Turbo sizing

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69stang_250
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Turbo sizing

Post #1 by 69stang_250 » Tue Jul 25, 2017 11:07 am

Hey guys,

I am not very keen on turboing an engine at all, but I have been thinking about adding one to my exitsting engine or building another engine specifically for turboing.

The current engine is:
250 .030 over
Forged pistons
CS 280 *110 HYD cam
CI aluminum head slight port and polish
1.6 adjustable rockers
10.25 CR

With that set up could I possibly run a turbo at 5lbs and be ok?
If so, will the felpro head gasket survive? Or do I need to find a thinner one? What size turbo should I go with for low boost, but spools up quicker for daily driving use?

If turboing is out of the question on that engine, how would you guys suggest building a 250 for turboing? What size turbo should I go with?

Thanks guys!
69 mustang coupe, 250 .030 over, forged pistons, port & polished CI AL head 54cc's 10.25CR, 280/280 Clay smith cam 1 degree advanced, 1.6 adjustable rockers,
Re curved DSII, MSD AL6, CI Intake, FITech 400HP fuel injection. T5 trans, 8" rearend w/3.00 gears.

pmuller9
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Re: Turbo sizing

Post #2 by pmuller9 » Tue Jul 25, 2017 12:08 pm

Just a couple questions to help figure this thing out using the engine as is.

If you go WOT in a higher gear, at what rpm does the engine start to pull hard and at what rpm does the power start tp drop off?

I'm assuming a header exhaust system?

69stang_250
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Re: Turbo sizing

Post #3 by 69stang_250 » Tue Jul 25, 2017 12:56 pm

It really kicks in between 2200-2500 and honestly I have not gotten it into the 6000s so I can not tell you where it drops off, but it pulls strong up to 5000.

I have a dual out header from CI. X pipe to mufflers are Waldren pieces.
69 mustang coupe, 250 .030 over, forged pistons, port & polished CI AL head 54cc's 10.25CR, 280/280 Clay smith cam 1 degree advanced, 1.6 adjustable rockers,
Re curved DSII, MSD AL6, CI Intake, FITech 400HP fuel injection. T5 trans, 8" rearend w/3.00 gears.

69stang_250
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Posts: 443
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Location: Covington, Louisiana
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Re: Turbo sizing

Post #4 by 69stang_250 » Tue Jul 25, 2017 12:59 pm

I am sure it has been asked or mentioned somewhere, but would the small turbo that was used on the 2.3 work for the 250? Or is there possibility of over speeding the turbo?
69 mustang coupe, 250 .030 over, forged pistons, port & polished CI AL head 54cc's 10.25CR, 280/280 Clay smith cam 1 degree advanced, 1.6 adjustable rockers,
Re curved DSII, MSD AL6, CI Intake, FITech 400HP fuel injection. T5 trans, 8" rearend w/3.00 gears.

powerband
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Re: Turbo sizing

Post #5 by powerband » Tue Jul 25, 2017 2:08 pm

Your built engine with Forged Pistons could probably easily handle @ 5 lbs boost. Preventing detonation with an SCR of @ 10.25 requires a Hi-Octane fuel, and specific control or limits on ignition timing advance. The CI Alum head is a total unknown, combustion chamber volume/ flow, porting and squench are skewed with forced induction.

My early attempt at turbocharging a stock 250 ended at @ 15-20 lbs boost when the (stock) Piston ring lands broke off. It used a Buick derived T3/Quadjet draw-thru setup.

Currently the stock block 250 has a Vortech centrifugal supercharger at @ 5-10 lbs boost through a highly modified 2Bbl on a freshened (not milled to get SCR @ 8.75) and ARP fasten'd D6xx head with standard blue outlined Fel-Pro (@.045") .

I am determining specs for forged Pistons and interested in the specs on your 250 pistons. (Coyote piston bore is close, my NA 250/tri-power has AMC 258 pistons for @ 260cid/@9.5:1)

If you haven't yet, read the MacInnes "Turbocharger" bible of forced induction so you don't need to re-invent the wheel ...

have fun

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"Take time to stop and smell... The roadkill..."

pmuller9
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Re: Turbo sizing

Post #6 by pmuller9 » Tue Jul 25, 2017 2:10 pm

I'm trying to figure out a good starting place so I'll just dive in.

