2.8 - 3.1 Stroker

[Shazamboobam]

So I've been looking in to making my 2.8l v6 more powerful and stumbled upon the 2.8-3.1 solution. As far as I'm seeing I essentially just need to get a 3.1 crank and pistons and throw them in the 2.8? (Making sure not to get aluminium pistons?) Is it essentially that simple? I'm going to be rebuilding the engine soon and figure might as well build her up a bit too. The 2.8 in question is out of a 1980 Chevy Citation if that helps at all.
Any information or links to information is greatly appreciated.
Thank you very much.

[davida1_hiwaay_net]

Yep. I've done it twice.

For whatever "type" of 2.8 you have, you have to get the pistons for that same "type" of 3.1 engine.

For instance:
If you have an iron-head 2.8 you would need to change to a 3.1 crank and driveplate; and iron-head 3.1 pistons.
If you have an aluminum-head 2.8 you would need to change to 3.1 crank and driveplate; and aluminum-head 3.1 pistons.

The driveplate is balanced to the crank, so it has to be for the 3.1 crank. If you keep the 2.8 driveplate with the 3.1 crank, it will vibrate. The harmonic balancer is the same between the 2, so that won't be an issue.

The aluminum heads and iron heads require different compression volume in the pistons. You need to have the correct specification pistons or the engine will have severe performance problems.

If your engine has speed-density fuel control, you may need to slightly tweak the fuel pressure up to get optimal performance. MAF and carb systems it won't matter.

Hope this helps!

Sincerely,
David

[Shazamboobam]

Yep. I've done it twice...

...Hope this helps!

Sincerely,
David

Thank you very much! That helped clear up how I thought it might be. I just didn't know if the engine being older would have affected things. Any other information I had found were 85+ which I assumed were all TBI. Would I also be able to use the 3.1 carb, or is another carb recommended for this upgrade? Again, thank you very much.

[davida1_hiwaay_net]

Thank you very much! That helped clear up how I thought it might be. I just didn't know if the engine being older would have affected things. Any other information I had found were 85+ which I assumed were all TBI. Would I also be able to use the 3.1 carb, or is another carb recommended for this upgrade? Again, thank you very much.

I'm not a carb guy so hopefully someone else can help with that question. The reason 85-plus matters is, GM changed the diameter of the crankshaft journals in 1985. The 1980 to 84 2.8 engines were all carb with iron heads (as far as I know). The 85 and up engines have larger crank journals. They were sold with the same iron-head setup as the earlier ones. They could have a Varajet carb, Throttle Body Injector, and Multiport fuel injection systems.

When I read your first post, I didn't think to ask about the year of your car. I mainly work on the front wheel drive cars, which are almost all 85 or newer. Sorry about that. Can you give details on the current setup?

The iron-head engines can be found with large and small valve heads. The large valve heads were on the Fiero and other high-output engines. The heads are marked with a triangle mark on the end of the head, at a bolt boss cast into the head.

If you're going to rebuild this engine for performance, you may want to look at my recent thread where I built up a 2.8 / 3.1 hybrid engine. It is turbocharged and fuel injected, but the basic engine build is the same as your conversion.

The problem I found was bad manufacturing on the block, causing restricted oiling of the main journals. This lead to the failure of the original 1985 2.8 engine when I turned the RPM's too high. I ended up locating a 1991 block for the build. The factory made many structural and machining improvements by that time. I took off the aluminum heads, timing gear cover, oilpan, manifold and everything related to the 3.1MPFI engine.All the original 1985-spec 2.8 parts fit this engine without any difficulties.

Sincerely,
David

[carbon]

There is an aftermarket carb manifold available that will work with any of the iron heads, as they were the same regardless of 2.8, 3.1 or 3.4 liters... Kinda spendy new (to me...), so you may want to shop around or find a used one. Other manufacturers made them too, but I think most are discontinued so you'll have to hit up ebay and such.

http://www.jegs.com/p/Edelbrock/Edelbrock-Performer-Intake-Manifolds-for-Chevy/745125/10002/-1?viewAll=1

The only 60* V6 engines that were carbed from the factory were the early 2.8s... so there is no higher output '3.1 carb' to use, unfortunately, but you can use the 2.8 carb on the 3.1...

Great thread on the Fiero forum with good info from guys that very successfully gave their 2.8 engines the "vacuum controlled fuel leak" treatment...

How do I put a carb on a 2.8?

Keep us updated on the project!

Edit: More good reading on the carb intake design features... Porting the Torker II - per Edelbrock technical support

[davida1_hiwaay_net]

.... successfully gave their 2.8 engines the "vacuum controlled fuel leak" treatment... ...

LOL that's a good one. More like a venturi assisted fuel induction system.

Don't forget about the distributor advance, too. Many of the carb 2.8's had the CCC system with electronic advance and electronic mixture control carb. I had a 83 ex-Diesel Buick Century with a transplanted 2.8 carb engine.

Mine had a vacuum / mechanical distributor and a non-computer carb. I installed an 'advance kit' in the distributor.

The non-computer parts were on the car when I got it. I was told if was spec'd for an early model Chevy S10 pickup application. That car ran very well for what it was, for a 16 year old kid's car it was totally adequate.

[Shazamboobam]

...
When I read your first post, I didn't think to ask about the year of your car. I mainly work on the front wheel drive cars, which are almost all 85 or newer. Sorry about that. Can you give details on the current setup?
...

