First off hello to all and thank you for this awesome site of info, everyone seems pretty cool and knowledgeable around here.

So I've been reading my arse off and trying to figure out a twin set up on my 402 bbc pick up.

There's only a few guys around me who have any knowledge of turbos but not extensive enough to help with determining what parts I need "spec wise" like turbo size/wastegate size/BOV size/pipe size/piston type/cam size and so on.

This will be my first turbo build and from scratch at that, I know I can do it I could just use some help in the right direction.

As is sits the motor is pretty much bone stock minus a performer rpm intake and edelbrock carb, the plan is to pull it and start with a block and start building.

Also the plan is to mount the turbos inside the bed just behind the driver and passanger, with that being said
1. What size turbos should I be looking at if im shooting for the 1k hp mark?

2. Are turbo specific pistons a absolute must?

3.I plan to use the long tube headers I have, should I reduce the piping diameter to the turbo from 3" to keep velocity or anything like that?

4. I've read a lot of people explain that rear mounted turbo system are a waste because the exhaust gases cool causing lag and its best to keep the exhaust gases hot for expansion, is that something I can combat with smaller turbos to prevent lag? Or possibly run thicker exhaust tubing wrapped in header wrap to keep the exhaust gases hotter to not have to run smaller then desired turbos?

 

keep on the smaller side for pre-turbine tubing to keep exhaust velocity fast ,, wrapping the exhaust to retain heat

id look into a t4 ptrim small ar turbines and about 65-70mm compressor wheels

 

Something like this?


http://trsmotorsport.com/index.php?...roduct_id=264&option=com_virtuemart&Itemid=26

OTE=M&M Turbochargers;1974465]keep on the smaller side for pre-turbine tubing to keep exhaust velocity fast ,, wrapping the exhaust to retain heat

id look into a t4 ptrim small ar turbines and about 65-70mm compressor wheels[/QUOTE]

 

You can make power with remote mount turbos, but you will give up power and have extra turbo lag. This is because the long pipes will lose a lot of heat and the engine has to pressurize them just like a big air tank. This will force you to run long small pipes, which adds back pressure.

I don't know much about turbos other than basics, but using a single modified 78 legal turbo and making all my pipes short and direct as possible, my 363 Ford is well over 1200 without mufflers and over 1100 with quiet mufflers. It spools to 15 psi in one second and 25 psi in 1.15 seconds coming off a fast idle. From data logs and the dyno, it looks like about 10% of the power is from the heat. That is based on fuel usage for a given power, pressure, and temperature data.

So if I lost the heat in my car with long pipes to the turbo, it looks like I would lose 100-120 HP or more. It would for sure have a longer much spooling time. I'd have a multitude of other problems, like needing a much larger BOV system.

Since I wanted maximum possible power for the turbo size and quickest possible response, I made all the pipes as straight, smooth, and as short as possible. The air outlet, for example, is just three feet total length including the intercooler path length. It is just a few tenths of a second away from running 4's on drag radial tires in a 3150 pound car through mufflers.

If you want looks, put the turbos in the bed. If you want maximum performance, you'll have to do what I did. A lot of this is common sense over looks.

 

From my research so far I Shouldn't have lag if I size the turbo properly I also plan to run thicker piping wrapped with header wrap to retain as much heat as possible which I haven't seen much on rear mount set ups.

Also I'm not trying to meet a class spec with my set up, its for street fun and the occasional 1/4 run, my only limitation is funds.

 

Watch out for Internet. The thicker the pipe is, the slower the thermal response. The thicker the metal the longer it will take to heat it, so it will cool the exhaust longer until it all heats up.

If you do not care about maximum power and are not worried about boost lag or having to blow off 5-10 gallons of air tank every time you let off the throttle, and pressurize the same 5-10 gallons when you go into boost, a rear mount is fine. It can look really cool.

If power and response time is more important, then you would want short pipes.

 

My advice is to leave the engine together, and have one less thing to worry about when getting it up and running... Then rebuild the engine later if it needs it. I say get the turbos under the hood if possible.

 

I have a single 80mm turbo mounted under my bed (check my build)
The engine is a build 496 ci, I have just about no lag, I do have a 2500 rpm converter dough.
2 X 2.5" going into a single 3" pipe before the turbo.
I took of the wrapping becouse of a fire incedent and it slowes spool up time just a tiny little bit on my aplication.
Check those youtube videos in my thread