1 5/8" headers- limitations?

[barronj]

In a discussion on another board, the topic is what heads for a stroked windsor. The use is a grunt, low rpm range motor, never intended to get above 3K in the theatre (rock crawling, trails). Some rigs are dual purpose built, driver+trail, but even then, it's a lifted brick on a short wheel base, not a race car.

The aftermarket headers for the application (early Bronco) max out at 1 5/8", there just aren't any choices beyond custom headers.

Where does a 1 5/8" header start to choke off a head?

Are they a big enough header for an AFR 205? 225?

[turbostang]

They're good for about 1250HP or so, depending on the size of the turbo....errrr...wait....

I don't think there's a clear, defined cut-off point for where they will and won't make power. I'd tend to believe the work better on mid sized engines, under say 400CID.

To answer your specific question, they choke the shit out of both of those heads. I have a car right now, with 205's - and they cover up a pretty good bit of the port. 225's - out of the question.

[greenbullitt]

Why such big heads if youre building a grunt motor? If it works down low, put a smaller head on it IMO. 205/225 would be a big waste...just my .02

[2cammer97]

Why such big heads if youre building a grunt motor? If it works down low, put a smaller head on it IMO. 205/225 would be a big waste...just my .02

I'm certainly not an expert, but I agree with Paul. Why put AFR 205/225 heads on an engine you say will rarely see over 3k rpms? You can make plenty of low end power even on a stroked windsor with AFR 165/185 heads and the 1 5/8" headers you mentioned.

Marcus

[barronj]

That's precisely my point.

Some are saying that a big motor should have big heads, and I'm arguing that if the intention is torque off idle, and you're ultimately limited by a 1 5/8" header, why spring for anything larger than 185/190 cc intake runner heads. I'd encouraged a friend to jump at the TFS 170cc Twisted Wedge heads on sale, and want to have reinforcement that I didn't steer him wrong.

My motor (351, AFR 185's) is a street cruiser. The thread was about heads on a 408, not my thread, not my build, and not my friend's motor either. Just a thread, and my arguments.

[2cammer97]

That's precisely my point.

Some are saying that a big motor should have big heads, and I'm arguing that if the intention is torque off idle, and you're ultimately limited by a 1 5/8" header, why spring for anything larger than 185/190 cc intake runner heads. I'd encouraged a friend to jump at the TFS 170cc Twisted Wedge heads on sale, and want to have reinforcement that I didn't steer him wrong.

My motor (351, AFR 185's) is a street cruiser. The thread was about heads on a 408, not my thread, not my build, and not my friend's motor either. Just a thread, and my arguments.

That doesn't surprise me. Isn't the number one rule in the car world "bigger is always better"?

Marcus

[greenbullitt]

That's precisely my point.

Some are saying that a big motor should have big heads, and I'm arguing that if the intention is torque off idle, and you're ultimately limited by a 1 5/8" header, why spring for anything larger than 185/190 cc intake runner heads. I'd encouraged a friend to jump at the TFS 170cc Twisted Wedge heads on sale, and want to have reinforcement that I didn't steer him wrong.

My motor (351, AFR 185's) is a street cruiser. The thread was about heads on a 408, not my thread, not my build, and not my friend's motor either. Just a thread, and my arguments.

Its very hard to find a "stopping point" for alot of people once they start, and some just dont know. Ask this, "do dump trucks with big cube gas motors have big ass ports?" NO. small ports make big torque. same reason truck heads TYPICALLY have small valves too. Youre not spinning it to the moon...

[garycrist]

I stole some formulas from another place.

1. Peak torque rpm = Primary pipe area x 88,200 / displacement of one cylinder. Given this relationship, we can perform some transposition to solve for the primary-pipe cross-section area.

2. Primary pipe area = peak-torque rpm / 88,200 x displacement of one cylinder. We can also determine the required displacement of one cylinder (multiplied by the number of cylinders for total engine size) by:

3. Displacement of one cylinder = Primary pipe area x 88,200 / peak-torque rpm.

Using the formula, Area = (3.1416) x (id radius) x (id radius), we obtain the following cross sections: 15⁄8 inches = 2.07 square inches; 13⁄4 inches = 2.19 square inches; 17⁄8 inches = 2.53 square inches.

408/8= 51cid per cyl.

Using formula 1 and 15/8 headers.

2.07*88200/51=3579 R.P.M

Adding a longer collector will help a bunch too!

[blownragtop]

In a discussion on another board, the topic is what heads for a stroked windsor. The use is a grunt, low rpm range motor, never intended to get above 3K in the theatre (rock crawling, trails).

Some are saying that a big motor should have big heads, and I'm arguing that if the intention is torque off idle, and you're ultimately limited by a 1 5/8" header, why spring for anything larger than 185/190 cc intake runner heads. I'd encouraged a friend to jump at the TFS 170cc Twisted Wedge heads on sale, and want to have reinforcement that I didn't steer him wrong.

This thread reminded me of MMFF’s ultimate cylinder head guide (Jan 2004). Test motor was a 393 stroker with XR286R cam (248/254 - .614/.621). They tested the motor with variety of heads including a set of E7s. Up to approximately 3800 rpm the stockers were virtually equal to any of the aftermarket heads. It just stands to reason that if a stroker needs 300+ cfm to turn 6500+ rpm then it needs approximately half of that airflow to turn your 3000 max rpm. If the factory heads that flow 166 are not a restriciton within your set operating parameters then the TFS heads that flow 270 (IIRC) certainly won't be.

[Fast.0]

How much do you think the 1 3/4 shorties can handle guys, that is what is on my brodix heads, Ive gone 60's with them on it. I hate messing with long tubes they bring out the bad in me.