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.

 

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.

 

Debating the megasquirt option for the ecu, it's expensive but not as expensive as some other options. Factory ecu's are like $50 from local scrapyards, but I've never dabbled in pre-obd2 tuning before. If the 3100 pistons would fit then i'll probably go with a 3100 as my "parts engine". Is there a common aftermarket external crank reluctor/sensor solution? When I look up a DIS conversion most of what I get is from fiero guys, and apparently thier engine is set up to rotate in the opposite direction or something, so an exact copy probably wouldn't work? Did any 3.4/3.1 come with aluminum heads/DIS, or just the 3400/3100?

 

The usual solution for the external crank reluctor is a kit you can get from BritishCarConversions, basically just a mount for the sensor + a notched damper. Hadn't heard of Fieros having opposite rotation on their cranks, but the signal from the DIS should be the same either way. It's just a notched wheel that gets picked up by a magnet as it rotates to let the ignition system know where it is, relatively simple system. Imagine the pickup from a distributor, but mounted remotely; same idea. OBD1 tuning/ chip flashing is certainly possible, and I've dabbled in it very lightly (to change speed sensor parameters and whatnot, nothing with the engine), but it takes some special equipment and there isn't going to be a ton of "live" support for it. Plenty of information over on the DIY PROM forum here, as well as over at the Gearhead-EFI site, but just know that it'll take quite a lot of research/ trial/ error, and the chip flashing hardware is gonna add some cost. The way I see it, as much as I love the '7730 ECU, I reckon if you're going to be rewiring the engine and adding a new computer anyways, Megasquirt is probably the way to go.

All of the RWD motors came with iron heads, aluminum was only on the FWD ones. The 3.4L from the 93-95 4thgen used DIS, and like the FWD motors, it had an internal crank reluctor and accompanying block-mounted sensor.

 

For the purpose of this reply when I refer to FWD parts, I'm including up to the LX9 3500, I am excluding the LZ4 3500 and LZ9 3900, and the variants of those engines, along with the 3.4 Quad cam. So the FWD engines include the 2.8/3.1/3100/3400/ LX9 3500.

The gen2 FWD engines, 2.8 and 3.1 were used from 1987 to 1994. The Gen3 FWD engines, 3100 and 3400, were used from 1993 to about 2004, and the Gen3.5, LX9 3500, was used from 2005 IIRC to about 2010, IIRC. Some people consider the LX9 to still be a gen3. It's a tad confusing because of overlap, and naming conventions being used in both FWD and RWD engines (IE "2.8" and "3.1")

When I say "3.4" I am talking about the F-Body 3.4 SFI from the 1993 to 1995 F-Body.

I posted the above simply to keep the following more coherent and not need to type out long engine designations over and over again.

Yes, the FWD heads will bolt onto the RWD blocks. There is nothing special to do here. Bolt pattern and bore spacings along with coolant passages are the same between FWD and RWD.

The intake manifold can be rotated 180 degrees so that the FWD intake will point the throttle body forward. Some modification to the RWD timing cover is needed to clear the lower thermostat housing though, which isn't a critical measured modification, but is necessary for the FWD intake to sit properly. It will be obvious what you need to do there, when you set the FWD intake on the RWD block.
Yes, the fWD pistions will fit in the RWD block, all 2.8 and 3.1/3100 blocks use the same 3.503" bore size. The 3.4 and 3400 use the same bore 3.6something... 3.62" IIRC, so those pistons can swap easily. the thing here is that due to compression height, the piston has to match the crank stroke. So there is no stock combination of piston and rod to destroke a 3,4, which would end up being a "short stroke 3.1", which has been discussed to death in 60DegreeV6 enthusiast circles, but no one has done it to my knowledge, because it requires custom pistons, and the projected loss of torque is the detractor, over just keeping the displacement at 3.4L Also, people have revved their 3.1s/3100s/3400s to over 7000 RPM, so the stroke is not a limiting factor here, but the stock rods are, since they are spec'd to have an RPM limit of about 7000 RPM. Also the head flow in combination with the cam is a bigger limiting factor of RPM than the stroke. I'll get back to this.

