Gentlemen, i have been scouring the net trying to find specifics on the Bentley Mulsanne Speed motor and have found nothing. I know that you smart guys will be able to fill in some of the blanks. First off, how in God's name can you build a turbocharged engine to produce 811 lb/ft of torque at 1750rpm on pump gas?
I mean how would you specifically design a system to accomplish this with a 6.75 litre v-8? That is more torque than a Duramax Diesel and i would love to get your ideas on how i could get this sort of monster torque under 2000 rpm out of a small block chevy. Would 600 lb/ft at 2000 rpm be impossible using two turbos and a blow through tbi such as the new fitech . I beleive that to reach these numbers at such a low rpm would require thinking out of the box as far as cam timing, compression ratio, ignition timing and turbo sizing goes. I have a 1 ton crew cab that i haul every day with so Hp is of little concern and i hardly ever rev more than 4000rpm. Any Ideas?

 

No idea on the Bentley, but I'd be concerned with kinking rods with the kinds of cyl pressure that it would take to make that kind of torque at such a low rpm.

 

What amazes me the most is that they are able to produce that kind of torque with gasoline and still be able to control detonation. I mean a Duramax Diesel produces 760ish lb/ft at around 1600 rpm but that is with a fuel that self ignites! Assuming that the block, rotating assembly and cylinder sealing are dead reliable, how could this kind of performance be duplicated on a conventional v-8 sbc with pump gasoline? Can you imagine how little ignition advance it would require ect?

 

My stock lq4 made 649 at 2400 so I cant imagine its not possible.

 

My guess would be a variable vane turbo to be able to spool that early and not choke out in the top.

 

It uses really small turbo's and tight ar on a 412 ci motor is my guess. It falls off hard after 4000 rpm.

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That is an impressive torque curve but i think it is typical of a 400 inch motor with a small turbo that most of you could duplicate fairly easily. Now, add 150 lb/ft at 750 rpm less (1750 rpm) and for me this is like stepping into no man's land. That is leaps and bounds better than what i have ever read about or heard about. Sure because of the small turbos the hp numbers are average but what kind of engine management enables you to control that amount of torque producing pressure at that low rpm with pump gas? Anyone that can explain to me how they do it, i'd be really impressed.

 

No different than the hell cat or gt500 with their pd blower. Ramp in fuel quick and pull a lot of timing with the addition of beefy hardware.

 

Man, that's what i'm saying. It is very different. Those two engines produce a ton of torque and horsepower but they are nowhere near 800 lb/ft at 1750 rpm. Not in the same league, not even the same sport! I am not trying to be a smart ass but i have yet seen anything built by hot-rodders that can match that. Sure 1000hp is impressive but thats not what i'm talking about here. I think a lot of people with cash can build a 1000hp plus engine. How many of those engines produce that kind of torque below 2000 rpm? I have never seen or read about any. C'mon guys you're not trying hard enough.

 

To put in better terms, to have that torque at that rpm in a performance application is useless. the only thing it is good for is to get you from 0-10mph in a hurry with a tight converter, easily replicated/overcome with a looser converter on a higher reving motor. the only time you would ever be in that rpm range at wot is in first gear for a brief moment
to be honest i would rather have 800tq at 6000 rpm

now for towing aplications this is a different story. if you bought a bently and blew it up do you think they will warranty if if you were pulling a camper?

 

I don't see what the big deal is, with idle around 900-1000rpms and even a stock converter your going to be at almost 2k rpms before you start moving. Don't get hung up on something you read an article on about a engine dyno test. The 8 speed automatic gearing likely has to do with as well. Can you even lock up in the 1:1 gear with it?
As you can see in the actual dyno testing sheet posted above the wheels didn't even start turning the rollers till 1800-1900rpms and peak torque was around 2500-2600rpms. That's more realistic for what the car would actually be doing.

If you want stupid low end torque on a truck that only revs to 4k rpms just put a little turbo or bi-turbo, sequential setup on it. When the turbine can't flow anymore to support what the compressor is moving, the turbo still spins up and the result is a huge gain in torque down low. 200-300 ft-lb jump in torque can be had by doing this. Peak power is going to shift down to 4k rpm range and then start dropping.

I tested this on my old single setup. I left the tubine wheel the same size and dropped to a .68ar turbine housing went from 510rwtq to 704rwtq. Peak power went from 650 to 639rwhp and shifted down to 4500rpms vice 6k rpms. To tune in spool add fuel and leave out timing and things get moving quick down low. Match that up with a heavy vehicle and the right gearing and there you go.

The tools to do it are nothing new, the need for a setup like that is not there, so most people would never build something like that.

Most common way its done is a bi-turbo setup where there is a low and high pressure turbo. The small turbo is going to be wicked small (25-30mm) and then its bypassed in the upper rpms and then the bigger turbo takes over.

 

"""I tested this on my old single setup. I left the tubine wheel the same size and dropped to a .68ar turbine housing went from 510rwtq to 704rwtq. Peak power went from 650 to 639rwhp and shifted down to 4500rpms vice 6k rpms. To tune in spool add fuel and leave out timing and things get moving quick down low. Match that up with a heavy vehicle and the right gearing and there you go.""""

