MGB v8 conversion

[windsurfhypo]

Restoring a converted mgb V8 . Engine was an early 3.5 10.5 cr and LT77. I have purchased a 3.9 EFI engine which is from an auto engine . I am hoping I can convert the 3.9 auto engine with the parts from the 3.5 engine . I see no problems with the front of the engine but what is put on the end of the drive shaft to mate with the gearbox, are they all sourced from the 3.5 . Are there any pitfall in using the 3.9 as manual in a m,gb conversion is it the same cam will it be more powerful. anybody with experience in this. I appreciate buying a 3.9 manual engine would have been simpler but this engine from a an auto car was available.

[Moderator]

Congratulations on your new engine, Robert. I'm confident this will all come together nicely for you.

I think probably the answer to your first question is "a pilot bushing". A pilot bushing is just a simple part to center the input shaft of the transmission in the tail of the crankshaft. Here's a link to one for purchase. https://www.ebay.com/itm/166269617030  (Verify before you buy. I'm not recommending any particular source.) Here's a pic of one (though not Rover) installed in a crankshaft.



These are a wear item. I don't remember us ever discussing these on BritishV8... but if we did it was probably to advise how to get an old one out. (As the picture implies, the trick is to put grease in the hole and then hammer some sort of cylindrical tool in so that the grease will force the bushing back out.)

I expect the camshaft that's already in your 3.9L will probably be okay until you decide to change it. You might prefer a different cam grind to shift performance to higher rpm... but then again you might not. Seems like everyone recommends a different favorite camshaft. We'd need to know more about the rest of your build and your driving needs to make a recommendation.

Did you get all the fuel injection parts with that 3.9 engine? Personally, I'm done with carburetors forever. You can of course shift over your old carbs to get your car running. Your new, bigger engine will need different carburetor jetting. There are a handful of people who are great at tuning carbs. Most people aren't as good as they wish or think they are. Then mixture/requirements change with wear, fuel quality, elevation, temperature, etc.     But fuel injection takes care of fuel/air mixture automatically.  This is the gateway to lots more info about EFI here on BritishV8: https://www.britishv8.org/Articles/Rover-14CUX-EFI.htm

[88v8]

[quote="Curtis Jacobson]This is the gateway to lots more info about EFI here on BritishV8: [www.britishv8.org][/quote]

Would you go that route nowadays? Age of parts n'all...
I have rather a horror of electronics and I recall even ten years ago a geezer on a forum who regularly discussed pin-out fixes on these older ECUs.

What do you think of the Sniper?

My Edelbrock is OK now, does still need dyno time. The Sniper is slightly tempting.

[spridget]

Just a note. You can use bread, yes bread to remove that old pilot bushing. It works just like the grease and doesn't make a mess like the grease. I have used this method successfully many times. I dislike putting grease anywhere near my clutch assembly.

[Moderator]

Would I go that route nowadays?

For someone who scores a running Rover Disco organ donor, I certainly wouldn't recommend against using its EFI. I believe someone could get it up and running quite quickly in their MGB's engine bay, and then remove/lower the plenum/fuel rail however much they need for clearance. Spare parts aren't hard to find or expensive (used).

The article I linked to includes theory-of-operation, etc., so I think it's a good starting point for whatever EFI decision.

For my own car, I used some Rover components (e.g. manifold, fuel rail, injectors) in combination with a MegaSquirt MS3-Pro computer. (Details are on my Photo Gallery page.)  Sequential fuel injection plus crank fired 8-coil ignition with side benefits such as programmable fan controllers and data logging. Cowl induction. Distinctive appearance. Horses for courses.

I know very little about Sniper. Surely it's much better than a carb for most applications. In combination with readily available intake manifolds, I'm skeptical it has any performance advantage over Rover's system unless/until other mods (big cam?) change the game.