Using the FWD heads and gen3 FWD pistons you will have a SCR (Static Compression Ratio) of about 9.6:1. Using gen2 pistons will yield about 8.9:1, so custom pistons are needed to go outside of these SCRs.Using RWD pistons will be between 12:1 and 13:1 IIRC with the FWD heads. If I was building an NA 60DegreeV6 for performance I would look at using the RWD pistons myself, since I'm not afraid of higher SCR, but the tuning window is tighter and I can understand not wanting to go that route.

It's about now that I need to mention that using a 2.8 RWD block will require a custom external crank trigger, since only the 3.4 had provisions for a crank trigger, which is just another reason to use that block for one of these builds. That being said, external crank triggers are not that difficult to set up and I ran one on my RWD hybrid back in the early 2000s. It was a custom one that mimicked the stock 60DegreeV6 crank trigger, "GM7X" as it's called in many circles, and I only did that because I was running a GM OBD1 ECM for engine control and the stock DIS system was the easiest, most cost effect option at the time. Today the options are much wider and still cost effective, I'll get back to this as well...

Fiero engines rotate in the same direction as any other 60DegreeV6 does, so I'm not sure what you're finding that is different about those engines, though they are transverse mounted, but use the gen1 iron heads and intake, the intake is specific to Fiero, even though it's similar to the F-Body 2/8/3.1 intakes.

Getting back to Engine management. If I were to do the same hybrid setup that I did back in the early 2000s, which I dubbed "Franken60", since I used parts from all 3 generations that were available at the time, since this was before the 3500s and 3900 were introduced. Gen1 block, rods (even though gen1 to gen 3 rods are all the same, the gen1 rods were what I had), and a few other miscellaneous parts, gen2 pistons, though they were aftermarket stock replacements, and if I knew then what I know now, I would've used gen3 pistons, a gen2 3.1 crank, and early gen3 3100 top end. Again, if I knew then what I know now, I would have used the 3400 heads I had sitting under my bench, though I was saving them for a different project, that never materialized. I then added a T3 turbo, and used stock GM MEMCAL for a Grand Prix TGP (Turbo 3.1), this was before I got into tuning, so it was the easiest and most cost effective way to go at the time. So if I were to build the same combination today, I would use a different engine management, likely a Megasquirt, since I am now a fan of them and have used them in my own projects as well as in other people's projects. This also opens the possibility for other combinations of parts, like a higher resolution trigger wheel, such as the common 36-1, which I'm currently installing on my own 3400, which I will get to in a bit. This also allows for the use of 6 individual coils, instead of being limited to the dual tower coils of the stock GMDIS ignition system. Don't get me wrong, the GMDIS system works well, but not as well as direct coil control. The higher resolution wheel I find also allows for a smoother running engine. On one of my own combinations I went from the GM7X trigger wheel, to a 24x (Same as LS1), and the engine ran smoother, revved cleaner and maybe a tad quicker, and driving felt smoother as well. So I would opt for the 36-1 trigger wheel as an easy to get option, using just about any aftermarket engine management system. LS coils are common and inexpensive, along with being quite reliable.

