Cam selection info help for boosted 250 ?

[powerband]

Help with information and/or AVAILABLE Cam selection for boosted small block six 250 appreciated, anecdotes not so much :

Basic SPECS, add'l as needed :

250 Small Block Six

Clean - 'low miles' D7xx stock block / brgs / Pistons.

D0xx Cyl head , 54 cc chambers , V8 springs, spring ringed seals w/machined seats, Back cut valves , ARP bolts , Composite Gskt.

Currently working on Direct - Mounting the 2Bbl Carb on the D0xx head.

(SCR = @ 8.7 : 1 by most calcs'.)

Vortech V2 Supercharger with pulley ratio optimizes 3-5 K RPM powerband.

Into Maverick with T5z OD , 3.80 Rear

.


( Holley 2300 modified for Blow-Thru BPV PV , Sealed shafts , Smoothed and Xtension tube into charge pipe, FP Ref' port in hat area, BOV current limit @ 6-8 PSI .
Currently 2Bbl adapter into original Single Barrel manifold intake. )

Also working on cam selection for previous Draw-Thru Turbo setup to use with a 200 or 250 and set of FORGED TRW pistons with similar other specs.

.

thanks

 

[aussie7mains]

What is your intended use? Are crowcams available in the US? Ive a blown crossflow, I run entirely street use, I speced my cam to allow it to rev to5000rpm (stock cam wont allow this). Its Hydraulic 208 degrees @0.050. This idles pretty smoothly. For a supercharged engine, less duration is needed, the compressor will push the air into it.https://www.crowcams.com.au/Portals/0/Crow2020/CrowCams2020.pdf?ver=2019-12-18-095023-240 The 63603 would be my pick. This is the cam card for my engine, this is for a crossflow, which can handle a bit more lift than the precrossflow.

 

[powerband]

don't think Crow Cams in U.S. market

... thanks for the feedback, intended as good-weather driver that will cruise at higher Interstate speeds (U.S.) and carve mountain roads rowing through the T5's gears, sometimes on way to 'test and tune' days at speedway.

good to compare cam specs and start to see key differences. my other 250 car has NA Tri-Power carbs and older Clifford (Clay Smith?) '272' Hydraulic cam - same T5 and 3.80 rear combo' for powerful 3-5K RPM (5500< if not careful! )

Your crossflow cam spec of Rocker Ratio stands out to me as much greater than U.S. logheads' are capable.

 

[aussie7mains]

don't think Crow Cams in U.S. market

... thanks for the feedback, intended as good-weather driver that will cruise at higher Interstate speeds (U.S.) and carve mountain roads rowing through the T5's gears, sometimes on way to 'test and tune' days at speedway.

good to compare cam specs and start to see key differences. my other 250 car has NA Tri-Power carbs and older Clifford (Clay Smith?) '272' Hydraulic cam - same T5 and 3.80 rear combo' for powerful 3-5K RPM (5500< if not careful! )

Your crossflow cam spec of Rocker Ratio stands out to me as much greater than U.S. logheads' are capable.

:You could run a fair bit taller final drive, IMO, even with a 0.8 O/D it comes out as 3.2:1, a blown 250 will pull that easily, you could come up to 3.25 even with the Od. A blown 250 will have peak torque around 2000rpm and about 500n/m even on lowish manifold pressure. As to the cam I use, its a crossflow which has the cleveland style valve train, same springs rocker arms etc, I did not want to risk breaking up the valve train, crossflows have a long pushrod and fairly big valves compared to the log head (1.84/1.54 stock). I have a the blown 3.3litre crossie, I estimate 500n/m torque, and I cant tell where it peak is, its doesnt seem to have one, its everywhere! I run a 3.25 final drive on 195x60x14 tyres, I have a 4 speed direct in 4th, you are always looking for another gear, I wish I had an O/D, but ratios on the common T5 here are low in first, which i dont want or need. I am pulling 2300rpm at 80km/h (50m/h)My engine revs very freely, but the torque available means you dont need to. The positive displacement compressors give abundant torque at any time, just what is needed for road driving.

 

[pmuller9]

What rpm do you start to see boost?

How much boost is there at 5000 rpm?

 

[powerband]

Not really sure how to answer - Currently limiting Boost to @ 6-10 PSI pending further engine mods. With serpentine 6.125” (5.0 V8) Crank Pulley and 2.5” Supercharger pulley, the two pulley sizes and internal SC step-up gearing yields an IMPELLER rotation speed calculated at @ 22,000 RPM at cruise speed with engine RPM @ 2500RPM. At typical 250 SIX upper shift point of @ 5,000 RPM the Supercharger impeller speed approaches 45,000 RPM

Charge pipe BOV limit references intake manifold vacuum permitting boost to rise as vacuum transitions to pressure in intake dependent on throttle position interaction.

