Yeah, the one thing I worry about with a turbo on a flathead is the lag, and it just isn't a high-rpm motor, so the instant boost of a supercharger seems like it would be better for overall street use on a flatmotor. But, I've read that you can help the turbo lag problem by proper sizing of the turbos, etc.

Unless this M-90 supercharger plan works out well, the turbo option does seem to be cheaper than most supercharger setups.

Gary

 

Something like that, you only need equal pressure in the throat and fuel bowls.

 

This one I can't refuse. Let's tak a theoretical flathead, say a 239 just for fun. Let's a put one of those little nifty superchargers on it, the one captchas is so in love with. Doesn't matter what size it is, how about a 4-71 for this educational post? Alrighty then, we are going to put this supercharged fattie on the road. Let's say we want 10psi, and say we are revving 5000rpm. Okay then, you with me so far 8flat, just something to look at. In order to get to that 10psi at 5000, I have to gear my supercharger accordingly, that means I won't get 10 psi until 5000. So what does that make, maybe 5 psi at 2500? Maybe 2 psi at 1500? I doubt your'e going to see any positive pressure at 1000rpm, and if your idle is say 700, how is 300 plus rpm going to be instant boost. You have to wait that long to get positive pressure, doesn't sound very instant to me. Same goes for a centrigul, but they are tons worse.

On the other hand, let's take that same motor, and we can put a 'lil turbo on it. Doens't matter if you put 1 or 2 or 3 or 4 or 5 or 6, depends on the sizing and setup. If I want 10psi on a turbo, I don't have to wait until redline to get it, I can be huffin' 10 psi before 2500rpm and hold it as high as I wanna rev. There is a such thing as turbo lag, the effects are so minimal that you would probably never notice it.

But hey, the instant boost of a superchaeger might be better.... lol, sure thing.

 

And why is that?

 

Well, the reference point I'm using is my work car, a pontiac Bonneville SSEi, with the 3.8 V6 (equates to ~230CID) with an Eaton M-90. This car hits 7 pounds of boost very quickly and at fairly low rpms, I'm not sure of the RPM but I go can try it and get back to you. All the turbo-vehicles I've driven or ridden in were noticeably slower in both the time it takes to reach boost, and the RPM at which the boost came on: Dodge Shadow Shelby, Chrysler Lebaron, Mistubishi Eclipse, Nissan 300ZX, volkswagon bug, diesel pickups (all 3 makes), Cougar RX-7 4cyl, Ford Turbo-coupe 4cyl, etc.

One thing I will say about turbos, there is less parasitic hp loss right? Volumetric efficiency is supposedly better from what I've read. Both can be intercooled, I found a place that makes neat little liquid cooled intercoolers that bolt underneath an M-90.

So, you admitted there is turbo lag, and the cost difference between an M-90 and turbos isn't much, why are you so against superchargers? Do you sell them or something? Did you have a roots blower explode and scatter shrapnel into your gas-pedal foot? I don't have an agenda either way, I think either solution is pretty cool, and I'm not going to get dragged into an argument about the subject, I'm just trying to learn. I would argue the EFI vs carb issue, but let's ignore that one for now....

naturally aspirated for now,
Gary

 

I can get turbos for damn cheap, mostly in the jy. Superchargers are nice, very simple, made just for the "bolt on" type of guy. I don't have an agenda, I don't even care that much, but when people go off and bad mouth something they have no experience with, seems they need a little education. Turbo deisels will always have a ton of lag, that's just how the deisel is. Turbo's make a ton more torque, than a supercharger. There is a slight loss in power due to the backpressure in the exhaust, but nothing like what a supercharger will eat up.

 

turbo on a flatie. it would be fun to see how it works.i'm just trying to bend my brain back to about 1962 the super charger we used spun up the power fast. and made the old low rpm motor run a lot better.
i'll try and find my old photos and see the name on the blower kit but i think it came of a 3-51 dd diesel as it was not very big.

