2.8 Build questions
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2.8 Build questions
Good morning, I am trying to plan out a 2.8 Build to go into a Triumph GT6 (the engine is already mounted in the car by the previous owner, I just want to get a bit more juice out of it) I'm wanting to do a "hybrid V6" build, and have a few questions to ask (Yes I know this would be better to post this on the V6 forums, but I'm still waiting for a mod to approve my sign up from 3 days ago).
Do the gen 3 fwd heads bolt on to a rwd 2.8 block? I've seen conflicting info on wether I have to use a fwd block or not, but ideally I would just have to switch the intake (because I know the 2.8 intake dosen't fit the heads) and the pistons (because the 2.8 pistons would create a crazy compression ratio). My plan is to buy a 1999+ 3400 fwd engine from a wrecker (like $400 in my area) and use the top end and pistons off of it. Or maybe order aftermarket pistons, I want to hit around 10 or 10.5 to one compression.
What ecu/harness should I use? My 2.8 is carburated, so I know I'll need to do some modifying to get a distributorless ignition working, what solitions would you reccomend?
I also plan on running the 1.6 Rocker arms, i've heard a lot of good things about the 260H cam, does it work with these rockers? What rpm range is it good for in practise?
Can you put the 2.8 crank into the 3.4 block to destroke it? Or is it better to just use the 3.4 heads on a 2.8? I want to keep the low displacement to run higher rpms.
Do the gen 3 fwd heads bolt on to a rwd 2.8 block? I've seen conflicting info on wether I have to use a fwd block or not, but ideally I would just have to switch the intake (because I know the 2.8 intake dosen't fit the heads) and the pistons (because the 2.8 pistons would create a crazy compression ratio). My plan is to buy a 1999+ 3400 fwd engine from a wrecker (like $400 in my area) and use the top end and pistons off of it. Or maybe order aftermarket pistons, I want to hit around 10 or 10.5 to one compression.
What ecu/harness should I use? My 2.8 is carburated, so I know I'll need to do some modifying to get a distributorless ignition working, what solitions would you reccomend?
I also plan on running the 1.6 Rocker arms, i've heard a lot of good things about the 260H cam, does it work with these rockers? What rpm range is it good for in practise?
Can you put the 2.8 crank into the 3.4 block to destroke it? Or is it better to just use the 3.4 heads on a 2.8? I want to keep the low displacement to run higher rpms.
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Joined: Mar 2018
Posts: 110
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From: Virginia, USA
Car: 1992 Firebird
Engine: 3.1L LHO
Transmission: Tremec TKX
Axle/Gears: 3.23 Torsen
Re: 2.8 Build questions
Howdy, welcome to the forums! The MG forums have helped me out a ton over the years as well, shoutouts to all the British car folks with their 60deg swaps!
So, to answer some of your questions:
YES, the 3400 heads will bolt to your 2.8! The sticky at the top of this thread from FastEddi has some pretty good info, though he used a 3.1 block. That being said, the 3.1 is just a 2.8 with a stroker crank, blocks themselves are identical (including piston bores). You DO NOT need a FWD block, but you WILL need the heads/ intake from the 3400 (this is the crux of the hybrid swap after all; the hybrid name comes from it being a hybrid of a RWD block and FWD top end). You WILL need pistons to lower compression, but NOT from a 3400; 3100 pistons will be the same bore as the 2.8/3.1, so you'll need to order a set of those instead of using the ones out of the 3400. You'll want to use 3100 head gaskets as well.
For ECU... I'm not super well-equipped to answer that question since you already have a carbed motor. Do also note that if you do indeed have a factory carbed 2.8, the crank will be a bit weaker than later 2.8s/ 3.1s, and the internals (conrods mainly) might be a bit weaker as well, though I cannot confirm this 100% since I have 0 experience with the carbed V6s. Safest bet would probably be a Megasquirt ECU, and these will be able to work with the DIS ignition as well. FastEddi's stickied thread covers getting the reluctor and sensor set up for the DIS ignition, but he used a stock ECU ('7730 from the 3.1), but I believe some other folks earlier on in the history of hybrid swaps have written guides (or logs, at least) on wiring up Megasquirts.
