8v Crank In An Xu9j4

[24seven 104]

I've read here and there about people using the 8v crank in the alloy block Mi16 engines, but why? What advantages do they offer, other than having fewer counter balances? I tried searching, but didn't get far, though I did come across a thread about rpm limits of the various crankshafts and how they're actually a lot stronger than they're credited with (8500rpm regularly for std XU5 cranks).

 

I'm rebuilding my old Mi16 at the moment and am beginning to think that since it's apart now would be the time to start making some future-proof changes to the bottom end, and so far I've decided I want an XU9J4 bottom end, 10J4RS head, minimum 8000rpm limit and hopefully somewhere close to 200bhp at the wheels (so 220+ at the fly I guess?). Is this realistically achievable without the need for custom rods/pistons?

 

I'm expecting work will be needed on raising the compression ratio though from what I gather that will mostly be taken care of by the smaller combustion chamber in the RS head (perhaps a light skim to bump it up a little?), Maintain the standard RS exhaust and inlet manifolds if possible (will the inlet be too much of a restriction for this kind of power?), and a different camshaft/regrind will be an absolute necessity. Management I'll deal with later once the engine is actually built but first thoughts are to use a complete '6 setup and have it remapped by chipwizards (providing all the sensors on the block match up).

 

This may all take a while and end up going in a completely different direction considering I'm just a skint student at the moment, plus I like to keep my options open as much as possible.

[Baz 421]

Probably the major reasoning would be the fact that it's getting harder to find decent Mi items.

 

Less weight because of less counter-balances, 4 instead of 8.

 

So rev-happier lower down, although won't be as balanced at higher-revs because of the less counter balances.

[petert 588]

220hp flywheel is approx. 180hp at the wheels. You can get the power either by revving higher, or more cfm. 220hp from 1.9L is certainly achievable without the need for revving that high. I did some head work for another member on here JeffR. It was only making approx. 205hp despite having all the goodies - forged 83.50mm pistons, big hydraulic cams, big valves and 45mm tb's. The rev limit was 7500 because of the hydraulic lifters. Dismantling the head revealed some fairly ordinary seat and throat work. After repairing and tidying up, some very impressive flow figures were achieved. To this were added some new Catcam springs, as the std. springs were almost spring binding with 0.448" of cam lift. Note the thickness of shims required to get the seat pressures correct. This is the kind of detail needed to make serious, reliable hp out of a smaller engine.

 

If you don't want to spend the money on cfm then you'll need to do it with RPM. That means solid lifters, quality springs etc. At 8000 rpm you should be making approx. 240hp. QEP sells steel cranks if you want to sit up there regularly.

 

Either way, making that sort of hp out of a 1.9L costs money.

 

You certainly won't do it with a standard RS inlet manifold, and the small primaries tubes on the RS exhaust manifold is less than desirable for 7500+.

 

I'm not sure I answered all your questions but hopefully you get the idea.

Edited April 12, 2010 by petert

[24seven 104]

Actually you answered quite a bit between you, thanks . More importantly I've got a better idea of what sort of figures I'm aiming for now too, mainly because I want to retain the standard manifolds for tidyness and simplicity (and it makes locating the ICV/MAP sensor/TPS a lot easier). Solid lifters were something I'd actually forgotten about when reading the threads on high crank speeds in the 8v's as they weren't mentioned (for obvious reasons !), but since the RS head limits at 7500 anyway would the hydraulic lifters and standard double springs really be under too much stress to reliably take that extra 500rpm occasionally?

 

I was reluctant to go down the 8v crank route because of the counterbalance difference as I do like a high revving engine, but thought perhaps there was some other difference in the metal that made the 8v items desirable. The original crank has already been reground/polished anyway and only needed 3thou taking off, so I'll stick with that.

 

I should probably add that this isn't a competition build but a fast road build so mechanical reliability is paramount.

 

Thanks again.

[brumster 135 1 Cars]

I can offer some second-hand comments; a friend used to run a heavily lightened/balanced 8v crank in a very competitive rally car which would quite happily see the naughty side of 8k. When I got chatting to one of the engine builders at Longman (Sid) he was saying they wouldn't recommend it for something that was more track-based, with sustained high revs, but given the nature of rally use the lighter crank made for a much revvier little engine and suited it well - there were no complaints. Then again, the rebuild period on the engine was pretty much annually, so if ever there was an issue with the crank it would have been spotted. I think for reliability and/or extended high-rev usage, flex without the counterbalances would be an issue (that was what was intimated to me), but if you're only looking at fast road/rally use - or, given hard use, regular checks/rebuilds, then an 8v crank is no problem. The engine I'm talking about needed regular stripping due to other factors - mainly around valve spring wear, I believe, but of course while it's all apart you check everything anyway.