Vortech specs are:

Supercharger	Gear case	Max Speed	Max Boost	Max Flow	Max Power	Peak Eff.	Inlet OD	Outlet OD

V-2 SC

Std

50000 RPM

20 PSI

1000 CFM

680 HP

72%

3.5"

2.75

 

[aussie7mains]

What rpm do you start to see boost?

How much boost is there at 5000 rpm?

Just in case your asking me, (dont think so) Ill give you info on my rig. Blower runs at 2.97 times crank speed, 8PK belt, manifold pressure starts at idle depending almost only on throttle opening. I can get boost any time. Blower is 1.1litres displacement per revolution, I have seen manifold pressure of 70 inches of mercury=34psi ABS, which is 18psi boost. It might be higher at full opening, I lifted off when I saw this pressure. Generally belt slips starts around 14psi boost at over 4000rpm. I have a completely stock bottom end which was used, but in good shape, I stuck rings and bearings in it, and the aforementioned camshaft. Ive done 5000km on it so far. IMO stock bits are better than most of us think.

 

[pmuller9]

Help with information and/or AVAILABLE Cam selection for boosted small block six 250 appreciated, anecdotes not so much :

Back to your original question.

As you know you have a centrifugal supercharger.
The airflow increases exponentially with rpm and the boost increases proportionally with rpm unlike a positive supercharger where the boost is relatively constant with rpm.
At throttle opening just above idle, the engine is pumping more air than the supercharger is flowing so the intake manifold sees a vacuum.
At some rpm the supercharger pumps more air than the engine is pumping and you begin to see intake manifold pressure. (boost)
This can be around 2500 rpm depending on engine displacement versus supercharger compressor size and drive ratio.
As the engine rpm increases, the boost increases until the engine reaches peak rpm at which point the boost is also at it's peak.

There are several ways to approach the camshaft selection.
The cam determines where the peak volumetric efficiency occurs for a given intake and exhaust system combination.
Since maximum boost is at peak engine rpm, if a person is looking at making the most hp for racing they would use a cam that made peak VE near the upper end of the rpm range.
A lot of times the engine is "overcammed" on purpose for drag racing.

If a person is looking for a wide power band for street use, then they can use a cam that makes peak torque just as boost is beginning and allow the supercharger to increase the torque with boost as the VE drops off due to the cam and head combination.
That's why I asked you if you knew at what rpm you started to see boost.

So, it depends on the type of power band you want?

Have you run this engine with the V2 SC supercharger?

 

[powerband]

getting closer to optimizing a cam selection with forum assistance,

" Have you run this engine with the V2 SC supercharger? "

Maverick 250 has a couple K miles with current V2 Blow-Thru setup. As a street car, a wider powerband than 'race' cam is desired for not a daily driver but fair weather performer with enthusiastic driving.

V2 boost is mostly diverted / released until RPM climbs but is quite linear at WOT from off idle to max RPM.


Boost is available at any throttle but dependent on RPM and throttle position . 2Bbl adapter to 1Bbl manifold limits flow/boost and currently working on direct-mount for the 2Bbl. Plan is to change Cam when modified head is installed.

. .

Maverick's - Stage 1 had Draw-Thru turbo until piston failure, stage 2 was getting V2 setup manageable, stage 3 was rebuilding car suspension, brakes, drivetrain etc. to manage power adder and current build stage is optimizing engine to the cars' capabilities...

hav e fun

 

[Kritas]

Did you mean Crower Cams? They've been around for a long time.

Camshafts | Aftermarket High Performance Cams | Racing Cams

Crower's high performance aftermarket camshafts for international and domestic automobiles, diesels, boats, tractors, motorcycles, and trucks. Crower leads the market by making high quality products at affordable price.

crower.com

 

[pmuller9]

If you want peak engine VE around 2500 rpm, go with a cam similar to Aussie7mains that has a 108 degree .050" duration.
Schneider 131H, 208/208, .435"/.435" on a 112 LSA.
Isky 321262, 208/208, .445"/.445" on a 109 LSA
Note: The Schneider cam will have a smoother idle than the Isky cam because of the wider LSA.

If you want to push peak VE up another few hundred rpm.
Schneider 135H, 214/214, .442"/.442" on a 110 LSA
Howards 280938, 213/213, .450"/.450" on a 110 LSA

Companies are having trouble getting cam cores.

 

[aussie7mains]

Did you mean Crower Cams? They've been around for a long time.