Sincerely,
David

It's from 1980, it's also FWD. Also it's not the high output. (The Citation was one of the first American made FWD cars. It was offered with with the high output in the X-11, but mine is base.) It's completely stock, 82k miles.

So on the note of the crank journals, what cars would I be looking for to get the right crank? I'm on a budget, so I was considering trying to get the parts from an auto-wrecker for now. Though if I can scrape together some cash I wouldn't mind going for better parts in the long run overall.
Especially with the interest of turbocharging in mind eventually, it intrigues me that you have a build leaning towards what I want to do. Would you be able to link me to the thread?

I also wouldn't entirely being against changing to fuel injection if it would make things easier in the long run again. (Especially being I don't know what complications turbos on carbs might bring.) Though it does appear that for now I could still run a carb regardless according to Carbon (Thank you for the info)

Again, thank you very much.

[davida1_hiwaay_net]

It's from 1980, it's also FWD. Also it's not the high output. (The Citation was one of the first American made FWD cars. It was offered with with the high output in the X-11, but mine is base.) It's completely stock, 82k miles.

So on the note of the crank journals, what cars would I be looking for to get the right crank? I'm on a budget, so I was considering trying to get the parts from an auto-wrecker for now. Though if I can scrape together some cash I wouldn't mind going for better parts in the long run overall.
Especially with the interest of turbocharging in mind eventually, it intrigues me that you have a build leaning towards what I want to do. Would you be able to link me to the thread?

I also wouldn't entirely being against changing to fuel injection if it would make things easier in the long run again. (Especially being I don't know what complications turbos on carbs might bring.) Though it does appear that for now I could still run a carb regardless according to Carbon (Thank you for the info)

Again, thank you very much.

You're welcome.

They never made a small-journal 3.1 crank. All 3.1 cranks are large-journal. I don't know if a shop could grind down the journals that much.

Your most cost-effective path (IMHO) would be like this:

A - Get a junkyard "short block" 3.1 from Pull-A-Part (about $100) which would provide a Generation II block, the correct crank and driveplate.
B - Buy new pistons spec'd for an iron-head 3.1
C - Build your engine using the 3.1 bottom end and same manifold / carb / distributor / etc.

It would be just like before, only more torque and a newer engine with stronger block design.

If you want to go EFI / Turbo this is how I did it. Note if the pictures don't show, please try later there is a 10 connection limit.

http://60degreev6.com/forum/showthread.php/51281-Iron-head-2-8MPFI-Turbo-Install-85-Celebrity

This engine turned out to be a formidable powerplant, capable of 0-60 in about 5 seconds.

Sincerely,
David

[Superdave]

Find a 90/91 Lumina APV minivan, they had a TBI injected 3.1 with iron heads in a FWD block. That would be your best bet if you want to stay with iron heads. They only made about 120 HP though.

Otherwise If it were me i'd swap in a Gen 3 engine, 3400/3500 would be tons more fun.

[Blacktree]

As mentioned above, there is no such thing as a small-journal 3.1 crankshaft. And you have a small-journal 2.8 V6. So I don't think the 3.1 stroker treatment is going to be feasible.

Unfortunately, the small-journal 2.8 doesn't have much of an upgrade path. You could swap on the HO heads, upgrade the camshaft, etc and get maybe another 20-30 HP out of it.

[davida1_hiwaay_net]

As mentioned above, there is no such thing as a small-journal 3.1 crankshaft. And you have a small-journal 2.8 V6. So I don't think the 3.1 stroker treatment is going to be feasible.

Unfortunately, the small-journal 2.8 doesn't have much of an upgrade path. You could swap on the HO heads, upgrade the camshaft, etc and get maybe another 20-30 HP out of it.

I wonder what it would cost to have a 3.1 crank machined to the early journal size, including the fillet radius treatment (if any)?

[geoffinbc]

You most likely would not be able to grind down the crank that much without putting the oil channels off center which might affect an already poor, early design oil system. And honestly it is not worth the money to make your engine less reliable.

The most affordable option has already been presented. Find a Lumina/Transport/Rodeo 3.1L. This engine has the HO iron heads on a 3.1L FWD block. Everything on your car will bolt up and the stock intake and carb will bolt on and work. These engines also had the larger all iron oil pump, 1 piece rear main seal and can also be set up with the old belt drive system. If you want the newer serpentine belt setup I believe the Van one will work in your car.

The only modifications that would have to be done to your car is an electric fuel pump designed for a carb which hundreds of companies sell. You may also need to increase the jets in your carb if you find it running a bit lean.

[Shazamboobam]

Thank you everybody for the information and replies. I was looking to just liven the engine up some, because hopefully in a few months or so I'll be going for a 3800 swap. I also will have access to tearing my engine apart at school while my car has down time, so I figured I might as well try getting some more power while I'd be in there any way. The simplest solution was looking to be the 3.1 stroker. Thank you all very much again for the suggestions and help.

[Superdave]

Why 3800? You can get tons of power with a gen 3 60v6 like a 3500.. and save some weight too. I put 275HP to the wheels on 89 octane in my 91 Cavalier with one.

[Shazamboobam]

Why 3800? You can get tons of power with a gen 3 60v6 like a 3500.. and save some weight too. I put 275HP to the wheels on 89 octane in my 91 Cavalier with one.

To be honest, I really like the way the 3800 looks. It was also the first swap I'd heard about when I started looking in to things and it stuck. But I'm still completely open to ideas as it could still be some time before getting her back on the road. It would just be a matter of cost, because I still have to find an engine cradle and fix up the front end.