MG Sports Cars

So many questions and such a little keyboard!

Cooling performance of the Roadmaster is quite sterling. I believe we used a 195 thermostat. The fan is a late model Camaro dual unit and I put the same one in my car. The controller is the remote bulb type and after Mike Moor and I routed the bulb inside the top radiator hose the combination became very effective, though before that it had a bit too much hysteresis. I found a Saab 2 stage switch that I used in Edith's TR7 that I like a lot. There should be a lot of detail in the Power Tour thread, but that big radiator really does the job.

I'm expecting boost to come in around 8 psi but on my last build I was expecting around 10 and got 16+ so there is no real way to know until it's running. I hope it won't be necessary to change the top pulley but much more than 10 and I think I may have to. But I have about a 40% increase in displacement with only a 20% increase in blower size so it may be fine. If I were a little better mathematician i could probably ballpark it pretty close. Don't know yet what the curve will look like either. On the last one it came in just off idle and built really fast. I'm not expecting that this time. For one thing the heads are bigger so there will be less restriction'and the cam is bigger too. For charge cooling I am running the air through a 2-3/4" thick X 8" X 13" liquid intercooler core. But less boost means less heat to take away. In an odd sort of way the restrictive heads of the 215 caused higher manifold pressure which made more heat which made the intercooler more effective, then the nozzle effect at the valve cooled the charge as it entered the cylinder. Although peak power mayhave been less the boost came in early and strong. This one will be different but how much is hard to say.

Jim

Jim, roots blowers create more heat, specially at low rpm. If a by pass valve could be install it would help on the cooling at low rpm.
Jim if you figure out to install a by pass on the root let me know. I am not working on mine, but I will soon.

Jim S. has a centrifugal, centrifugal chargers do not create as much heat as the roots. Actually the centrifugal runs a bit cooler than the roots at lower rpm. The centrifugal will create heat in the upper rpm range when it is making max boost, but is also getting for fuel as needed and fuel cools and there is also alcohol spray available.
Looking at Jim's S. Super Charge B ( Lic plate JSSCB) radiator and wide engine bay, I do not think he will have any cooling problems.

My old 1996 LT-4 Vette with a Vortech super charger never got hot and no mods were made to the cooling system. C-4 Vettes used low pressure air from under the car to cool the radiator. I drove from Flagstaff to Camarillo with outside temps of 109 degrees and the Vette got to 245 degrees max was 260 for quite a few miles. Kept my eyes on the gauge until it got back to normal 210 degrees.

Bill

I bought a book several years ago by Joseph Katz called Race Car Aerodynamics and he has a section in it called Internal Flow where he talks about cooling. The section is several pages long but here are a few of the high points.

Of several air exit strategies he showed the one that provided the best Cd was taking the entire radiator exhaust out through the hood similar to the GT40 Ford, the Cobra Daytona Coupe and Corvette CSR race cars. The 2nd best was exiting the air out through the wheel wells and the worst was just dumping it into the engine compartment.

A smoothly expanding and leak free diffuser from the air intake opening to the core of the radiator will significantly increase the static pressure at the face of the radiator. The pressure drops like a rock after passing through the core so it essential to find a low pressure area to dump the air into to so pressure does not build behind the core and reduce flow. Fans help here since the pressure effect only comes with forward velocity and nothing is happening at rest.

It also discusses very small openings as found on aircraft and while they can make significant reductions in drag and high static pressure increases at the core they are optimized for a given speed. If you exceed the design speed, there is boundary layer separation for air passing over the body around the opening causing increased drag. If you are going slower than the design speed there is internal flow separation causing reduced cooling efficiency (probably not what you want in a street driven car).

So after reading that I may try something like the diagram below. The dashed lines are aluminum sheets that span the full width of the core and would be contained on the ends with vertical aluminum pieces creating two ducts into the radiator core. The increase in area from the front of the duct to the face of the core should provide some increase in static pressure at the core while the inlet area should be sufficient to satisfy the flow requirements over the full range of speeds of the car.



My sense is that designing for this effect in the radiator inlet is similar to what you find in exhaust tuning - you can have a lower increase in power over a broader rpm range or a higher increase but the engine then becomes very "peaky" over a narrow rpm band.

Jim B

Good news abot how well the Roadmaster cools. I have one of the Camaro dual fan setups and it fits the core perfectly but the air duct to the filter interfers with the drivers side fan and I can't use it. The Taurus fan pulls about the same amount of air as the two 12" fans in the Camaro unit so I should be OK.

The Vortech kit for the C4 Vette LT1/4 came with a pulley that gave about 8 psi boost (correct me if I'm wrong Bill) and the stock compression was 10.4:1 (10.8:1 for the LT4). My engine has higher compression due to decking the block to get a quench just under .040" but I also have a more agressive cam that will reduce boost somewhat, I'm guessing around 6-6.5 psi from what I have read. I should be ok on detonation with 12-15 gph of water/meth injection under boost.

