from the HR article.......
Chrysler testing resulted in a formula to calculate where the ram effect will come into play. To wit: N x L = 84,000, where N represents the desired engine rpm to tune for and L is the length in inches from the opening of the ram tube to the valve head. Shope explains: "Let's say you're running at Bonneville with an engine that develops peak horsepower at 8400 rpm and want to tune for maximum ram effect at that level. Then, L should equal 10 inches, as in 8400x10 inches=84,000." To achieve ram tuning at 5500 rpm simply divide the constant, 84,000 by 5500 rpm. The result is 15.27 inches, the ideal distance for the intake tract as measured from the opening of the ram tube to the valve head.

What now???????

------------------
86 T/A 5.0 A4 & 2.77 gear
15.62 @ 86 mph
93 Civic 1.6L
13.5 @ 100 mph

 

The good setups involve using one, two or three different sized chambers within the intake plenum, and doors which open and close to add or seal off the chambers, so that the Helmholtz tuned intake can resonate at a progressively increasing frequency, and in so doing match the increasing rpms during a WOT event.


Very interesting. The question I have is whether anyone has implemented a baffled plenum for a Vee-type engine. This type of plenum would seem fairly straight-forward to design for an inline configuration, but it would seem that the complexity and bulk would rise dramatically if you had to feed two banks of cylinders.

I've read some discussions on a device known as a "Compton Cube", and wonder if there would be a practical automotive application. Supposedly, the device would allow a wide range of resonant tunings for a given pipe length. Unfortunately, the mentioned discussions revolve around what the device can do, and do not mention or illustrate how it does it.

From my own calcs, it seems the tuning of the intake tract on a TPI engine(length from plenum to intake valve) should result in a "tuned" resonance at slightly above 4000 RPM. Of course we know that is not the case in reality, but your explanation of the dampening effect of the plenum helps explain the lower resonance point of this intake.

------------------
"The reasonable man adapts himself to the world.
The unreasonable one persists in trying to adapt the world to himself.
Therefore all progress depends on the unreasonable man"
--George Bernard Shaw.

 

cool thanks.
do we know from that article what temp the air is at for this calculation or where they derive it.

I think mad max or whoever else is doing siamesing will tell you that 10 inches is still pretty long for 8000+ rpm. I think the TPI runners are somewhere around 18 inches right??

well now that we have the formula lets start asking how short people have gone and see what it did!
(witness my next post)

 

That's not correct.

momentum = mass*v

d/dt (momentum) = mass*{d/dt (v)}
+ v*{d/dt (mass)}

the d/dt (mass) term occurs because some of the mass is lost (converted to a gas) and dumped (into the exhaust) so it doesn't go for the ride anymore. This term is tiny for all but high-end drag racing cars (top fuel is one example), but it is very important in rocket science... <vbg>.

The other term, mass*{d/dt (v) } is the more important one.

So d/dt (m*v) is NOT, as you said, 0.5*m*v^2.

Now where did the 0.5*m*v^2 come into this?

If you integrate (m*v), you get 0.5*m*v^2 but that happens only if the mass is constant. btw 0.5*m*v^2 is kinetic energy, not momentum, and that why I said Ylwfvr got a bit confused.

Integration is the inverse of a derivative. A derivate is like finding the slope of a curve; integration is finding the area UNDER the curve. They can be related by math --- but I think everyone's had enough of that by now. FYI. - Ken

 

There is a webiste which chronicles such a design for the Nissan 3.0 l v6, and it specifically addresses the intake plenum, and acoustical tuning, to enhance torque across a wide range of rpms. I have the URL at work, and I'll find it and post it. It's a good read and engine dyno data is shown for the distinct plenum-door configs, so you can pretty much see on the dyno charts which pleunum set up you would want vs rpm. They probably also did a similar set of dyno measurements for part throttle ops, to enhance cylinder filling at 65-75 mph, and thereby achieve optimum fuel economy.



Yes. I think BMW and Mercedes both have... but I'd be hard pressed to back that up with a URL. I'll have to try to find one.



One trick is to keep use a separate plenum for each cylinder bank, and ONLY conect the plenums (open the connecting door) when appropriate. ChrycoDodgePlym did this on the 3.5 l sohc v6 used in the Intrepid family of cars, and there isn't any reason why you couldn't do it on a v8.



