robertfrank

iTrader: (27)

So i'm sure this has been covered before but what would be the difficulty of converting a FWD block to RWD? I know the starter and mounts are the challenge but in my opinion it would be more beneficial to just swap a FWD block than to modify a rwd engine. Any thoughts?

project89

iTrader: (1)

just swap in fwd piston and make a wheel or the dis to bolt to the balancer
much easier then fabing up new mounts and dealing with the starter

Six_Shooter

iTrader: (2)

There's a few different ways to look at this.

The starter issue may be easy to overcome or insurmountable, depending on what compromises you're willing to make.

The starter on a FWD has to stay where it is. The block on the (would be) passenger side is different than the RWD block, to clear the FWD trans, and is missing material that is need to to properly support the starter. Some people have moved the starter and report no issues, but that's not something I want to risk. Keeping the starter where it is will need to have the oil filter relocated because they will be trying to occupy the same space. (IIRC the F-body uses an oil filter adapter similar to the S-series that points the filter down and back.
This location will also require modifying the bellhousing, either simply cutting out part of it to clear the starter nose, or cutting and welding a filler piece back in.

If you use the RWD flexplate/flywheel you will also need to add a 14mm spacer between the block and the starter for proper engagement.IIRC '87+ F-bodies have a thicker flywheel than the S10 and FWD so the use of the RWD flywheel is needed.

You can use the RWD front cover on the FWD block, however there is a bypass port that needs to be plugged since the FWD block doesn't have provisions for it and will need to be done differently. Also the belt driven accessories won't just simply bolt onto the heads, because the pattern is different, it's close enough that some people have simply slotted holes, but not the same pattern.
The front cover will also need to be modified slightly to clear the thermostat housing of the FWD lower intake once it's turned around.

The oil pan will need to be modified to clear the K-member, and doesn't share any bolt hole spacing with the RWD oil pan mounting pattern, besides the only FWD blocks that would be a good consideration for this require the aluminum oil pan due to the crossbolted mains.

The benefits of the FWD blocks ('96 and later, yes there are some earlier blocks that share the same benefits, but there is overlap with blocks that don't before '96) is the stronger block, especially through the intake valley, crossbolted mains, windage tray, and roller cam.

The FWD heads and intake are FAR superior to the RWD counterparts and is where most of the increase in output comes from.

So you need to decided if the work needed to install a FWD engine/block in a RWD is worth the effort, or just build a RWD block that will bolt in.

Back when I built my first hybrid, I used a RWD block simply because it made mounting of the block much easier, I plan to use a gen 3 block the next time I do a swap in that same vehicle, because the gen3 blocks are so much better and can be had in larger displacements.

I used a complete LX9 in my Datsun 240Z, which I needed to fabricate mounts for anyway.

robertfrank

iTrader: (27)

My thoughts with the benefits are the roller cam (bigger cam stock), stronger and all ready built for the aluminum top end. Plus the starters are damn tiny which helps with weight.

On another note, is the biggest reason that a distributor can't be used with a top end swap is there's no clearance? What if someone made a custom intake that bolts to aluminum heads? Has that been done before?

project89

iTrader: (1)

ive built 1 and its not worth the effort , alls u really need to make is an offset drive distibutor if u really wanted to

instro84

there are a few guys on the tubobuick forum that have done it, i'd look there for info.

Six_Shooter

iTrader: (2)

Yeah. One time I cut a 3400 lower intake to clear a dizzy to see exactly how far it would intrude into #6 runner. It would basically close off the #6 runner.

Just go DIS, it's not difficult and the FWD block will already be set up for it with the crank trigger. Using the 3400 will be literally a plug in for everything you need, using a 3.1 FWD MEMCAL in a '7730, or you can tune a BIN yourself with the right programs and hardware, which is not that difficult really.

As someone who has ran both dizzy and DIS on the same engine, I will put DIS on as many engines as I can, it's smoother and just over all runs better than dizzy.

1slow8t3

I used the 3.4 accessories on my 3100. The 3.4 alternator and ac bracket need one hole drilled to bolt on and I had to make some clearance with the 3x00 valve cover and 3.4 alternator.

P/S pump bracket need to be trimmed a little

Timing cover need some bolt holes enlarged, and the hole on the back of the coolant inlet plugged. Also the ear on the top of the cover needed cut off (grinder / hacksaw )

One of the coolant ports on the lower intake I plugged because I did not have enough room to use a sensor in that spot or coolant pipe.

