how large can the 2.8 be oversized, without hindering the riability of the car and without having to modify the engine management?

i want to use the car as a daily driver

thanks for the help

They've been bored to 3.62" or .120" over... A typical rebuild is .020" or .030" overbore. Like I said in the other thread, my first 2.8 was so beat up it required a .060" overbore. I also stroked it at that time with the 3.1 crank and pistons...making it essentially a 3.2L engine.

quote Originally posted by vladfiero: how large can the 2.8 be oversized, without hindering the riability of the car and without having to modify the engine management?

You can simply swap a 3.1 crankshaft and pistons into an internally-balanced ('88) Fiero 2.8, which will yield 3.1 liters (+11%) displacement. You cannot swap a 3.1 crankshaft into an earlier year (externally-balanced) Fiero V6. I would not advise boring a 2.8 any larger than necessary to clean up previous wear, as the cylinder walls are rather thin; an additional 0.1 liters of displacement is about the most you can safely achieve by overboring a 2.8 block. A 3.1 conversion will run just fine with the original, unmodified 2.8 ECM. You should definitely use the shallow dish-top 3.1 pistons with the original Fiero HO heads, though, otherwise the compression ratio will be too high.

FWIW, some have tried both swapping the 3.1 crankshaft into a 2.8 and boring it out to use 3.4 liter pistons, but the results have been mixed and I wouldn't recommend it. The 3.1 and 3.4 V6 use the same crankshaft, but the casting for the 3.4 block is designed to provide adequate thickness around the larger cylinder bores. The 3.4 has enough greater displacement vs. the 2.8 (+21%) that different injectors and/or different ECM tuning become almost a requirement.

3.1: Same bore as 2.8, but longer stroke
3.4: Same stroke as 3.1, but larger bore

[This message has been edited by Marvin McInnis (edited 04-09-2013).]

There's nothing wrong with using a balanced crank in an older block to my knowledge. He should also do the things GM recommends to the block to improve the oiling.
My first 87GT got a 3.1 stroke with a .060" overbore with an Engle cam.

You absolutely can use the 3.1 crank in a pre-'88 block. As a matter of fact, I've done it myself. You just need to use the appropriate flywheel or flexplate (i.e. for '88 Fiero V6). The only blocks you can't swap the 3.1 crank into are the small-journal (pre-'85) engines. But all the Fiero V6 engines are large-journal. So it's not an issue.

You also have to use 3.1 pistons. The 2.8 pistons cannot be used with the 3.1 crankshaft. Specifically, you want pistons for a 3.1 V6 with iron heads (i.e. shallow dish). The 3.1 pistons for aluminum heads (deep dish) will yield a ridiculously low compression ratio.

[This message has been edited by Blacktree (edited 04-09-2013).]

I have not worked on a displacement upgrade but I did a couple 2.8 rebuilds about a decade ago. I seem to recall that the stock heads flowed marginal for 2.8 liter displacement. by going up to 3.1 I would expect a 10% low end torque increase but at higher rpms, wouldn't the HP suffer due to the inability of the heads to flow air?

Just a question for someone else on the board to answer (who has done this upgrade) so you know what hp increaases you will get and at what RPM's.

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84 Formula Clone, 3800SC, VS Cam, 3.2 Pulley, 4T65E-HD, HP Tuners, AEM Wideband, , Regal GS Gauges, S-10 Brake Booster. 12.53 at 106.5 1/4 mile

quote Originally posted by lou_dias: There's nothing wrong with using a balanced crank in an older block to my knowledge.

quote Originally posted by Blacktree: You absolutely can use the 3.1 crank in a pre-'88 block. As a matter of fact, I've done it myself. You just need to use the appropriate flywheel or flexplate (i.e. for '88 Fiero V6). The only blocks you can't swap the 3.1 crank into are the small-journal (pre-'85) engines. But all the Fiero V6 engines are large-journal. So it's not an issue.

Thanks for the correction; I have edited my original post. I mistakenly thought there was an interference issue with the large tonewheel on the 3.1 crankshaft in the earlier 2.8 blocks.

[This message has been edited by Marvin McInnis (edited 04-09-2013).]

quote Originally posted by Marvin McInnis: You can simply swap a 3.1 crankshaft and pistons into an internally-balanced ('88) Fiero 2.8, which will yield 3.1 liters (+11%) displacement. You cannot swap a 3.1 crankshaft into an earlier year (externally-balanced) Fiero V6. I would not advise boring a 2.8 any larger than necessary to clean up previous wear, as the cylinder walls are rather thin; an additional 0.1 liters of displacement is about the most you can safely achieve by overboring a 2.8 block. A 3.1 conversion will run just fine with the original, unmodified 2.8 ECM. You should definitely use the shallow dish-top 3.1 pistons with the original Fiero HO heads, though, otherwise the compression ratio will be too high. FWIW, some have tried both swapping the 3.1 crankshaft into a 2.8 and boring it out to use 3.4 liter pistons, but the results have been mixed and I wouldn't recommend it. The 3.1 and 3.4 V6 use the same crankshaft, but the casting for the 3.4 block is designed to provide adequate thickness around the larger cylinder bores. The 3.4 has enough greater displacement vs. the 2.8 (+21%) that different injectors and/or different ECM tuning become almost a requirement. 3.1: Same bore as 2.8, but longer stroke 3.4: Same stroke as 3.1, but larger bore

I have actually used the 3.1 crank in my 2.8 and it works fine, you just need to go with a neutrally balanced (88) flywheel on your Fiero.

