Cam discussion - Supercharger

Mostly stock 250 with Vortech centrifugal supercharger, 2Bbl Holley , boost referenced FI type 'return' fuel system :



Road tuning of stock trim- supercharged 250 is getting more stable, the next upgrade should be a more boost-able camshaft. Centrifugal Vortech SC builds boost with RPM more like a turbo than Roots type Eaton SC's etc. / Maverick 3Spd Toploader , 2.79 rear gears will get a T5 and 3.80 posi .

Any favorite working forced induction cam grinds with limits of iron log 2bbl mod' head and 250 rpm limits ? .

I don't find any Hydraulic grinds labelled as 'turbo' . Solid lifter 'turbo' 200 cams emphasize higher RPMs, maybe not best range cam grind for the 200 stroker version - 250 RPM's-? .

have fun

If I remember correctly a blower cam is going to be a split duration cam say like 270 / 284 with a wider lobe separation of 112 to 114 degrees. Good luck

as always, my answer to any "which cam?" question is:

Call Schneider Racing Cams (619) 297-0227, speak to Jerry Cantrell, tell him what you have, what you want to do, and leave the rest to him (you will be glad you did)

Declaimer: I do not work for them, or have any business with them, other then being a very happy customer. (they ground me a custom turbo cam for my 200 at normal price)

You will need to supply more info either for here or when you go to order a cam.

Which Vortech supercharger?
What is the max rpm you are running presently and how much boost does it show at that rpm?
What is the Vortech supercharger drive ratio from the crank?

Are you using a header or the stock log exhaust manifold?

pmuller9":3o5euig3 said:

You will need to supply more info either for here or when you go to order a cam.

Which Vortech supercharger?
What is the max rpm you are running presently and how much boost does it show at that rpm?
What is the Vortech supercharger drive ratio from the crank?

Are you using a header or the stock log exhaust manifold?

Click to expand...

thanks, I will get the info together as needed:

> Vortech V2 ( 52000 max impeller rpm)


> with current fuel/ign 4500 RPM is max held rpm but crappy car gearing prevents effective boost range. The blow-off is a XSTurbo WRX application, with @ six washers gets @6 lbs boost if I hold second gear ...

> 6.5" crank / 2.87" SC pulley yields @ 37000 rpm impeller speed @ 4500 rpm, just received a compressor map from another forum, will probably reduce to @ 2.5" for more low rpm boost.

> for initial tuning using stock mid 70's 250 exhaust with a Bosch wide band sensor/ Autometer AFR with good 13-14's with boost. A neat dual out header is saved for cam swap.


. /

Maybe I am to old school, but if it is not car that you will put a lot of miles on, I would go solid lifter. I think they perform better even with a mild grind. Easy to adjust , no is it pumped up is it collapsed, it is exactly what it is. Will runs one in Kelly's car .

Question
At 37,000 impeller rpm you should be getting at least 10 lbs of manifold pressure.
It the XSTurbo BOV blowing off some of the pressure?
I would think 6 washers should hold it closed at WOT.
From the picture it looks like the BOV reference line is going to the intake manifold?
If so that is correct.

Correct me if I'm wrong but looking at the compressor map it appears that the operation is close to the surge line?
The reason I'm bringing this up is one possible reason for low boost is the compressor is being run into the surge zone and not pumping at full capacity.

On the cam question.
The cam should have more exhaust duration than intake duration to help evacuate the increased exhaust gas volume. The header will help with this also.
The cam should provide peak HP at max rpm since that is where peak boost will be, meaning you can look at fairly long durations.
You get to decide what the max rpm will be. Not sure how far you want to push the stock bottom end. I'm thinking 5000 rpm
Overlap is not critical with Centrifugal superchargers since high boost is at the upper rpm range. LSA can be 110* to 112*

For a hydraulic cam the Schneider 270-80H would work.
The Schneider solid lifter cams are all single profile. You would need a custom grind if you wanted a solid lifter cam.
The one problem with solid lifter cams is the advertised duration is shorter than a comparable hydraulic which raises the DCR and make the engine more prone to detonation on pump gas.
Give Schneider Cams a call.

thanks for the additional input,

I am leaning towards a solid lifter cam as I don't plan on too many miles and adjustment is simple enough. The learning curve for forced induction brings many aspects to push my understanding of fuel, ignition and mechanical limits - that's why I got onto this project. I believe I have a basic understanding of the surge line limits on the map but would appreciate a simple explanation of factors.

