Building for low revs, part 2: The turbo(s). (long post)

Reading through this makes me sad. I have been following this group of people since it started back on Cliffords website years ago and went through a few different versions/sites. Everyone has always been willing to discuss theory with out getting rude.

Keep us up to date on what you find and don't take the short answers personally. Some people people just operate in short answer mode and don't understand you may want more detail to back up the answers.

I understand what your getting add. The fascination with torque is driven by the fact that torque make you move and HP is just a formula that combines torque with rpm. One of these days, I will get the time and money priotities right so I can build a motor that make the most torque under the curve below 4000 rpm also. In normal day to day driving, you rarely get over 3 k much less 4k so for a daily driver punching up the torque under 4k makes sense. It would be interesting to know just how much faster spool up would be with 2 smaller turbos. Actual numbers would be great if you find some.

My thoughts on this would be to use a very short cam and as high a compression ratio as you could to maximize torque before a turbo kicked in and also provide as much heat/flow into the exhaust which would help the turbo spool up. Size the turbo such that the turbo is really kicking in when the cam starts to "go soft" and is really running out of steam at 4000. it would seem to get you fast spool up to maximize the turbo impact but aslo help with fuel economy when your foot is not in it.

Good luck

Now that's what I'm talking about. Not about what's the most sensible option to the most number of people, but taking a specific idea and running with it to see where the idea goes. I'm not saying I'm definitely going to stick two or three small turbos on the engine. I really wanted to discuss it, though.. and whether there were any possible strengths that could be exploited.


The 250 I'm trying to acquire is from a '76 Comet. I am not quite sure how to read the small six specs page in that regard. My guess was that the 9.2 static CR was for early 250s, and the 8.2 for later smog/economy-minded engines. Is this correct? (and yes, I did see it mentioned many times that static CR was not the only stat to go by) In our discussions about it, a friend and I talked about keeping compression up there, like you said, to help out when off boost. He also said I should stick with the stock cam for something like that. I figured on a truck/RV type cam, but don't have a problem with either.. or a custom grind if there was anything to be gained from it.

While I'm thinking about it, I should mention that I'd be willing to try and stuff a T56 (6-speed) in there behind that built 250, and do some serious gear thrashing to take advantage of the situation.


I try not to take anything too personally unless it has my real and full name on it. Since I rarely give out more than my first name online, it rarely becomes an issue. I'm just so used to the squabbling from every other site I've ever visited that it's easy to switch into tetchy (as the brits would say) mode and fire back without even thinking about it.

9.2 compression was from the 60s. Youon the right track with a short cam duration cam for what it is you want to do. Iwould go with more than stock since you can get cams now with similar duration but with more and faster lift. The short duration leads to short over lap which leads to higher dynamic compression which leads to low rpm torque. The idea would be to use pressure to fill the cylinders when the rpm goes past the pount where the intake tract is the bottleneck.

Don't forget to use thermal coatings on valves, cylinder, chamber, piston top, and exhaust manifold. This will assist in keeping the heat 1. in the chamber for expansion and 2 in the exhaust to help spooling up.

Just commenting to the tune of what I know and have learned.

Twin turbos = Manual tranny
Single = Auto= or no need for Twins

Small Twins will spool faster, but not by much

I'd never run with out an intercooler, but not using one will spool faster. However I strongly suggest water/meth injection to increase power and keep temps down.

DO NOT run it like two inline 3's
Always have a balance pipe on the boost side of things or run a 1-6 intake manifold

Your talking about 2 throttle bodys but a single throttle body will spool faster if the volume of the piping is less. But were talking only a 100rpm or so.
Depending on how talented you are research intake and exhaust manifolds for other I6's for efficient design. Most notably the 2JZ in Toyota Supra's and the RB26 in Nissian Skylines.

The manifolds, especially the exhaust is going to have the single most effect upon spool time (other than the turbo it self). So design is Key. No logs, you want equal length tubes that merge at the turbo flange and at angles that balance flow pressure evenly on the turbine wheel. like a "Good" collector, not at cheap one.

