The Dilemma , Horse Power or Streetability

[TC]

I've been researching how to size a turbo for months now, and I've come to a point where I have to pick streetablity over HP......My goal with the twin turbo small block is to make 1200hp, but matching a turbo up to make full boost at 3000rpm and peak HP at about 7500rpm has become almost an impossible feat........What I have found that works is a pair of T61 turbos, but using a pair of them would only really support 1100hp, but they would bring full boost in by 3000 rpm pretty much riding right on the surge line of the compressor map.......I feel the T61 would be great on the street since I wouldn't have to rpm the motor up to get to full boost like I would have to do with bigger turbos.... Thus the friendly street manners I can see with the T61's........Also if I decide to turn down the boost the make less hp, the points on the map fall right in line with the highest efficiency island on the map, so they'll support from 700hp to 1100hp without a problem......But they will most likely not get me to my 1200hp goal, and I'm not going to get much more boost out of them like I could with a bigger turbo, but the problem with the bigger turbo is I won't be able to get full boost by 3000rpm and might have to go up to 4000rpm or ever 4500rpm before achieving full boost.......Isn't turbo sizing wonderful...........

Anyway what would you do, go with the smaller turbos that will get me close to my goal and have a car with decent street manners or go for the bigger turbos that will get me to my goal of 1200hp but at a sacrifice to low end boost and power??.........

On a side note I have a set of AFR 220cc Eliminator heads that AFR says will support 700HP on a naturally aspirated motor, but I'm not sure if the better flowing heads will push points on the map higher and off the map or if it'll bring them down an into the meat of the map......I do know your BSFC numbers have huge effects on the plotting points on the maps.......

[TheSilverBuick]

If you want 1200HP go for that. You are asking for a 4500rpm power band, that's a pretty lengthy power band, way over what the rpm drop will be between gear changes. So why not start with a 4500+'ish stall converter and be only a downshift or converter stall away from being in your power band?

[dieselgeek]

is this a carbureted application? If so, I wouldn't count on being able to tune that wide of a powerband, and you need to know what boost you're going to run ahead of time. Slip up and you'll melt a pile of pistons in a nanosecond.

Remember that your good heads and the cam you are probably selecting, won't be optimized for low RPM torque. It takes a torquey motor to begin with, to spool a turbo at low RPMs. As for converter, my advise is - pick at least one stall rpm LOWER than what you decide on after reading the internet. Everyone always seems to be blowing through their converters on first pick.

[Bob Holmes]

What will the power curve look like naturally aspirated?

[Huskinhano]

Where are you going to be driving it the most?

[SuperBuickGuy]

why not sequential turbos like is on the newest cummins and ford motors? or even a supercharger (like a PS1 or 2) and a turbo?

[A/Fuel]

I, honestly, don't think you're going to make anywhere close to the power you think you're going to make. So, I'd go with the smaller one.
I wish you luck, and hope to see pic's soon!

[TC]

I, honestly, don't think you're going to make anywhere close to the power you think you're going to make. So, I'd go with the smaller one.
I wish you luck, and hope to see pic's soon!

I'm not saying the CompCams cam selection software is the holy grail, but with 16lbs of boost it has peak HP at 1200hp using a pair of T61's.......And at 26lbs of boost it puts HP at over 1400hp.........

[TC]

why not sequential turbos like is on the newest cummins and ford motors? or even a supercharger (like a PS1 or 2) and a turbo?

Though it sounds cool I think I'll have my hands full with just the two turbo's.........

[TC]

Where are you going to be driving it the most?

The car will be a 1980 Monte Carlo, I'd like to be able to drive the car across the country and do events along the way......Everything from drag racing, to LSR, to road racing..........I do plan on getting one of those TCI 6 speed auto's, which should make it real highway friendly......

[TC]

What will the power curve look like naturally aspirated?

I'm looking at a Comp solid roller with 292/297 adv, 254/260 @ .050, .582/.588 lift on a 110 LSA......it has a rpm range of 3200-7200rpm which pretty much falls in line with the points I plotted on the T61's turbo map......

[Stich496]

start by FORGETTING ABOUT HP. and build for a big fat torque curve.. with mid range power that pulls like a freight train without downshifting..
figure out where the trans gearing and rear gears/tire dia is gonna put the rpm most of the time, and build for power in the spot the engine will be at 90% of the time..
my turbo t/a (400cid blow through carb ) was all done at 5500rpm, but on the highway, at 65mph it not walk, it ran away from almost anything as the torque was killer, zr1's didn't like see'n tail lights, they'd catch the t/a and pass it.. but they had to chase it down.. ;)
the small turbo was all done by 4200 on the 400 but from 1800-3800rpm it was a rocket.. and with 2.30ish gears. it didn't need high rpm

[dieselgeek]

The car will be a 1980 Monte Carlo, I'd like to be able to drive the car across the country and do events along the way......Everything from drag racing, to LSR, to road racing..........I do plan on getting one of those TCI 6 speed auto's, which should make it real highway friendly......

My advice would be to "get real" about what the car is going to do. Whenever I hear the "I'm buildling it for everything!" routine, it's basically a guarantee of a car that will never get finished, or that the finished product will suck balls at everything. Meanwhile, how's one of those TCI 6-speeds going to handle 1400hp??? You should skip all the "requirements" and simply have one: "finish the project" IMO. Just get something that runs and drives and you'll be light years ahead at that point.

[Beagle]

the converter comment is probably very valid - turbos like something to pull against. I think that is a big reason why you see so many 'glides.

[SuperBuickGuy]

My advice would be to "get real" about what the car is going to do. Whenever I hear the "I'm buildling it for everything!" routine, it's basically a guarantee of a car that will never get finished, or that the finished product will suck balls at everything. Meanwhile, how's one of those TCI 6-speeds going to handle 1400hp??? You should skip all the "requirements" and simply have one: "finish the project" IMO. Just get something that runs and drives and you'll be light years ahead at that point.

yep. the best way to have a car that does everything is to buy a 10-car car hauler and have one car for each thing on the trailer. Also, if you want just one turbo or two - use a variable geometry turbo ala duramax