The aluminum head flows over 200 cfm which is as good or better than the best ported 300 head.
As a result the Volumetric Efficiency of your 250 is very high and requires a fairly large turbo to support it.
The turbo compressor inducer needs to be between 57mm and 61 mm in size to make power up to 5500 - 6000 rpm.

Boost level does not effect the size turbo needed. That is still mainly based on Engine displacement, VE and Engine rpm.
In fact at 5 lbs of boost the turbo could to be a little larger than at upper boost levels since the compressor band width is narrow at that low pressure ratio.

As you already figured out the present cam and compression is not a good match for a turbo with any amount of boost.
A turbo with 5 pounds of boost can be made to work with the engine as is but you probably won't be happy with the results.

The reason I asked about the power band is, the turbo will follow the torque curve meaning there will not be significant power till 2500 rpm and the cam profile with a 110* LSA (a lot of overlap) will minimize the power result once there is boost.

You would need to fabricate an exhaust manifold for the turbo. The stock log exhaust manifold is not an option with the CI head and present cam.
Blow through carbs are OK at 5 lbs of boost.
At 5 lbs of boost air intake temps are about 150 degrees. An intercooler may not be necessary but it would be better if there was one.
A lot of work for just 5 lbs of boost.

pmuller9
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Re: Turbo sizing

Post #7 by pmuller9 » Tue Jul 25, 2017 2:25 pm

In order to run a fair amount of boost and have the power available early would be a matter of piston and cam change as far as engine internals go.

The compression ratio would need to be reduced to 9:1.
The cam duration is also reduced depending on how early you want the boost to come in versus upper rpm operation.
The LSA would be 114* instead of the present 110*

400+ horsepower is easily accomplished with the CI head and 15 lbs of boost.

powerband
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Re: Turbo sizing

Post #8 by powerband » Tue Jul 25, 2017 2:51 pm

The 250's combustion chamber volume is the main determining factor for safe compression ratio for boost levels without extensive ignition / fuel control management . Converting a traditional high compression - hot cam performance build to 'suitable for boost' is back to basic assemblies ... .

have fun
"Take time to stop and smell... The roadkill..."

pmuller9
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Re: Turbo sizing

Post #9 by pmuller9 » Tue Jul 25, 2017 7:26 pm

OK so I just looked back through your engine build and noticed that the headers are closer to shorty style.
It will take some planning but if there is room to bring the exhaust back to the passenger side or cross over to the driver side, the headers would make a great turbo exhaust system.

If you use a twin scroll turbine housing then one header could feed one side of the inlet while the other header would feed the other.

I'm lookin at the BorgWarner AirWerks S200SX-E 57mm turbo (#12769095003) with a .83 A/R turbine housing with T4 inlet (#177191)

69stang_250
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Re: Turbo sizing

Post #10 by 69stang_250 » Thu Jul 27, 2017 8:34 am

Ok. So you guys made my mind up that If I turboed a 250, I would be better off just rebuilding an engine to be turboed vs turboing the engine I have.

I have a plan on installing an FITECH system in the car around October and then going to bring it to get dynoed to see what the power is and also see what the TQ curve looks like. I can say that it has more pull of the line than my old 2010 mustang GT did and traffic light to traffic light it surprises most.

What I am wanting to do Is a build that peaks around 400-450HP (not I'm portant) and 450 or higher Torque. Of the very few dyno sheets I have seen from inline 6s the TQ curve seems to stay flat and I think an engine with a great average power curve Is what I want to try building.