Oh and E-bay crap manifolds break at more than 7 psi. so stay away.

IMHO... your getting good advice from the few people who have Ford Inline six-turbo experience.

What you choose to do with that info is up to you.

I do agree with the advice given.

For a daily driver a intercooler is up to you, you will be limited to about 7lbs boost but your still going to get a noticeable boost in power.

Bort62 is also correct that if your looking for good low end throttle repsonse then you should look at a positive displacement supercharger. Thats one of the superchargers trademarks, neck snapping throttle response.

Under no circumstances, even if I was racing, would I consider running twin turbos. If you get a properly tuned and setup engine with a properly matched turbocharger you will have good low end power with minimum turbo lag but it will probably limit your top end power.

You said you want to still keep teh car as a daily driver then you need to remember the golden rule for daily drivers.

"KEEP IT SIMPLE" The more complicated it is the more maintenance and tuning you will need to do.

Do a turbo cam, properly matched turbo, and either a carb prepped for turbos or a CFI unit with a Megasquirt or the system Mike will sell at Classic Inlines.

I think EFI with the CFI unit will give best power and driveability.

CJ455":3pj0f4cc said:

DO NOT run it like two inline 3's
Always have a balance pipe on the boost side of things or run a 1-6 intake manifold

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Any particular reason why? I'd say it would be very effective with a divorced scroll turbine housing. The V8 and Cummins guys use them to great effect, why not us?

There isn't much room in there, and an equal length header would be very tough. I'd say the gains are minimal at best anyhow. You'll never notice a 50 rpm difference in air production.

Anyhow, sized properly, turbos can have almost the boost response of a Roots blower and still outflow them on the top end.

2.3L guys make plenty of power on a log style exhaust.....eq. length not worth it for the effort on a SIX (thats ALOT of pipping)

best off idle would be to find a small split scroll and have the two "banks" feed it. dump this into whatever intake. I would spend the time to find a proper sized turbo (or at least one witha common flange on it for the "perfect one" later on) and set it up on a decent manifold or J pipe. then get the oil lines sorted out. I ran mine into the pan (welded in a -10 nipple to drain into)

then get some fuel going to it. if you are hard bent on EFI out of the box I would get that up and running first to cut down on the tuning/learning curve.

you have to balance the charge tubing (intake manifold side) so that all cylinders see the same pressure. if you are feeding off twins you need to have a balance tube ot else you will be working th eengine against itself (what if one half the motor is seeing 12 psi and the other 8 psi?)

no one builds the perfect turbo system their first go at it. I don't think ANYONE on here has ran their first combo they built.

Well I am only because I put the car in longterm storage right after I finished the first try at it.

Tommy went through a learning curve (dumped the IHI for a larger turbo.....then blew a trans)

don't even get me started on Linc200

Dan (importkiller) was the same way with constant upgrading and improvment.


the 250 will build all the off idle torque you need. you put a smallish turbo on it and huff and puff and you will have LOTS of torque SOON

The T56 is a poor trans for a 250. they eat ALOT of power compared to a T5 or Tremec. They weigh a TON. they are physicaly huge. I have one sitting in my garage going in my truck in a couple months (350 s10)

I would run the 250 as it with a 2bbl adaptor on it. I would rather melt a piston on a 80K motor learning than a set of $600 forged pistons.

if you are building a road racer type car with a turbo 250 I would run a 3.27 or so gear. a 3.73 will have a usless first gear in a manual trans. my fairlane has 3.50's stock and with the T5 I hate it. would rather have 3.25 gear for the highway driving. You WILL have the torque to make this not a problem.

build a motor for more than 5-7 psi. you will not have alot of exhaust pressure to effiecntly drive the turbine nor will the compressor be in a decent range (you are going to have large volume flow with a low pressure ratio...low on a map and far to the right side)

I would rather plumb for an intercooler and run more boost then not do anything. you will be suprised where an intercooler can be placed and still get air.

megasquirt would be a good way to go. do the 2bbl adaptor on the stock motor and run a 350cfm carb. get it running and kinks worked out. then you can always swap a CFi unit in its place pretty easily (it will require bonnet mods)

Best advice I can give on it though....


