1970coupe

how about the size of the header tubing for torque? im looking at a 4v shorty header made by sanderson but i have a 2v 351 cleveland so i would use their copper adapter. The tubing is 1 7/8 vs the hedmans are 1 5/8.

Will this make a dramatic diffrence in low end torque if its ment for a 4v head but its a shorty?

JMD

There is one drawback to headers, blown header gaskets. I spent a good portion of the day changing gaskets on the 66... I replaced the "paper type" gaskets with copper today....

I should have gotten some locking header bolts also,,, but I didn't....

1970coupe

yeah copper is the best. and locking if you can afford it. or just use some locktight if you dont plan on taking them off soon

xian67

http://store.summitracing.com/partde...p;autoview=sku

67mustang302

Actually, backpressure is bad because it's a resistance to exhaust flow. Think about it, pressure in the exhaust system is a force that the piston has to push against on the exhaust stroke, reducing the effectiveness of the exhaust cycle. The "backpressure" that everyone thinks of isn't pressure at all, at least not positive pressure. It's a negative pressure wave generated by a reflective pulse from the collector, that's created when the exhaust pulse from one of the primaries enters the collector. The oft misunderstood(or at least mis named leading to misunderstanding) "backpressure" is actually a vacuum generated by the negative presure wave that helps draw exhaust gasses out. Ideally you want to time it so that the - pressure wave works to draw as much exhuast gas out and pull as much intake charge in during overlap as possible. The pulsing itself is determined by the diameter and length of the primaries, the diameter of the collector, the ratio of the diameter of the primary to the collector, and exhaust gas tempurature and velocity(and both temp and velocity are related, as exhaust gasses cool they become denser and slower).

So if by needing backpressure you mean you have to have a pressure in the exhaust system that is positive pushing against the flow of exhaust gas, then no, you don't want that. If by backpressure you mean a negative pressure in the primary and exhaust port generated by power pulsing, then yes, that's what you want(though it's a misnomer to call it backpressure, it's more acurately back-negative-pressure, or vacuum). It seems that most of the "black magic" that people see in exhaust systems, or the misunderstand, is in large part a nomenclature issue

http://www.burnsstainless.com/TechAr...ry/theory.html

1970coupe

eh? lol you just lost me on that. so my question is if you have a 1.65 port and you go to a 1.875 tube will it make a sugnificant diffrence? check out my topic and let me know. i really need help on this. the sanderson shorty is the only header made for a 351c 2v.

67mustang302

It's gonna depend on how much exhaust gas your engine is pumping out. With a larger diamter tube that's shorter you may notice a drop in bottom end power, but you may also notice an increase in top end power. It may be too big for a stock engine

1970coupe

hmm ok. 0.225 bigger is a huge diffrence? does anybody know where i can find a good shorty, tri-y or longtube that will fit a 351c 2v fmx trans w/ auto for a 70 coupe. the hookers hit the idler arm.

67mustang302

Welcome to having a Cleveland, though it's true for most any performance application. You could always find a local shop with a good fabricator that can make you some headers, if you got the cash

1970coupe

well i just figured out after trying to fit, getting fustrated therefore rushing and sending them back that i could have bought a 1-2" idler arm drop bracket that probably would have fixed my problem of it hitting that. so should i try to find something else? or have them sent back and get the bracket? i find it hard to believe that no ones ever found this problem with headers on a 351c.