As far as "high revving", that's subjective, and the stroke is not the limiting factor, like I said before. In my Datsun, I installed an LX9 3500, initially with the stock cam, though I did upgrade the valve springs, just as a safety measure since I also added a turbo. Now this combination hit a pretty hard wall at about 5800 RPM, it would rev past, but not like it would up to that point, no amount of tuning, or boost pressure (which will increase the effective RPM range a bit, because of the forced air), just wouldn't rev cleanly past about 5800. I swapped to the cam to an aftermarket cam, really meant for NA, but the 60DegreeV6 have very low overlap and pretty wide LSA to start with anyway, and immediately, with no other changes, my RPM range went well above 7000 RPM, I think I went as far as about 7400 once or twice, but ended up setting a rev limiter below this and shift point about 6500, just because I was still running stock rods that were never meant to rev beyond about 5000 RPM, let alone with boost on them. I did end up with some rod failures anyway, but these were also powdered metal rods of the LX9, not the forged rods that the Gen1, 2 and 3 use. I say all of this to point out that destroking isn't necessary to rev high with these engines, but flow into and out of the engine is important, which brings me to my next suggestion. The LX9 3500 top end flows even better than the 3400 top end, and will bolt onto the 3.4 and 3400 blocks. Due to the combustion chamber size being a little larger than the earlier FWD heads, it's not recommended to use the LX9 3500 heads on the 2.8 or 3.1 blocks. If you stick with the 2.8/3.1 bore block, you can use the 3400 heads and lower intake and then bolt the LX9 3500 upper intake manifold on, that many report improves power. You will need an adapter to use a cable driven throttle body though, however, there are options with aftermarket engine management to use DBW throttle bodies.

No RWD 60DegreeV6 came with aluminum heads from GM, all were iron head. The 3.4 did have the same DIS system as the FWD gen2 and gen3 60DegreeV6s.

 

Excellent write-up, Six_Shooter! Very much appreciate you sharing your expertise on this. I had a question about the LX9 upper intake though.... is it different from the LZ4? When I pulled my 3400 heads from a 2001 Impala last year, I had also pulled the upper intake from a 3500 (unsure if LX9 or LZ4) and test fit it on the 3400 parts there in the junkyard, but found that it didn't exactly line-up, so I ended up leaving it. I intended to (and would still like to) use a 3500 upper when I finally get to my hybrid swap, will I need to track down an LX9 upper specifically?

 

Yes, LX9 and LZ4 are very different, all over, but including the upper intake, they are not interchangeable, and only the LX9 upper intake will swap onto a 3400 lower intake.

The LX9 upper intake has a rectangular shape, while the LZ4 upper intake has a large notch in the plenum at the opposite end from the throttle body.

 

Gotcha, that makes sense! Looked up pictures to compare, it definitely was an LZ4 intake that I was trying to fit there in the junkyard, I remember that big goiter under the throttle body I'll have to go back out and find an LX9 at the yard. Not to highjack this thread, but I was hoping to pick your brain a little while you were here. I was also wondering if you'd know about a tach signal for the DIS ignition.... I was doing some reading the other day and realized that the '01 Impala didn't have a tach, and that the ICM harness didn't have a lead for one. I see later Impala ICMs had more wires on the harness, and they had a tach; FastEddi's stickied guide mentions that he wired an aftermarket tach in later, but didn't explain how.... do you reckon that the ICM from a later Impala or one from a 3.4 Firebird would be able to provide the right signal for the stock tach?

 

Assuming you mean "later 3.4" to mean up to about 2004, the DIS ICM is exactly the same as when it was introduced in 1987. If you mean the later version that was more common on the 2005ish+ that is a different animal entirely, and doesn't have a tach output from the ICM.

Anyway, assuming the 1987 to 2004 ICM, there is a dedicated tach output pin, however, it seems that whether this pin works is hit and miss. Personally I think I might have only come across one GMDIS ICM where the tach output may not have worked, but IIRC it was also of questionable condition.

I don't recall the exact pinout, but it can be found online.

 

Interesting! My memory must be failing me already, I could have sworn that pre-'03 DIS systems had a 4 pin + 2 pin on one side, then 2 pin CPS connector on the other... I was so convinced of this, I even sent myself an email about it on April 3rd checking on it again, they do all look to be 6 pin + 3 pin + 2 pin CPS though, so that answers that question! I have a bad habit of sitting and overthinking car stuff while I have downtime at work lol, you'd think I'd have learned to quit second guessing everything after 25 years Thanks a ton, and apologies for my confusion!