Taking forced induction project methodically and have more work/fun to complete on the Maverick before serious engine power is added. With the cars' current gearing there isn't much road opportunity to wind up the engine for sustained boost testing.

have fun

Here is an "S" trim map which is supposed to be the same as the "SC" trim.
The SC trim compressor is good for 680 HP.

A stock head, stock cam 250 has at best a 70% Volumetric Efficiency at peak torque and it falls off as the rpm increases.
The second area which reduces airflow is the lack of an intercooler.
The point of interest will be 4500 rpm where you observed 6 lbs of boost. At that point the impeller speed is 37,000 rpm.
Looking at the compressor map, at 37,000 rpm the pressure ratio is about 1.68 or 10 lbs of boost
Plugging the engine info into the following calculator, if you look at the corrected airflow in lbs/min you will see the flow is about 19 lbs/min at 4500 engine rpm.

Calculator Link

If you look at the turbo compressor map below the calculator section you will see all the points which represents the Load Line. That Load Line can be transposed onto the "S" trim map.

Going back to the compressor map, the point that represents 19 lbs/min at 37,000 rpm is shown by the arrow.
You will notice that it is clearly in the surge zone where the compressor fails to pump at capacity.
If it was a turbo, the compressor quits pumping which unloads the turbo and the turbo rpm spikes.
The engine quits pulling and the reduced exhaust pressure allows the turbo to spin back down where it begins pumping again and the cycle begins again. Been there when an exhaust rocker broke eliminating one cylinder.
In your case the impeller rpm can't run away since it is tied to the crank but you can still get reduced pressure.

Some points:
If you add an intercooler the airflow increases and the Load Line on the map moves to the right away from the surge zone.
If you increase the camshaft duration to help the VE at the upper rpm those points will move to the right.
If you increase the drive ratio in order to increase low end torque, the load line moves back towards the left into the surge zone.

A better match would have been the smaller V5 F trim supercharger. Link

powerband":2u1z9yyl said:

I am leaning towards a solid lifter cam as I don't plan on too many miles and adjustment is simple enough.

Click to expand...

Just something to consider.

If you go to a solid lifter cam, the advertised duration is typically much shorter than the same hydraulic cam profile.
The DCR will be raised a significant amount making the engine more prone to detonation.

SAE standard Hydraulic cam advertised duration is measured from .006" lobe lift.
Solid lifter advertised duration is measured from (Tappet clearance)/(Rocker ratio) + .006"

bubba22349":299h34qf said:

If I remember correctly a blower cam is going to be a split duration cam say like 270 / 284 with a wider lobe separation of 112 to 114 degrees. Good luck

Click to expand...

What you just described was most of the Crane street cams.

in the 80 and into the 90 they were listed in the catalog as for Turbo and supercharger useage.

Both of the cams for the 250 will have numbers

Ending in in ..3901 (H260) specs are 260/272 112 Lobe separation

ending in ..3941 (H272) specs are 272/280 112 lobe seperation

I did that from memory sorry I can't look them up have to hit the sack

thanks pmuller for clearing up some basic factors involved.

? > Can the crank driven Vortech be tested static for it's output or need loading like a turbo to really build boost? .

I am merging the forced induction concepts with the observed behaviours of the supercharger 250 build. Frankly I'm a little confused with SC results, setup gets to @ 10lbs at the SC outlet and carb hat but with road testing the manifold boost doesn't match or spool up like a turbo could be expected to under load.

Using SC port and manifold port Vac/Boost gauges and wideband AFR to keep track. I don't think I'm losing any significant pressure due to leakage. The stock cam limits upper rpm breathing but after road tuning observed air fuel ratios, the re-jetting and PV set to open mainly with boost ,the 2300's AFR's stay in safe range at cruise and with boost . The Maverick is easily driveable and the mild boost adds power where 250 would otherwise poop out.

