What is the “easiest” engine swap thats most reliable to most HP?

[opethmike]

It comes down to personal preference... which I think is the lesson of this thread. LOL

No. It comes down to LS swap.

[FABombjoy]

I don't think Legend left power on the table. Fred claimed they could easily exceed the 300HP target for the "Type S" DeLorean package.

vehicle ignition system development has been
limited to slight retard of basic engine timing in order
to eliminate detonation

This says to me that the spark map is not good and is probably hurting performance.

300 HP cocktail napkin math:
Legend baseline n/a engine: 127HP @ 5600 RPM
VE = 64.42%, 96g/s airflow

To make 300 net HP in that scenario you need 227g/s, around 240Kpa MAP, or about 20psi boost. That assumes 0 temperature increase so higher than that in the real world.
The RHB52 family seem to be generically good for around 180-200HP
300 is probably possible under ideal conditions but k-jet tuning becomes even more critical since primary pressure isn't compensated for intake manifold pressure.
At that pressure ratio the turbo exhaust configuration becomes a pretty big deal but "final prototype" specs aren't published.

Biggest problem was blowing up gear boxes.

Development testing of turbocharged vehicle no. 502 has
confirmed that we have exceeded the torque capacity of
the production clutch.
[...]
Implementation of this fix has been hindered by
the fact that no less than three different types of
transmission input shaft splines have been found on our
test vehicles.

I suspect they were breaking 10-spline input shafts which were likely cut, versus later 21-spline versions which were likely rolled. I've never heard of a 3rd style though, can anyone shed light on that?

[David T]

Lotus figured out how to push 250 HP through that gearbox. Of course they did limit boost in 1st gear. I remember Fred D telling us how they kept popping input shafts. Going to a one piece without the coupler and pin is probably the way to go. As I said in a previous post, an auto manufacturer must limit things because of warranty, emissions, and longevity issues. An owner doing a swap to get more power is not held back by such considerations. After the input shaft the next weak link is the final drive. Because in the Delorean application, (Lotus too) they flopped over the Crown gear so they would not have 5 speeds in reverse. That makes the pinon run the "wrong way" against the Crown wheel putting enormous stress on the teeth in the wrong direction. I have seen the teeth ripped off of the Crown wheel in a Lotus from "dropping the clutch" at high revs. Can't lie about that, just have to do a dump of the ECU to see what the RPM's vs road speed were. We just had a "group buy" for those who wanted the beefed up input shaft and re-engineered pinion and Crown wheel. Some also went for the Quaiffe limited slip diff. If you are tracking the car you are past the point that other systems can't keep up. Now you must upgrade the cooling system, brakes, and suspension. Pretty soon you are basically rebuilding the whole car. It's always more than just adding more HP.

[opethmike]

Lotus figured out how to push 250 HP through that gearbox. Of course they did limit boost in 1st gear. I remember Fred D telling us how they kept popping input shafts. Going to a one piece without the coupler and pin is probably the way to go. As I said in a previous post, an auto manufacturer must limit things because of warranty, emissions, and longevity issues. An owner doing a swap to get more power is not held back by such considerations. After the input shaft the next weak link is the final drive. Because in the Delorean application, (Lotus too) they flopped over the Crown gear so they would not have 5 speeds in reverse. That makes the pinon run the "wrong way" against the Crown wheel putting enormous stress on the teeth in the wrong direction. I have seen the teeth ripped off of the Crown wheel in a Lotus from "dropping the clutch" at high revs. Can't lie about that, just have to do a dump of the ECU to see what the RPM's vs road speed were. We just had a "group buy" for those who wanted the beefed up input shaft and re-engineered pinion and Crown wheel. Some also went for the Quaiffe limited slip diff. If you are tracking the car you are past the point that other systems can't keep up. Now you must upgrade the cooling system, brakes, and suspension. Pretty soon you are basically rebuilding the whole car. It's always more than just adding more HP.

250? No. Try 350. Lots and lots and lots and loooooooooots of V8 Esprits with blown up transmission.

[Nicholas R]

I suspect they were breaking 10-spline input shafts which were likely cut, versus later 21-spline versions which were likely rolled. I've never heard of a 3rd style though, can anyone shed light on that?

The failure of the input shafts doesn't have anything to do with the clutch spline pattern; it has to do with where the shaft splines into the coupler. Regardless of the clutch pattern, the splines going into the coupler are the same, and they're all rolled. The stock input shaft coupler (on both 10 and 21 splined gearboxes) is garbage. It's only partially splined, and it's significantly softer than the 2 shafts it's joining, both of which are case hardened.

And before anyone tries to make the BS "the coupler is a mechanical fuse and designed to fail" arguement; see below. This is what happens when a coupler fails; it takes the main shaft with it by breaking the end off. It's hardly a fuse when it destroys the most expensive part of the gearbox in the process. Also for reference, this failed gearbox is from a 100% stock PRV car; no performance enhancements:

1.jpg2.jpg3.jpg4.jpg5.jpg

[FABombjoy]

Ah, interesting. Thank you for providing actual data!

