What could I expect in horsepower/torque gains with a well-done porting job on a stock intake and TBI- on a stock 2.8L?
Thanks.

Honestly, I wouldn't expect anything measurable without supporting engine mods like a cam and/or exhaust work. You will get a bit higher rpm out of it, but that's about it. And you may not even notice that, depending on how you drive.

The exhaust manifold has to be ported first,,the reason for this is the exhaust is 1/3 blocked by the manifold pipeiping,,you only have to look inside the manifold exit port hole,, the metal from the tubing protrudes into the passageway,and the welding,Flange to tube blocks off the ,grinding the exhaust manifold is a labor intensive job,,plus often some of the bolts snap/break and it is a real bear to extract broken bolts,,to do the job correctly takes 30 hours with the tools most of us have ..It is my opinion that at least 75% of the fiero exhaust manifolds that have been ported are not properly done (wish I could post photos)) a proper port of the manifold and Y pipe and running a glass pack(cherry bomb,thrush) will yield 5 to 15 horse power ..8 to 12 for most port jobs
Opening up the exhaust or install headers like truelo is REQUIRED because the normal Fiero exhaust is so restrictive ..that cams,ported intakes ,ported heads ect will not deliver thier potential,, the first time you eyeball the ex manifold all will be revealed..
with out an open exhaust manifold porting TBI & intake will yield 1 to 3 hp if you do an excellent job

If you port the biggest restriction in the upper intake plenum and have the TB bored you will raise the RPM where the engine peters out of air by around 700 rpm.

It's enough to make a difference in racing, but not enough to do anything for the butt dyno. spend another 12-16 hours porting and port matching the plenums and you'll be where it will make a decent difference.

If you do all that, you HAVE to port the exaust logs and Y pipe to get any gains. if you flow more air in, you will flow more air out. that air has to go somewhere.

quote Originally posted by topher_time: Honestly, I wouldn't expect anything measurable without supporting engine mods like a cam and/or exhaust work. You will get a bit higher rpm out of it, but that's about it. And you may not even notice that, depending on how you drive.

exactly. by itself - wont do much. but - it surely wont hurt anything, and makes room to grow.

quote Originally posted by timgray: If you port the biggest restriction in the upper intake plenum and have the TB bored you will raise the RPM where the engine peters out of air by around 700 rpm. It's enough to make a difference in racing, but not enough to do anything for the butt dyno. spend another 12-16 hours porting and port matching the plenums and you'll be where it will make a decent difference. If you do all that, you HAVE to port the exaust logs and Y pipe to get any gains. if you flow more air in, you will flow more air out. that air has to go somewhere.

What about running Fiero Store SPRINT manifolds along with a set of Darrel Morse ported intake manifolds and throttle body?

quote Originally posted by FieroFanatic13: What about running Fiero Store SPRINT manifolds along with a set of Darrel Morse ported intake manifolds and throttle body?

the TBI setup discards the Fiero intake completely.the spring manifolds are a good start - but still got the y-pipe restriction. but - the right idea. add in a cam, some head porting - and your in the 200 HP's

quote Originally posted by Pyrthian: the TBI setup discards the Fiero intake completely.the spring manifolds are a good start - but still got the y-pipe restriction. but - the right idea. add in a cam, some head porting - and your in the 200 HP's

I have a stock intake set up and throttle body that has been ported by Darrel Morse. So mine hasn't discarded the stock intake completely...

quote Originally posted by FieroFanatic13: I have a stock intake set up and throttle body that has been ported by Darrel Morse. So mine hasn't discarded the stock intake completely...

I think you are mixing up TBI (Throttle Body Injection) - with the fact that our MPFI (Multi Port Fuel Injection) - uses a throttle body

TBI fuel injection on first glance looks just like a carb setup.

I was making same mistake. In the original post, I was intending "ported throttle body", not TBI.
Thanks for all the info, guys.
FieroFanatic13- did you notice any substantial change with the DM intake and throttle body? Have you done other mods?

well, I myself did in fact bore my own throttle body, and hog out the exhaust manifolds - and - yes - noticable improvement.

quote Originally posted by Pyrthian: I think you are mixing up TBI (Throttle Body Injection) - with the fact that our MPFI (Multi Port Fuel Injection) - uses a throttle body TBI fuel injection on first glance looks just like a carb setup.

I don't believe I ever used the term "TBI?" I said "throttle body" in my original question.

well, lets just make it all clear for everyone:
ported stock intake manifold, ported stock plenums, & bored to 57mm stock throttle body
I do beleive the highest HP's dyno'd with engine using these is 170 HP's.
and, I would expect - with all else remaining stock - 140HP

proper exhaust, decent ignition, and a camshaft tops off the intake nicely.

quote Originally posted by jpmurray: What could I expect in horsepower/torque gains with a well-done porting job on a stock intake and TBI- on a stock 2.8L? Thanks.

Here is the rub. The stock intake really can't deliver enough air to get the job done. I personally haven't seen 170hp with a ported stock Fiero intake. This is the reason FrancisT designed the Trueleo and the reason others like my self have gone to a carb setup.

I personally would not spend the money required to rework cast iron heads if I wasn't able to improve the intake manifold. It is kind of like trying to operate a toilet with a 1&1/2 inch drain pipe.

Arn

quote Originally posted by Arns85GT: Here is the rub. The stock intake really can't deliver enough air to get the job done. I personally haven't seen 170hp with a ported stock Fiero intake. This is the reason FrancisT designed the Trueleo and the reason others like my self have gone to a carb setup. I personally would not spend the money required to rework cast iron heads if I wasn't able to improve the intake manifold. It is kind of like trying to operate a toilet with a 1&1/2 inch drain pipe. Arn

https://www.fiero.nl/forum/F...2/HTML/075502-3.html

Good read. And a nice 3400 build. Here is a Francis T quote for quick reference

"On the flow bench our intake flowed enough CFM with a stock iron head to support well over 300HP. The stock intake is the main CFM limiting factor on these engines."

"Flow-bench numbers for Stock intake and SR14 & LR17 below.

Valve lift
.100"
.200"
.300"
.400"
.500"

stock intake CFM
55.945
106.88
124.415
131.93
139.445

no intake-head CFM
64.295
116.9
133.6
146.96
146.96"

Arn

Good posts guys. Im putting the Sprint headers on this week and it looks like I may have some competition for that Darryl Morse TBI on "some auction website" ending late this week. A couple of you mentioned the stock Y-Pipe is quite restrictive as well.....know a good place to get a better one or should i just have someone bore out the stock one? I think next for me would be to have someone bore out the upper plenum as I know that is quite restrictive as well.

Side note: after these changes, is it a good idea to change to a Hypertech performance chip?

The chip won't do much for you. I know a guy with one and it was a little disappointing.

If you cut the Y pipe do it with this kind of cut. > It then goes back together at the right angle. If you have a burr for your electric drill it is easily ported but you need a welder.

This is a major thing for performance.

Arn

Most significant gains are as has been said, the exhaust manifold, then the lower and middle intake manifold then intake ports. The throttle body enlargement won't get you anything - the bottleneck is in the manifold and is not easy to rectify unless you replace it (eg Truleo)