Stock internals power threshold

[351 celi]

For those who have actually done it, what is the maximum horsepower output a turbocharged 250 with stock internals can sustain and survive in a daily driver (not beat on daily though)? My big MHI 16g seems to run out of steam at 4500 RPM, which is fine for me and push 10 PSI at the manifold, but I am dropping 4 PSI across the intercooler, and 14 PSI is the maximum output I get from my little turbo on a "big" six. My timing is limited to 10 degrees mechanical advance + 17 static, running no ethanol content 93. I ask because I breifly bypassed my FMIC, and registerd 14 at the manifold and the car pulled amazing for an old six. What are your thoughts on running this turbo without an intercooler on E85 at 14 psi? IAn option would be to upgrade to a larger turbo that can push 14 through the FMIC, but I would have to rebuild my J-pipe and downpipe to clear the larger compressor housing for a 20g.

My setup if it matters: Stock '77 250, felpro headgasket, CI 302 valve springs, CI chromoly pushrods, OEM adjustable rockers, duraspark II w/ 925 recurve kit welded slot to 10 degrees max, accel 300 ignition, motorcraft 42's gapped at .030, stock 4 degree retarded cam and timing set, direct mount autolite 2100 1.08 rejetted and PVCR's drilled to .063, AEM wideband O2, modified Carter superstrip for boost reference, all AN lines fuel/oil lines, MHI big 16g, ported TD05 exhaust housing & oem exhaust manifold, internal wastegate shimmed inoperative for testing, 2-1/2" J-pipe, 3" down pipe wrapped and exhaust, 2-1/2" charge pipes, bosche BOV, 12x12x3 FMIC, K&N filter.
C4, B&M sh%t kit, 8" 3.40 open
A big THANKS to all the guys who created the great write-ups and answered numerous questions!!!

 

[Turbo_B]

Sorta off topic, but a Big 16g is not so big on a 250ci engine. The big 16 is not far from what I run on my 114ci MGB. I have a Holset HX25 with an 8cm^2 turbine that is in full boost by 3krpm.

I would consider converting to a T3 style exhaust flange for adaptability and then going to something with a larger turbine.

FYI. with a Garrett GT2052 on 6.5psi my MGB made a 10.28 at 68mph pass on the 1/8th mile.
With a Holset HX25W on 6.5 psi my MGB made a 9.91 pass at 71mph

Too small of a turbine will choke the engine.

 

[351 celi]

Thanks for your suggestion, and I totally agree, a big 16g is a misnomer, I got a great deal on a bunch of parts and figured it was a good place to start before investing tons of $. I convinced myself it may be okay since it is a common turbo for smaller displacement engines that have much better flowing heads that also rev much higher than a near stock 250 is capable. I was hoping to come up with a solution that could utilize my existing piping and banjo oil/water fittings, we'll see, 20g still uses the same small exhaust housing if I want it to mate up, but full boost at 2k on a 5k rev limit is nice.

 

[Turbo_B]

The other part to be concerned with is not using the intercooler. Even if the internals could handle the power, they may not handle the detonation. I have seen un-intercooled IAT's quickly climb over 250F at just 7psi. This robs power and requires less timing to maintain detonation free driving. In a setup with an undersized turbo the IATS can climb to much higher levels as the compressor is working out of its efficiency range.

 

[351 celi]

Thanks again B, looks like I'll be redesigning for a larger turbo this winter and keep the IC. I'll keep you guys posted on the changes and results.

 

[63stl_comet]

You can keep the same flange and go with one of the larger turbos for DSM cars. You can go with the fp green or similar. It is true that that big 16g is very undersized for this set up. It is made to run on a 2.0 liter 4 cylinder not the 4.1 monster it is bolted to now.

Just like a have a good sized ported and polished 18g on my Subaru and it make a ton of boost(36psi when the wastgate vac hose blew off!) But it would not perform very well on the 250 in my comet. Though the Fp green or Fp red are large enough to support the size of one of these engines, if you are not planning to run 30psi or anything crazy.