[Nicholas R]

After the input shaft the next weak link is the final drive. Because in the Delorean application, (Lotus too) they flopped over the Crown gear so they would not have 5 speeds in reverse. That makes the pinon run the "wrong way" against the Crown wheel putting enormous stress on the teeth in the wrong direction. I have seen the teeth ripped off of the Crown wheel in a Lotus from "dropping the clutch" at high revs. Can't lie about that, just have to do a dump of the ECU to see what the RPM's vs road speed were. We just had a "group buy" for those who wanted the beefed up input shaft and re-engineered pinion and Crown wheel. Some also went for the Quaiffe limited slip diff. If you are tracking the car you are past the point that other systems can't keep up. Now you must upgrade the cooling system, brakes, and suspension. Pretty soon you are basically rebuilding the whole car. It's always more than just adding more HP.

Are you saying the DeLorean differential is running on the wrong side of the differential teeth? Because if you are, you're wrong. Yes its true that versions of the 369/UN1 run in the reverse orientation, but the pinion & diffs are cut the opposite direction to run in those orientations. In the DeLorean, the teeth are cut to run in our rear-engine configuration. A hypoid gear has a drive and a coast side, and what you're saying would mean that the DeLoeran is running on the coast side of the gear. This is not true. The DeLorean loads the drive side of the hypoid gear as intended. See below:
ring.jpg
The outside of the curvature of the hypoid is the drive side; the inside is the coast side. We load the drive side.

For reference, here is a photo of an excerpt from the Renault R20 Service Manual, which uses a 369 gearbox in the front wheel drive configuration. You'll note that the differential crown gear is cut with the teeth in the reverse orientation because this is a FWD application.
R20.jpg
Conversely, below is an excerpt from the DMC service manual, which uses the 369 in the RWD config. The teeth are cut for RWD.
DeLorean.jpg

The weak part of the differential is the not the crown and pinion, it's the shaft between the spider gears, and the fact that there are only 2 spider gears instead of 4. I've seen multiple instances of broken spider gear shafts.

The other weak part of the transmission is the cast aluminum case. Enough load and you'll crack the aluminum case where it holds the input shaft main bearing, and dislodge the whole input shaft. Ask me how I know...

EDIT: Added service manual stuff.

[dn010]

The weak part of the differential is the not the crown and pinion, it's the shaft between the spider gears, and the fact that there are only 2 spider gears instead of 4. I've seen multiple instances of broken spider gear shafts.

I've had the unfortunate experience of having this spider gear shaft shatter where the pin goes through.

[David T]

We can disagree over which is the weakest point, they all are subject to failure under shock loads and heavy stresses. Don't forget the 5th gear overhanging on the rear. My point in bringing up the shortcomings of the transaxle is you can't just add HP without paying attention to other things too. And while the Renault trasnaxle was never meant for so much HP, there are ways to handle it. Lotus did. But not if you flog it or subject it to shock loads like letting a wheel spin and then catch or dumping the clutch at high revs. Yes, there are blown Renault transaxles in Lotus's, but abuse anything and you can break it. As for blown spider gears, I have seen many Deloreans running with little to no gear oil in the transaxle. It gets a little hard to shift but it keeps on going for a long time. If you are blowing spider gears either you had no oil in there or you were spinning a rear wheel and when it caught the shock loads killed it. Doesn't always happen right away, it is a cumulative affect and eventually it breaks. This stuff was not made for drag racing but if you insist on using it for that you will be buying a lot of expensive parts. Lotus too (those parts are a lot more expensive and harder to find!). Thanks for correcting me on the way the Crown wheel is loaded. I will check but it must be the wrong way in the Lotus application and not the Delorean.

[opethmike]

We can disagree over which is the weakest point, they all are subject to failure under shock loads and heavy stresses. Don't forget the 5th gear overhanging on the rear. My point in bringing up the shortcomings of the transaxle is you can't just add HP without paying attention to other things too. And while the Renault trasnaxle was never meant for so much HP, there are ways to handle it. Lotus did. But not if you flog it or subject it to shock loads like letting a wheel spin and then catch or dumping the clutch at high revs. Yes, there are blown Renault transaxles in Lotus's, but abuse anything and you can break it. As for blown spider gears, I have seen many Deloreans running with little to no gear oil in the transaxle. It gets a little hard to shift but it keeps on going for a long time. If you are blowing spider gears either you had no oil in there or you were spinning a rear wheel and when it caught the shock loads killed it. Doesn't always happen right away, it is a cumulative affect and eventually it breaks. This stuff was not made for drag racing but if you insist on using it for that you will be buying a lot of expensive parts. Lotus too (those parts are a lot more expensive and harder to find!). Thanks for correcting me on the way the Crown wheel is loaded. I will check but it must be the wrong way in the Lotus application and not the Delorean.

So is your idea of abusing the gearbox in a Lotus just driving the car normally? 'Cause plenty o' Esprits get driven without much vigor and still lunch gearboxes.

By the way, do you like turbos?