I'm getting ready to order turbo header materials and turbos soon and I've just spent 4 hours researching, reading, and calculating. I just want to make sure I'm in the correct direction before I plop down the big green.

The plan for the car was to set up turbos on the stock L98 longblock and run at a conservative 6 PSI to take time to tune the computer and build up cash to make a more stout lower end. After I have the lower end built, the plan was to up the boost to 12-15 PSI. I looked for a turbo that would suit both situations, leaning towards the latter setup.

I came up with twin T04E hybrids with 60 trim compressor wheels, .60 compressor housings, .63 A/R stage 3 turbines. According to the compressor maps I'd be in the 75% efficiency zone at 6# and 5900 RPM (RPM crossing the traps in the 1/4), and 80% efficiency at 12# and 5900 RPM, and on the right side of the surge line at 20% of max RPM. At 12# I should be around 550-575 horsepower which is the ultimate goal. Plus the turbos should have some room to up the boost later if I get the itch.

Figuring out exhaust A/R is a pain because there's very little information (including in the Maximum Boost book) other than "ask the manufacturer". I figured on .63 due to the success the 20+ turbo setups I've researched had. Is this a good guess?

The stock TPI throttle body only flows around 660 CFM. At 12# my airflow will be in the 922 CFM arena (if I'm calculating correctly). Am I correct in guessing I'll need to upgrade the throttle body when I move to 12#?

Thanks. I'm going to try and get rid of the headache now.

 

I, for one, think that's too big of a turbo. You say you want 550-575 as your ultimate goal which is just more than half of what two of those are good for. A 350 could use everything these have to offer, but that doesn't sound like what you're planning. You want to be in the maps peak eff. at your torque peak, and with what you described above you'd just be getting there at redline. I would suggest something smaller like the T3 super 60:



A pair of these are good for about 600hp at your 12psi, and if you wanted to up the boost later you might be able to tack about another 100 hp onto that. I think this would more than satisfy your goal while having a much quicker spool time than the TO4E60's and they'd be much easier to fit in the engine bay. Going this route will probobly require a larger A/R then you mentioned to keep you away from surge.

About the throttle body...I'm not sure how you got 922cfm. By my calcs, that's worth almost 650hp. That being said, I don't think the stock TB would be a problem even at this level. If you weren't aware, the L98 TB is used on the GMPP 502 ramjet crate which puts out over 500hp in NA form. Remember that your 922cfm (or whatever your flowing) is a pre-compressor flow. Post compressor, ie at the TB, you can divide this number by your PR to get an idea of your cfm at this point.

BTW, if you want to avoid further headaches, I put all of the calcs from Maximum Boost (and a bunch more) into an excel spreadsheet to make this type of stuff a little more enjoyable. Don't mind the combo it shows, you can change any of the grey cells to suit your needs. You can download it here .

 

I just looked over my calcs, and you're right. I was looking at the wrong column. They did sound a little bigger than average.

No more math for me after 10pm. Thanks.

 

I ran through all the math again at the torque peak this time (and hid the HP column) and the T3 Super 60 compressor looks like it'll be perfect. It'll produce decent amounts of boost in the RPM ranges I run in the 1/4 and stays on the island or just 2-4% below as the RPM comes up.

Now you know why I asked to have my math checked.

 

A small T04, like a TO4B S3 or a T04e 40 trim or one of the newer GT series (smaller then a GT35) would be easier to find, probably cheaper and move about the same amount of air more efficiently. That would also leave you with an obvious upgrade path later if you’re looking for bigger turbos down the road.

Really, people have seen the numbers that you’re looking for out of a set of plain 60 trim T3’s also, which again, would be much easier/cheaper… then super 60’s

 

I ordered the header U-bends and flanges today and the guy on the phone just happened to be really into turbos and suggested a smaller trim T04E because it's a better upgrade path later, also. He said that boost is pretty addictive so keep upgrades in mind.

Could I upgrade a T04E just by replacing the compressor wheel when I'm ready to go big in a year or so? The 40 trim is less efficient at 6#, but 2% more efficient at 12# than the T3, so in the long, long run it'd probably be better off. The two maps are actually pretty close.

If I can upgrade the T04E just by replacing the wheel instead of the whole housing like the T3 it'd be worth the ~$90 increase in price (which is less than a housing.) Plus I'm getting the header materials at jobber prices and saved around 100 bucks on that anyway. It all works out.

Question about wastegates: I've been told that internal wastegates aren't really adjustable and I should order turbos without them and use externals. Are a majority of external wastegates adjustable?

 

I don’t know of any instance where changing compressor trims doesn’t involve at least just he wheel and housing.

the biggest reason to go external is because packaging tends to be easier, both can be made adjustable, but there is deffinitly a bigger aftermarket for the external ones

 

T3 super 60s. I'm running two 50 trims on a 302 and its MORE than enough to blow the block into pieces. when I upgrade to 60 trim T4 hybrids next month (via ebay)I'll let you know how it goes.

 

I already decided on GT28R turbos. I found a killer deal on a set (from a Honda forum, incidentally) and they're water cooled ball bearing turbos. They'll go as high as I'll probably ever need on boost as long as I keep my RPMs below 6200 which is fine for a street motor. I shift at 5500 as it is.

What boost are you running on the 302? You and your damn forged pistons from the factory. If I have enough cash left over after the turbo setup (intercooler, tubing, etc) and I sell the rotary motor I can probably build a decent all forged lower end for it.

Say a prayer for the 700R4.

 

The GT28R is exactly in the range that I was suggesting…. Nice choice, should be capable of pushing up to about 700HP if pushed hard and 5-600hp very happily…



Depends on they year… as time went on they went to hypereutectic just like chevy did. Either way the block is not nearly as strong and in the 5-600hp range you start getting crank flex because of it and they start splitting.

I would love to see a concrete good solution for a TH700r4 and some big hp. Right now the way things are stacking up I really expect to be going with a TH400 after I blow mine up, but really don’t want to loose the OD and gearing.

 

The solution I came up with when the 700R4 gives up the goat is to go to a 4L80E. The transmission is a couple hundred more than a 700R4, but I'll need an electronics module to run it. Plus I won't blow the tires off so bad in first gear.... maybe.

 

Well, the boost guage spiked up to 11 pounds while I was racing an 01 ram air trans am tonight(which I smoked btw easing into it at half throttle) but that is way more than I want to be running so I need to play around with my wastegates and get the boost down around to 8-10. I have no idea how much boost its going to blow once I go 100% WOT as I haven't gone full blast yet since I haven't installed my 42 pound injectors and 76MM blow-thru MAF. I'm Running 19 pound injectors, the STOCK MAF, and an FMU right now which is NOT the ideal setup. I'm getting my car dynoed at Apex (thanx to arlo) next week after the injectors and MAF are in and I'll be tuning it on the wideband and hopefully get a nice safe 10-12 pound 91 octane street tune.



Btw--water cooling turbos on a high mount twin turbo small block setup is absolutely USELESS, do some research and you'll agree. My 50 trim T3s are water cooled but I didn't even bother hooking that crap up.

 

he's talking about mine...which is a 91, which did in fact come with forged pistons and rods from the factory. These motors hold up just fine to 500RWHP but that is about the limit, which is just where I want to be. The weak link in the Ford motor is not the pistons or rods...its the block, like you mentioned, which tends to split right down the middle once you start pushing 600+RWHP.

 

Where do you get a 4L80 for anything close to a 700?

 

Retired transmission shop owners that owe you a favor.

 

that's about how I can get a TH400 for cheap, but haven't found friends in low places thare are in a high enough place to get me a 4L80e... if that made any sense.