OK, my Lingenfelter book says you should use 1 5/8" headers up to 400 something horsepower with a 350cid. SLP recommends using 1 3/4" with any 350. I have a slightly modded 350,andplan to do more, but I may never see 400HP. I think I would tend to trust Lingenfelter over SLP, but I wonder what you alls experience the 1 3/4" vs 1 5/8". It all has to do with back pressuer vs scavenging and wave resonance in the pipes or some such s***.

 

I agree with Lingenfelter. I have a book that says the same.

 

This topic has been discussed to death. Do a search on this forum and you'll find all the answers you want.

My dad and I both have SLP 1 3/4" headers on our cars, and dynoing over 300 HP to the wheels.

 

i would follow what slp says! i mean they do make the headers..

 

I know there has been a lot of discussion on this, but I wanted to hear some recent personal experiences. It seems like there is not much agreemente on which is best, so If someone could say, hey, I have a similar setup and I experienced this,,,,,,,, that would be very helpful.

 

Where in the Lingenfelter book does it talk about shorties?

Nowhere, you say? Imagine that!

Lingenfelter & SLP are apples and oranges. If you're buying apples, go with Lingenfelter's recommendation. If you're in the market for oranges, listen to SLP.

 

Very interesting comment. ON reviewing the book, he does say in two different places that pipe diameter is much more important than pipe length in determining engine power, but he doesn't specifically say anything about shorties or long tubes. He just explains about the effect of pipe diameter on exaust gas velocity and on enginer power,in terms of hi and low end torque,then goes into his chart where for a 350 he doesn't recommend 1 3/4" diamter headers until 450 HP.

Can you explain what you are saying about shorties andlong tubes a little more detailed.?

thanks for the help

 

Long tubes tune the pulses of the exhaust flow so that the reflected wave arrives back at the exhaust valve at the same time the valve is opening (similar to what Tuned Port Injection is doing on the intake side). Since there are many variables involved in that statement, such as exhaust gas density (affects the speed of sound, and therefore the timing of the pulse arriving back at the exhaust valve) and engine RPM, to mention a couple, the tubes do not stay optimally tuned when the engine conditions (load, speed, temp, etc.) are constantly changing. That is why he says length is not as important a factor as flow area. However, the effect is still significant vs. no tuning at all.

Shorties are too short to provide such tuning (shock wave arrives back at the exhaust valve long before the valve opens again), so all they do is provide improved flow area.

Unless the engine is operated over a vary narrow RPM band and under a fairly constant load, this pulse tuning will never be completely effective. But, you'll notice that long tubes are still the product of choice for the vast majority of racers and on dyno runs.

 

You've done a good job explaining that, but it still doesn't answer his question. Although it is all true.

Based on what you've said.......Using 1 3/4" over 1 5/8" is not going to improve your low-mid RPM torque, only upper RPM HP. If you're going to make over 450 HP, it's gonna have to be in the upper RPM range (on a 350 mind you). When's the last time you saw a 350 make 450HP peak at 4000 RPM (NA that is )? Therefore I'd say that 450HP would be a safe haven.

Shorties are "good for high RPM" (<--- Smokey Yunik).To me that's a nice way of saying they suck for low-mid RPM grunt. You're going to loose even more low-mid RPM torque with 1 3/4" primaries from loss of velocity. And if you're building a motor with less than 450 HP, then low-mid RPM would be something you DO NOT want to lose. Heck..... you're already loosing some by using shorties.

The nice thing about long tubes is you get more low-mid torque WITHOUT loosing any upper RPM HP. I wish they did fit easier on our cars.

 

Sure. The issue with primary diameter is keeping it small enough so the flow velocity stays high enough and doesn't "die" right outside the exhaust port and hurt low RPM power, but not so small that higher RPM/power flow is restricted.

But, tube length still does come in to play there (pulse reflection will aid flow in the high power scenerio), so the Lingenfelter/Smokey statements are not fully applicable to our situation (top fuelers have short, large diameter, individual tubes, which works fine for them). I would tend to rely on the experiences that are directly related to our application, which is largely affected by space limitations. In that case, I'll trust Hooker with their 1-5/8" primaries; and take at face-value SLP's recommendations for 1-5/8" primaries with 305 engines, and 1-3/4" for 350 & larger engines when using their product.

I think you'd only get into trouble with doing things like 1-1/2" primary shorties on a heavy-breathing 406, or 1-3/4" primary LTs on a mild 283. 1-5/8" or 1-3/4" shorties on a slightly warmed-up 3rd gen 350 will not make that much of a difference either way.

 

I whole-heartedly agree with you.

I feel SLP concentrates on TPI engines, therefore they say 1 3/4" will be best because you don't need to worry about torque on a TPI engine. That's primarily handled by the intake runners. And as we all know, the TPI (stock) is not good for upper RPM HP.

So using a 1 3/4" on TPI would only help on upper RPM, but probably not hurt much on low-mid RPM torque.

I also agree that Hooker 1 5/8" would be plenty UP TO 450 HP. After all, isn't that how you should plan everything that goes on/in an engine? Only use what the plan requires?

I'm not saying the above intentions of SLP are true, it's just the only conclusion I can come up with why they'd say 1 3/4" are good for "all 350s". If that's true, then I guess Lingenfelter needs to re-learn how to build an engine.....

NOT!!!!!!