If memory serves, I recently read (somewhere?) that one higher end mfg was going to produce an engine that used a (my terms) trombone-slider to allow a intake pipe resonance tuning that would exactly match the engne rpm and give optimal tuning for all conditions. My GUESS is that it's not a pure pipe by itself because the runners would have to be extremly long for part throttle highway use... so there is probably a clever hybrid of plenum box mass loading as well as runner length tuning.

I'm sure one of the higher-end auto mags will do a feature on it, because it's also promo for the mfg.




There would be some added mass due to the finite slug of air at the top of each runner, and there would also be some added mass due to the fuel sprayed by the injector on the base, so both of these things would lower your calculated eng speed of 4000 rpm. In addition, the math formula doesn't take into account the damping of the tube walls on the flow, and that tends to lower the rpm for resonance as well.

Plenum damping plus tube wall damping plus finite Q damping of the air itself. There's also vorticity (think micro swirl) that also helps damp things, but I've never tried to work that math into a resonance formula before, so I'll stop right there.

btw, the following is NOT the article I was referring to, but it covers most of the goods:

http://www.fortunecity.com/silversto...h_engine_2.htm

FYI. - Ken


[This message has been edited by kdrolt (edited July 21, 2001).]

[This message has been edited by kdrolt (edited July 21, 2001).]

 

Ken,

Thanx for the explanations. Some very interesting food for thought .

Unfortunately, the link you provided was not as helpful. The technical explanations the author trys to present are laughable in their lack of understanding. And he/she makes no attempt to hide a very Japan-centric view of automotive technolgy which is rife with factual errors.

 

Well, I was wrong -- it wasn't Nissan it was Madza.

Here are the two relevant URLs, one on the Mazda work and other by an engr in the UK:

http://www.highlandsun.com/hyc/sae920677

which is an SAE paper #920677 by five engrs from Madza, and

http://www.atalink.co.uk/mira2000/html/p139.htm

which is a MIRA Technology 2000 paper.

Both papers have detailed engr info on acoustically tuned intakes, among other things. I hope the links still work; I printed both papers last Nov so I am not sure if the links are still active. FYI. - Ken

 

kdrolt: Thanks for the links, I love reading articles like this. I understand your point that its actually energy that is 1/2 m*v^2. Great thread and inputs guys, I really enjoy these discusions, really learn alot. Let me ask a question I have never seen adressed. If acoustical tuning aids cylinder filing at resonance, why does it not HURT performance at other rpm points where you would get "distructive" interference of the pressure waves??????? I would expect some rather significant nulls in the torque response at some point in the rpm range......

 

It does hurt.

To be more specific, wave tuning on the intake side helps in compression-aided cylinder filling at odd multiples (1,3,5...) of the fundamental frequency (which can be expressed in terms of engine rpm), but it also hurts at even multiples because those correspond to a slight vacuum at the backside of the intake valve(s).

However, since the gain in intake filling in the cylinder is small from wave effects at the 1,3,5... as compared to the cylinder filling from non-acoustic mechanisms (momentum & pressure gradient), then the reduction is also small at the 2,4,6...

That said, the plumbing lengths tend to be very long for even the fundamental (mode 1 for cylinder filling). So if you were designing an engine for drag racing, where you are going to sweep through a band of rpms, you might design for enhanced acoustic wave filling for the fundamental mode (1) and the third harmonic (3), while taking some lumps at the second harmonic. You don't have many of these harmonics to work from, unless you are working an engine used in Formula 1 racing, and engine that will see 12,000+ rpms. Then you have a lot of latitude but more things to worry about.

If you were running a high speed event, you might design the engine to be near max speed at the tuning point for the third harmonic, so you get enhanced filling of the cylinder(s) for 95% of the race, because the engine will sit at that speed for long durations (say on an Indy car).


Well, you're exactly right but they wouldn't be that deep (the nulls) because the effect we're talking about is small relative the the filling of the cylinder with out wave tuning. i.e. the peaks and nulls from acoustical tuning aren't that big as compared to what you would get without them.

Btw, all of this also works on the exhaust too, so the real craft is putting the two together in a way that's optimum for the use of the engine. - Ken