Pennock's Fiero Forum
  Technical Discussion & Questions - Archive
  2.8L and 3.1L Crankshaft Comparison Conversion and Recommendations

T H I S   I S   A N   A R C H I V E D   T O P I C
  

Email This Page to Someone! | Printable Version


2.8L and 3.1L Crankshaft Comparison Conversion and Recommendations by mindscape
Started on: 03-01-2002 01:32 AM
Replies: 3
Last post by: mindscape on 03-01-2002 06:24 PM
mindscape
Member
Posts: 854
From: Bristol, TN
Registered: Jul 2001


Feedback score: N/A
Leave feedback

Rate this member

Report this Post03-01-2002 01:32 AM Click Here to See the Profile for mindscapeClick Here to Email mindscapeSend a Private Message to mindscapeDirect Link to This Post
In my opinion I feel that it is more economical to buy a 3.1L crankshaft, than to buy a stroker kit for the 2.8L, especially if you already have a 1988 2.8L Fiero.

1990 Pontiac 6000 3.1L with cast iron heads and distributor or a 1990 camaro 3.1L with cast iron heads and distributor are good reference vehicles.

Crankshafts CAST # 981, 186, 268. WITH DISTRIBUTOR IGNITION

Below is a comparison of the 2.8L crankshaft from a 1988GT and the #981 cast 3.1L crankshaft.

What you need for a conversion are:

1. 3.1L crankshaft CAST # 981, 186, 268. WITH DISTRIBUTOR IGNITION The #981 is suppose to be stronger. However, I've used a #981 and a #268 and saw no real difference. The #268 is in block and crankshaft picture below; left hand side you can see the cast number even though it is fuzzy.

2. Neutrally balanced flexplate/flywheel. Have yours balanced or buy one for a 1988 Fiero 2.8L

3. 3.1L pistons Sealed Power H562CP Teflon coated.

4. New 1988 Fiero 2.8L harmonic blancer - which is neutrally balanced.

Buy rings to go with the pistons, i.e., buy 3.1L pistons. For reference and part warranties I specified parts for a 1990 Pontiac 6000 3.1L with cast iron heads and distributor.

2.8L/3.1L/3.4L use the same cylinder heads and connecting rods as well as the same stock camshaft.

Now, since you have gone to the effort to stroke the 2.8L to a 3.1L then go the whole mile. Rework the cylinder heads and use new valve springs, such as Melling VS-380. Roller-tip rocker arms are good too, such as Comp Cams 1413-12 1.52 ratio, or spend just a little more and go with full roller rockers. A Melling MTC-5 performance camshaft is good, similiar to the GM performance camshaft 12363220, and with the 1.52 rockers results in .427" intake valve lift and .450" exhaust valve lift, or the GM 12364059 Crane Kit or CompuCam 2030 are also good choices. A higher lift cam will affect the idle quality - too much and it won't idle at sane RPMs. A high-volume oil pump is also recommended, such as the Melling M-95HV.

IF YOU PLAN on racing or running the engine hard, THEN have a machine shop cross-drill the center two main jounals. This is what GM recommends for racing - helps keep the connecting rods from losing lubrication at high RPM.

Flat-Top Pistons?

Are flat-top pistons available? I don't think so, I've looked, but didn't find any. There was a reference to Speed Pro pistons recently, but I didn't see any listed for the GM 60 degree engine family. I think the fellow may have been considering using flat-tops specified for a V8 application as this is what I saw in the their piston list; don't know.

If money isn't an issue I say use Total-Seal gapless piston rings.

If you bore the block 0.030" over you get a 3.16L engine.
If you bore the block 0.040" over you get a 3.2L engine.


Extra Issues To Consider

FUEL PRESSURE

If you have the block bored, an adjustable fuel pressure regulator is a good idea; helps deal with the increased cylinder volume and resulting fuel demands. BUT, a 0.65mm (0.5mm to 0.7mm) thick washer can be installed in the stock regulator between the cover and spring to up the pressure slightly for bored engines. This works well for my engine, and I don't claim it will work well for yours. Alternatively you can modify your fuel pressure regulator to make it adjustable.


EXHAUST MANIFOLDS

Since your engine is out. It is recommended that all the flanges on the exhaust manifolds be welded around the outside of the flange. After they are welded have them run across a surface-plainer; this makes them flat and will create a better seal they are bolted to the heads. Now is the time to have them ported or port them yourself. Also, I recommend that the welds on the cross-over pipe, oxygen sensor fitting and cross-over pipe to down-pipe flange be welded as well. On my 88GT all of the welds were cracked.

Heat management - thinking about this I wrapped the exhaust manifolds and the cross-over pipe with Thermo-Tec insulating exhaust wrap. I liked the results and wrapped the exhaust to the muffler and wrapped the catalytic converter.

