this is for all of us who cant afford to buy and/or dont have the knowledge to build a custom upper intake. this may be a lil lengthy, but its for detail on what im doing and how/why its being done.

ill be flowing the stock upper and lower intake plenums on an air flow machine, modifying it, and then flowing it after to see the differences in cfm air flow for a class im taking. it will be a relatively simple process. basically im just going to modify the area where that wicked/restrictive 135 degree bend is between the upper and lower plenum. im expecting to see some pretty impressive increase in numbers.

now keep in mind that more flow doesnt always mean more power, but in this case i can imagine that it would since we all know that this specific area is the most restrictive of the intake.... next to the heads. id love to do more but i dont have the time to do it for my project in my Air Flow Analysis class.

this will be DIY job by me, i am by no means a machinist and have very little "hands on" experience in porting, so if i can pull this off, i hope most of us can as well. ill keep everyone updated as to what flow numbers are and how the process is going. its due by the beginning of Dec, so itll be done by then.

oh, if anyone has read this far, if you know anything about this area of the intake, let me know.

 

ur talking about the 3.4 plenum right?? im trying to do the same to the 2.8 top and bottom plenums i havent asked anyone at machine shops yet but im gonna call and if its possible to run all the way down th the intake with the bored/ported...


i wanna try and do it myself but i dont have the right kinda drill or press...

 

no i mean the 2.8/3.1 plenum. the 3.4 is 1 piece and a totally different design, so you really cant do what you can on the 2.8 intake.

 

damn im a day away from finishing my new upper plenum,it actually cuts down on runner lenght by about 5-6 inches and instead of the runner having to make a 140-160* turn it only has to make an 60*-80* turn maybe i can send u out one to flow for me?.oh and i can give u some really good tips for porting the stock upper and mid section if ya like ive been threw this before myself with my own manifolds.the best thing u can do is stay away from the outer edge of the bend,grinding there actually makes the turn sharper and u lose alot of velocity in doing so

 

yeah ill flow your intake for ya, ill even test it on my car too if youd like . i was looking at the intake parts and noticed most of the meat to grind out is on the inside edge. my plan is to open it up and decrease how sharp the angle is on the short side radius to help out the flow.

 

Does your intake look something like this?

 

sort of ill grab some pics shortly,though its the same basic design,mine has a few differences,the base plate is angled up in the middle to clear my afpr,also the base plate is made from 1/2 inch thick aluminum,the reason for the thick base plate was to be able to mill a nice radius on the entrance to the runners to smooth airflow.without that radius u may have some turbulance at the entrance to the runners.then theres a few other differences in plenum design im gonna keep to myself.

 

daves12secv6 what do you have as far as advise for porting the upper and lower intake plenum.

due to issues with mounting, im going to have to flow the two parts along with the lower manifold. ill post pics as i flow the intake and get the results, i should have the stock flow numbers next week monday by this time. then ill start my porting on the upper/lower intake plenums. i should have the final results by mid december, and i can update inbetween if youd like since i have to have 2 in progress flow number data sheets anyways.

 

dont grind on the outside radius,and when u grind the inside radius u dont want any sharp angles.u want real nice rolled bends.installing a 1/2 inch to 3/4 inch spacer inbetween the upper and mid halfs would work pretty nice as well,though this would move the location of the tb up the same amount.

dont take out alot of material either,just try to get a nice smooth radius on the iner sid eof the bend,grinding the outsid eof the bend actually just makes it a sharper bend.can u flow individual runners. if so do each runner a diff way to find out what works best

 

I would be very intersted in how well the individual pieces flow. Just so everyone is on the same page, I consider there to be 3 intake pieces. Upper (TB mounts to it), Middle (FI rail bolts to it), and Lower (FI fit in it). The Lower and Middle have the least to gain IMO. Being that they are a straight shot. The best that could be done is porting or polishing. The Upper and Middle plenums have the most to benefit from.

So if possible, I'd like to know what the Middle and Lower manifolds flow without the Upper attached. Then maybe polish them and see what the difference is.

 

you actually dont want to polish anything on the intake, it should be slightly rough, you polish the exhaust and bowl area. ill be flowing the upper and lower plenums and the manifold base together as an assembly but the work will be done in the upper and lower plenums where they bolt together. the reason im doing that is because of how i have to mount it on the flow bench. if i had a lot more time and supplies to work with id do it differently but this will give more accurate numbers because there is more of the intake there.