Before the Vortech sc, the Maverick 250 used a Buick based draw-through turbo setup that pulled @ 10 lbs boost until loaded and could push 20 psi at manifold gauge . The head gasket let go with no other apparent damage, SC now using ARP head bolts ... . ( At 20 psi boost, the 250 with BOP turbo -Quadrajet would howl..)

The Vortech centrifugal supercharger setup inadvertently became available to me but I think the cost of most SC setups prohibit amateur project level builders from considering it a serious option. I paid @ $1K for an untested - head unit only - out of a blown and maybe internally trashed Ford Lightning. The Buick Regal /GN turbo setup cost @ $250 and a brand new 'offshore' turbo cost less than a good clutch. I started with an Eaton 'roots' type SC which are available inexpensively but found difficult to work with mounting and carb setups.

have fun

Are saying that the SC outlet and hat pressure is 10 psi at the same time the intake manifold is at 6 psi?
Is the carb at WOT during this time?

pmuller9":3f3sho53 said:

Are saying that the SC outlet and hat pressure is 10 psi at the same time the intake manifold is at 6 psi?

Click to expand...

Initial driving of the Maverick it seems the manifold pressure isn't reaching the SC pressure until sustained revs/close to WOT - I can't manage it on the street and really need more road testing, gauge testing and interpretation of the two boost gauges and AFR at different driving conditions. Current Vortech pulleys are from the SBF V8 application , considering the lower rpm - torquey' stock cam 250 may need a slightly different pulley gearing to have use of available powerband . Spec'ing a cam to shift 250 powerband up marginally and also help the SC blow through the big 2Bbl and adapter in to the log manifold efficiently with simple fabrication.



have fun

To answer a previous question.
A centrifugal SC does not need engine loading to produce boost like a turbo
The SC pressure is strictly a function of rpm.
When the engine is at 4500 rpm and the SC is at 37,000, the gauge pressure will be 10 psi at sea level providing the SC compressor is being operated within the efficiency areas shown on the compressor map.

The only way there can be a difference between hat and manifold pressure is if the carb is not at WOT or the carb adapter plate hole is too small.

However as you stated it is difficult to drive and watch multiple gauges.
Maybe the gauges respond differently where one lags behind the other?
This is where a data logger comes in handy.

Back to cams:
The centrifugal SC where boost is proportional to rpm presents a different challenge over a positive displacement SC or a turbo.
A cam with a tight LSA and more overlap helps initial intake charge flow when the intake valve opens when there is little to no boost while cams with wide LSA work better under higher boost conditions.

In your case the cam needs to have more duration to help higher rpm VE but still needs to support low rpm at low or no boost.
The Schneider cam I suggested meets the need.
Having a centrifugal SC that is on the large side for the engine is a headache.

It is common practice to use a centrifugal SC that is on the small side and gear it up for low rpm boost then limit the engine rpm to prevent overrunning the SC rpm limit.

There aren't many companies that have Off the shelf cams for the 200/250 Ford six and those that do carry mainly single pattern profiles.
If you want a cam with split duration and a 112* LSA it will have to be custom. Schneider will do that for you.

With my limited forced induction experience, this focused discussion upgraded my understanding. I'm sure anyone following this thread has also benefited.

Supercharger vs Turbocharger applications of fuel, ignition and Ford six metrics continue to make me question my understanding of the basics. Turbo and SC specific forums are helpful but usually have no Ford small block six experience or interest.

BTW the aforementioned BOP turbo setup on the 250 worked pretty well in initial road testing on the worn 250 that was in the 74 Maverick I got for this project. The problem simply was the fabbed' intake adapter was spec'd on my '61 Comet' engine bay with the 250. THe much lower fender and hood line of the 74 MAverick placed the turbo and carb @ 8 inches above the hood and looked ridiculous. So the waiting 'built' 250 was refitted with the Vortech/Blow Tru setup to build a mild driveable car with the kick of the torquey supercharged 250. The complete BOP turbo setup is shelved but ready for an earlier car, shorter 200 block or a Mav' tunnel ram hood and a turbo cam ... .

.. .



have fun