Get doing something!!! there are talkers and doers.....I was a talker for over a year....

Please keep all topic images to 800x600 pixels, with a maximum size of 100K

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EEC4 ford dizzy in a 200 (this was a spare block.....has been in the car running)



the new project to turbo:

I will take a shot here but keep in mind I am probably one of the least knowlegable posters on this board.

For running literal twin setups, make sure you pipe it right, from what I remember two of the cylinders exhausts slow eachother down, so if piped into different turbo's you wouldn't have that problem.

Well.. I tried.

Other than the extra compexity of 2 seperate turbos, 2 seperate turbos would be gettin 3 pulses of exhaust versus 6 for a single turbo. This fact may cancel out the increased response due to shorter piping you may beable to get with 2 seperate 3 cylinder turbos.

I seem to recall the diesel dudes running turbos in series, that is, the smaller stock one directly driving the larger after market unit. Seems like cheap grace, but if you just have to run two, that seems the simplest method.

Just wanted to stop in and update things, and thank people for indulging me on this little speculation trip.

I never got that chance to spend most of yesterday reading up on TTF like I said I would.. so I haven't posted there yet to get their input as well.

I've found a guy who would do welding work for me in trade for powdercoating work from time to time, so my current thinking is that if I did this, I'd ask him to help me fabricate a log-style intake for the CI aluminum head. If we did that, I'd go for multi-port injection. (but not sure on if I'd go bank-fire or sequential, if the MS2 box can handle sequential) I'm browsing through Megasquirt's forums right now to see if there's anything about setting up secondary injectors for methanol injection as well.


To hit a few points brought up since my last post:

- On a 4.1L engine, I was thinking a pair of turbos each suited for a 1.6-2.0L engine by itself. Does it matter if those turbos get 3 pulses vs. 6 when they should be getting the right volume of exhaust gases for their size?

- Looking at the firing order of the 6, pairing up the front 3 and the back 3 means the engine will fire front-back-front-back-front-back.. so at least it seems to me the exhaust pulses would be evenly spaced on each side.

- I was thinking of an exhaust that was just big enough to merge three exhaust pipes from the head into a triangle at the turbo mounting without using any radical bends. Not exactly equal length, but not a log either. Not sure if that could even be made to fit.. I need to spend an afternoon taking measurements under the hood, I think.

- Our current thinking on the intake is to do a single log-style for the CI head as mentioned above, but with two throttle bodies. Perhaps a pair of methanol injectors could be added, one behind each throttle body but not mounted in the log itself. I might need to draw a picture of what I'm thinking if this sounds too much like I'm on crack with that description.

- I picked 3.73s because of a spreadsheet I have for inputting gear ratios and tire sizes and such for comparison. Right now I have a C5 and a 2.73 rear end. Whatever transmission I use is going to be an overdrive transmission, (T5, T56, AOD, etc.. but likely stick at this point) and 3.73s with an AOD's (for example) overdrive gear come out to a 2.5:1 final drive ratio.. still numerically lower than what I'm using now.

(if anyone would like the formulas to make their own spreadsheet, I can list them. My spreadsheet takes transmission ratios, possible gear splitter ratios, rear end ratios, and tire size. It outputs a final drive ratio and uses tire size to calculate MPH at three RPM points.. 1000, 4000, and 6000. It could be given more columns to output MPH at every 500 RPM, for example. I could also see if I could make a blank copy and post it somewhere for download)

- While on the subject of gearing, I should point out that this car will hardly ever see Interstate speeds for long periods of time. (70-80 mph) The road layout of our area means I can get from town to town just as easily on US 41, which is 45-55 for most of the time. Going out to I-75 takes me a few miles out of town. Also, I still have my '89 Lincoln Mark VII, which will be tweaked to be a better highway car. Took it to Chicago and back late last year.

