I know there have been some debate as to the efforts and rewards for porting/polishing the intake/heads for the 2.8 intake. As I promised, I will be giving the flow bench results showing before and after data and plugging in the numbers in the 'Engine Anaylzer' software to show whatever gains and losses materialized. I can tell you based on the results so far for an normally asperated motor, that a maximum of about 20HP was realized at about 4500rpm. This was using a cam with a very modest grind of Int/Exh 210/204 Dur. 445/440 Lift @ .050 and a 114 Centerline.
You can take it for what its worth if you want to use the stock setup and port/polish to your hearts content. My machinest related to me that the weakest spots are the middle/upper intake and valve size. The biggest gains were made at the exhaust since the stock exhaust valve bowls "were horrible" as the machinest says. Anyway the EA data will be given also to show what rpm ranges were affected. That is all for now!

 

HE knows exactly what he is talking about. When i built my 3.1L to push 14.9 on motor alone, the intake and the heads were looked at BIG TIME. I have posted this many a time and will again..... MORE AIR IN = MORE POWER OUT.... Think of a engine as a big metal air pump.

Heads:

Focus your time or money on the exhast side, do a complete port and polish on the exhuast side, this is the biggest restriction in the engine. Do a light port/polish on the intake side. Out of the box the intake side is pretty good, a smooth-over and such will aid tho.

Intakes:

Top and middle are the biggest robbers in the bunch... Do a complete match and smooth - do not go more then 1" into the ports. Use dye blue and a scribe to match the runner ports. The object is NOT to remove a bunch of metal, rather smooth and match the openings to the others - make sure you do the gaskets too. On the bottom runner... SMOOTH the runners/openings only... do not grind, the metal is thin. LIGHTLY radius the injector holes. There are writeups on how to do this, i did not, rather i polished the holes when 1500 grit, they say you can open them up for better spray pattern. Be sure to gasket match it too.

I do know that this was one of the first things i did when i first got the car (intakes) and it was a NOTICEABLE difference both in feel and on G-tech. It reved cleaner, and faster and the power came in at about 2500 to 5700. I was not running a coil or MSD at the time either.

The fiero store can do your TB's too for about 200.00. They will open them up and make them flow better. The trick here really tho is to get a high pressure even flow into the TB. The best way to do it is with a impeller at the tb to swirl the air and as little curves or bumps from filter to TB. From the TB run a rubber sleeve 3 inches wide and long to a K&N filter, thats the shortest and smoothest you can get. Currently i run the stock setup cept i drilled the horn out of the airbox, and ran a aluminum pipe down under the car connected to a fiberglass scoop. Its cold air but really turbulant. Anyways, take it with a grain of salt on the heads and intakes. OR, build a strong motor.


DO:

Stock shortblock
2030 cam
6000 rpm springs
ported/polished heads
ported/matched intakes
Direct air setup/K&N
Jet Chip stage 2
Underdrive crank pully
MSD 6AL with 6K rev limiter
Coil


You WILL be running mid to low 15's easy

Add

50hp NOS and run mid/high 14's


Take the shortblock and add 10.0:1 forged pistons and an aggressive cam - run into the low 15's to high 14's on engine - this assumes the right stall and gears are used. NOS in the 50 to 90 range will net mid to high 13's depending on tires, driver and gears.


David

 

hmmmm......that's what i was planning on doing..........higher compression..........my question is though how much would it cost to have a machine shop port the heads and intake??? i dont need an exact figure but just a ballpark range.........

 

Depends on the shop. Usually around 150 per - or - thats what i paid anyways. Plane on getting the cam, roller rockers, valve covers (chrome fiero covers) All at the same time... might as well do it then, easier the first time. Also if you are gonna go NOS, go Nitrious works import EFI DRY kit... comes with 35, 50 and 75 jets. You can get 90 jets for it. IF you go new cast pistons don't go more the 75. If ya go forged you can go upto 140 but expect a engine build within 50K miles unless you set up a good progressive system.

David

 

well, what i was planning was a 3.4 with 10.0 to 1 comp..........someone told me though that the highest you can get the comp is 9.6 to 1 becuz of the cylinder heads............? also another problem i will have is getting a computer chip to handle all of this................?


oh yeah i am planning on forged pistons also

 

Good point about the injector ports. I'll have to check those. I failed to mention that the flow tests were done with the old and new TB. The old TB port size to the upper intake had a diameter of 2 1/16" while the new TB that I will be using is 2 3/4".
I don't know what 1/4 times to expect with my setup due to all the mods I will be making with the mild cam.
I also am thinking about increasing the valve sizes as my machinest says I can go as large as 1.8/1.5 Int/Exh. The analyzer will help make my decision a little easier.

One thing interesting to note, on the intake side, flow started peaking at .400 lift (after porting) which determines that a cam with greater than .450 lift would be overkill according to my machinest. He goes by a general rule of thumb that useful cam lift is equal to the max CFM of the intake/heads + .050.
This is what makes flow bench testing so invaluable.

 

Where's the writeup on the injector ports? I saw what I think's a restriction to the fuel spray.. seems like 1/2 the injector fires at the wall of the intake manifold, while the other half is in the airflow. I'd imagine if that wall was taken back just a bit, and made into a smooth angle, it might help...

------------------
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---Think your car could be pic of the week? Visit http://www.f-body.net for details!

 

I pulled out my 2.8 intake that i was gonna use and looked at the injector holes. It looks to me like what tomp says. There appers to be alot of metal to be radiused back there as well. Not really sure how much needs to be taken or how far ya can go with it. It also looks like the piece is solid meaning the water jackets don't seem to be a concern. Pay attention to the ports that go into the heads, theres a good 1/8 to 1/4 inch of metal "step" in this area that would really kill smooth flow. Again, i am not sure how much can be taken before ya go into the water jacet. They say smooth only in this base piece, rounded would be better then flat. Equal would be better still but i dunno if i wanna chance killing a base. I will have to get around to getting a extra for a 3.1 and totally match it. I do not think the 2.8L i got will work as i do not recall seeing a cold start injector on my 3.1, will have to look, if it does/will work i plan on eating some metal and replacing that base as the last time we did not touch the injector holes nor the intake ports on the bottom - just the middle and top. That alone made a difference tho, both on time and feel. The only other thing i can see doing is using the intake and capping the cold start hole if i do not have one on the 3.1L again i don't remember one being there - age, it does weird things to yer mind lemme tell ya lol....

Update, just pulled the injectors from the spare rail... and test fit one into the hole... what it "looks" like to me is there is good flow to 1/2 the bore, the other half hits the wall. BUT thats where a good 1/8 to 1/4 inch of material can come off - i think... I am gonna clean it up and play with it in the next few days, it is looking like i am off work for the week so might be a good project to play with as i may have to change gaskets anyways. IF it don't fit the 3.1L i may have a fully ported and polished intake for a 2.8L for sale WITH fuel rail and injectors. The top of the intake says 2.8L in a round emblem - blah.... I may try and use my "normal" top intake to get away from that till i can get the emblem off and get one made that says HO 3.1L or NOS powered or something fun heheheh

David

[This message has been edited by Red91Bird (edited July 31, 2001).]