2800SFI

[Autox88GT]

I forgot the zero in the post, lol. I have it written in my notebook as .0096063". Anyway, if these numbers look correct to all then I'll have to check piston pin height on a OE piston.

[ericjon262]

if you're doing a full on build, I wouldn't worry about OE Reciprocating part specs.

[Autox88GT]

if you're doing a full on build, I wouldn't worry about OE Reciprocating part specs.

It's not a "full on build" but rather, it is the best of the 3x00 family of engines in a short stroke 2.8l displacement. I read the 3400 connecting rods were forged, so having thrown a rod in my previous 2.8 I would like to use those, plus the small dish 2.8l pistons I have, 2.8l crank, 3100 block, pan, windage tray and roller lifters. I will use 3400 heads, fuel rail and LIM but an LX9 UIM. Intake and exhaust will be ported and i will be using Ls6 valve springs. I am going to make up some headers too. For now I will just run the stock cam but later will be looking for something else. I am using OE internals so I will be going by those measurements.

My issue is that the nominal measurements are not coming out to the correct .017" below deck. I need to get OE piston measurements myself or if someone knows the piston pin height it would be a great help.

[trotterlg]

I built very close to what you are doing, but 3100 heads also the LS6 springs, roller tip rockers and iron head pistons for a 12 to 1 CR. I went with a flat tappet cam in the roller cam block to save valve train weight and used a custom upper with a carb. I did go with a fairly radical cam (some seem think too much). It runs and sounds great. There are some stock exhaust manifolds I used off of an Impala I think, used two front ones, looks like they will flow really well, and will make up a true duel exhaust for it. Larry

[Autox88GT]

I built very close to what you are doing, but 3100 heads also the LS6 springs, roller tip rockers and iron head pistons for a 12 to 1 CR. I went with a flat tappet cam in the roller cam block to save valve train weight and used a custom upper with a carb. I did go with a fairly radical cam (some seem think too much). It runs and sounds great. There are some stock exhaust manifolds I used off of an Impala I think, used two front ones, looks like they will flow really well, and will make up a true duel exhaust for it. Larry

I like that a lot Larry! I like the sound too, is that going in a Fiero? Did you do anything with the bottom end or is it stock 2.8?

[trotterlg]

It is a stock 3100 bottom end. Yes, it is going in a Fiero. Larry

[Autox88GT]

I found an old 2.8L OE piston from my original 2.8, I check the piston pin height and found that it is .49mm taller than the new pistons I have. So I went through the box of new pistons to make sure I wasn't measuring a faulty piston. I measured all of them; they are within .04mm of each other.

I am now very confused. So my OE piston would still be above deck height using GM's spec of 224mm for the deck height? (38mm + 144.78mm + 42.05mm {half of stroke + rod length + piston pin height, respectively}) 224.83mm is my calculated height. That means it would sit .0326772" above deck and is nearly .050" out of specs.

The only variable I can think of is the connecting rod length. I cannot find the connecting rod length spec in the GM service manual I have, I used the 5.7" number listed in WOT-Tech's catalog and what GM published for the 1999 3100 and 3400 engines.

[trotterlg]

So if your new pistons are shorter than the OEM ones regardless of the con rod length, the smaller dish in the new ones will have less of an effect raising the CR of your engine. The wieght of the pistons were changed several times during the run of 2.8/3.1 engines, so that may be what you are looking at. Larry

[Autox88GT]

I think you are right, Larry. The difference in dish volume is close to the loss in piston height. I noticed the piston ring heights are different between OE and the replacements. I think it must be for ease of installation. If the rings are lower than stock you won't have to worry about the cylinder ridge... I'm still going to worry about it.

I guess what I am asking is this: Why are my numbers not matching GM spec with OE and aftermarket pistons? The assembled height should be less than 224mm and in both cases is greater than spec. Where did the .017 below deck spec come from?

[trotterlg]

Why don't you bolt one on a crank in the block and do a reality check. Larry

[Autox88GT]

Why don't you bolt one on a crank in the block and do a reality check. Larry

As I stated earlier, I am looking to do this, but I don't want to pull my running 2.8l apart just yet. I wanted to have a list together of the requirements for this build. Now if I can't get good results using the specs GM offers me I may have to get a 3100 block and do just what you are saying.

[trotterlg]

You will be far better off just getting a FWD 3100 even if you just use the block. It has better oiling, you can use either flat tappet or roller lifters and every thing will bolt to it. It has room for an internal ballanced crank and has a windage tray in it. Larry

[Autox88GT]

Those are the very reasons I am going to get a 3100 block. If you look back, I listed all the components I hope to use in this build.

[Autox88GT]

I pulled the head off my 2.8 to check and am a little disappointed. After pulling the head, I remembered what had happened. I had done a quick rebuild of that motor back in college and had it all back together and had the car idling; to get things up to temp to check fluids. I was putting away some tools listening to the idle when it suddenly stopped. No overheat, and I could turn the engine over clockwise and counter-clockwise but never a full rotation. after removing the front valve cover I found I had a failed valve; ruined the piston but no damage to the head amazingly. I had used some pistons I had on hand (another set of sealed power pistons) since it was not anything special and I had to finish it up so I could get to school. No proud of using different pistons in the engine, but I had Zero issues with the car since putting 30K miles on since 2008-2010 when I parked it.

I didn't think back then to check the compression height but now I did. It is about .033" different than the OE pistons in the bank next to it. So either I mill the block or find taller pistons. The OE piston was about .015" at TDC: nearly spec.

I was tinkering with Desktopdyno2000 last night and found the 3400 spec file on the main sites download page. Can anyone verify the cam info? Is it all OE spec?