--------------------------------------------

Also, do a search as there is plenty of information, and some disinformation floating around in Tech on PFF about the 2.8L to 3.1L. Go and talk to some fellows at your local machine shop. Most likely, they have seen it, heard about it and/or done it.

Advice, before you build your engine, KNOW all the details of what is going to be done.

----
Why write this? I'm bookmarking this for all the 2.8L to 3.1L how to post.

I'll leave it up to everyone else to fill in missing details.

IP: Logged
PFF
System Bot
GTDude
Member
Posts: 9056
From: Keysville, Virginia, USA
Registered: Nov 2001


Feedback score: N/A
Leave feedback





Total ratings: 287
Rate this member

Report this Post03-01-2002 08:34 AM Click Here to See the Profile for GTDudeClick Here to Email GTDudeDirect Link to This Post
Great info mindscape! Thanks

Phil

------------------
GTDude
25 years GM experience

IP: Logged
kslish
Member
Posts: 1444
From: Womelsdorf, PA
Registered: Apr 2000


Feedback score: (1)
Leave feedback

Rate this member

Report this Post03-01-2002 04:31 PM Click Here to See the Profile for kslishClick Here to Email kslishDirect Link to This Post
Do you have a GM (or other manufacturer) part number for 3.1L crank? I'd like to price around....

Ken S.

IP: Logged
mindscape
Member
Posts: 854
From: Bristol, TN
Registered: Jul 2001


Feedback score: N/A
Leave feedback

Rate this member

Report this Post03-01-2002 06:24 PM Click Here to See the Profile for mindscapeClick Here to Email mindscapeDirect Link to This Post
 
quote
Originally posted by kslish:
Do you have a GM (or other manufacturer) part number for 3.1L crank? I'd like to price around....

Ken S.

Use one of the reference vehicles listed above. Call a parts store and ask for a crankshaft kit for a 1990 Pontiac 6000 with a 3.1L engine. They will probably ask what casting number you have, #981 and #268 are good bets. You might have to tell them it is a 1990 6000 with cast iron heads and a distributor.

Another source is a salvage yard. I called a local yard and they had a few bad 3.1L engines. They said if I wanted to come down and take them apart and find a good crank... Who knows, you might get lucky and find one with a bad block (froze and busted), but a good crankshaft; maybe a bad top-end but a good bottom-end.


--------------------------------------------

Crankkshaft Rebuilders - Advance Auto Parts - Probably other automotive parts stores as well.

10610P (Premium) Premium Reman. Crankshaft Kit; .10 OS Mains/Rods; Federal Mogul Bearings 90 DAY REPL

This crankshaft is not turned down anymore than 0.010" - that's why its Permium. Also, this one comes with the GOOD bearings. They have tappered lead-in grooves in the bearing that goes into the main cap; helps with oiling.

10610 $156.99 OE Forging #981; 186; w/Magnetic Ignition; w/Notches Cut In Center Full-Round Counterweight; Incl. Eng. Bearings

This one is like buying a pig in a poke. It will be cut at least 0.020" or more. Bearings included may be like mystery meat, probably good bearings but the manufacturer may not be known.

10620 $202.99 OE Forging #981; 186; 268; w/Distributor Type Ignition; w/Full-Round Center Counterweight w/o Notches; Incl. Eng. Bearings 90 DAY REPL

Why this one is listed I haven't a clue; don't know how it differs, but they are the same cranks. Maybe this one is guaranteed not to be welded back together.

If you are going to use one of these the I would go with the 10610P. Also consider this crankshaft kit comes with the main and rod bearings - the Federal Mogul REDs.

---- What will SUPRISE most people is that the 3.4 uses the SAME crankshaft. Look up a crankshaft kit for a 1993 Camaro with a 3.4L engine. HOWEVER, the main bearings are different.

Main and rod bearings specified for the 3.1L are:

Mains Bearings
SEALED POWER 7242M-.25MM $33.99
Set; Oversize .25 MM; Fed. Mogul; w/3/4 Grooved Bearing

Rod Bearings
SEALED POWER 6-4020AP-.25MM $13.99
Set; Oversize .25 MM; Fed. Mogul

[This message has been edited by mindscape (edited 03-02-2002).]

IP: Logged



All times are ET (US)

T H I S   I S   A N   A R C H I V E D   T O P I C
  

Contact Us | Back To Main Page

Advertizing on PFF | Fiero Parts Vendors
PFF Merchandise | Fiero Gallery | Ogre's Cave
Real-Time Chat | Fiero Related Auctions on eBay



Copyright (c) 1999, C. Pennock