Camshafts | Aftermarket High Performance Cams | Racing Cams

Crower's high performance aftermarket camshafts for international and domestic automobiles, diesels, boats, tractors, motorcycles, and trucks. Crower leads the market by making high quality products at affordable price.

crower.com

https://www.crowcams.com.au/Portals/0/Crow2020/CrowCams2020.pdf?ver=2019-12-18-095023-240o,

Crowcams Australia, they are probably the biggest supplier down here, they do have stuff for the precrossflows, a bit limited. The crossflow, sohc and barra are better cater for.

 

[powerband]

thanks for the useful suggestions , the differences between specs with typical high compression NA and denser' Boost become evident with comparison.

'Small Block Six' 170 > 250 cams are a niche / low production run item contributing to lack of availability. 'Big Block' 300 / 240 has more later model use and more available parts .

Clay Smith catalog has excellent specs for powerband comparisons and offers this solid' cam -( current availability unknown) :

C-7872-14-B ( Excellent Solid Cam Turbo ) Ford 144,170,200,250

C-7872-14-B ( Excellent Solid Cam Turbo ) Ford 144,170,200,250

Clay Smith Cams, home of Mr. Horsepower engineers world class camshafts and custom cams. If you need extra horsepower, performance and the muscle car sound, check out our line of cams.

claysmithcams.com

the '61 with NA Tri-Power has Clifford 272 cam believed sourced from Clay Smith :


.

Companies are having trouble getting cam cores.
' should donate a few...


hav fun

 

[drag-200stang]

Mr. Muller, could you look at the solid cam specs, in the small six for sale section. Would it be good for a centrifugal boosted or a turbo what is your opinion of it?
Thanks'

 

[pmuller9]

Mr. Muller, could you look at the solid cam specs, in the small six for sale section. Would it be good for a centrifugal boosted or a turbo what is your opinion of it?
Thanks'

I don't see a spec for LSA but I suspect it is tight since the cam was designed for circle track and it shows a relatively low rpm range.
Being split duration and possibly a tight LSA, it will not work well with a turbocharger.
The split duration will work ok with a centrifugal supercharger if the cam had a wide LSA.
In any case this is a high rpm racing cam that offers little power below 3000 rpm

 

[pmuller9]

Clay Smith catalog has excellent specs for powerband comparisons and offers this solid' cam -( current availability unknown) :

C-7872-14-B ( Excellent Solid Cam Turbo ) Ford 144,170,200,250

The C-7872-14-B cam will have a peak engine VE around 4000 rpm.
It will make power to 6000 rpm.
This is the case I referred to where you move the peak engine VE to the upper end of the rpm range to make the most horsepower.

Your response was:

Maverick 250 has a couple K miles with current V2 Blow-Thru setup. As a street car, a wider powerband than 'race' cam is desired for not a daily driver but fair weather performer with enthusiastic driving.

You will lose torque below 2500 rpm.
This cam seems to be a lot more aggressive than what you described for performance needs.
Is this what you want?

 

[aussie7mains]

The camshaft I have shown on my post was designed by Camtech for a blown application, as I said this works very well in my car, idles like a stock engine when bypass is open, goes into blower surge if its closed, I have to force this. Ive run this to about 4500rpm, there is no sign of letup there. I have the full kit with springs (cleveland) retainers etc, I have stock rocker arms and fulcrums, no problems at all, I run mineral oil 10w-30 which gives 15psi idling hot and 50psi @2000rpm hot. I used tonnes of assembly lube when assembling the engine. I would recommend something around this grind for boost, you dont need a lot of overlap to give high rpm power, the blower will do that, so stick with something more civilised.

 

[powerband]

"This cam seems to be a lot more aggressive than what you described for performance needs.
Is this what you want?" :

.. that was also my take on the Clay Smith C-7872-14-B cam, I want a notch below those specs on RPM / powerband and manageability.

availability is also involved and along with cam(hyd?) - would order complementary or suggested springs, etc and have machinist finish cut valves and seals .. .

Schneider also has listings for aggressive use 200 / 250 cams.

'have a set of Forged pistons (TRW 2217's - .030 over) for SC or next turbo project 250 or 200 ... .



have fun

 

[pmuller9]

.. that was also my take on the Clay Smith C-7872-14-B cam, I want a notch below those specs on RPM / powerband and manageability.

availability is also involved and along with cam(hyd?) - would order complementary or suggested springs, etc and have machinist finish cut valves and seals .. .

Use one of the two slightly aggressive cams I previously listed.
It will put peak engine VE around 3000 rpm for a very strong midrange.

Schneider 135H, 214/214, .442"/.442" on a 110 LSA
Howards 280938, 213/213, .450"/.450" on a 110 LSA

There is no reason to go with a larger cam unless you have a better breathing head.
If you try to push a stock log head, it will only produce a shorter power band.

Before you can decide on a valve spring, you will need to know the retainer height.