Sizing Boost vs Horsepower Cart ot HP first?

brnwaxa

New member
I am hoping to call on experience here. I am turbocharging a 300 in pick up. I want a good daily driver. It's a standard shift and will have EFI manifold and Mega squirt. The cam is stock and the compression ratio is 8.8 to 1. Max RPM would be 4800. Through what I have read here I had decided on 10 lbs boost or less to avoid head gasket issues and I want to make it dependable. I have JE forged pistons. I called the local turbo shop to help me size the turbo. I have an Air Research housing with interigal waste gate. I said I would like to limit the boost to 9 lbs. The question the turbo tech asked was, "ok but How much horsepower do I want to make. I need to know to size the compressor?" I have always thought you went for boost and HP is what it is or you went for HP and calulated the boost it took to get there. All help,is appreciated including sizing the turbine and compressor. I am in a stage where I can start over on the turbo selection
 
You got a stock in trade question, because most people don't know how to size. You are on the right track though, the power will be the dependent variable.

The head gasket won't be an issue if the bmep stays within bounds and that is heavily dependent on the advertised duration (valve events), plus whether you keep enough fuel going in to cool things down. I always subscribe to making the head gasket the weakest link, because it is far less expensive to fix than legs out of bed, broken transmissions and the like.

Post the specs for the cam, intercooler efficiency, rod length, stroke and I'll rough estimate for you.
 
I am not able to find the cam card that was supplied by Crower. According to Crower it is a turbo grind and is very near stock for the truck engine but with a little more lift. The rods are 6.790â€￾ and are from the 240 Cu In engine. The engine is balanced and blueprinted. The pistons, valves and combustion chambers are ceramic coated. That is all set in stone-done. I have not acquired an intercooler yet. I would not rate it as high efficiency as it may need to be remote mounted because the truck has air conditioning and there is little room if front of the radiator. It will be EFI so a rich AFR under boost is easy. Timing will be via the ECM also, this will be MegaSquirt. All help is appreciated.

Bill
 
Are you ready for some math?!

Here is where it all starts for any particular engine, so get out your best calculator and a note pad and get to work on finding your turbo. Then take your calculations you have and plot them on compressor maps to find what's right for you. Your calculations should be in 500rpm increments, say from 1000rpm to 5000rpm and vary with boost levels (account for the boost at each rpm level: 2psi@1500rpm, 4psi@2000rpm,etc... to 10psi@5000rpm)

www.mrcontrols.com/primers/sizing.htm

Let us know what turbo you find right for your application. Good luck.

Kirk
ps. you can find compressor maps on any of the turbo makers websites.
 
XPC66 had asked for a few items and I listed them in a previous reply. I am sure it would be figured out but I had forgot to list the stroke. 3.980" and the bore is 4.030". I have an Air Research turbo. It has an internal waste gate. I am not sure of the ratios but I did find VW cast into both housings. It has water cooling ports. I am not set on using this turbo if there is a better match. Also I found the MegaSquirt will operate a boost controller.
 
I do not have a compression reading. The shortblock is on the engine stand. I like a few details before I install the head. I will remove the timming cover this evening and search the end of the cam for a grind number. I may be able to get this information this way.
Thanks for your help and patience.
 
For XPC66's question on cam specs. I will list but the web site at Crower is

http://www.crower.com/misc/cam_spec/cam ... 9&x=22&y=4

ADVERTISED CAMSHAFT SPECIFICATIONS:
INTAKE: Duration: 259º Lift: .477
EXHAUST: Duration: 265º Lift: .498

@050" tappet lift.
INTAKE Opens: -9.0 ATDC
Closes: 28.0 ABDC
EXHAUST Opens: 40.0 BBDC
Closes: -13.0 BTDC

LOBE SEPERATION 112º


Duration at .050" Intake: 199
Exhaust: 207
LOBE LIFT Intake: .276
Exhaust: .288

installed on an intake centerline of: 108º and uses 1.7 to 1 rockers

This is good information

Thanks in advance
 
Damnit I should have looked before I started working up some rubbery figures. Here's what I did before I saw your post (you might like to try substituting your figures while I find time to) :

I would guess the engine is a stump puller, maybe 250° in/260°ex advertised duration with about 112° LSA, intake advance about 5° and buggerall overlap say 30°?

