Im starting a build on a 468 big block chevy with 9.5 to 1 compession and was directed to run twin mp t70. I want to run meth injection just wondering if this set up will work and if so around what kind of hp could I make.

 

what type of fuel? You should be able to make 1300-1500 with those turbos. Any reason why you have been told to run them?

 

I wanted to stay with 93 octane and run meth/water injection and i believe the turbo choice was because they are a good bang for the buck and gets me to hp I wanted.

 

Being on pump gas and using meth you are going to want to size up your turbos fairly well to keep them efficient thus helping keep your IAT's in check as much as possible. You can run some numbers from the link below and also plot out your engine CFM on the compressor map and see where you fall. I did not do the work for you however if you would like me to post the formulas if you do not have them I would be happy to.

This site might help you out some.
http://www.turbodriven.com/performanceturbos/matchbot/index.html

 

Any info and help Ill take more info from informed people the better.

 

Well the ebay gt45 is technically a t70 compressor minus a couple mm off the exducer but has a bigger turbine wheel than most t70s. If you are looking to go cheap then they are the ticket. 2 can do 1100hp+ and they can be had for $260/each. They are heavy bastards tho

 

Also, I think the turbine wheel and housing will keep them more efficient than say a t70 with a smaller wheel/housing on the turbine side. Sacrifice a lil smaller comp for a bigger turbine. Makes since on that size motor, plus old school engines dont flow the same as the new ish out there.

 

I plan on running twin mp t70 have a lead a 2

 

Are they matching turbos? And what price range? New? Many factors to your purchase. Also, are they t4 t70 or t3 t70? If they are coming from ebay they very well could be t3 t70s which wont work for your displacement. 2 true t70 turbos would work but would need .96 a/r turbines for proper efficiency. Maybe smaller turbines but thats alot of cubes to force thru them. If you're spending over 500 for both I personally would opt for the gt45 because of the larger turbine. What is your power goal and pupose... street/strip or all out drag?

 

They are master power t70 and mostly street alittle strip use .Hp goal want to start around 700-800 and add more when I upgrade drive train.

 

Well on those cubes with 2 mp t70s 700 hp will make them inefficient. The compressors would surge that low on twins. Turbos can be tricky when trying to match them. One of those turbos can push 700hp worth of air. Basically, they wouldnt be spinning fast enough to support the low boost you want from them. I say, id they're good price, pick them up and hold on to them until you have a setup capable of supporting 1200+ hp. Dont want to ruin two good turbos on a motor that can hit those numbers NA

 

ON that big of a motor you want something like a 78-83mm.

 

Look into the S471 that should be real nice on that motor

 

I plan on uping hp once trans and rear get upgraded my end hp is going to be in 1000 + range.

 

Just look at the engine as half its size. A 234ci engine running a single 70mm would really need to be pretty serious to stay out of surge. I just don't get why people hear big block and automatically think it needs 2000hp worth of turbos just to make 1000hp.

Here is what twin 70s on a basic 1200hp 468ci big block would look like. Surge city.

http://www.squirrelpf.com/turbocalc...3=135&intake_temp_4=140&turbo_n=2&map_sel0=72

Here is something more spec'd to your goals, and not to just thinking that all big blocks are going in a Pro Mod.

http://www.squirrelpf.com/turbocalc...3=135&intake_temp_4=140&turbo_n=2&map_sel0=70

Here are a couple of twin $250 eBay 68mm GT45 turbo big blocks.

 

Really? My S475 is starting to get inefficient at 10 psi on a 452 cube BBM...

I'd put at least an S480 on it.

 

But his target hp might not be 1200. Put in 800hp and the boost comes down from 20 to 13psi. Then it is to the right of the surge, and right about the middle of the island from 4500 and up.

 

Its twins not a single. S400 or s475 would be more than enough.

Ploting the map would be the best however om not dping the work for someone this is just guessing. I have twin 70's on a 352" motor with .81 exhaust housings and according to my math they fit very well keeping them near prime cfm inturn keeping heat down.

Just because a turbo can make 1200hp each or more doesn't mean its efficient in doing so.

 

I know you mention surge but wont the wastegates and bov control that

 

No, there is one kind of surge, but two situations that can make it happen. One is full load surge by running too large of a compressor and as boost comes on it runs to the left of the surge line on the map. That kind is the worst. The other kind is what you get with no BOV to vent the pressure from closing the throttle, and while not great for a turbo isn't as bad as when it happens under full load. The wastegate and BOV aren't even in the picture yet when full load surge happens. Specing a turbo(s) big enough to stay right in the center island is fine, but spool will be slower due to it being a bigger wheel overall and you still have to stay away from the surge line.