That said, is there any benefit, or hinderance, to having a longer stroke?


I bored mine out to .040 so I could roughly end up with 3.2 liters of displacement.

quote Originally posted by 82-T/A [At Work]: ... is there any benefit, or hinderance, to having a longer stroke?

Increasing the stroke will increase the inertial loads on main and rod bearings at any given rpm. The bearing loads due to combustion pressure will be slightly lower with a longer stroke, but at virtually all rpms above idle the inertial loads dominate.

As a broad generalization, for a given displacement a longer stroke (i.e. undersquare: stroke greater than bore diameter) favors higher low-end torque, while a shorter stroke (i.e. oversquare: stroke less than bore diameter) favors higher rpm and higher peak horsepower.

The long-term trend over more than 50 years has been toward shorter strokes (less undersquare), and most modern engines now fall into a relatively narrow range roughly centered on square (i.e. bore = stroke).

Examples:

Jaguar 3.4 XK engine (DOHC in-line 6): bore = 83mm, stroke = 106mm
GM 2.8 V6: bore = 89mm, stroke = 76mm
GM 3.1 V6: bore = 89mm, stroke = 84mm
GM 3.4 V6: bore = 92mm, stroke = 84mm

[This message has been edited by Marvin McInnis (edited 04-09-2013).]

the main preformance boost will come from new parts,not hogging out cylinder
if you want more go fast,it is in the head & exhaust
cheap seat mechanic
lay garden hose in sun,have very hot soppy water in pail,clean head using hot water & brushes
dry IMMEDIATELY,HAVE ABSORBENT COTTON t-SHIRTS RAGS TO DRY
if no compressor ,have a hose you blow thru,,Im a fat wind bag very effective hose pressure
you can open up your valve seat throat,using a drill or dremal tool,make them equal & port match the exhaust ports
if valve seats,valves are not pitted,
reseat valve seats by hand,very effective! easy to do
always replace the timing chain,, this is a major source of poor performance,,,one slip by me recently,I thought it was injector timing (Pick up coil), the fiero timing chain is shot at 70,000 or 10 years
check valve clearance in guides
you can port the valve seat throats with a simple drill or dremel tool.,make the throats EQUAL,you can make a template from a bottle cap or cut out stiff paper circle
the stock exhaust manifolds must be ported,one look will tell you why
get help from local Fiero club member if you lack porting experience!
you can have machine shop do a performance valve job,if your valves & guides are servicible,a 3 angle valve job will increase performance .

the stock exhaust manifolds must be ported ,if you have the stock Fiero manifolds they hurt engine power, mpg,efficientcy & cooling.
if you have any questions just ask,, there are many knowledgeable fiero gear heads that will help

quote Originally posted by Marvin McInnis: Increasing the stroke will increase the inertial loads on main and rod bearings at any given rpm. The bearing loads due to combustion pressure will be slightly lower with a longer stroke, but at virtually all rpms above idle the inertial loads dominate. As a broad generalization, for a given displacement a longer stroke (i.e. undersquare: stroke greater than bore diameter) favors higher low-end torque, while a shorter stroke (i.e. oversquare: stroke less than bore diameter) favors higher rpm and higher peak horsepower. The long-term trend over more than 50 years has been toward shorter strokes (less undersquare), and most modern engines now fall into a relatively narrow range roughly centered on square (i.e. bore = stroke). Examples: Jaguar 3.4 XK engine (DOHC in-line 6): bore = 83mm, stroke = 106mm GM 2.8 V6: bore = 89mm, stroke = 76mm GM 3.1 V6: bore = 89mm, stroke = 84mm GM 3.4 V6: bore = 92mm, stroke = 84mm

Ok, thanks... I had heard something about the longer stroke resulting in improved low-end torque, but wasn't sure exactly the science behind it.

I guess it's probably negligible from 2.8 to 3.1 though...

thanks everyone for all this info theres alot of info so les see if i understand

so i can put in a 3.1 crankshaft into the block and it will increase the stroke (whats the original fiero 2.8 stroke ? is there a that much of a difference ?)

from what car can i get the 3.1 crankshaft ? a camaro?

if i keep the 2.8 shaft will it end up twisting over time since there will be a bgger load on them?

if i do put in a 3.1 crankshaft can i put oversized fiero pistons on them ? or do i have to go with something else?

what tool can i use to port the manifold ? i havent found anything capable of eating the metal o

quote Originally posted by vladfiero: ... (whats the original fiero 2.8 stroke ? is there a that much of a difference ?)

quote Originally posted by Marvin McInnis: GM 2.8 V6: bore = 89mm, stroke = 76mm GM 3.1 V6: bore = 89mm, stroke = 84mm GM 3.4 V6: bore = 92mm, stroke = 84mm

Did you bother to read the information I and others posted?