Inliners International Forums General Discussion Blown and Injected Honest power estimate

Can anyone give me an honest power estimate on a 250 build.... I’m having the worst time trying to decide which engine to use in place of my blown (up) 250.

Full built 250 head, lumps, 1.94/1.60 ss valves, porting and blown blend.
Forged Ross pistons 9.4:1
Forged Manley 6” rods
Medium turbo cam
Offy intake
292 exhaust
GT35 turbo 15-18 psi?
Air to air ic
Happy to use an alky injection unit.

I understand this combo will not net 800HP or anything near! But, what could I expect?

I have a BMW M50B25 available... needs a good head gasket and studs to boost. It won’t be a monster, but decent.
Seriously considering the 4200... but it looks to be near as expensive as a 2JZ... which is far superior.
1JZ is cheaper and still very capable (probably equal to the 4200 for power output once both are built). It would fit my engine bay easier.
Meanwhile, the 250 is quite reasonable to build and I’m already set up for it.

Perhaps the move is the build the 250 and work on whichever other engine over time.

Truly, I’m awful at making decisions! But, once my mind is made up, nothing changes it!

One JZ negative is that the only manual transmission that survives is the Supra TT 6-speed, which is about $4,500 used (+ bellhousing, clutch dribeshaft, controls). The only automatic is the TT-only A340E safe to perhaps 500, after that $$$. Serious cars use TH400.

It's very difficult to estimate the power, because different engines will not produce the same power per inch with the same boost. The JZ has made over 1,000 many times using the original block and head - there are no secrets at that level, just follow the instructions.
Personally, I would never use a BMW engine, there are too few known success stories (and those are $30,000). There is no DIY or cheap BMW speed equipment. Figure it for for a SBC, and add a zero. Don't invent the wheel, just get a wheel.
For your specs 500 is a safe bet but needs really sharp tuning for the best balance between boost, static CR, cam, intake air temperature, spark advance and A:F. 9.4:1 and 18 psi is dangerous, would have to run rich & retarded. A weak boosted engine will need to run 15 degrees of spark and 10:1 A:F at high pressure with disappointing results.

I have a TH400 in the car now.

As much as I want 1000 + ... it’s not even close to practical!

Honestly, a little disappointed in 500... I know it’s estimated and I’d really need to Dyno for accuracy.

Doubt I’d run 18 on the street... octane just isn’t there.

So, at 15, and a good tune... 🤔

The cost of building another 250 is significantly less than any of the other options... especially since I’m already set up for it.

Sorry, please bear with me... I’m always a mental case when big decisions are presented.

You won't know what you're doing with just a wide band, the final tune may be worth over 100 hp and needs hours of dyno time.
If I were starting with a blank sheet of paper and insisted on an L6 it would be a Barra and a lot of $$$.
But that's the question: do you want 1,000, or an L6?
A JY LS will do that with truck manifolds and a single turbo...

An Atlas will make over 500 HP for less money than you will spend on the 250 to make less!

I’ll never use an LS. Not because they’re not good engines, I just don’t follow the crowd!
And any fool can make a V8 fast! There is no talent/skill/ingenuity/work involved in that!

I’m not looking to break records with my 6! But it will be a 6! ... I’m stubborn like that!

I have no idea what a fully prepared Gen-3 L6 will do with enough boost, but using an original head casting, but at high power levels the Atlas, Barra etc. are going to pull away.

The Atlas motor came stock @ 270 HP with a tweak on the comp. They made right at 300hp Just food for thought if you want all that comp. head ack.

Add 10# of boost to a stock 4200 and you get 400 rwhp....

Buy a rusted out 2wd donor. Around Calgary complete engines with harness/pcm can be had for C$500.

watch this... he is using a TH400.

https://www.youtube.com/watch?v=hGYuPENQZHM&feature=youtu.be

Nice vid. 441 hp.

Th Atlas looks like the best choice.
The chief reason I have a 2JZ-GTE (factory turbo) is that it's a bolt-in to the car: 1992 Lexus SC300.

Nice project. Tell us more about the build.

The usual used JDM Aristo TT engine & transmission on a pallet.
Tial BOV, 3" Vibrant exhaust, AEM boost controller (18 psi), NEO A:F management, 550cc injectors, HKS 264° "mini" cams, ATF Stage 2 O/D A340E transmission, 3.77:1 LSD, D2 very stiff coilovers, LS400 front calipers & rotors, big IC, huge ATF cooler, ROH (Australian) “Modena” 19” staggered wheels: 8½” × 19”, 9½” × 19”.
About 520 hp. Turns 2,688 @ 80 mph.

Just a note - its running E85.

The parts you have listed for the 250 will easily make 350HP and could put out up around 400 and live a long life. May need to use a Clifford intake.
Also try to give the head only a straight cut and maybe the same to block to help keep the compression down a bit.

Honestly, I’m quite surprised at those numbers... the dyno testing you had done made almost 300 NA and with only 4psi(?) was about 350HP, no?
I had expected 500 or more at 15 psi.
Mine certainly FELT more than 350 at 15 psi. It was a rocket!

Please understand that I am not doubting... you all have heaps more experience than I do! It’s just... surprising.

You are correct. Like I said easy to make 350-400 HP and make it live a long life. 16 PSI is going to make it into a monster. It will also require precise timing control or a very short life of engine.
A good rule of thumb. For every 1 PSI you will gain about 6% gain in TQ. So in your case. If you can make 270 tq N/A Add 16.2 ft lbs per psi. So about 532 FT LBs at 16 PSI.

Torque can often convince you that you have more HP than you really do. As Tom said, going beyond the range he mentioned is a slippery slope between tuning, fuel management and longevity.

W/r/t "For every 1 PSI you will gain about 6% gain in TQ"
Never heard that, source?

Does it compound?

For the first few psi (especially going from the stock 3" of WOT vacuum to even 1" of boost) it may be more than that, but it definitely decays as the boost rises (not linear).

There are "calculations" on the net and elsewhere that claim to predict power by the following, where:
HP = new hp
ATM = atmospheric pressure (14.7 psi @ sea level)
Boost = psi
HP = old HP × (ATM + boost) ÷ ATM
(1 atmosphere of boost doubles power)
Example:
HP = 200 hp × (14.7 + 10 psi) ÷ 14.7 = 336 hp

Similar to predict new static CR
New CR = old CR × (14.7 + boost) ÷ 14.7
(14.7 psi boost doubles CR)
Example:
New CR = 10:1 × (14.7 + 10 psi) ÷ 14.7 = 16.8:1

Always wrong

Who's Dyno is that?

Here is a nice Jeep turbo inline build

https://www.youtube.com/watch?v=F7o4OkKjXZc

Sorta shows what an old engine with newer tech can do

nice build that is for sure.