Help wanted - exhaust flow

[johnbeck]

I need to know at what rpms the exhaust flow of the factory manifolds will significantly(key word) effect my Bronco's performance. The rebuilt 302 I'm installing has the old Mustang H.P. grind cam, 165 AFR heads, 1406 Edelbrock carb. and manifold. Driving with my foot in it, 80 per cent of the time under 50 mph, when will the stock manifolds significantly choke the car's performance? Much thanks, John (I failed to mention that the Bronco has a stock rebuilt C4 auto trans. - a factor as to when it will up shift)

 

[DirtDonk]

With those specs, I would expect the stock exhaust to have a mild effect pretty much from 2000 to about 4000 rpm, but have a much bigger effect above 4000 rpm.

And frankly, the harder you push the pedal, the more the effect of the smaller exhaust runners becomes. So you might not notice, or hardly notice what most would consider normal driving around town, but if you're really wanting to jump on it all the time, you'd be leaving some performance on the table.
Just more of it above 4,000.

With a stock truck engine, cam and exhaust, they literally would run out of breath at just about 5,000 rpm anyway.

Paul

 

[73azbronco]

I need to know at what rpms the exhaust flow of the factory manifolds will significantly(key word) effect my Bronco's performance. The rebuilt 302 I'm installing has the old Mustang H.P. grind cam, 165 AFR heads, 1406 Edelbrock carb. and manifold. Driving with my foot in it, 80 per cent of the time under 50 mph, when will the stock manifolds significantly choke the car's performance? Much thanks, John (I failed to mention that the Bronco has a stock rebuilt C4 auto trans. - a factor as to when it will up shift)

Stock, never.

 

[chuck1022]

I have watched about 10,000 videos on youtube about this. My takeaway was headers are good for higher rpm driving......which I dont do in my Bronco. Engine Masters did some shows on it.

 

[johnbeck]

mustang H.P. manifold

I'm running out of time getting together final components for my engine install. I'm seriously considering using my original 302 exhaust manifolds but a last hope are the early 289 H.P. Mustang headers. What makes them a challenge to adapt to a 302 Bronco exhaust system? Paul from Wildhorses stated the stock manifolds wouldn't have much negative effect 2000 to 4000 rpm. Would the H.P. Mustangs manifolds work much better in the under 4000 rpm range?I don't want to beat this exhaust issue into the ground, it's just I'm going to be stuck with whatever I select for probably the next 10 years. Thanks for your much appreciated advice.

 

[DirtDonk]

The keyword being "much" in this scenario. Remember I said that they "would have a mild" effect between 2000 and 4000, and much more after that. Because after 4,000 rpm the stock setup kind of falls on it's face and is tapped out by 5,000 rpm. Below that you would not notice the loss as much if you were driving mildly. But even a mild effect means you leave something on the table and lose some by not upgrading the manifolds.
Certainly some of that is cam, some is heads, some is intake. But some of it is stock exhaust manifolds too.

But I think I also stated that if you're pushing it hard and racing around, you'd likely be losing some even below 2000 rpm because it's all about flow at high throttle settings as well, and not just at high rpm.
A full throttle pull is what they do on dynos, and why you see bigger numbers with headers more often. But it's also your truth, if you're going to be driving that way.

Simply stated, if you're building a mild engine for cruising and don't need to use all it's potential all the time, then exhaust manifolds are fine. If you want to get the most out of whatever package you put together, then headers are pretty much a must no matter how you look at it.

From what we've read here on the forum the HP 289 manifolds are actually pretty good. I know a few here are using them, but don't remember hearing what they had to do, if anything, to get them to work on a Bronco. Sounded pretty straightforward.

Hopefully the users will chime in now. I was hoping they would before.

If you want to eek the max out of what you're building and won't be happy leaving any on the table, upgrade to bigger manifolds, or headers.

Paul

 

[68ford]

Do you know the lobe separation on that cam? If it's relatively tight like 110 and scavenging at lower RPM is there, it could make noticable improvements as low as 2500. The theory of circle track cams designed to make great mid-range torque to pull hard out of corners. Exhaust flow and zero restriction is crucial and makes a big difference between 2000 to 4000 RPM torque. If it's 112 or high like most efi cams designed to make good low RPM vacuum, it is not as necessary. Those cams always have less torque and torque is at higher RPM.