That would be something like 17/51 67/13 advertised cam or about -11/23 39/-15 @0.050

With a closing angle of 23 @ 0.050 it will go on cam and reach peak VE about 1850 rpm, and because peak torque is generally around 200 rpm above peak VE, lets say 2000 rpm fro peak trorque. The corresponding power peak would be about 3400-3500 rpm.

Based on the intake valve closing at 51° ABDC a stroke of 3.98" , rod length of 6.79" and a CR of 8.8 your actual compression ratio will be 7.7 and a bmep/compression test of about 187 psi. On 9 psi that is going to push the boost ratio to 12.4 so a bmep of around 295 psi. The 7.7 tells me you are going to need to run on premium fuel or higher and have strong rods and pistons.

From the 187 psi we can ballpark the expected torque using average VE an therein we can then predict the expected power.

On your engine with the usual restricted stock everything and single cam that would be about

116kW @ 3400
327Nm @ 2000
from showroom?

With a better cam and exhaust ~:

133kW and 375Nm

at the same rpms


So in an ideal world with a good exhaust, same cam, a bit of porting, no intercooler and on a nice day you should be getting up around 205kW (275hp) and 550 Nm running 9 psi boost (in the plenum).

You'll be sucking 440 cfm and exhausting 610 cfm. Your exhaust should be about 3 1/4", your throttle body and charge pipe should be at least about 67mm. The fresh air pipe from the filter to the turbo should be 3 1/2".

If you are looking at maps you will find the x axis has various units. Your pressure ratio at 9 psi is 1.61, but the calcs are based on plenum pressure so we need to account for line losses between the compressor and the plenum. This is where the throttle bodysizing becomes important. Ideally you want about 1 psi drop across the TB and still have good authority with the pedal. So we need to deliver 9+1 = 10 psig from the compressor . This means the pressure ratio rises to 1.68.

In this instance you need to find a map that has the x-y intercept that meets to the right of the highest efficiency island when "Y" is PR = 1.68 and "X" is 26.7 lbs (or 207 l/s or 441 cfm), but left of the most right island to prevent choke. Preferably want it as close to the centre island as possible, but this will also increase the compressor range and therefore lag.

You are going to have pretty high temps in the charge pipe from the heat of compression (~90°C) so an intercooler is going to be worthwhile and it will give you some extra ponies (maybe 50hp with a high eff% unit) the trade off being you will have to add the pressure drop to the boost requirement of the map. So allowing 2 psi drop you will need increase the pressure at the compressor to 12 psig, thus a pressure ratio (PR) of 1.82.

At the 4800 rpm you want to run at the engine will have lost volumetric efficiency and without an intercooler running 9 psig in the plenum (PR 1.68 ) you will be developing about 169kW (226hp, 21.8lbs, 170l/s, 359cfm). The x intercept in this instance will fall to the left of the previous intercept and the right of the peak torque intercept.

When you are going on cam at 2000 rpm you will be making 550Nm = 115kW ( 155hp, 14.8lbs, 116 l/s). The X intercept in this case should fall within the left most island to prevent surge.

So you map minimum range should be between 14.8lbs and 26.7lbs at a PR of 1.68 when running 9 psig in plenum without intercooler.
 
Remember these are just sizing calcs to ballpark. Actual dyno will invariably be different.

259°/265°
-9/28 40/-13 @0.050
21/58 69/16 adv Intake advanced 4° LSA112.5 overlap 37°
On cam at ~ 2250 rpm = peak torque about 2500 rpm; peak power ~ 4000 rpm
Effective compression ratio valve closing @ 58° = DCR 7.4. Bmep ~ 182 psig
Boost ratio 11.9

Unboosted power ~137kW @ 4000
Torque 347Nm @ 2250

9 psig plenum pressure 244kW @4000
720 cfm exhaust 520 cfm intake
73mm throttle body 3 ½" exhaust 3 ½" fresh air pipe.

Non IC:

max power 4000 rpm PR = 1.68 @ 31.4 lbs/min (520 cfm, 245 l/s)
power 4800rpm = flat curve cam = 242kW , but drop ~100Nm torque PR= 1.68 @ 31.2lbs/min
Peak torque 650Nm @ 2500rpm PR = 1.68 @ 19.6 lbs/min ( 323 cfm. 152 l/s)

So say you want something that gives a good daily drive you would choose something that clusters the 31 lbs/min around the peak efficiency island and 20 lbs/min a little to the right of surge line. The PR 1.68 should ideally cut a horizontal line through the middle of the peak efficiency island.

e.g. http://www.turbobygarrett.com/turbobyga ... 5330_2.htm

The turbine selection is based on the expansion ratio which I like to keep below 2.. In this instance the exhaust flow is:

At 4000 rpm = 13.3 lbs/min
at 2250 rpm = 8.3 lbs/min

so you would run the 76 trim wheel and maybe live with a slight lag before spooling.

