Supercharging a 1256

[1303r]

i'm very tempted to boost my 1256, thou i'd be going round the turbocharger route .i have a few renault turbo carbs, a couple of turbo's and charge cooler, all sitting in a box waiting for me to do somthing silly with.
10psi of boost should give the little ohv a bit of go

[viva2300]

10psi will probably blow it sky high!

[1303r]

10 psi should be around a 74% increase in power if done properly. but yeh, forged pistons would be needed really. and unsure how much torque the crank/rods can handle. any ideas? anyone actully boosted a ohv?

[Icedmunkie]

Think turboing deserves another thread for sure! Both interesting topics people have often wondered

[viva2300]

I can only say what i know about tuning a normally aspirated.
Standard bottom end setup starts to get pretty stressed over 80-85bhp, and same with pistons i would think although not sure on that part. Balancing and lightening makes it all a lot smoother and free reving and should add 1000 rpm to the rev ceiling....also im sure ARP would have some bots for Mains caps and end caps?? That would help strengthen things.
I am going to be looking into whether it is possible to have mains straps fitted as per Mini, as they also have 3 bearing cranks, and it makes them a lot more durable. Problem with this is the oil pickup pipe, it runs very close to the mains caps. A re-route may be possible, dont know yet. Also the standard rockers are a bit flimsy....solid ones would be good......wonder if roller tip rockers could be bashed around to fit? You engineering guys (Chris!!) might be able help re solid rockers etc.....

Paul

[pbottomley]

A balanced and lighted bottom end will still top out at about 7000 at a push 7500 rpm (tops no matter what anyone says) any more and its rebuild every 500 miles, the design just doesn't support revs no matter how hard you bolts mains down with fancy sounding bolts and or straps.

The mains "can" be strapped but as mentioned once before one needs to machine new caps to enable you the ability to use a strap, the originals have outer half moon shapes and wouldn't naturally work with straps. Also as Paul says the oil pick-up pipe is connected on the middle main cap.

ARP bolts, what a waste of time, I would rather have a bolt break than be so strong that it breaks the crank. Secondly these special bolts apart from costing the earth (if you can find ones made for a Viva OHV engine) are designed to give strength for HIGH rpm and or Pressure loads as seen with high boost engines, we have already said more than the guessed 10psi is possible going to kill it, and likewise excessive Revs will do the same.

People get so hung up on brand names they forget the end goal and just have an engine that's got all the names on it.

Look the truth of the matter is the bottom end if built well, is fine, albeit the inherent end float due to only being a three bearing main (cure by using double thrust main bearings in the middle bearing not single as per standard fitments) The real issue is the head..... Get the head breathing and the exhaust system exiting well and it will be good.

If you want to go faster start with an engine that has capacity and capability, one that's already well known and worked on, one that's popular and has good after-market support.... none of the above apply to the weazy OHV its fools like me who play with them...

then again its time House started talking more about his 16v thoughts?

[1303r]

the big bonus with going forced induction rather then N/A tuning is the fact that you don't need to be using high revs to make power.
so all the concerns about how the crank performs at high rpm is not the issue. having it strong enough so as not to bend the crank or rods is thou.
also the pistons need to deal with a lot more heat, hence need for forged pistons.
the head is not really an issue, just turn the boost up and that will compensate for small/poor flowing ports . thou having larger exhaust valves and exhaust ports are a benifit. also stainless or sodium filled valves to dissepate the excessive heat.
don't need long duration camshaft, so idle will be much smother.

forced induction is, in my opinion a much better way of tunning and will give better results for time/money invested.
i'm gonna have to turbo mine now, just to prove a point
might just go for a small boost thou, say 5psi and see how it likes it

[Jon-HPF]

Just reading this thread makes the bank balance shrink Lots of good ideas - but would the expense and hassle be worth it

As Paul says , the bottom end would need to be beefed up (3 main crank dont help matters) , as a project it seems viable - as long as cost isnt an issue

Jon

[1303r]

cost needn't be an issue.
i still think that for the amount of time/money invested, forced induction gives more bang per pound note.
i'm buying a viva 1300 spares car so i will have a spare engine if i blow a hole in my current lump. i'm gonna have a go at turbo charging at the start of next year.

[hbpeter]

While I like forced induction, especially supercharging, turning the boost up to compensate for a poor breathing head I never heard before!!

Peter