2 inch is the way to go. You need like 700 hp or so to begin to see any real delta worth the extra hassle and cost and fitment of the 2 1/8 inch. Most have a 3.5 inch collector then you would go to your 3 inch exhaust which is great for your motor. Breakpoint for the 2.5 to 3 inch exhaust is about 500 hp. A 1 7/8 might work well also some guys might chime in that have dealt with this size.

 

I'd run the 1&7/8. bigger is not better.

 

I ve seen an improvement at the track with a 2 over 1 and 3/4 - pn Hedman 66002

 

Just curious... how much of an improvement? What size exhaust behind the header?

 

Oliver has a pretty gnarly Vortecpro (Mark Jones ) in his car in Italy. It's very unlikely you need those big headers.

Alternatively, you could ask Mark since you are already a customer of his. his recommendation will be dead on. Mark is the real deal.

 

I did speak to Mark about it right after the dyno run, and he said 1 7/8", but 2" would be fine also. My initial thought was indeed 1 7/8", but I thought I'd ask here just to get additional opinions - not that I don't trust Mark's implicitly. My plan was to go with Doug's headers and have them coated at Jet Hot Coatings. The engine pulled 588 foot/lbs. at 4,200, and 588 horsepower at 6,000. He and I both think it has a little more in it at my elevation (near Maple Grove). Using a Holley Terminator on top.

My first inclination was to stay at 1 7/8", if for anything to get just a tad more clearance. Will be running 3" X-pipe, and very likely 2½" out of the mufflers.

 

I have a 454 around 580hp, had 2" then changed to 1 7/8". Seems to have more torque and hp feels the same as before.

 

Mark told me to use 2” headers when I was at his shop dynoing and picking up my engine, 467 all roller, 600/600. I bought some uncoated hedman’s and had them ceramic coated in Joplin.

 

Bronze 68, I was there when we dyno'd that engine! all BLACK and SILVER! Glad it made it "home" ok!

Either will work fine. Look PEAK HEADER TORQUE is a minor measurement which tells you were peak "port torque" occurs in the primaries given the bore area. smaller will give you more 3000 rpm boost, larger more after 4500. That's all it is, no more, no less. So its a"secondary" optimization equation, not a primary.

I thought about "optimizing" mine to 1.875", but Mark said 2" are fine, actually preferred FOR MY APP ( maybe as it's a clutch, no stall) So i had my 2" Hookers coated a "TURD" time! In White! Smaller coated Hedmans NEW would have been cheaper.

I cant speak to lack of TQ, as you cant go WOT on street rubber with an MJ mill. Not with my race Holley, maybe with EFI you can.

They actually use the math in this article;; Math dont lie, PEOPLE do! The Correct-Sized Headers Will Give You the Best Performance

Based on that 2" works for an MJ468. Smaller only means you'll shred more rubber, earlier. But if you already had 1.875"; I'd run 'em. No headers yet - WHATEVER FITS BEST! I 'd say. But at least using the math in the article, you can bust out a calculator ( I'm not an engineer, but a numbers guy) and know where the 2" versus the 1.87" put their peak header TQ ( approximately 4500 and 3900 respectively on a 468).

Your engine likely shows peak TQ at 4400, as mine did with the same cam. So, given the math, you can dial in the headers to give you peak HEADER TQ right above the engine ( as I did, as I'll drop the clutch at 5200 to HOOK up at 4200...) or to come in just under the engine's 4400 rpm peak TQ at 3800. ( if for example you were using a 3500 or less rpm stall, flashing to the peak pipe TQ - this makes sense)

So, as Mark said, either will work, the math shows what you might expect from an A/B test.


PS I had my system pro -designed ( Dr Gas engineer), the 2" hookers feed into a 3.5" collector; then thru a 3.5" to 3" Dr Gas X pipe to 3" head pipes and 3" Magnaflow 12578s. 2.5" Torque tech ( not in biz anymore) tails finish off an engineered system for 500-700 hp, meaning it should run same with open headers.

 

With your gear and where you're going to be driving that thing 1 7/8 is plenty and I would rather have 1 and 3/4 over 2 in. Let's put it this way if the header is you test against each other have identical Dimensions other than the primary diameter it will make as much horsepower with the 1 and 7/8 headers as it does with the 2inch headers but it will pick up torque especially down low where you are driving 90% of the time

 

heres a good video to watch that compares the 1-3/4 - 2-1/8 headers

https://youtu.be/O1bXPNy1Yn4