Good news about the 1.6 rockers: the 3400 came with 1.6 ratio rollers standard! You won't have to worry about swapping those out, most don't from what I've read. With or without a cam, with the head swap, you'll need to take measurements so you can order a set of pushrods in the correct length. Rockers should clear the covers just fine with a 260H cam, I believe that's what FastEddi used to run in his hybrid build...
Lastly, assuming you mean the 3400 when you say 3.4 there (usually the RWD blocks get called 2.8/ 3.1/ 3.4, and FWD is usually 3100/ 3400/ 3500/ 3900 etc), you can't exactly swap the 2.8 crank in. With the gen 3 FWD blocks, the cranks have a reluctor in the middle, which feeds a signal to the crank sensor (mounted to the side of the block) for the DIS ignition. The RWD blocks do NOT have provisions for this, as they did not have crank sensors (aside from the 3.4 found in 93-95 F-bodies). Now, dimensionally, it MAY be possible, haven't looked into that.... if the bearing journals and overall length match, there's a decent chance you could, but I'm not sure if the spacing of the crank journals is different at all because of the addition of the reluctor. You would also have to run an external crank sensor/ reluctor as you would if you put the 3400 heads on the 2.8 block.
So, to answer some of your questions:
YES, the 3400 heads will bolt to your 2.8! The sticky at the top of this thread from FastEddi has some pretty good info, though he used a 3.1 block. That being said, the 3.1 is just a 2.8 with a stroker crank, blocks themselves are identical (including piston bores). You DO NOT need a FWD block, but you WILL need the heads/ intake from the 3400 (this is the crux of the hybrid swap after all; the hybrid name comes from it being a hybrid of a RWD block and FWD top end). You WILL need pistons to lower compression, but NOT from a 3400; 3100 pistons will be the same bore as the 2.8/3.1, so you'll need to order a set of those instead of using the ones out of the 3400. You'll want to use 3100 head gaskets as well.
For ECU... I'm not super well-equipped to answer that question since you already have a carbed motor. Do also note that if you do indeed have a factory carbed 2.8, the crank will be a bit weaker than later 2.8s/ 3.1s, and the internals (conrods mainly) might be a bit weaker as well, though I cannot confirm this 100% since I have 0 experience with the carbed V6s. Safest bet would probably be a Megasquirt ECU, and these will be able to work with the DIS ignition as well. FastEddi's stickied thread covers getting the reluctor and sensor set up for the DIS ignition, but he used a stock ECU ('7730 from the 3.1), but I believe some other folks earlier on in the history of hybrid swaps have written guides (or logs, at least) on wiring up Megasquirts.
Good news about the 1.6 rockers: the 3400 came with 1.6 ratio rollers standard! You won't have to worry about swapping those out, most don't from what I've read. With or without a cam, with the head swap, you'll need to take measurements so you can order a set of pushrods in the correct length. Rockers should clear the covers just fine with a 260H cam, I believe that's what FastEddi used to run in his hybrid build...
Lastly, assuming you mean the 3400 when you say 3.4 there (usually the RWD blocks get called 2.8/ 3.1/ 3.4, and FWD is usually 3100/ 3400/ 3500/ 3900 etc), you can't exactly swap the 2.8 crank in. With the gen 3 FWD blocks, the cranks have a reluctor in the middle, which feeds a signal to the crank sensor (mounted to the side of the block) for the DIS ignition. The RWD blocks do NOT have provisions for this, as they did not have crank sensors (aside from the 3.4 found in 93-95 F-bodies). Now, dimensionally, it MAY be possible, haven't looked into that.... if the bearing journals and overall length match, there's a decent chance you could, but I'm not sure if the spacing of the crank journals is different at all because of the addition of the reluctor. You would also have to run an external crank sensor/ reluctor as you would if you put the 3400 heads on the 2.8 block.
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