a few quick turbo questions

[rommaster2]

Ok well i'm looking to get a bit of a plan on long term build for my six cylinder. I am not looking to make big numbers, just a bit of a boost. Basically power expectations i'd say 130 to 140 RWHP (and i'd assume torque would be pretty damn good). However my six is pretty much a stock 65 (just with pertronix and a pony carberator) 200ci. Also i'd like to keep some reliability and economy (20 mpg?).

So my question is for this would a low boost (8psi) near instant spool turbo put me anywhere near that power and still be economical? or would it be better to put a larger one that spooled at about 2500rpm. I would think the larger one would be more economical because i could cruise below spool and not need the extra gas.

Also if i'm going low boost couldn't i keep fairly simple in terms of my setup (no intercooler) and pretty much just need plumbing, turbo, and wastegate?

I figure that between me, my friend, and the engine teacher at my college we could figure out how to get it all tuned (that guy was gonna help us turbo our lawn mower, and knows way more then anybody should ) and working. Just i need to know if my ideas are realistic (power expectations and economy).

 

[wallaka]

I'd say that a low boost setup could put you way over that horsepower mark while still maintaining pretty good gas mileage. Remember, the turbo won't be making "boost" when there's not much of a load on the engine. That is one of the beauties of turbo vs. supercharger. I've heard that some people actually have better gas mileage after the turbo is installed because torque generation is so augmented at lower rpm levels. This translates into less throttle and less gas used.

Your insight on the intercooler situation is also correct. In fact, this is the way that the famous Ak Miller made most of his turbo setups. Get a turbo with an integrated wastegate and there is another plumbing issue out of the way.

 

[hasa68mustang]

I would say a nice little T3 could EASILY get you to your goal. I had an IHI turbo off a ford probe that had pretty much instant spool times with no intercooler, however it choked the engine when really trying to wind it out, but with the 6 you dont have to get it up past 5 grand to make your power, and the nice low rpm torque would do you pretty good.

 

[XPC66]

You know, a turbo has a habit of increasing volumetric efficiency. With increased volumetric efficiency fuel consumption rate tends to drop, because there are less losses (reciprocating, friction, etc).

So if you are not tempted to plant the foot, a turbo which spools early and still provides unchoked delivery at peak rpms should return some economies, even though you will need to make the AFR lower to keep the exhaust valves from burning.

 

[XFlow_Fairlane]

while it was EFI and had a 5 speed but weighed more.

my 2.3L turbo coupe was making about 170hp I would guess and still getting 25-27 mpg.

with the increased power/torque from a turbo a numerically lower gear can be ran (I have a 3.50 rear and a 4cyl T5 and first is so useless for me other than parking lots) plan on a goal of 200hp at the wheels which should be doable with 8psi and a mildly built 200 (port cleanup, a little cam, rockers, ignition)

my best advice is if you are planning on a carb setup look into a holley 350 setup. get it done and running (you can do most of the boost mods then to the carb like the float) get it running and tuned on that then get a decent ignition lined out on it. do all the little things you need to SUPPORT a turbo and increased power first.

 

[rommaster2]

man the more i read the responses and the more i drive this car the more i'm wanting to get a turbo going for it. Of course there are a few things to get done first those definetly being my 3.03 installed and 5 lugs front (disc) and back (v8 rear axle) then what turbo fairlane suggested (at the very least a 2 barrel, as i'd hate to go lean and burn up my valves).

Damn though, this falcons pretty quick from stoplight to stoplight already (well for stock), with a turbo it would be well just insane.

Thanks for all the info, now to begin researching prices for parts to make a price plan, and wait for the school year to begin so i have a rack and whole garage to use. Now if only i can get them to let me use the smog dyno

 

[XPC66]

Put a request out there for a knowledgable member to size the turbo for you.

Ignore the "Joe Bloggs had this setup, Jane Doe had that setup and it was wicked, held the land speed record, ..." or "get a TD03/T4 hi-flow hybrid" or "You should get a copy of Stumpy Smith's 10,000 page abridged book, 'The Origins of Mankind Predicated on Turbocharger Basics Using Hyper Kinematic Transform Theorems' .

 

[Lazy JW]

... With increased volumetric efficiency fuel consumption rate tends to drop, because there are less losses (reciprocating, friction, etc)...

That is, of course true in theory. The challenge is keeping the thing from melting down under boost, so air/fuel ratios tend to be run a bit richer. All the info I have seen shows BSFC numbers being slightly worse on turbocharged engines. It would require a really skookum fuel management system to maintain stoichiometric under boost with no meltdown. Not that it can't be done, I hope someone can prove me wrong.
Joe

 

[XPC66]

Yes of course things run richer to keep the engine cool. Stoich is hardly ever a condition anyone with best power in mind would consider....... AFR12.7 (CO5%) or thereabouts is usually best power and minimum for cooling. I tend to run around the AFR11s for turbo engines in full flight, although I'm very much aware that there's a point where the engine powere transfer becomes too inefficient from overfueling and the risk of stress fractures increases from things heating up again.

Hard limts for turbocharged engines are:

Turbine speed
EGT
Ignition
Knock/det
Cylinder pressure

 

[Lazy JW]

...even though you will need to make the AFR lower to keep the exhaust valves from burning.

Reckon I'm confused as to how burning more fuel makes for better economy

 

[XPC66]

You familiar with the pyramid of combustion?