 

Hope you find those photos and post them. I love to see any pictures of souped up flatties especially those that were done that far back.

 

Those photos would be sweet, I'm starting to collect the parts to turbo a flattie, just don't have anything to put it in yet.

 

i'm going try right after the holiday. hundreds of boxes of 35mms slides, just got to find a box or more or dated 196?. and this old fart don't move to fast any more but this brain and pair of hands have built a lot of old motors. and i don't mind shareing whats in it. and for sure i don't want to take it all with me.

 

No pics yet?

 

Awesome, happy holidays and can't wait to see the pics!

 

It is clear from your example you don't understand the dynamics of either system.

The S/C is geared so that it puts out a certain amount of air relative to engine speed. That relationship is the same whether you are at idle or at wide-open-throttle. Specifically, it is geared to provide an excess amount of air so that the design pressure is available any time you mash the throttle, at any speed. At some point, something in the intake system will limit the amount of air that can be pushed into the engine (either the intake tract, the S/C, carbs, or the intake valves).

With a turbo, by definition you have to already be burning enough gas to have enough waste energy available in the exhaust to spin the compressor. That's why there is always lag on a turbo (always). If you size the turbo to produce 10 psi at 2500 RPM, it will choke the engine's exhaust side at higher engine speeds/higher outputs; in other words, it becomes the limiting factor on higher output. If you size it for 10 psi at 7,000 RPM, it's going to be a dog below (probably) 4,000 RPM. There is a very definite trade-off on the sweet spot for a turbo, it all has to do with the area ratios within the turbine and compressor sections.

Turbo'ing a flathead Ford for the street is not likely to be successful because of the long internal exhaust passages and the low RPM's they function at. They transfer a lot of heat (= energy) to the water and the long passages have the effect of moving the turbo almost another foot away from the engine, and the three ports are widely spaced. All these add up to a sure-fire formula for lag. Add to this the problems of a turbo without EFI and you can see why people have been supercharging flatties for 50+ years.

 

I'm not here to bash anybody, but you have no idea what you are talking about. I can take a turbo and make 10psi from a little over 2000rpm all the way past 7000rpm. Been there done that.

Have you ever ran a remote mount turbo system? With the turbo by the rear end of a car? They run, and run hard, with very little lag at all. No more lag than a standard front mount turbo system. Just my personal expeirence.

 

"I'm not here to bash anybody, but you have no idea what you are talking about. I can take a turbo and make 10psi from a little over 2000rpm all the way past 7000rpm. Been there done that." -- on what, a DOHC 4-cylinder? Nothing could be easier. They are a completely different animal.


Let's confine this to a "real" flathead. They produce usable power from 1,200 RPM to at most 5,000 RPM. Anything above that, the crank is not going to take it (5,000 is unusual for any length of time on the street).
The difference between a flathead and any OHV or OHC engine is that there is a very long exhaust pipe within the block, surrounded by cooling water. A turbo operates on heat. The best turbo designs have the turbo inlet housing right on the exhaust manifold, up close to the block. The exhaust valves are maybe 3-4" from the manifold. On a flathead the valves are almost 16" from the edge of the block. Turbos also depend on a free-flowing exhaust, which the flathead doesn't have.

Yeh, I'm sure you can get a turbo sized to work properly in the RPM range we're talking about, and it would have to be remote mounted (unless you're talking about two of them, it would be better to put it up front, that's where the exhaust is and the two banks could be tied together easier there). So to summarize, you've got relatively cool exhaust, travelling thru an exhaust tract with double or triple the volume of any OHV or OHC engine, to a turbo that's mounted a fair distance away from both banks. Under steady state conditions, I'm sure it would work dandy, but on the street I doubt you'd ever know it's there. By the time it spooled up you'd be reaching for the next gear.

Just for reference, what style flatty are you running? (59AB or 8BA or are you talking about a 6-banger??)