- I just did a search for "T5 transmission ratios" and got this site, which lists a T5 (second from bottom) with a 2.95 first gear and a .63 overdrive. Would that be better suited to a 3.73 or 3.55? I'm using a 24.9" tire size.

- I did give some thought to mounting an air-to-water intercooler inside the passenger side fender, as close as I could get it to the turbo(s).. or even two smaller ones, one for each turbo.. but I'm told that an air-to-water is sheer overkill for this application. We even went off on a flight of fancy thinking about using things like another A/C system or multiple Peltier coolers to chill water running to the IC(s).. but that's getting really really out there.


- I should point out that when I say "daily driver", I don't mean I need this for a regular 50 mile per day commute. I work for myself, or will be doing so shortly. I'm setting up a powdercoating business with some help. For now I'll be working out of my home, but eventually I may pick up a rented garage bay about 2-3 miles from home. I want the setup to be reasonably reliable, but it doesn't have to be 5-day-a-week reliable 52 weeks a year. I also have an '85 Ram I can drive on occasion if the Fairmont is down and if the woman has the Mark VII out.. and I even have a 21-speed road bicycle if I absolutely have to get somewhere within 5-6 miles of here. (and there's a LOT of stuff within 5 miles of me.. Wal-Mart, Target, Sam's Club, my bank, a major mall, Circuit City, etc.) I'm up to riding that 10+ miles a day for getting in shape. In other words, I have options if this car should be down for awhile because it got fussy with me.


Thanks again for indulging me on this speculative stuff.


EDIT: I would prefer to run them in parallel, if I did this.

Running them in parallel is the way to go. Sequential (in the sense of one's output going to the input of another) is only for very high boost applications (over 45 psi). Sequential in the other sense, of one being used for low boost, then switching over to a bigger one when the rpms rise, ala the RX-7, is another can of worms.

Think about this, though: The 1.5-6L engines that you mention put out more exhaust volume and pressure than a 3 cylinder of the same size. This is because there are more power pulses per revolution and because they generally rev to the moon (which you are not going to do). You might look into the specs of the turbos used on the 3-cylinder Chevy Sprints/Geo Metros. You will find that they are quite small, but probably the best match for what you want to do.

Hi,

I built a 250 based on the same idea - produce heaps of torque and keep the revs low. The motor was slaped together 5 years ago and is still going strong.
I actually drove my car to the race trak over 50klm away, ran a 10.8 sec 1/4 mile (without reving it over 4900rpm) and drove it home. The motor has done over 100 drag passes without any failure (Apart from snapping the input shaft on the auto - too much torque??) and is driven on the street almost every weekend.
My combination is C4 automatic with 2600stall, T04P with 1.0 exhaust, 9 inch diff with 3:1 ratio, EFI, Multicoil, Intercooled blah blah...
Boost starts at about 1900rpm and is over 10psi by 2500 rpm. Reducing the exhaust housing size to .8 would improve the low end response, but with the 2600 stall in the auto this is not a problem anyway.
All the valve gear in the motor are factory standard - pressed rockers.
A big influence on boost response is in the exhaust outlet from the turbo itself and any restrictions in the muflers. Get a good diameter dump pipe connected straight out the back of the turbo.
Another thing to consider is the the exhaust gas exiting the turbo is spinning at a very high velosity and sticking to the outide wall of the dump pipe - how can you convert the spin into forward motion quickly to get the gasses out? Changing the diameter of the dump pipe only slows the gas down. I am looking at doing some experiments with adjustable deflector flaps inside the dump pipe to see if any gains can be made.
Twin turbo = less lag? Every twin turbo vehicle I have driven has lag and lots of it. Has anyone driven a twin turbo skyline GT-R? This is the king of lag with power only starting to sing after 4000rpm! Supras, Soarers, 300zx all drive like turbo cars with lag. IMO - Even if the combined rotating mass of the two smaller turbos is less than a big single, you have less pulse energy reaching the turbines so your back to where you started.
The best factory turbo car I have owned was the Ford F6 Typhoon 4.0l Single turbo. Power 270kw and 550nm from 2000 - 4000 rpm. In complete standard trim (approx 1700kg+), I ran a 13.2 1/4 mile with a 6 speed manual.