 

You can polish the intake, plenum, and runners down to the injectors. Just not past the injectors. You need a slight roughness on the intake port wallsleading to the cylinders after the injectors. That roughness creates a little turbulance that actually aids in the air & gas mixture into combustable fuel atoms (a.k.a.- better fuel atomiztion)

 

I was always under the impression that you only polish the runners leading up to the injectors, but not after that. This would increase the surface area for the gas to vaporize if it got pulled to the walls.

 

ive always been told to leave the intake slightly rough, even coming in to the port on the head before the injectors. but any modification on these engines will help, lol.

 

on a carbed engine u dont want to polish the entire runner,since fuel travels the entire lenght of it.on a fuel injected motor u can smoot/polish upto the injector.
the lower manifold on the 60* engines is a nice piece,could deff use some manifold to head port matching.and lower to mid matching.


the only place i see to pic up alot of flow in the lower is were the injectors stick into the manifold.the way the manifold is cast the port size shrinks way down were the injector potrudes into the lower manifold.

theres not much u can grind here without breaking threw the manifold,but there is a bit u can grind.

the other option im looking at is welding up the injector bungs,so i can grind away the injector boss inside the manifold so the runner does not shrink down.
then i can weld in new bungs that sit up higher on the runner and dont potrude into the lower manfiold .ill have to get some pics so u guys can see what im talking about.


the mid section by its self is a pretty overall decent piece.without the upper manifold/plenum bolted on the bend in the middle isnt that bad.and could flow really well with some good porting/polishing work.

once u get the mid and upper together that bend now becomes a huge restriction in flow.not to mention the over all runer lenght is very long and meant to make power down in the low rpm range

 

picture attached was too big

 

thats pretty much what mine looks like with some differences.in th eforst pic why do u have the middle of the back raised.the one i did th ebase isnt actually flat from each side it bends up around 15* to the middle

 

I had to clearance it forshraeder valve and the fuel PSI sending unit.

 

actually, from looking at the lower, i think by grinding that out, yeah youll gain flow, but im wondering if youll lose velocity due to everything else being so much smaller. i dont have any numbers or anything, but when i matched up the manifold base on mine last winter, i seemed to have almost noticed a small loss, no gain at all. i was talking w/ my prof. and he agrees that i may have lost velocity in the process, but w/o any dyno numbers or anything i dont know for sure. more flow doesnt always mean more power

 

might lose some down low power but it will deff pick up at higher rpms,the problem is the stock manifold and cam are designed for low rpms.though that section is were the runner shrinks down to the smallest cross section,once it follow that runner from the manifold to the cyl head port it opens back up again,it just necks down the runne rin that one section.i have some spare manifolds and iron heads that i may cut apart so u can get a better view of the runners/ports


see what may work for me isnt gonna work for u guys,with a forced induction engine u can use heads/manifold that flow great but dont have much velocity since the turbo makes up for it,

 

i got the intake flowed tonight. i flowed the throttle body, upper and lower plenums. it was done at WOT, and tested each runner, and then the whole intake. there was 0cfm leakage, which is almost never possible, i was surprised. heres the results stock:

runner 1: 157.8cfm
runner 2: 143.6cfm
runner 3: 141.3cfm
runner 4: 149.3cfm
runner 5: 152.4cfm
runner 6: 143.1cfm
intake/TB assy: 418.7cfm

not too bad, fairly close across the board. i forgot to get pics of the setup, so ill try to when i flow again after some work on it as well as progress flow numbers. might be next week, but probably 2 weeks yet, so stay tuned.

 

So, how I see things...

Thats a combined CFM of 729.7, but the TB limits it to 418.

A 3.4 will draw approx 416CFM at 7000RPM.
A 3.1 will draw approx 379CFM at 7000RPM
A 2.8 will draw approx 343CFM at 7000RPM

So i guess the next question is, at what pressure drop did you do the intake tests? 1" H2O? or 1psi?

I've heard of a professionally PP iron head will flow 160CFM.

Just to toss some numbers back at you

 

it was done at 25" H2O

i can flow the intake w/o the T/B, but honestly, i dont see it making that much of a difference. i dont think you can just add them up and get a total, youve gotta take into account a lot of different things going on inside the upper plenum that will also take those numbers down.

i wish i had access to a set of heads to flow for our engines. mine are here, but theyre on the engine and i cant really take them off right now. i dont have the $$ ot pick up a head or two to flow either (since mine are slightly modded, id want stock #s first).

and just out of curiousity, whered you find those numbers of flow at RPM?

