Aero / cooling front sheetmetal

[Jim Stabe]

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.

[BlownMGB-V8]

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

[MGB-FV8]

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:

http://ecommerce.mossmotors.com/p/miata-mx-5/stainless-steel-engine-shield-by-cobalt/907-301?CategoryPath=All+Products%2F%2F%2F%2FMazda+Miata%2FMX-5%2F%2F%2F%2FUserSearch%3Dsrc_results%2F%2F%2F%2FAttribSelect%3DYear%3D%271990%27%3B%3B%3B%3BYear%3D%271991%27%3B%3B%3B%3BYear%3D%271992%27%3B%3B%3B%3BYear%3D%271993%27%3B%3B%3B%3BYear%3D%271994%27%3B%3B%3B%3BYear%3D%271995%27%3B%3B%3B%3BYear%3D%271996%27%3B%3B%3B%3BYear%3D%271997%27

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:

http://www.xtrememotorworks.com/Cooling.htm

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 Stabe]

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.

[roverman]

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.

[flitner]

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?

[BlownMGB-V8]

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

[Jim Stabe]

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.

[Jim Stabe]

Quote
"But I want a ride! "

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

Quote
"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.

[flitner]

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

[Jim Stabe]

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

[classic conversions]

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.

[classic conversions]

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.

[Jim Stabe]

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

[BlownMGB-V8]

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

[MGBV8]

...air can pass over the slam panel and pressurize the engine compartment.

Why wouldn't the air passing through the radiator do the same thing?

[Jim Stabe]

It does, but why would you want to add pressure with air that isn't doing any cooling to impede the air coming through the radiator that is actually doing some work. The radiator is a restriction to flow so air will take the path of least resistance if it is available - around the radiator. Air flows from high pressure to low so you want to keep the area behind the radiator at as low a pressure as possible. The closer the pressure behind comes to matching the pressure in front the slower air will flow until pressures equalize and the flow will stop. At rest the two pressures are equal and no air flows, hence the fan.

[classic conversions]

Will do Jim.

My RD has similar but not perfect.  The opening for the radiator will be smaller about 50% and yes everything will be seal.

[Jim Stabe]

I finished up the top section baffleing.The top edge of the baffle will have a 1" bulb seal that will press against the underside of the hood. The bottom portion will be part of the front valence and will have an opening only as wide as the radiator core. If you look at the front of the core you will see a ding, a hammer fell and bounced against the core denting one of the tubes and the surrounding fins - stupid, stupid stupid...

[BlownMGB-V8]

All that extra room and... HEY! where's all the extra room!??

It is really looking good. But radiators are hammer magnets. No matter what you do to protect them...
I feel your pain.

Jim

[Jim Stabe]

I remember when it was going to be naturally aspirated and how much room there was in the engine compartment. Where did it all go?



Good thing I hadn't planned on an intercooler