 

[blubuckaroo]

The Small Block Ford motor's head has an exhaust port defency. That was fixed with the Cleveland head design.
Good long tube headers create a suction (referred to as evacuation) that can really wake up a Small Block Ford.
With a stock cam, there's no need for headers. But increasing the pipe diameter or going to dual exhaust will help a stock cam.

 

[johnbeck]

68ford, The speed-pro cam, CS-108R, lists the distance between lobe centers as 113degrees. Valve lift .460, duration 298degrees, gross lift at cam .288, duration @ .050 cam lift .218degrees. Max Lift intake 107 A.T.C. Rocker ratio 1.6 - 1 All Greek to me. The AFR heads; intake port volume 165cc, exhaust port volume 68cc, combustion chamber size 58cc. Any thoughts? Thanks, John

 

[68ford]

68ford, The speed-pro cam, CS-108R, lists the distance between lobe centers as 113degrees. Valve lift .460, duration 298degrees, gross lift at cam .288, duration @ .050 cam lift .218degrees. Max Lift intake 107 A.T.C. Rocker ratio 1.6 - 1 All Greek to me. The AFR heads; intake port volume 165cc, exhaust port volume 68cc, combustion chamber size 58cc. Any thoughts? Thanks, John

Being you're at basically 300 degrees of duration even though it's on a 113 lobe sep, with the AFR 165 I would absolutely run long tube headers and preferably with 1 5/8 primaries

 

[DirtDonk]

That's a small lift for such a long duration, isn't it? Not that it's bad. Just uncommon I think.

Here's the description:

Cam style: Hydraulic flat tappet

Basic Operating RPM Range: 1,500-4,500

Intake Duration at 050 inch Lift: 204

Exhaust Duration at 050 inch Lift: 214


Advertised Intake Duration: 282

Advertised Exhaust Duration: 292


Intake Valve Lift with Factory Rocker Arm Ratio: 0.476 in.

Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.501 in.


Lobe Separation (degrees): 112

Computer-Controlled Compatible: No

Valve Springs Required: No

Camshaft Manufacturers Description:
Good idle. Reliable performance with significant power increase versus stock. Good low to mid range torque. Recommended for tow vehicle, street rod, or muscle car. Cruise 1,500-4,500 rpm.

Paul

 

[johnbeck]

Are any quality long tube headers easy to install? Thanks

 

[68ford]

Are any quality long tube headers easy to install? Thanks

I used to run hooker long tubes with 1 5/8 primaries and with 2.5in collectors. They fit very nice I thought. Spark plugs still easy to get to. 45 degree plug wires were enough but I ran 90s just to not be near the tubes at all. We're on for 8 yrs and never retightened. Still tight when I took them off.

 

[68ford]

Cam is very similar to edelbrock performer

 

[johnbeck]

68ford your right, the machine shop said it was basically that cam. My muffler shop said the hooker headers were a good bang for the buck header. Why did you switch?

 

[68ford]

Only because I went full width and my axle goes up at least an inch past original bumpstops, so my headers had to go outside the frame

https://www.instagram.com/p/Bwk7t2WAoYV/?igshid=1szgmtolc7hc1

 

[johnbeck]

Looks like a serious desert Bronco. Has to be a thrill! Thanks for your heip.

 

[pcf_mark]

In the most simple terms when considering headers the length of the intake "pipe" and exhaust "pipe" should be in a ratio to each other. If the intake has a 16" long runner from carb throat to valve head shouldn't the exhaust have a long length also? You have a nice cam, not a high rpm "race" cam so you picked a good street head with good mid-range flow characteristics. Then you picked a dual plane intake or long tube EFI - both of which have long (very long!) runners. Then you pluck short, tightly packed iron manifold on the exhaust side. Long on the intake go long on the exhaust. Short intake , short exhaust. A long tube header builds torque along the entire operating range. Intake resonate and exhaust resonance tuning is different because one has suction of piston going down and the other has piston coming up but both valves opening. Tune your "system" make more power. The exception is super or turbocharging - then throw all these guidelines out the window.

 

[johnbeck]

I am so appreciative of the guys on this forum. In spite of my ignorance and being slow to absorb your suggestions you've continued to work with me on this project. Strong holds of the American spirit still live. Thanks to All. John

 

[bronconut73]

I am so appreciative of the guys on this forum. In spite of my ignorance and being slow to absorb your suggestions you've continued to work with me on this project. Strong holds of the American spirit still live. Thanks to All. John

Nice.....

You are very welcome.