2800SFI

[Autox88GT]

I know this has come up in the past, I read several articles mostly involving a top end swap. Maybe it has been done already but at least hear me out. I am going to take the 2.8mpfi out of my '88 Beretta and using a 3100 block, install the 2.8 crank, rods and new pistons that I bought a while ago. I'll be using LX9 lower and upper intakes. This is going to be NA, so CR is important, too. the 3100 is 9.55:1CR while the 2.8 is 8.77:1. from using the CR calculator, the loss is from the piston to deck clearance. Now I have read a number of specs for 3100, 3400, 3.1, 3.5,and 2.8 all have the same deck height. What I found was that the Gen II V6 engines have positive clearance numbers of around .017" on the 2.8 and .0165" on the 3.1 while the Gen III 3x00 engines all have -.020".
where is this difference found? I am assuming pistons since the 3.1 and 3100 have the same stroke. Any enlightenment, and also how can this be remedied? I want to be around 10:1 minimum so I am already looking at milling the heads. I would measure this to verify, but the 2.8 I have is running and I hate to pull the heads just to check this since I am not ready to do the build just yet. Thanks!

[Superdave]

Welcome to 60v6!


the LX9 lower intake only fits the LX9 heads, won't work with 3100/3400 heads at all. The uppers can be swapped around though.

You are right, the deck height is the same. Gen 1/2 pistons all sit down in the bore a little while the gen 3 pistons pop out of the deck (.020" for the 3100 and 3400). The gen 3 also has a larger combustion chamber than the gen 2 head. 26.4cc VS 28.6cc

Without custom pistons you are going to have a hard time hitting your 10:1 goal. It's either way under or way over.


With 2.8 iron head (Camaro/S10) pistons, Gen 3 heads and .060" thick head gaskets you'll be at 11.93:1
With stock 2.8 Gen 2 pistons, Gen 3 heads you get 8.94:1 with .040 gaskets and 8.5:1 with .060 gaskets


Hope that helps...

[Autox88GT]

It does help, thanks! I needed to bounce these ideas off someone other than my Wife, Lol!
I am hoping to overcome the combustion chamber differences by milling the heads. What is the milling limit on Gen III heads? What about milling the block? I only need .020" off the block and get the heads down 4.6cc in each combustion chamber. Also, what is the minimum bore to use the LX9 heads? I have 3400 parts, but I was hoping to use the LX9 parts, but can use them on a future project too.

[Autox88GT]

After doing a little reading I found that it is possible to mill the heads up to .020", just that there is greater possibility of warping the head the further you go. I'll take an old head I have and try milling it down that far to see what the volume is at that point, obviously the relationship between head material removed and combustion chamber volume will not be a linear relationship. I am assuming it should be worth a cc or two, hopefully more, I'll post volume change in increments of .005" of thickness removed.

Now the engine block can be machined quite a lot i understand, but too much and you will run into LIM alignment issues, in which case some minor machining of the LIM needs to be done. No big deal. I am looking at at least zero decking the block, but might just go to .020" anyway. This will need to be removed from each bank and the area where the LIM is RTV'ed to the block. So, .020" off the heads and .020" off the block is .040" total change; my biggest worry is that I will need custom pushrods... Not interested if at all possible; I like to keep my money. I am trying to keep this pretty low buck and I will be doing the machine work myself, too. I'll assume that taking .020" off the head decreases combustion chamber volume by 4cc, I have no proof this is true and may be a little optimistic, combine that with the -.003" piston to deck clearance and .060" head gaskets will yield 9.52:1CR. With .040" head gaskets it yields 10.07:1, my target CR, of course, I am taking .060" off the entire assembly to accomplish this.

This raises a couple of questions

1. how much "adjustment" can the lifters accommodate?

2. Are pushrods from early 3100s without roller fulcrum rockers a shorter length?

3. Are pushrods from 3.1/2.8 Gen 2 engines a shorter length?

4. Where does someone find the fabled .040" gaskets? All I could find was the cometic MLS gaskets...

[1QUICKHATCH]

After doing a little reading I found that it is possible to mill the heads up to .020", just that there is greater possibility of warping the head the further you go. I'll take an old head I have and try milling it down that far to see what the volume is at that point, obviously the relationship between head material removed and combustion chamber volume will not be a linear relationship. I am assuming it should be worth a cc or two, hopefully more, I'll post volume change in increments of .005" of thickness removed.