Bill

I didn't know you had an LT4 Vette. Am I correct that the Vortech kit produced about 8 psi? Did you have any issues with detonation? Did you have to use water/meth injection?

I know that the C4's had issues with cooling at speed for the reasons you mentioned. How did it behave in traffic with the fan on? Were you running the stock thermostat and fan turn on settings?

Jim S., I used the standard MGB cowl vents ,(2) and had them sectioned shorter, on their length, to 12" oal. ? They will go behind front wheel wells, as vents and still keep the MGB look. Cheers, roverman.

Art

I'm not going to do anything until the car is drivable and I can gather some data. If it looks like I have a problem to solve I'll start looking at how and where to put some vents.

That is probably the best approach. I've been thinking about this though. You remember the 50's era chevy trucks with the cowl vent? You moved a lever under the dash and it raised a flush fit panel to let air in the cabin and it was very effective. The hinge was down below the surface so that it was concealed. I think you could do something very similar using carbon fiber to accurately copy the curve of the hood and light enough that the pressure differential would lift it. Normally it would lay flush and with enough attention to fit all you would have is a narrow line around it to give it away. Most people might never even see it, but at speed it would lift to vent pressure.

Jim, on my engine I really am not in pursuit of horsepower, appearances notwithstanding. I want good reliable power above 300 hp, a flat torque curve, and fuel efficiency. Oh, and here's the zinger: I want to be able to hit 7 grand on occasion. Not power to 7 grand mind you, just the capability of getting there without falling off the cliff. Your build will undoubtedly produce substantially more power, but I had plenty of power with the last engine. What I did not have was reliability and efficiency, to be honest the thing was a time bomb. It was all I could do to keep it together. I think this engine will fix all that so I can just play and not worry about it. If I get lucky the boost will be at 8 or less and I think it will be OK. I thought about the methanol but I'd be constantly filling that tank and hey, isn't it just too cool to be able to say, "Blown, injected, AND intercooled!" ? So I went that route and here' the absolute gas, I'm using gas as the intercooler liquid! Then cool it and send it back to the tank.

We all dreamed as teenagers about the car we would like to have one day, but only a very few of us get to actually make that happen. I really am a lucky guy.

Jim

Jim, I think that if you want to keep the hood with an original look then I'm sure that your plan will give you result. Here's a belly pan from Moss Motor where it seems to have louvers cut-out in it. I would imagine that it can possibly extract or help with the radiator flow coming through:

[ecommerce.mossmotors.com]

Also, as far as the radiator sizing mentioned by Jim Blackwood, he is right on maxing out the surface area but, lots of people have to rely on adding thickness but it only increases the cooling power by around 25%. Here's an interesting link for anyone interested on the subject:

[www.xtrememotorworks.com]

To be honest, I have a little concern with my Ford 331 stroker being adequately cooled but I have an unbelievable aluminum shroud with a built-in electric fan that will hold a credit card on all four front corners when activated; time will tell!

Jim

Sadly, I do remember the truck cowl vents of the 50's - when they were new! Having a lightweight flap hinged and balanced so underhood pressure would open it would work really slick. Have to wait and see what the testing shows.

I can't imagine your engine won't produce AT LEAST 1 hp/ cu in especially if you have cam enough to have some power left at 7k and you are running 6-8 psi boost. I needed a supercharger on my car like a hole in the head but Lloyd Faust made me a deal I couldn't refuse. So now I have an engine built to be naturally aspirated with almost 11:1 compression and stock pistons that I'm going to be adding boost to. Why? Same reason as you - how cool is it to pop the hood and not only have an LT1 sitting there but a blower as well. The whine driving it around has to be worth something too. The engine N/A is probably over 400 hp and Vortech claims 30% - 50% increase - let's say it's only 20% that's 480 hp in a 2,300 lb car. I think the pistons will live with reduced boost (~5-6 psi) and water injection but if not I already have forged dish pistons picked out that weigh the same as stockers that will drop the compression to 10.2:1. I'm hoping to get close to 30 mpg highway with the O.D. 6th gear.

I'm a hot rod guy at the core. I went to the first Winternationals 3 days after my 16th birthday and I was at Lions drag strip many a Saturday night. Somehow I went astray and got an MGB when I was in college but the hot rodder was never quite purged from the system.

Jim S., I ran a 1946 Dodge business coupe,(single bench seat), at Lions, in 1966. You'll notice I didn't say "raced", I'm not sure a 20+ sec. et., would be racing/lol. Onward, roverman.