What do you guys think? I know this is going to cost a good bit, but after the last engine build I think I am hooked on these underrated engines! Lol

Also, I do not have the spec sheet any more for the pistons I had made for the current engine. I do know that they are .010 out the cylinder, 7cc dish, and with getting the quench area in check I have not ran into any detonation or pining issues at all running premium 91-93 octane fuel.
69 mustang coupe, 250 .030 over, forged pistons, port & polished CI AL head 54cc's 10.25CR, 280/280 Clay smith cam 1 degree advanced, 1.6 adjustable rockers,
Re curved DSII, MSD AL6, CI Intake, FITech 400HP fuel injection. T5 trans, 8" rearend w/3.00 gears.

powerband
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Posts: 1733
Joined: Fri Nov 08, 2002 6:45 pm
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Re: Turbo sizing

Post #11 by powerband » Thu Jul 27, 2017 8:51 am

> in MacInnes' book, there are Dyno HP results for Log 250 bolt-on Draw-Thru turbo system that uses a thicker head gasket for reducing CR. At 4000 RPM the system claimed 88 HP NA and 191 HP (@14lbs) with the T3 TC setup. I used the similar Buick (BOP) DrawThru setup with comparative results...


'don't know if it will display :

Image

have (boosted) fun
"Take time to stop and smell... The roadkill..."

pmuller9
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Re: Turbo sizing

Post #12 by pmuller9 » Thu Jul 27, 2017 10:28 am

Would you be willing to run E85?

69stang_250
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Re: Turbo sizing

Post #13 by 69stang_250 » Thu Jul 27, 2017 2:30 pm

I will be reading that book man. Thank you!
No I want to see if I can get it to run on pump gas.
I will be doing a lot of research and figuring out the components I will need and how I will need to plumb the turbo.

What is you guys take on using a small turbo for more lower RPM use vs a larger for upper RPM use?
Take into consideration that this will be going into a car that is more a daily driver.
69 mustang coupe, 250 .030 over, forged pistons, port & polished CI AL head 54cc's 10.25CR, 280/280 Clay smith cam 1 degree advanced, 1.6 adjustable rockers,
Re curved DSII, MSD AL6, CI Intake, FITech 400HP fuel injection. T5 trans, 8" rearend w/3.00 gears.

pmuller9
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Posts: 1382
Joined: Tue Aug 06, 2013 12:33 am
Location: Columbus, Indiana

Re: Turbo sizing

Post #14 by pmuller9 » Sat Jul 29, 2017 11:22 pm

69stang_250 wrote:What I am wanting to do Is a build that peaks around 400-450HP (not I'm portant) and 450 or higher Torque. Of the very few dyno sheets I have seen from inline 6s the TQ curve seems to stay flat and I think an engine with a great average power curve Is what I want to try building.

What is you guys take on using a small turbo for more lower RPM use vs a larger for upper RPM use?
Take into consideration that this will be going into a car that is more a daily driver.

The turbocharger size is set by the engine displacement, the engines volumetric efficiency and the engine max rpm.
For street use where you want a wide power band there is not much room to stray from the ideal size.

I thought it would be better showing you some results than just telling you about it.
You can also change values in the calculators to get a good look at how changes affect performance. Have fun.

Since you are using the CI head the engine VE is very high. I used conservative VE values in the following MatchBot calculator.
Camshaft specs are around 220/212 (.050") duration, 114 LSA.
The intercooler efficiency is set at 50% and the lower compressor map is for a 57mm turbo.
I ran the rpm out to 5500 for 427 hp at 15 lbs of boost. Torque values are just under 500 ft lbs
http://www.turbos.bwauto.com/aftermarke ... sin=92044&

Next we drop the cam duration by 10 degrees to lower the rpm range and move to a smaller 52mm turbo.
The max rpm that puts the last dot on the 70% efficiency line (same as the 57mm turbo) is now 4800 instead of 5500.
Torque is about the same but max HP is down to 370.
http://www.turbos.bwauto.com/aftermarke ... sin=92044&

In order to restore the 400+ HP with the smaller 52mm turbo, the boost needs to be increased to 20 lbs.
The torque has increased to 550 ft lbs which puts a strain on the engine and the boost level along with the intake manifold air temp is not so gas pump friendly.
http://www.turbos.bwauto.com/aftermarke ... sin=92044&

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