Thread: Supercharge a 4BD1?

Originally Posted by Dougal

Sure there are lots of low revving 4 cyl 4 stroke engines. But I haven't found one producing max torque below 1500rpm. The very low rpm engines have more cylinders. Even 6 cylinders rather than 4 reduces vibration at low revs enormously.

Yes the 20kw parasitic power is calculated for a 4BD1T at 15psi at 2000rpm with a 60% efficient compressor.

Turbochargers feed off heat and pressure, the more heat you feed into the turbine, the less pressure it takes to do it's work. My previous turbo would cross-over when EGT's hit about 600C. If revs were kept down (i.e. under 2000rpm) and EGT's above 600C then it produced more boost than backpressure.

my klr 650 is a single that pulls hardest from 3k to 5k, that would be the equivilent to a 4cyl at around 1000rpm wouldnt it, but yes its a vibrator.
would a 5cyl engine be better at the lower revs? theyre supposed to be much better balanced, ie 5cyl better than 4 and 6 or is it just plainly the more cylenders the better due to less rotation per power stroke

Yes it's simply more cylinders firing means smaller and more torque pulses.
Inline 6 cylinders are the best balanced engine this side of a V12, 5 cylinders are just a compromise between 4 and 6.

I'd like to double the weight and inertia of my 4BD1T flywheel at some stage, this will let me use a lot more torque at lower revs without the vibration.

It was fine in lower gears if you could accelerate through, but climbing hills in 4th and 5th below 1700rpm it had issues. I'm now using a slightly bigger turbo which doesn't produce boost as low down and it appears to have side-stepped the problem for now.

Originally Posted by JDNSW

Superchargers are less reliable and much more expensive - and need to be where they can be driven, whereas turbos can be put where there is room, more or less without restriction. If superchargers were worthwhile as you suggest, I suspect you would find at least a few on the market.

John

My experience with Commers and Detroits was that blowers last virtually forever if clean oil is getting to the bearings and clean air down the hole. Commer blowers did wear out but most likely from a combination of tight clearances between lobes and housing and the inefficient OEM oil bath air cleaners of the day. Detroits often lasted the life of the engine without overhaul. Wish I could have said the same about turbochargers which crack housings, spit out bearings and seals (emptying sumps in the process), swallow impellers etc. and do need overhauls reasonably regularly.

Theoretically turbos can be mounted anywhere but practically, on passenger and light commercial vehicles, they must go under the bonnet with everything else on a modern vehicle, heating and a/c compressors and units, alternator, starter, ps pump and so on. You have a very hot, often red or white hot, component in close proximity to all the wiring and other sensitive stuff. Things have got a bit crowded under modern bonnets and a red/white hot bit should properly be mounted elsewhere but there is no elsewhere. Good examples were the first turbo Offys at Indianapolis in the first half of the sixties. The front engine cars had the turbos completely outside the bonnet, and the rear engined cars had the turbo hanging out about a foot behind the engine. No room in a race car to fit them inside.

Virtually every thing in automotive design is a compromise between cost, performance, fuel economy, responsiveness, reliability, legislation. There are few perfect solutions.

My personal preference is for cubic inches ahead of complication, particularly for vehicles that are to be used in rough conditions and remote areas where you don't want things breaking and immobilising the vehicle. Start with a big enough engine to do the job without having to add complex pressurising systems

There are some good facts posted so far and some rubbish
I haven’t sorted out how to do multiple quotes but from previous posts.

Its all about vibrations, or and torque pulses, where and how they happen

A 4 cylinder is not the best balanced motor, but as Dougal posted a 6 and 12 are the best. A V6 is the worse. There are many things done to counteract these vibrations. The earliest is the flywheel, offset cranks, balance shafts and harmonic balancers. Only 2 of them interest us, flywheel and harmonic balancers as they assist in smoothing out the toque impulses that the Isuzu produces at low reves.

Toque impulses are a result that a piston doesn’t move at a steady pace down the bore. The angle of the conrod to the crack shaft plays a part and of course the firing of each cylinder.
In short the crank shaft speeds up and slows down 2 times each revolution. That’s important to remember.

Super charging takes power from the crank shaft and turns in into a air pressure system. most super chargers are a Positive displacement. That means that the limiting factor to boost pressure is volume. IE the motor takes air at the same rate the super charger supply’s it at a given pressure. If you were to block the output of a super charger the pressure will keep climbing, usually until you blow a seal.
They are a fine tolerance built item with a bit of machining and therefore cost. A little bit harder to get working well but no harder than a turbo in a diesel ( SO much harder in a petrol)
fiscal limitations, like where and how to mount it and getting a drive to it.
a more constant boost across the reve range may sound attractive but it means it will be harder on clutch. Torque impulses are magnified, since toque impulses are already topic with the Isuzu magnifying these is some thing I would wish to avoid.

Turbo charging. Does not uses waste energy, well it does but at a cost. Back pressure is raised reducing the effective savaging of the combustion chamber. No back pressure is good, when we talk about power or efficacy. Back pressure is not necessary either. Back pressure was used in days gone by to smooth out toque impulses but that’s about it ( zephyr ford 6s with offset crank and hockey stick manifolds were in there day a very smooth motor)

Just as a super charger has to firstly replace the power it takes off the crank. a turbo charger has to over come its own backpressure. this is where the statement of a turbo charger being more efficient falls to peaces. But then there’s bad turbo setups just as there are bad supercharger setups.

Turbo chargers have the advantage of being cheep to manufacture, small and into days world of electronics management systems easy to manage.

But for no other reason the toque impulses should be enough to push you away from the super charging and into the lap of the turbo

so how do all these things effect say a td42? is turbo charging still the way to go?

Originally Posted by 85 county

[COLOR=black][FONT=Verdana]Just as a super charger has to firstly replace the power it takes off the crank. a turbo charger has to over come its own backpressure. this is where the statement of a turbo charger being more efficient falls to peaces.

I run a backpressure gauge on my Isuzu whenever I change the turbo setup and the results of this prove very interesting.

At 100km/h cruise with EGT's around 430C backpressure is ~1.5 times boost. 12-13psi backpressure for 8-9psi boost.
At the same rpm (2000 near enough) and full load the backpressure drops as EGT's rise. Above 600C I have slightly more boost than backpressure, the hotter the EGT's get, the lower the backpressure.

In these high load conditions, the turbo is essentially working off just the waste-heat, the backpressure it also needs to work is compensated for completely by the boost it provides. This mode of operation a supercharger just can't match.

Most of the time comments about turbocharger efficiency are talking about the compressors efficiency. Superchargers used to be a lot less efficient so the air charge was a lot hotter, but new superchargers have made big gains there.

Originally Posted by mopar

so how do all these things effect say a td42? is turbo charging still the way to go?

Simpler easier, more acceptable by the masses so yes

Originally Posted by Dougal

I run a backpressure gauge on my Isuzu whenever I change the turbo setup and the results of this prove very interesting.

Is that the same as what the Americans call a drive pressure gauge? How have you made it - just a coil of copper pipe to let the gasses cool and then plumbed into a normal boost gauge?