[windsurfhypo]

I will post some pics as this was an early. mgb roadster v8 conversion to 3.5.  Bought as a stripped shell but replacing £.5 with 3.9 have full efi kit
Thanks for info
another question is about reducing the 3.9 eft plenum for bonnet fit.
 I planned 7mm off cover , 5mm off plenum top  and 15 mm off plenum base
Question is - take trumpets out and take 5mm of the plenum top then do I also take something off the bottom xof each trumpet

The  base of the actual  plenums if milled to 15mm. removes the ledge that a few of the smaller  trumpets sit on . I assume this is okay and you somehow glue these trumpets in to stop them moving into manifold with the ledge gone.
Any comment.

I think the

[Moderator]

The trumpets are easily trimmed with a hacksaw or with a belt sander. I think I used one and then the other.  How much to trim is a judgement call. Some people shorten them quite a bit. If you're only trimming 7mm off the cover you might be able to get buy without trimming them. For certain though, they won't fall down into the manifold. The ports in it are a little smaller in diameter than the OD of the trumpets. I didn't feel a need to glue them, but it wouldn't hurt if you did.  Have fun with it!

[windsurfhypo]

thank you Curtis exactly what I needed. It was the machine shop that pointed out the smaller trumpet touch  a ridge which they sit on and that would be lost milling 15mm. I can now tell them that's ok . That's the 15mm of plenum base sorted. Now for the other reductions.

 I realise now taking 5 mm of top of plenum  and 7mm off cover will reduce height total by 12mm plus 15 mm from base.  That's my 27 mm required.

The only issue is then the  trumpets will be 12 mm closed to top of cover. .It may still fit but I suppose what is more important is do I  keep the total length of trumpets or make a larger gap  to roof of plenum cover. as per original build by shortening all trumpets which as you say is easy. If length of trumpets more important than the original gap to platinum cover top that will be the way . Any thoughts . The minimum distaance to top cover irom trumpet top .... is there one.

[BlownMGB-V8]

It's not all that critical, shortening the trumpets will shift the power band upwards a little but you probably won't notice it especially with the increased displacement.

Jim

[Moderator]

You probably noticed already that all 8 steel trumpets are the same length. (100mm?) It made sense for Rover to make them interchangeable. I agree with Jim that trumpet length isn't critical and you're unlikely to notice any changes from the driver's seat, but on the other hand there's no reason you couldn't trim them to different lengths. For example, you could stagger them so their ends are all equidistant from the ceiling. And/or you could do what I did after noting that the runners in the intake manifold casting aren't all identical in length or volume.



(original photo caption)

The volume of each intake tract, measured from valve seat to trumpet top, has been
carefully cc'd and equalized. Note that the trumpets for cylinders #1 and #7 were
shortened significantly compared to the trumpets for cylinders #2 and #8.

[BlownMGB-V8]

Equalizing the runner length should at least in theory make the power peak a little higher and sharper and making them unequal should make the peak wider but lower.

Jim

[windsurfhypo]

3.9 was an auto engine  and in couse of building it up to fit the mgb in replacement of the 3.5 as a manual with the LT77 manual gearbox. Only issue currently is the flywheel from the 3.5 and is it a straightforward  attachment to the 3.9 .
Three pics attached .

1st is the end of the 3.5 crankshaft which the flywheel was fitted on. iThe flywheel fits the  6 holes falthough crank has eight holes.it slides on the crank also a bit for support

2nd is the end of the 3.9 crankshaft which fitted to the auto parts. I have removed the Allen bolts and the flywheel fits using the longer bolts from the 3.5.
3rd is the flywheel. ie 6 bolts.. There is no slide on it mates. a flat surface.

3rd isa the flywheel

Whilst this appears to work and I appreciate I have to put the smaller spigot in the end of the crankshaft is this the right way of doing it . the flywheel on the 3.5 crank slide over the centre a bit whilst the flywheel allotted to the 3.9 crankshaft end just lies flat although held by the bolts.