I made a starter spacer like Six_Shooter did, along with longer bolts.... works great!

I think that Mars had room for the drivers side starter when he first swapped the 3400 (when it was still n/a) before he killed the 700r4!

It's a little more work but well worth the results especially if you add boost too!

robertfrank

iTrader: (27)

So this would be the top end I'd like to run. I really like the look of this intake setup

cosmick

Many years ago, I put a FWD 3.4 into an '86 Firebird, I recall I had to drill some holes in the 2.8 oilpan to bolt it to the block.
I recall hacksaw-ing my 700R-4s bellhousing to clear the FWD starter.
But it's been so long that the only other thing I remember is that I never actually drove it with either engine.

cosmick

In the 20 or so months that I've had my '94 Camaro, the 3.4 has always had an intermittent misfire, and I think it might be the ICM, but that's a costly gamble if buying a new one doesn't solve it. I can't see how it could be a fuel pressure regulator problem, but the ICM doesn't make sense either. On cold mornings, the first WOT pull through first and second pulls really strong, no misfiring at all, so how could it be weak spark or insufficient fuel?
These OBD1.5 computers can't be diagnosed nor tuned, so I just have to suffer the bad driveability until I do the 3500 top end. Also, no converter lockup, traced that to the effing computer also.
I'll be happily swapping to a '96-up 3500 computer when I get around to the 3500-heads-and-intake.
Meanwhile, if you need a sort-of-running example to get reference pics of, mine's in the Logan area, and still fires right up every time. Multiple coils can work, but HEI is cheaper and more reliable, and easier to diagnose and repair. How much cheaper would the LSx be if it had 1 coil instead of 8? And how much cleaner would it look, plus easier fit. Multiple coils is not a good thing. A Nascar 358 can make 900 HP at 9000 RPM with one coil.

robertfrank

iTrader: (27)

So I do have a stock 7730 computer and what's left of its harness from my old 91 L98 car. How would I go about switching this to DIS? How much of my 2.8 harness could I get away with?

Six_Shooter

iTrader: (2)

To start with, I think you mean '96 and up 3400 computer, since the 3500 didn't come out until 2005.

the OBD1 PCMs are tunable now, several people have been tuning their 3.4 F-bodies with the original PCM.

NASCAR runs a single coil and dizzy because the rules state that's what they need to run. They would be running DIS instantly if the rules allowed it. With the switch to EFI in the last year or two I see DIS being used in teh not so distant future, once the rules allow.

If anything DIS is easier to diagnose, because there's less parts to fail, and less to wear out. I have vehicles that run both currently, my Yukon (with a 5.3) I have not replaced any ignition component ever, in the 5 or so years I've owned it, mean while my dizzy (HEI) equipped car, I've put all of the typical dizzy tune up parts on at least once in the time I've owned it and has not run more than 2 hours before a few months ago. Exposed parts to corrode/rust, moving parts that wear out (have swapped dizzys a couple times because it seemed like a pick up problem. Like I said I've run the same engines with both dizzy and DIS and DIS is hands down smoother and seems to make more power throughout the entire power band. I'm SERIOUSLY considering moving to wasted spark COP on my T-Bucket because of how much smoother DIS tends to run and less parts to wear out.

multiple coils IS a good thing and is why every engine I can think of on the market today does so. You can create a hotter spark without resorting to a CDI box, thanks to increased dwell capability. Add in the fact that the spark now only needs to jump 2 to 3 gaps (I consider the connection point of the spark plug wires to be a "gap" even though it is very very small) instead of 7 from the coil through the dizzy cap to the rotor and back out the dizzy cap to the plug, makes for a hotter spark as well.

As far as how pretty an engine may or may not be, that is purely subjective and while I think the placement of the LS coils is poor from an aesthetics standpoint in stock form, other engines look good with DIS or COP. Some dizzy equipped engines look ugly with the cap sticking up in an odd spot and wire running across the valve covers, so it's all in who's looking at it.

Dizzys are familiar and to some people that's a good thing, but don't try to pretend that they are better than DIS/COP because of it.

