I have seen several Eaton M90s floating around on ebay for a decent price. They were good for 12 psi stock on the thunderbird 3.8. I am still in the research phase of how I want to boost my FE. The fab work would be the easy part for me but will this M90 choke my 352 down or will it make decent power in the 3500 RPM and down range? I would make a pully to limit the boost to 5 or 6 psi just so I don't pretzel my internals. I am looking to be able to get a little silly on the street and do an occasional pass or two. I could do a blow through carb setup i guess. What about a draw through? Is it possible to flow air and fuel throught the screws without jacking something up? Any ideas boost Gurus?

 

Draw through, and I would guess given your increased displacment that you would be getting your target boost without having to overspin the SC.

 

Draw through would be the easier setup given the construction and intake location of the M90. I could build a liquid intercooler since the air to air would be dangerous with the air fuel mix. So given that I have a larger dispalcement, the M90 would not produce 12psi with a stock pulley?

 

Monkey math to the rescue.

Donor CID x Donor Redline = destination CID x destination redline x QTY.

231 cid (3.8L) x 6000 = 390 cid x 5000 x QTY

1386000 = 1950000 x QTY

1386000/1950000 = QTY

0.710769 = QTY

This means the Eaton M90 off a 3.8L is about 30% undersized for your 390 if you run a 5000 rpm redline.

So, you'd need 1.3 of them to achieve the same boost on the 390. Obviously less RPMs on the 390 require less CFMs and you can do the math again to arrive at a lower figure, or up it if your redline is higher.

This is not precision mathematics as there are many, many other factors, but it's good enough for rough ballparking to determine how many donor turbos/superchargers you need to achieve the same boost on a different engine.

 

Thanks for the cool equation Frederic. Best I can tell the Super Coupe had a 5000 redline so that makes a .65 when compared to my 352 at 5000 rpm. Ouch, that may be too small. I imagine I could spin the M90 faster to make up for it though.

 

I think the SC redline is higher, but I'm no expert. Maybe google can offer you some help there. My monkey math doesn't take into consideration the need to change the pulley ratios if mounted on a different engine with a lower, or higher redline so this is where the math starts to become more intricate - but the formula I gave you as least takes displacement and redline (meaning CFM) into consideration to get you started.

While the eatons can take some overspeeding, their lifespan is reduced by doing so, and I would instead recommend using two of them, and pulleying them differently. With two of them being "yanked" on the same belt that opens a whole new can of worms, however it can be done if there is a tensioner pulley between the two eaton pulleys, and mounted much below the imaginary line between the two eatons, so that more of the belts wrap around the pulleys - that is the key with those things - pulley wrapping and maximizing this as much as possible since the pulleys, like your alternator pulley, are very tiny (and why the alternator is often on the outside of the engine, almost fully wrapped by the belt).

I know someone who slapped a pair of M90's on a well built chevy 350 with great results - boost wise. Since he skipped the tensioner fabrication neither eaton had enough "belt bite" to handle the higher boost levels and this resulted in disintegrating serpentine belts, leaving a thick, sooty, rubbery coating on everything under the hood and the need to replace serpentine belts every 200 miles or something ridiculous like that. He and I had long discussion about tensioners but he had enough fabrication I guess.

This is one of the advantages of turbocharging - no belts. The disadvantage of course is having exhaust manifolds made, though I don't consider that any more work than fabricating an intake to host a pair of M90's. If it's one thing it's another.

Dual "anything" also makes cooling the intake charge more complicated to fabricate, as most stock intercoolers have one inlet and one outlet. One could of course get a pair of smaller intercoolers and mount one in series with each supercharger/turbocharger - that's certainly been done before. Regardless, it's one thing of many that you'll have to ponder regardless what you try to put together.

I have seen 390 FE supercharger intakes before, though not recently. They used to use the 8-71 GMC/Roots blower if I'm not mistaken... but please don't quote me.

 

Ahh, decisions and math. Thanks again Frederic for you input and knowledge. If I were to have to use to M90s I might as well do a single turbo setup. I am just trying to come up with a cheap means of putting 5-6 psi into my 352. I was hoping to find a stock application turbo or supercharger that I could adapt to my application. I am well versed at fabrication as I use to own a fab shop and still build bikes and cars on my days off from the F.D. I am just leary to take the reliablity away from my truck since I drive it mostly everyday. I don't want to spend months of tuning. Draw through turbo or supercharger seems like it would reduce the major tuning issues.

Blue Thunder makes a blower intake but anything they make is out of my current budget.

 

352cid with a pair of T3's (dodge Daytona turbos) is almost perfectly sized... You can make your own manifolds out of black pipe like I did...

http://frederic.woodbridgedata.com/i...turbomanifolds

 

That is a good idea Frederic. I appreciate your ingenuity with your manifolds. I am well versed with making custom headers so that should be the fun part. Do you have any idea what the specs on the Daytona turbos are? I will be hitting the Pick a Parts soon.

 

The method I used to make the black pipe manifolds as you can see was very basic - cutting 'wedges" out of black pipe and welding them together to make crude bends. Certainly not "optimal" but reasonably easy to construct, and by far cheaper than purchasing weld-els of mild or stainless. Since you can fabricate you can make something more professional/tidy with smoother bends for better flow. I used black pipe simply because it's available, cheap, common as dirt, and did I say cheap? Also the thick wall means it will last for many years and survive lots of abuse unlike such things made of ordinary thin-wall exhaust tubing. This is where stainless really shines, no pun intended - thinner wall yet still strong.

Offhand, no I don't have any info handy, but I used a pair of them for a 4800 redline 451cid mopar stroker in a prior project I no longer have. I maxed them out right around 4500 which was fine considering that I rarely, if ever, tried to hit the 4800 redline that was simply "decided" upon thus allowing me to use junkyard components for the build.

RPM's still kill engines faster than boost does

 

Just how hard to tune right is the blow through carb? I have read a pretty thorough process to setup the holley double pumpers on a turbo mustang site. The modifications sound easy enough but the actual tuning is what concerns me. Any insight?

 

I'm really not a carb guy and have never had any real luck with them on anything - modified or not - except for a twin-turbo blow-through I put together using a pair of predator carbs - that worked exceptionally well as predators are self-adjusting within the range they are designed for.

 

Don't forget that a difference between the lower pulley diameters between the 3.8 and 352 will also make a difference.

 

I was thinking about that Herman. The M90 is good up to 14k rpm. I am not sure what RPM it spun at on the Super Coupe at redline. I may just try it if I can find one cheap enough.

 

I *believe* Ford kept the M90's below 12.5K RPM.