Anyway, 250's are the ultimate at producing massive torque at low revs!

Good luck with your project.

g

I was told by an old turbo hot rodder, "Turbo lag is really fuel lag"
Think port injection.

Well, turbo lag is volume flow lag, and injecting more fuel will result in more volume out the exhaust, even if it doesn't all combust. (it will boil and expand rapidly from the heat of combustion).

You could accomplish much of the same, I imagine, with a bigger acc pump shot.

This guy is doing stuff that may give you some ideas:
http://www.cletusracin.com/index.php?page=page-2

Thanks for keeping the thread going. I spent some time reading that last link this morning.. good stuff.

A question, since I honestly don't know: Those stock twin-turbo setups that lagged badly.. were those two small turbos in parallel like I'm thinking, or were they one big/one small in series, (engine -> big turbo -> small turbo -> exhaust) or switched as was described above? (small turbo at low revs, large turbo at high revs)

Another question while I'm thinking about it: let's say I went with two small Sprint turbos.. how would it change things to go to a log-type exhaust manifold with those on it vs. the twin 3-into-1s? You all keep talking about exhaust pulses and such. Wouldn't that give the turbos the same volume of exhaust but with six pulses vs. three, and how would that change how they respond?



Just so you know this is still on the theoretical side, I'm currently leaning towards a single turbo with intercooler setup. I'd just like to exhaust (BAD pun) this line of thinking before then. Not shoot it down.. just see if anything good could be done with it.



Regarding that, I have another off-the-wall theoretical type question: Is there a reasonable method of calculating just how much heat an intercooler would be dissipating?

The reason I ask is that I was looking at air-to-water intercoolers. Yes, I've heard that they're sheer overkill for the street.. but I kinda like the thought of tucking one under my right front quarter panel and just running water tubing vs. a bunch of air conduit all around the front of the car.

I also learned in my days of personal computer overclocking about Peltier coolers or TECs. (do you have one of those coolers you plug into a cigarette lighter, that can also heat items in the cooler? You probably have a Peltier cooler) I had some oddball ideas about cooling the water from the IC, and then chilling it from there with one or more (probably multiple) Peltiers. Going by the first article I could find on a quick search just now, an average Peltier can move 80 watts of heat across it at 16v/8.5 amps. Could a noticeable benefit be gained from using a couple of these? (note: I will be going to a 3G/130A alt. if possible.. I've done two 3G conversions already on other cars) Or is that just too much power being wasted trying to gain a few more degrees of cooling?


Yeah, I'm probably not all there when I think of stuff like this. I was even thinking about the possibility of running rows of backwards-facing louvers up the top of each quarter panel (one row on each) to try to pull air through an IC.. although I think that would definitely damage the sleeper look I'm going for. It's bad enough that I want to do a custom hood and black out or remove most of the chrome..

LincolnMarkVII":2jva92ju said:

Yeah, I'm probably not all there when I think of stuff like this. I was even thinking about the possibility of running rows of backwards-facing louvers up the top of each quarter panel (one row on each) to try to pull air through an IC.. although I think that would definitely damage the sleeper look I'm going for. It's bad enough that I want to do a custom hood and black out or remove most of the chrome..

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How about a Shaker with the intercooler under it - that would look cool and keep the plumbing short.

As for your ideas of using refrigeration systems to cool the incoming air to make more power, you need to remember the basic concept that energy cannot be created or destroyed, it can only be transfered and, by and large, whenever you transfer energy using a mechanical system, losses will occur...

I couldn't see the Peltier thing being cost/power efficient. It'd be interesting, but perhaps only to gain a slight "edge" in competitive applications. Rejecting the heat on the hot side, would be one concern.

Yes, you can calculate exactly how much heat the IC is dumping.