To run that top end you would also need to run that bottom end. That is an LZ4 you have pictured there and the heads do not fit on the older 60 degree V6 blocks. The chambers are much larger than even the LX9 bore. It's also questionable where the valves are concerned, they might hit the top of the bore on a running engine, since they are close to the outside of the bore when placed on a LX9. I know, I took a good long look at that with my LZ9 (same as the LZ4 just longer stroke) with my LX9 block and deemed it not worth the hassle to swap the LZx heads onto the LX9.

You could retain quite a lot of your 2.8 harness, though you would need to change the connector for the MAF to one for a MAP and IAT/MAT, along with some re-pinning at the ECM. Probably a few other changes too.

cosmick

I thought you could put the 3900 intake on the 3500 heads, but maybe it was the FWD 3400 intake that fits the 3500 heads? Whichever, you still have a choice of how you want your 3500 top end to look.
Either way, the 3500 heads are the best for a RWD 3.4 block, the 3900 heads need the 3900 block.
With the old 396 back in the late '60s, they notched the block to clear the valves, but that won't work with a 3.4 because the 396 block was designed for it where the 3.4 wasn't, and the 396 had the rings a lot lower on the pistons. Other than that, you could probably make it work using 3900 head gaskets.

cosmick

Those Nascar coils are not only capable of 72000 sparks per minute, but those sparks are each hot enough to get through the cylinder pressures ( charge densities ) necessary for 150 HP per liter. So the multiple coil development wasn't for power nor for RPM, it was strictly emissions. But how they figure that gives more control or less cost is illogical. It was more likely that they couldn't figure out a good way to get rid of the distributor without at least 1 coil per 2 cylinders. Getting rid of the dizzy wasn't necessary anyway, had they redesigned it to bolt to the front of the engine, to run directly off the crankshaft. The only argument against that is transverse installations which shouldn't even exist anyway.
And while we're discussing ignition, Mazda was so lazy that my '83 RX-7 had 2 coils just so they could fire 2 plugs per chamber, which it didn't need, and could have been done by 1 coil with a different design of distributor cap, since that cap was rotary-specific anyway.
Lastly, no matter how you argue it, a HEI with 1 coil is both cheaper and lighter than 8 new coils.

Six_Shooter

iTrader: (2)

No, the LZ series of engine parts is almost entirely non-interchangeable with other 660 engines, including the intakes. The pattern and port sies are different for one thing, the intake is what is considered to be a "dry" intake (no coolant flows through any part of it) and is therefore unique to the LZx engines.

The LZx headgaskets also will not work on the older 660s, again, I've tried this, I have all of the parts in my possession. The bore size of the headgasket is 101mm, which is 7mm larger than the LX9 bore so that's 3.5mm of gap around the cylinder for fuel to get trapped and cause issues and a place for a flame front to start acting like a cutting torch... To be more accurate though it's not an even 3.5mm all around the bore, because the LZx engines have the bores offset towards the outside of the block which means it's more like 3mm on one side and 4mm on the other.

You can live under a rock where DIS is concerned if you want, I've seen the benefits of DIS first hand and KNOW that it is FAR superior to ANY DIZZY set up. The fact that most people ignite highly dense fuel mixtures with simple 12V ignitors where a dizzy needs something like an MSD or similar CDI box (200+V) should be clear enough to see that the DIS ignition due to the longer possible dwell times is better than dizzy just on that front.

You bring up the other point I forgot about, accuracy. DIS is FAR more accurate than any dizzy could ever be. No mechanical slop to work around, far fewer mechanical parts to wear out and fail.

Like I said NASCAR teams would switch to DIS the minute the rules allow.

By your thinking we should all run carbs, because they will get an engine running... hahaha

Sure, one coil could have been used on a Rotary, but the dizzy cap would have pairs of terminals very close together and might have caused crossing of the spark. Even Mazda back then could see the benefits of multiple coils.

No matter how you slice it DIS/COP is far superior to any dizzy set up when it comes to less mechanical parts to fail, higher potential spark energy without needing extra amplifiers, far more accurate, better combustion, and cleaner emissions.

Keep running your dizzy, but I don't know of anybody who really understands ignition systems that would agree with you.

robertfrank

iTrader: (27)

Ok guys let's be civil lol. As much as I'd like to keep me distributor, it looks like I might not have much choice if I want to upgrade to the aluminum top end or swap over to a 3.9 altogether.

Six_Shooter

iTrader: (2)

Yeah, installing a dizzy in a hybrid or LZx engines is more work IMO than going DIS and for an ignition system that has more trade offs than benefits in comparison.