I suggest you confirm these figures with your turbo supplier, before buying, because I’m doing the maths between phone calls.
 
Thanks XPC66

Some of this is over my current level. However I will study this and learn the terms and their meanings. After I listed the cam specs last evening I went to the Crower web site to see if the cam was listed in the catalog. It is not. When I ordered it I visited with Mr. Crower about what the use was going to be and this is what he recommended and produced. I will measure the throttle body this evening; it is a twin from the Ford V8 light truck engine family. It is larger than the factory 4.9 I6 and I have modified the intake and plenum to match. The head is ported, the intake is matched, and the intake is also polished smooth inside and coated with a Techline Coatings finish. Premium fuel as expected and is ok. Pistons are custom made by JE forged and rings are TotalSeal gapless. Rods are stock from a 240 but polished and shot peined now equipped with ARP bolts. XPC, thanks for your help. You should give me one more freebee while you are being so generous and that is injector size. I will be using stock tanks and pumps from a mid 90’s Ford light truck. A note. Maybe I ought to consider backing off the boost a little if I am pushing the limit on anything. I live near Dallas Texas and we see some heat in the summer.

Later

Bill
 
I just checked some figures...I overestimated your boosted power and flow figures. Multiply each by 0.85.


Based on 242 x 0.85 = 205kW and 20% latency for the injectors at full flow you will need 360cc (34lb) or thereabouts with the megasquirt on bank fire.

TYou will get away with a ~ 72mm throttle body. If you have the V8 explorer type twin throat: 2 x50mm you'll be close.
 
I would have to thank the Queen for our system of measurements, Gauges, inches, feet and yards. I am in the lost generation of the metric/English mix up. If they would have just switched a generation before! In short what is the conversion for Newton’s Meters to Ft-lbs And KW to horsepower?

I will be at the home workshop in a few minutes and will confirm the 50mm x 2 for the throttle body. The missing ARP head bolt came by mail today, APR is a good company, I needed 1 bolt and they sold it to me with no minimum billing and no BS. I ordered the 36 tooth-timing wheel today from MegsSquirt.

Mr. XPC66. Thanks you for your help. This will be a running vehicle in a few months.

Bill
Waxahachie , Texas
 
brnwaxa":yw2p5gol said:
I would have to thank the Queen for our system of measurements, Gauges, inches, feet and yards. I am in the lost generation of the metric/English mix up. If they would have just switched a generation before! In short what is the conversion for Newton’s Meters to Ft-lbs And KW to horsepower?

...........
Bill
Waxahachie , Texas

I was at primary school in the time when the Oz govt changed teaching from the imperial to metric, pounds to dollars and ink to ballpoint, so I guess I'm a little ambidextrous.

However, why anyone would deliberately choose to revert back to lbs, feet and inches defies logic (unless it was for industry protectionism). I will admit I do all my calcs in metric then use something likethisto convert back to the primitive system.
 
XPC66

Thanks for the link to the conversion link


I was grown and with kids and grand kids and our goverment is still going through the motions of converting. In day to day business here in the US 90% of measurement is still English system. I do however appreciate the vast benifits of all metric.
 
brnwaxa":3sob75qj said:
I would have to thank the Queen for our system of measurements, Gauges, inches, feet and yards. I am in the lost generation of the metric/English mix up. If they would have just switched a generation before! In short what is the conversion for Newton’s Meters to Ft-lbs And KW to horsepower?

I will be at the home workshop in a few minutes and will confirm the 50mm x 2 for the throttle body. The missing ARP head bolt came by mail today, APR is a good company, I needed 1 bolt and they sold it to me with no minimum billing and no BS. I ordered the 36 tooth-timing wheel today from MegsSquirt.

Mr. XPC66. Thanks you for your help. This will be a running vehicle in a few months.

Bill
Waxahachie , Texas
I hope you are still connected. Six years later and I have regrouped and I am back on this porject. For some reason I can not log in and have created a new account. User name is brnwaxa52
 
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