[windsurfhypo]

Fitting 3.9 V8 . Have the old 3.5 rover timing cover and water pump which fits , The  3.9 timing cover and water pump looks tight around the roll bar. I see you can now get RV8 remanufactured roll bars which give more space but expensive. Cannot see anyone recommending the 3.9 setup on mgb conversions, but seen a few pics that might have been successful with engine right up to radiator

For now I would stick with the 3.5 pulley water pump and timing cover but notice two things.

1. Oil pump gears on 3.9 are bigger can't swop to 3.5. Guess 3.9 oil pump is more efficient hoping can use 3.5 type in the 3.9 engine is this ok.

2. Attach image.
 I need to use the 3.9 distributor as I am sticking with EFI . It is extended by a flexible end. Is it possible to remove this and how is that done .. It seems likely it would be the  same size as the 3.5 distributor alongside. in the pic. Looks like Lucas just added an extension to improve the oil pump on the 3.9 timing cover.

Any help appreciated

[windsurfhypo]

seems I have part of the answer, the longer distributor end comes off after knocking through a holding pin. I am not sure if the drive end will then match the earlier distributor end , be nice to know.

However I am more concerned with the smaller gears on the 3.5 cover meaning less oil pressure flow in the 3.9 engine the upgrade must have has purpose, so will continue to research a water pump that fits a 3.9 eft rover engine timing cover with the smallest nose for clearance.

[mstemp]

Robert,
Look closely at the piece u removed. Old has the opposite drive for the oil pump shaft. Your old one is the Buick style, while the 3.9 is the later Rover if I recall.
1976 and up oil pump shaft has a piece sticking up that fits into a slot in your distributor. Old was the opposite.

[BlownMGB-V8]

So Rover also fell victim to the "longer oil pump gears" hype as well? This could spark a whole new round of issues although I suppose there is a possibility of it being an aftermarket mod. First thing is to take a very close look at the pump cavity to see if there has been an extender of some sort added on. This is the first mention of extended gears in a stock motor that I'm aware of.

You're headed down the wrong street. With these engines you get superior oil pressure by maintaining close control of oil loss by using tight clearances, not by increasing the pump displacement. The latter approach causes accelerated drive gear wear and reduced engine life.

Do a search for "oiling mods".

Jim

[MGBV8]

I believe Buick started this.

Rover thought the P5/P6 oiling was on the weak side.  Beginning with the new SD1 in 1976, they increased the oil pump gears from 0.875" to 1.048"

Buick did the same, except before Rover.  The 215 & 300 was also 0.875".   With the 1967-1969 400 & 430 (which has very similar oiling issues), Buick went to 1.123" oil pump gears.  Same for the 1970-1976 455.

My high volume gears from D&D measure 1.123".  Maybe just 455 gears?

The HV 455 oil pump gears are 1.373".  I think that is where all the wear issue woes started.


Jim, maybe you have some 340 & 350 oil pump gears you could measure.  I have read that the Buick 350 HV gears are the same length as the stock 455 gears.

[BlownMGB-V8]

Pretty sure they are the same as the 215 ones but I do have some front covers and can measure the cavities. I'll try to do that this morning.

Jim

[MGBV8]

The Buick 400, 430, & 455 engines all use the same oil pump gears & timing covers ('71 & up had some oiling improvements).

So, I edited my above post to read:

"Buick did the same, except before Rover.  The 215 & 300 was also 0.875".   With the 1967-1969 400 & 430 (which has very similar oiling issues), Buick went to 1.123" oil pump gears.  Same for the 1970-1976 455."

[BlownMGB-V8]

I did think the gears for the 430 and 455 were larger, we had both of those for the Roadmaster. As for the small blocks I onlu have experience with those up to '67. After that I don't know if they made any changes. The V6 of course went to the concentric pump in the 3800. That eliminated the drive gear issue entirely.

Jim