 

wow thats really not that good for a stock manifold considering the stock heads flow what almost 155 cfm on the intake side.though like u said with everything flowing at once it would be diff but im willing to bet the flow drops

 

if a stock head flows 155cfm (details on what cyl/average/etc?) then that means that the upper and lower intake plenums arent that restrictive. because that number is only 6cfm above the average of the 6 runners for the intake. so porting wont do that much as far as power gains. the main work would then be in the heads.

if you can tell me where you found that info for the heads, and if i can get ahold of a head to flow, id love to compare those. ill check out the JYs as soon as i can.

 

give me a few mins and ill post up flow sheets for stock iron heads

havent located the flow sheets yet but i did find this info
Fully Ported Iron Heads (@.500" lift):
158cfm Intake / 142cfm Exhaust

Stock Aluminum Heads (@.500" lift) (1996 or so model year):
162cfm Intake / 139cfm Exhaust

Stock Aluminum Heads (@.500" lift) (2000 or newer):
200cfm Intake / 180cfm Exhaust

 

here ya go stock 2.8/3.1/3.4 cyl flow sheet


the 158cfm is at stock cam list a cam with mor elift really wakes up a stock set of heads

 

Is there any way you could do the test at 1" H2O?

It looks as if the upper intake manifold could benefit from some upgrading for sure. I'm going to ask my mechanical engineers at work what sized throttle body is required for the 700CFM potential the heads have. This thread really has my attention, especially since I want to do something about the stock intake problems (like build a new upper intake piece).

Dave, is the flow chart for a 3.1L head? I'm under the impression that all of the iron RWD heads are the same from 1986 and up. Is this applicable for these years of iron RWD heads?

 

yeah these flow numbers go for all the rwd iron heads from 86 on i belive.
or whatever the first year for mpfi was,though on an engine with a larger bore it will flow a lil better,those numbers were taken with a 2.8/3.1L bore.On a 3.4 they will flow slightly more,but not much at all

 

I saw that you already mentioned that right above the chart, sorry bout that.

Just for my knowledge, what is the pressure that most bench flowers flow to? 1psi or 1"h2o (27"h2o = 1psi)? I would assume that 1" h2o would be a better number. I hope I don't have 1psi drop at the valve!

 

the most common to flow at is 25" or some do 28" to make their numbers look better for advertising. at 1" there really wouldnt be any flow at all, the valve on the machine would barely be cracked.

 

but those exhaust numbers make any improvements to the intake almost trivial if its not getting that exhaust back out. Isn't it a waste of money to do anything else until you can get that port to flow almost as well as the intake?

 

Intake maximum pressure, 14psi
Exhaust maximum pressure, 1900psi

Exhaust is trivial due to the high exhaust gas pressures.

 

when youre talking about flowing, like i am w/ the flow bench, its not based on psi, its cfm. and as far as the exhaust, it only needs to flow at about 80% of the intake on the flow bench because of the pressure pushing the exhaust out, so it will end up matching on the engine.

 

So i guess all efforts in making the V6 get more power should be aimed at redesigning the upper intake manifold. This would support the general notion that the V6 TB is way restrictive. Its good to have some actual numbers. Thank you for the effort put in thus far Dr. Dave!

I'm going to aim at getting my bent metal intake done soon and get it on the dyno. Not to mention get a bigger throttle body. I'll be sure to keep on the progress reports.

What is the next flowbench test? Could you test the entire system with and without the throttle body? This could show the possible improvements of upgrading just the throttle body.

 

yeah i can flow it w/ and w/o the TB. ill wait to do it till ive got the intake done since i dont want to take it off and change numbers right now, itll all be done by early december, since thats when the projects due, lol.

the next flow test will be once ive done some work on the intake. i have to do an initial flow test, two in progress, and the final. i should have updates in a week or so w/ progress numbers.

 

i stated this in another thread, but ill mention it here too. i should be able to get ahold of some flow numbers of the (gen II?) aluminum heads if anyones interested. a friend is doing some work on this for his project and i dont think hell mind if i get his data.

 

i already posted flow nubers for the gen 2 and gen 3 heads

 

stock 2.8/3.1/3.4 iron head flow sheet

gen 2 stock fwd head flow sheet

and gen 3 fwd head flow sheet (stock)





run down of avg flow
stock iron heads 119 cfm intake 99 cfm ex
stock gen 2 aluminum 127 cfm intake 112 cfm ex
stock gen 3 aluminum 146 cfm intake 112 cfm ex

the above are just the averages,the sheets show actual flow @ whatever valve lift

 

Took me a second to realize what was going on. The iron heads list intake 1-3 and exhaust 4-6 while the aluminum heads are listed exhaust 1-3 and intake 4-6. I don't know if anyone else missed this but I did.