That's the kind of info and "lessons learnt" that i am looking for for my truck engine build. Now, on a gen1 350 chevy 8.5:1 compression and the right cam and heads, would a self learning throttle body efi such as a fitech or Holley equivalent handle that sort of non-conventional tune? If you were aiming for max torque at 2500 rpm what size turbo and a/r housing would you use on a single turbo application?Also when you tested that setup on your single turbo build, what was the ball park figure on your ignition timing?
Was it in the low 20 degree fully advanced at a lowish rpm? Or high 20 degree? Thanks guys this is great info.

 

I'm not a tuner, I let my guy do that I just pick his brain and that's how he said he does it. IIRC my max timing up top was 15 degrees on pump gas. My setup was a 281 v8 with a 65mm turbine wheel btw.

What is you peak power goal and max rpm? That will better determine what size to get. A revised billet compressor wheel design would be idea as well. My setup spooled 1k rpms faster going from a cast wheel designed to a more aggressive billet wheel design.

A billet 6765 T4 with a .68ar would be pretty damn responsive on that motor, would probably max around 500rwhp though.

 

500 wrhp would be enough for my truck, i'd settle for 400 if i could get the torque up to 600 + at 2500 rpm which is my highway rpm @ 65mph.
Here are some newbie questions for you though: with a .68 ar should i route both banks of my v8's exhaust to the turbo or only 1? Also, do you think it would be better if i bulit my engine to be 383 inches and maybe use a little less boost or 355 inches with a bit more boost? How much compression should i aim for? ( i was thinking 8.5:1) My trans is a towing/rv th400 with a tight convertor and 3.73 rear axle. I tow 5000-10000 lb daily ( 20k miles in 4 months). Any more advice would me much appreciated. Thank you.

 

At those kinds of loads a 600 ft lb small block won't last a month (or a day with the wrong tune). Keep in mind that torque comes from cylinder pressure, the lower the engine speed the more cylinder pressure has to be created which combined with high cylinder temperatures for long periods of time will destroy pistons, bend connecting rods, pound out rod and main bearings, cause main caps and main webs to move around, broken crankshafts etc. Ever noticed that engines in higher GVW trucks were rated at less power? That's because they have been detuned to live in an environement where they operate at max torque for long periods of time. Honestly anything over 40o ft lbs is going to be short lived.

The Bently (Eco-boosts as well) use direct injection to help prevent detonation and pre-ignition and have extremely well refined engine management systems that help control cylinder pressure especially in high load high heat situations.

If you want that kind of torque for pulling those kinds of loads you will be a lot farther ahead to get a diesel. If you have to do it with a gasser then the more cubic inches the better, a 454 has more bearing area, has a much stronger block and will last a lot longer than a small block, though it won't be a 100k mile motor. I have a pickup with a supercharged 454 that makes 600 ft lbs @ 2,400 and 420 horse @3,800 at the flywheel with 5 psi boost. It is quite octane sensitive above 85 degrees ambient so I've had to scale the timing back to make it last. I pull a 12k+ trailer with it and while it does quite well it uses a lot of fuel (5-6 mpg) and after about 40k the oil pressure is starting to go away because the rod bearings are worn out.

 

Yeah, i know that i should get a big block. My truck is a 77 gmc crew cab and i want to keep it because it draws lots of attention and is good for business and ok i'll be honest, i love it and there is not a new truck on the market that can hold a candle to it as far as maintenance and running costs, a part from fuel economy (including my 2015 sierra 2500hd) . It gets 6-7 mpg with a double pump holley but is limited power wise even with a r/v cam, performer rpm intake and long tube 1-5/8 headers. It does have crappy stock 882 heads though. I already have a fully machined 350 block (030 over) 4 bolt splayed mains with new dart shp200 heads and i've got too much money in it to sell it and start over with a big block. A Duramax transplant is too expensive and an old school 6.5 liter diesel is crap. My other options were to go with a 383 stroker rotating assembly and upgrade to a 4.56 rear gear and a gear vendors overdrive ( i wanted to rebuild my 14 bolt axle anyways ). A very mild 383 can easily produce over 400 lb/ft which is 50-75 lb/ft more than my tired 350. The steeper gears wil give me 22% more torque at the wheels. I'm also looking to up the compression ratio to about 10:1 and use propane. (Up here in quebec a liter of propane is about 50 cents). That way i can have a bit more power, good durability and lower operating costs. I Would have loved the torque from a turbo though... Anyone else have an opinion on this or has anything to add?

 

put a cummins in it. you are looking for diesel torque at this point. something from the 94-98 vintage with a p-7100 on it. easily surpass your goals.

 

Yep, I got an 05 with a few bolt on mods. There is times I tow 2cars at once empty I can out run most little Honda cars and it gets well
over 20mpg on the highway

 

Thanks for your replies guys. A diesel conversion is not presently in the cards. If it was, i'd just buy a whole new truck. Plus, most of the diesel guys i know want to switch back to gasoline because of the running costs of their trucks once they go over 150k miles. Lowest running cost of the big three is the duramax followed by the cummins and the worst being the ford. One of them has a fleet of ford diesel pickups that he is slowly trading in for v-10's. I know that i'm probably opening up a can of worms here but this seems to be the trend for guys who work with their trucks every day.
Cheers, everyone.

 

With electronic diesels that is the case, but with a mechanical 5.9 Cummins its a bit different, many run 4-500k with nothing more than injectors, and possibly some pump work, but at a fraction of the cost of the electronic diesels. Just FYI.