Now the engine block can be machined quite a lot i understand, but too much and you will run into LIM alignment issues, in which case some minor machining of the LIM needs to be done. No big deal. I am looking at at least zero decking the block, but might just go to .020" anyway. This will need to be removed from each bank and the area where the LIM is RTV'ed to the block. So, .020" off the heads and .020" off the block is .040" total change; my biggest worry is that I will need custom pushrods... Not interested if at all possible; I like to keep my money. I am trying to keep this pretty low buck and I will be doing the machine work myself, too. I'll assume that taking .020" off the head decreases combustion chamber volume by 4cc, I have no proof this is true and may be a little optimistic, combine that with the -.003" piston to deck clearance and .060" head gaskets will yield 9.52:1CR. With .040" head gaskets it yields 10.07:1, my target CR, of course, I am taking .060" off the entire assembly to accomplish this.

This raises a couple of questions

1. how much "adjustment" can the lifters accommodate?

2. Are pushrods from early 3100s without roller fulcrum rockers a shorter length?

3. Are pushrods from 3.1/2.8 Gen 2 engines a shorter length?

4. Where does someone find the fabled .040" gaskets? All I could find was the cometic MLS gaskets...

The .040" gaskets are for the 2.8/3.1 iron head engines.

If you are trying to make some decent power with the gen 3 heads you will end up opening up the chambers a little, so you will be adding a few cc's. Just something to keep in mind.

[Autox88GT]

Ok, I see it now. I was following the 2.8l/3.1l aluminum heads, I didn't really look at the iron head's specs too much. Thank you! This may seem like a stupid question, but why would I add volume to my combustion chamber? I can see a little smoothing here and there but It probably won't add more than 1cc to total volume, is this what you mean?

So I was looking through my storage to find some heads to play around with and check combustion chamber volume. I found my 3500 heads and a 2.8 head, but no 3400 heads. I guess I scrapped them... I'll have to pull them off my complete 3400 engine. My father was busy with the mill anyway... It'll be a couple more days before I have the results.

[pocket-rocket]

I needed to bounce these ideas off someone other than my Wife, Lol!

This kind of logic also usually helps in the budget aspect as well

[Autox88GT]

True story bro.

I also found push rod lengths, according to NAPA's website:
2.8l/3.1l aluminum head pushrods are 6.042" on the intake and 6.389" on the exhaust
Iron head 3.1 pushrods are 6.163"
3100/3400 pushrods are 5.746" on the intake and 6.074" on the exhaust.
Ball fulcrum 3100's specs seemed to vary around 1/4" from the same manufacturer... seems odd but I guess it means that .060" difference SHOULDN'T make any operational difference to valvetrain geometry.

I still would like to know the lifter's limitations if possible.

Also, I was checking total seal piston rings for the 2.8l pistons and found that they cannot give me the price online... before I spend my time e-mailing them does anyone have a ballpark cost on a set of those? thought it may be worth it for a little less blow-by.

[Autox88GT]

Out of curiosity I roughly measured my replacement pistons dish volume. Surprisingly, I found that the dish volume was 18.12cc instead of the OE volume of 21.2cc. I'll need to confirm this with an actual volume measurement but I am fairly confident that my calculations were conservative by rounding up to the nearest mm. My new pistons are Federal Mogul sterling pistons, for what it's worth.

[trotterlg]

You really need to measure the piston pin heght. That will have more effect on the CR than the same amount of change in dish depth. Larry

[Autox88GT]

From the center of the piston pin to the top of the piston, right? That would be 41.6mm measured.

[Autox88GT]

So something is not matching up. The deck height on our engines are 224mm. If I assume my connecting rods are 144.78mm (5.7") from the center of the big end to the center of the little end, my measured piston height remeasured was 41.5mm and the stroke of the engine is 75.946mm (2.99") divided by 2 is 37.973mm. The sum of these numbers should be .017" below the deck height. However, my measurements add up to .0996063" above the block. I guess 224mm is a nominal measurement? Either that or I gained about .023" on some component. Are my measurements consistent?

[Autox88GT]

No help, huh? I figured someone on here would at least be a little interested in building an efficient, low displacement engine instead of just big displacement LX9s...

[Guest]

So something is not matching up. The deck height on our engines are 224mm. If I assume my connecting rods are 144.78mm (5.7") from the center of the big end to the center of the little end, my measured piston height remeasured was 41.5mm and the stroke of the engine is 75.946mm (2.99") divided by 2 is 37.973mm. The sum of these numbers should be .017" below the deck height. However, my measurements add up to .0996063" above the block. I guess 224mm is a nominal measurement? Either that or I gained about .023" on some component. Are my measurements consistent?

I got 224.253mm. .25mm is .00984 above the deck. Your math is wrong or you forgot a zero

[Purple pit]

No help, huh? I figured someone on here would at least be a little interested in building an efficient, low displacement engine instead of just big displacement LX9s...

I want the one thing that car makers don't care about. Low RPM torque.