I guess it goes to show that the aluminum heads are by far a better design. I didn't realize that the stock irons flowed 180cfm tho! Thats a good number. I guess the problem now is.... how do you make the intake flow that!

 

i accidently posted the gen 3 sheets twice instead of gen 1 gen 2 gen3.ill fix it when i get home from work later FIXED NOW
----------
they do flow well around .500 lift but max lift numbers arent as important as mid lift numbers,the valve passes the mid lift numbers 2xs while as it only makes the max lift number once.

the problem is most computer compatable cams only have around .430 valve lift,now if u can get the cam lift higher and use a 1.6 rocker to squeeze a lil more lift iron heads wouldnt be that bad

 

i flowed my intake tonight after making a lil modification to the bend inbetween the upper and lower intake plenums. basically all i did so far was gasket match the ports. ive got pics up of how much i took off and how it is mounted on the flow bench. again there was 0cfm leakage. ive got it all posted on my website so check it out

http://www.cardomain.com/ride/461596/3

 

so on the 2.8 with the flow being better than normal now i seen that u shouldnt mess with the top plenum now what if u just used a bigger TB like the performance fiero 2.8 TB they have, it's alot larger then the stock but the stocks not so bad either but would the combo with this TB and the ported plenums and intake be better? by #s

 

Well sometime the engineers at GM get more say then the accountants but not often.
Id suspect the same after spending so much time handling the intake filing on it.
Exhaust mods should come before intake mods.

But should be easy enough to flow bench like your intake. See how much the stock TB

Funny how handy a vac gauge and a shop vac can be.

 

so i did a lil more work on the intake, opening it up here and there, smoothing things out and trying to get the cfm's a lil closer to eachother. it gained another +/-5cfm in each runner and is more balanced than before. i left the sheet with the numbers in the lab so ill post them later. i think im going to do a little polishing on the throttle body and see if i can gain any #'s there.

 

Why not go the easier better/intake route...more air better throttle responce. Way easier to make as well. If you need better pics just let me know.

 

it snice to see ppl with 660's who have done other work like this besides the few here that activly mod and do custom stuff on this board.any chance u have better pics of the throttle brackets(how u linked them together,also it apears u only have one iac hooked up,how does that work out with the divorced plenums??

 

Okay here we go...first off this is a fiero with a 3.1 dual stock TBs turn upside down because of fitment. This intake is very ugly and it is "caveman" in design, but what it lacks in looks it definetly makes up for it in performance. I say function over form.

The IAC has little to do with anything to be honest. The MAP is what really matters everything from the fuel side is relied upon by the load and that is why the plenums are connected in the back. The map senses the load from both plenums. They are linked by the steel rod. I have alot of changes to make but this is only a prototype. I am going to have another made that will be better. I have been a member on here for a while but I never posted before. I am on the fiero forums and 60degreev6 as well. This was a big learning experience for me. From 40 to 100 is fun now. I always speed because I am not used to the acceleration. I have a cam and spec stage 3, but this is the second best mod I have done...N20 is the best...lol.
This might help...the physical making of the intake is on page two.
http://www.fiero.nl/forum/Forum2/HTML/077346.html

 

the only reason im doing this is because i had to do a project for my engine air flow analysis and i figured if ive gotta do something, i might as well benefit from it. so i thought id see what this thing can do if its worked a lil bit. but i am planning on getting a different intake manifold w/ the next loan refund check this summer. who needs groceries and rent money, lol.

 

ok so heres the final flow data after working on the bend between the upper and lower plenums. i also found when i opened the throttle plate that there was a bunch of material that stuck out on the left side of the intake. so i ground that out and heres what i got.

Runner 1: 165.7 cfm
Runner 2: 162.9 cfm
Runner 3: 166.9 cfm
Runner 4: 162.0 cfm
Runner 5: 160.4 cfm
Runner 6: 161.7 cfm
Intake/TB assy: 432.2 cfm

not a bad increase from the stock flow numbers. i wont know if there is any difference in how it drives until probably march once the roads are clear of all the salt and crap. im now starting to polish the throttle body only because i have the time after exams and ive heard throttle response is better, so why not. so add that to your list of free mods and see how it goes for all of you. good luck and i hope this helps some of us on the boards!!!!