7000rpm /480hp

I am currently making around 435fwhp @6200RPM from my 347 with 10.1. comp alloy heads,solid flat [email protected] etc....
If I was to go up in cam to a solid roller about mid .600 lift,250 ish@ .050
would I make around 480 maybe 500 at no more than 7000rpm?
Would my 10.1comp make to undrivable down low in the revs when I drive it on the street(occasionally)
I have a tremmec 3550 and 4.1 gears

 

[Mark Worthington]

Probably, but I think the answer really depends on whether or not your heads and intake will support the increased airflow.

on edit - Oh yeah...at 480 hp, especially at 7000 rpm, you are running up against the limitations of the stock 302 block. At a minimum, you would need a stud girdle. Ideally wou would use a Boss 302 block, Dart block, or other race-prepped block along with a forged crank ond rods for a stroker to live long and prosper at that rpm.

 

[Kevin M]

List the Heads, Intake Manifold, Carb, type of bottom end components (Forged, Cast), etc. Without that there is no way to give you any meaningful information. Also, how frequently are you willing to go into the motor and replace valvetrain components, etc.

 

Ok......scat cast steel crank,scat h beam rods,srp forged pistons,quad 44 mm idf webers,windsor snr's,shaft mounted roller rockers,Intake cfm Exhaust cfm
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[Kevin M]

Your problem does not appear to be the cam.

With the cam you have, you should be making 500 hp at about 6,500 RPM. The problem is the 44 IDF carbs. The venturi (choke) is probably in the range of 38 to 40 mm on those.

Assuming a 100% VE (which you should be able to get if the flow numbers on the heads are correct) you need 44mm to 45mm venturis to feed that engine at those RPMs. You are badly choking the engine off at the top end by running those carbs.

You have several choices. You can go to 48 IDAs or 48 IDFs with 44mm chokes (Venturis). You can go to an independent runner EFI system with 48mm throttle bodies. You could go to a 750 cfm 4 barrel carb on a single plane manifold like a Victor Jr. (I would recommend a Race Demon RS 775cfm). Any of those should get you close to 500 hp.

I would keep the engine under 7,000 RPM if it were mine, because of the cast steel crank. 7,000 is fine with a forged crank and a good stud girdle, but is pushing it a little without the forged crank. (If you don’t have a stud girdle in the engine now, get one before you start running to or above 6,500 RPM.)

If you ever do change the cam, I would suggest going to a dual pattern cam with 6 to 8 degrees more timing on the exhaust side. The numbers on those heads are good, but the exhaust flow is a little low relative to the intake flow and they would probably do better with the split profile.

The 10.0:1 compression ratio is fine and could actually be raised to 10.5:1 for street use with those heads as long as you always run minimum 92 octane gas.

Just out of curiosity, what kind of car are you running this engine in, how much does it weigh, and what is the front to rear weight distribution? (The Tremec 3550 suggests that this is not a mid engine car)

Kevin

 

The car is a 68 mustang,weight 1320kgs.

Assuming a 100% VE (which you should be able to get if the flow numbers on the heads are correct) you need 44mm to 45mm venturis to feed that engine at those RPMs. You are badly choking the engine off at the top end by running those carbs.
Its funny you say that......i have tried and tried to find out if I would benefit any from going to 48 ida's and I couldn't for love nor money get an answer !At last !
If I can sell my 44's I have a set of 48ida's I can get my hands on.

 

[Kevin M]

I would recommend you talk to two companies about this before you begin.

http://www.piercemanifolds.com/products.htm

http://www.inglese.com/

Since you are in Australia you could e-mail them.

The cross sectional area of the intake has a very large effect on the RPMs where the engine makes peak torque. There are two simple formulas for calculating this.

The first (and more accurate) is:

Cross Sectional Area of a Port:
Area = Volume of One Cylinder(Cubic Inches) x Peak Torque RPM / 88200

Once you have the Area (in Sq. Inches) you divide it by 3.14 then take the square root of the resulting number and multiply that by 2 to get the diameter of a round port in inches. Then multiply that by 25.4 to get millimeters.

For your car, assuming a torque peak at 5,000 rpm which should give us a power peak at about 6,500 rpm, we get 2.46 sq. in. – 1.77 inches dia. – 44.95 mm.

If your current carbs have 38 mm venturis, working it backwards would give you a cross sectional area of 1.76 sq inches and that would give a torque peak at 3,575 RPM, which is right for a power peak at a little over 5,000 RPM.

