Destroked 3.4

[1971mgb]

Okay this is a question for all who really know the 660 engine specs.If I use a large journal 2.8 crank in a 3.4 block are the bearings the same?looking at bore/stroke ratio and rod/stroke ratio this seems to be the mother of all v6 combos.The numbers mimic the 331cu.in. destroked 350 and it would wind like no tommorow.Hooked up with forged pistons and 10psi dual turbo,should produce 330tq. in my 2300 lb mgb.Any thoughts?and is my calc. about the rod and crank bearings correct?
thanks for all the great help.
Rob

[Superdave]

Yes, the 2.8 crank will fit in the 3400 block and net a 3.0 liter @ stock bore and about 3.1 liters at .030". It's been talked about for a while but nobody's had the guts to build one. You would need a custom set of pistons but the stock rods could be used. :P

BTW, you could make ALOT more HP than that with this combo

[SappySE107]

So long as you make use of the higher RPM ability, then its probably worthwhile. Otherwise the extra displacement from using the stock crank would be ideal.

Find me a 2.8 crank that doesn't suck and ill throw it in the 3400 I got on my stand and use the 3400 crank in the 3100 block

[Guest]

Yep, I have the block, crank and heads.

I just have to decide on what rods I'm going to use and what SCR I want to start with.

I will build it.

The Frankenbeast cometh.

[bszopi]

I know of someone building something similar, but I think slightly more extreme... Unfortunately, I'm not at liberty to discuss it anymore But lets just say it'll be a beast when its done.

[donk_316]

its being done. "wills fiero" is using a Falconer 2.8 Forged crank and a DOHC block and heads.

[Superdave]

its being done. "wills fiero" is using a Falconer 2.8 Forged crank and a DOHC block and heads.

ooh, that sounds like a fun combo as well

[1971mgb]

destroked 3.4

Knew you guys would have the numbers.So at 3 liters with a 3.68 bore 2.99 stroke and fiero style stainless headers swapped side for side so the exhaust ext to the front of the engine and mount 2 t25's turbos.small intercooler,i.e. starion.at 8-10 boost it would seriously out flow the heads after the 330tq. figure I calculated.Anyone have head flow figures for a good set of p and p'd iron heads with aftermarket large s/s valves? Should put me into the high 11's low 12's if I can find the traction to hold it down.
Rob

[BillS]

Re: destroked 3.4

Knew you guys would have the numbers.So at 3 liters with a 3.68 bore 2.99 stroke and fiero style stainless headers swapped side for side so the exhaust ext to the front of the engine and mount 2 t25's turbos.small intercooler,

Am I missing something or are you just talking about using a short stroke Fiero crank in a 3.4?

That is no big deal and it sure doesn't turn a boat anchor into a high revving screamer.

The advantage of the longer 3.1/3.4 stroke is additional torque, which in an engine that really does not rev very high in the first place is a good thing. There is no point in you giving that away by going short stroke, particularly as you intend to turbo, which gives great mid range torque - and again, does not require using the engine at higher RPM (even if you could get those ratbag heads to breath up there)

If you were going for a conventionally tuned engine I could maybe see the point in the short stroke, but having put in a lot of miles in a 2.8, I can tell you that the stroke does NOT automatically get you the ability to rev.

For an MGB, the 3.4 with stock displacement makes the most sense and so does using the much better flowing alloy Gen 3 heads.

Assuming that you can find room in the engine bay for a turbo (you don't need twins - you'll have enough problem finding space for one), you can expect somewhere between 225 and 285 BHP depending on how you build it, with a bit more being possible. Whether that gets you the times you predict is another question.

My street Fiero with a 3.2 blown at 13 psi is good for low 13s.

I went conventional tuning on the 3.4 I am using in my MG project - you can get up around 200 bhp at the crank and that is enough on a 2000 lb. car (unless you are power mad....

[GPXSS]

I'd have to agree, although the idea of a short stroke 3.4 is nice and looks fine with high rev's and hp numbers, you really are short changing yourself without the added torque of the longer stroke. On an engine this small theres not much to be gained from going that way.

You also have to remember that even the 3.4 has an excellent rod/stroke ratio compared to a 350, which is the main reason they do the shortstroke swap.