Very interesting stuff here, I've been following along and have come to the conclusion that 1: I need to make the plenum and use my cowl hood for what it was intended for, cool air to carb, block off the cowl vent.
2: Get some ventilation into the inner wings to get some better flow characteristics because when on the x-way it still likes to get around 210°but once back on surface streets and stop and go traffic it stays at 190-195°. Completely bass ackwards from what I dealt with before with the smaller radiator and the foreward facing hood scoop, it would run 180° on x-way and climb like a homesick angel in traffic.
Thougts?

With the water injection I expect you will be OK. But I want a ride!

Bill asked about the bypass valve and yes indeed, this blower has one built in. It is an Eaton M-112 from a Ford Lightning truck. So until vacuum drops off the blower is basically freewheeling. Apparently that is a good thing.

I do not really know what power levels the 112 will support. Plus the pulley is bigger than the one that was on my M-90. That should also help some. In the end the egt should tell the tale.

Jim did you say you are going to drive the car in primer for awhile? That would give you a good chance to add the vent if you decide it would help.

Jim

Climbs like a homesick angel - I love that expression. I just looked at your car and my guess on what's happening is that you have air coming in over the top of your slam panel and radiator shroud and it is pressurizing the engine compartment. You did a nice job with the shroud funneling the air into the radiator and the fan is shrouded well on the back side but when you get moving the air flows freely over the top of the radiator into the engine compartment raising the pressure and restricting the airflow through the radiator. At rest the fan is drawing sufficient air through the radiator to keep it cool and there is sufficient room to exhaust the air out of the engine compartment but in motion the air cannot escape quickly enough due to the extra volume flowing over the top. The solution is to make a baffle that seals the area in front of the radiator from the area behind that seals against the underside of the hood. Every molecule of air that enters the grille has to pass through the radiator, not around it.

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"But I want a ride! "

You shall have one if you're coming to the 2014 meet in Colorado Springs.

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"Jim did you say you are going to drive the car in primer for awhile? That would give you a good chance to add the vent if you decide it would help."

Exactly why I'm not painting it right away. I know the car will need a lot of sorting out in a lot of areas.

Hmm, good eye mate! I will have to get busy and do that, Thanks!

John

Make sure you check the lower portion of the radiator as well so that all the air entering the vent holes in the valence is directed through the radiator also. You want to block off any passage from the front of the car that allows air into the engine compartment without passing through the radiator

Jim S. yes the LT 4 was a brute in lower end torque and with the SC was a hand full. You are correct the 7-8 psi if measured at the exit of the SC, if measured at the exit of the inter cooler the psi drops about 1-1.5 psi and if measured behind the throttle body it would read 0-1 at rpm 5000 if would read 4-5. that is the norm. That been said timing was not an issue mainly due to the GM knock sensor which are the best in the world, good enough for Ferrari. Vortech did the calibration on the ECU and they only drop about 2-3 degree of max timing, so instead of 36-38 it was set at 32-34. Timing is a big issue when the SC is pumping more than 10 psi. 6-8 is not a problem.

The LT series has about 9.8 honest compression, it varies in year model.
GM up the hp every year by cr, cams etc. To this day is the norm in the Corvette.
I would not worry to much about detonation with 8 psi from the SC. My LS 2 has 7-8 psi with an engine with 10;5 to 1 compression and Vortech Diablo ECU program. No crazy boost enough for 500+

The nice thing about centrifugal is that it is linear on the boost, so heat is not a problem.

The by pass valve will free wheel the roots and minimize the heat of the hot air that is compress during idle or low speed, yes a good thing but hard to adapt to a roots that it does no have one. but with 5-7 psi this is not a real issue.

Some of you may think that 5 psi is not much, 5 psi is good for 35 to 50% power gain.

Notice the size of the pulley, this SC can pump 12 psi but 6-8 psi is enough, trust me on this one.

What you are doing is what I am doing on the GT. The grill opening will be smaller than the radiator, rush the air in then slow it down to cool and exit in an orderly manner. The exit is at the cowl and the hood. The rear of the hood is modified to own an opening and by cutting the lip on the cowl that retains the seal, it creates an exit that is very effective.

Here are two pictures, one is of the GT lower panel modification and the other is what I have in my orange RD, the picture is before I installed the SC. The other picture of the GT in progress.

Yes those big holes on the radiator mount brace will be gone. No air in engine bay, only the lazy low speed air that will exit on the cowl and bottom of car.

Bill

Thanks for the info on the LT4 - very encouraging.

I think you are going to see the same Issue John Fenner is seeing and for the same reason - air can pass over the slam panel and pressurize the engine compartment. You need to install a baffle over the the radiator that seals against the hood to keep that air out.

Please PM me your phone #, I would like to talk to you more about supercharging

I guess that is one thing we did right on the GT. Since the grille is mounted to the slam panel and it then locates the top of the radiator that pretty much eliminates the need to seal the radiator to the hood.

Jim