An AFR lower than ~12.7 just means you have more fuel than req'd, but the oxygen content stays the same. Combustion is just oxidisation, so once you use up all those O2 molecules you are left with a load of uncombusted fuel, which just happens to lower the gas temp because in a pressure environment those uncombusted mols want to superheat as per the ideal gas laws.

 

[wallaka]

I think he's questioning the (misunderstood) statement that putting more fuel in directly uses less fuel. I think you and he were talking about different things.

There shouldn't be many ill effects when using a light foot. The VE is much improved, and torque output is as well. This means for a given rate of accelleration, less throttle can be used, so overall a streetable, mildly turbocharged car will get better or similar mileage if driving habits stay the same. It will easily get much better mileage than a naturally aspirated engine of the same output.

Most driving is not at full throttle, so the most egregious fuel richening will never be seen. At cruise, turbocharged engines use hardly any more fuel than their N/A counterparts, due to rising-rate fuel regulators and the well-programmed EFI counterparts. Since there isn't much of a load, the turbocharger isn't spooled up and is just putting enough air out to get by.

The temptation, of course, is to bury the throttle. This will understandably make the fuel economy worse.

 

[XPC66]

I was in a rush out the door. Yeah the BMEP is higher and the expansion pressure gradient much less peaky, so the burn efficiency exceeds that of an NA for the same torque. Much smoother forces on the internals. And as mentioned taller gearing = lower engine revs = less inertial losses. The flip side is when you want that extra power, it's there and the fuel gauge shows it.

 

[Lazy JW]

... are left with a load of uncombusted fuel, which just happens to lower the gas temp ...

Yup. And this improves fuel economy how?

 

[Lazy JW]

... At cruise, turbocharged engines use hardly any more fuel than their N/A counterparts...

This appears to be the "real world" result as reported by reliable observers. Still no sure how anyone can interpret that into "improved fuel economy". Oh well
Joe

 

[XPC66]

... are left with a load of uncombusted fuel, which just happens to lower the gas temp ...

Yup. And this improves fuel economy how?

Well you have already had this answered, but the penny has obviously not dropping. In a nutshell the burn efficiency with a turbo is much better. There is also the benefit of higher impedance exhaust at light load.

Lets say you are running 8 psi and the engine makes 100kW peak. For an equivalent N/A version the peak power would be, say 75kW ; the revs will be about the same. So for equivalent the 75kW the turbo engine doesn't have to rev so high, thus operating closer to the peak torque rpms (which is max bmep = ~ max VE). If you have ever looked at a fuel map you will know that at peak power the VE is pretty poor. So even though a turbo engine may fuel at say AFR11 compared to the AFR12.7, that 15% is more than offset by the increased VE and thus less losses.... the AFR at part load (75kW) will actually be closer to AFR12 so 6% difference.

As a corrollary if you had a big truck, one with a small turbo engine and the other with an equivalent powered N/A engine, the truck with the NA will be heavier, have shorter gearing, etc.

 

[Lazy JW]

Just trying to learn. I have read repeated references on this site and others quoting BSFC numbers around .50 lbs/hp/hour for good, modern NA engines and .55-.60 for boosted engines. No one argued those figures so I took them to be at least approximately correct. This appears to me to give a decided advantage to the NA engine (speaking gasoline fueled).

Anecdotal evidence from drivers of boosted vehicle typically go something like "Turbocharged cars get almost as good fuel economy as their NA counterparts".

I have read of certain aviation gasoline powered piston engines approaching .40 lb/hp/hr but don't know for sure which engine. Might have been the compound type that had the turbo geared to the crankshaft.

I do understand your explanation of Volumetric Efficiency, etc. Not sure how to reconcile this with the conflicting reports/anecdotal evidence to the contrary. Reckon maybe some things work better in the classroom than real life

According to your theory, I should be able to turbocharge the White Ox so as to develop the same power at lower RPM and get better fuel economy with the appropriate gearing. Reckon I can get the hay hauled without melting a piston?
Joe

 

[addo]

That would be interesting, turbo-ing the White Ox.

 

[wallaka]

As I said before, there is more of a temptation and a tendancy to get into the loud pedal when it actually does something. It is probably this that makes fuel consumption go up after a car is turbocharged.

Gotta take the human factor into consideration

 

[rommaster2]

well this conversation has so far been pretty interesting. I'm going pretty much with the theory that when i install a v8 rear end and a 3.03 i will probably end up with taller gears as it is (i'm 90% certain i have a 3.5 rear end right now) so that will help a bit in mileage, well theoretically.

I've gotta get this thing broken in though (almost done), and that 3.03 installed soon though cause i keep getting people who want to race it from stoplight to stoplight.

So far a GMC envoy learned not to mess with it on a stop light run, and some teens in a station wagon got embaressed when jumped off the line ahead of me (they had an automatic, and i didn't know they wanted to race), long story short my falcon caught up with em pretty quick.

Damn though i'm just so worried i'm gonna fry that 2.77. My dad split one in half with a 144 powershifting it when he was my age.

Another question though for you guys to give an opinion on. What sort of methods do you recommend for making the manifold accept it? I know that chrysler guys just splice the manifolds togethor, but i've seen some ways on it here. The two i can think of would be a J-pipe (which i don't fully understand) or a direct mount (looked simple, but wouldn't heat be a problem?)