If you current carbs have 40 mm venturis, working it backwards would give you a cross sectional area of 1.95 sq inches and that would give a torque peak at 3,950 RPM, which is right for a power peak at about 5,500 RPM.

In either case, you can see that the carbs are sized to make peak torque and power much lower in the RPM range than the Heads and Cam.

The other Formula is actually a “Rule of thumb” that was developed by Alfa Romeo for sizing webers. This is not as accurate as the other formula and only gives you a ballpark approximation. It is:

Size (mm) = CC’s (of 1 cylinder) x Peak HP RPM x Square Root / 50 (for Venturi size)

With this we get 43mm for a 6,500 rpm power peak.

Weber makes 44 mm and 46 mm venturis for the 48 IDAs. The 46 mm are really too large for a 48 mm carb body, don’t idle well and have poor low speed throttle response. The 44 mm venturis will be much better all around. As you can see, you are at the upper limit of Weber 48s with your engine. If you try to go higher at some point in future you will have to go to EFI or a single 4 barrel carb.

 

[Dave Wharran]

You might inquire about the use of Gene Berg's larger IDA flanged carbs. They make them in 48,50, 52, 54, 56, and 58mm sizes.
I've never used these particular pieces, but have used many, many other Berg parts throughout the years. Not inexpensive, but the best quality stuff you'll find. I've never went wrong with their parts.

http://www.geneberg.com/58ida.htm

There is at least one other VW racer that makes large bore IDA pattern carbs. I'd have to search a bit, but I remember his name being Jack Sachette (or something similar!)
Memoriies don't always survive the test of time so well!!

 

[Kevin M]

That’s really interesting Dave.

I’ve seen companies that bore Weber 48 bodies out to 51mm, but these things look big enough to substitute for the old Weber 58 IDAs. You might have to have the manifold extrude honed to work with the larger sizes, but that wouldn’t be too difficult.

Great Information!

 

[Ian Clark]

Hi Kevin, Maybe you can solve this one: how do the Nascar boys get 700+hp out of a 352 V8 with a restrictor plate and 650cfm carb? Seems to me 8 44mm throttle plates have greater surface are than 650 cfm carb. I don't think our Australian pal is under caburated.

 

[Gary Gibbs]

Individual runners (e.g. webbers) have to rely on one carb (and thus area) per cylinder. When cylinder one is filling it only draws air through carb barrel one. When cylinder one is not filling then cylinder one carb barrel is doing nothing. With single carb each cylinder shares the area. Thus each cylinder has the full area of the carb when it is that cylinders time to fill. That is why a webber setup always seems over carbed, but it is actually not because each carb barrel is only getting used 1/8th of the time.

 

[Kevin M]

Ian,

As Gary pointed out, the main difference is that the NASCAR engine has a manifold with a plenum with all 4 barrels of the carburetor feeding the plenum so that when each cylinder draws air, it draws through all 4 Venturis at the same time. With Webers each cylinder draws through only one barrel on the carb directly attached to it. To greatly over simplify, in theory, you need as much Venturi area in one barrel of a Weber as you have in the entire 4-barrel carb on a single plane manifold. In Practice there are issues that modify that, such as the fact that you have two intake valves open at the same time in a V8 engine, but you get the idea.

Restrictor plates create an absolute limit on airflow because when the flow through the plate reaches the speed of sound it cannot go faster and flow any additional air. For a normal engine there is a great loss of efficiency when the flow speed goes above a mean inlet mach number of .5 (which we could badly over simplify by calling half the speed of sound). The NASCAR engine builders do their best to find ways to get their engines to work with this, and given millions of dollars and some of the most talented engine builders in the world, they do an incredible job. But it is not something you could (or would want to) duplicate on your own for a street driven engine.

Some other things to remember are that NASCAR engines turn about 8,000 RPM, use completely different Cylinder Heads with 30% to 40% more flow, have compression ratios above 14:1, and don’t make 700 hp in speedway trim. The small restrictor plates that NASCAR uses for the high speed circuits reduce the horsepower considerably for those races.

Kevin

 

[Neal]

Your motor won't last long at 7k rpm with a cast crank. I have a similar setup but used 48IDAs. 462hp on pump gas @6000rpm. Race gas and timing adjustments gave us an addition 12hp but I backed the setup off for street use. What does you cam profile look like? Mine is asymetrical with a max lift of .550.

 

248 @.050.560lift,110 lobes single pattern.

 

[Ian Clark]

Thanks Kevin and Gary, Makes perfect sense to me now!

Cheers