[Henry Yorke 269 3 Cars]

Historically I know a few people used to upgrade to Mi cranks in 8v engines as they were meant to be stronger. Exactly how they quantified this I don't know. I think Kyri put one in his old TT which easypug now has

[GilesW 41]

Interesting.

 

My 20XE vaxhalll engine - running circa 270bhp on a standard early 20xe crank (lighter) never had any issues at running at sustained high rpm.

 

Indeed they are well sort after as there was no issue with them percieved as 'week'.

 

So... what exactly is the issue with the pug 8v cranks?

They can flex?

They are imbalanced? (of course you would get it checked/balanced on any half series engine anyway).

 

What was teh reason for more counterweight on teh 16v engine? To smooth/dampen it? To increase rotational mass for smoother pulling away/changing gears/idle?

[James_R 3]

Giles - Find a pic of a 8v crank and you'll see instantly.

 

24/7- If you're interested in the 8v crnak idea it's done for a)weight b)easy to source c)oil control [have a search of crf450's results]

 

As for the number's you're after that's a long and expensive road. 87x88mm would be your friend for that spec.

[24seven 104]

Thanks for the advice guys. I realise now the numbers were a bit optimistic, I definitely want to stick the standard manifolds and '6 ECU with a remap. As it is though it's could definitely be quicker, the throttle response on a stock D6C isn't too bad and is still quicker than a lot of cars, so if that's the only real gain to be made I'll stick with the Mi16 crankshaft for everyday smoothness. The one I'll be using has been recently reground/polished and only needed 3thou taking off it, but if I've got the money at the time of building I'll send it off to be better balanced to compensate before it goes in. If I can make 200bhp at the fly (what would be a realistic wheel figure that would achieve this?) then I think I'll leave the engine at that and move on and start working on the chassis/handling.

 

I'll update this as I go along, perhaps it could be moved to the projects section at a later date when the ball starts rolling.

 

Thanks again.

[unariciflocos 49 1 Cars]

I'm going to start rebuilding my xu9j4 soon and I was thinking of using an 8v crank and rods, but i have a few questions related to this.

 

Can I use 8v rods on the xu9j4 crank? The xu9j4 crank needs an R3 regrind and I'm worried there will be too little material left to sustain high rpm operation. Will a crank with an R3 regrind be reliable in an engine used for hillclimbing or should I use my 8v crank which has an R1 regrind?

 

If I use the 8v rods and machine the mi16 pistons, which pins do I use?

 

Thanks in advance for your answers.

[JeffR 51]

.....I did some head work for another member on here JeffR. It was only making approx. 205hp despite having all the goodies - forged 83.50mm pistons, big hydraulic cams, big valves and 45mm tb's. The rev limit was 7500 because of the hydraulic lifters. Dismantling the head revealed some fairly ordinary seat and throat work. After repairing and tidying up, some very impressive flow figures were achieved. To this were added some new Catcam springs, as the std. springs were almost spring binding with 0.448" of cam lift. Note the thickness of shims required to get the seat pressures correct. This is the kind of detail needed to make serious, reliable hp out of a smaller engine.

 

If you don't want to spend the money on cfm then you'll need to do it with RPM. That means solid lifters, quality springs etc. At 8000 rpm you should be making approx. 240hp. QEP sells steel cranks if you want to sit up there regularly.

 

Either way, making that sort of hp out of a 1.9L costs money.

 

You certainly won't do it with a standard RS inlet manifold, and the small primaries tubes on the RS exhaust manifold is less than desirable for 7500+.

 

I'm not sure I answered all your questions but hopefully you get the idea.

 

I must have missed this post at the time, but to expand on Peter's comments about a properly prepared cylinder head.

 

My BV engine previously was all top end. I had to flog the be-jeezus out of it & even ran it at 7800rpm for a season to get anything like decent performance out of it. If I got baulked by a slower car it fell out of the upper rev range & was sh!te. Like Sandy described in another post a poorly worked BV head has no mid-range & is 'doughy' & flat.

 

Since Peter's remedial work of cleaning up the ports, new valve springs, seats & corrected seat pressures, the head flows at 302cfm (with inlet mani) with good gains throughout the entire valve lift (0-0.500"). It's now got immediate throttle response, a strong mid-range & pulls hard to the 7400 limit even in an 1100kg 405. It would be a weapon in a 205!

 

Certainly a great result for the cost of the work & achievable within a safe rev limit.

[Sandy 191]

Good stuff