Header diameter and collector suggestions

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Illahe

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Needing to build a set of headers for a 1984 Daytona and spoke with a couple of racers a few weeks ago about diameter. The Gt/? racers with similar cars are running in the mid tens with what appears to be 1 5/8 x 1 3/4 in chassis headers with 318/340ci. I'm looking for someone with experience with 410+ ci small block combo.

I have spoken with several fab shops and 1 3/4 flanges seem readily available, but there is some buzz on the forum about 1 7/8 header diameter for the big small blocks. The chassis is fairly tight with the boxed rails are coming in at about 20" wide under the engine. The previous owner ran them out the fender and I'm concerned about the headers being too short for optimum torque. Merge collectors were suggested, but they're $ are they the key to optimum scavenging?

My combo is 12:1 414 with 272/282@.050 solid flat tappet on 108lsa.

Thanks,
 
I have a 418 with a flat tappet. It’s smaller than yours, with similar compression.
I went with 1 3/4 to 1 7/8 step headers, with 3 inch merge collectors and think it turned out to be the perfect choice. That said, I have a much heavier car. It will run 10.20’s at 3350 give or take fuel load(15 gallon cell)
Regards collectors, long time ago I went from a 3 inch collector to a 3.5 inch collector or a very well sorted, healthy W5 roller stroker.
I saw zero going to the bigger collector.
 
B3422w5 said:
I have a 418 with a flat tappet. It’s smaller than yours, with similar compression.
I went with 1 3/4 to 1 7/8 step headers, with 3 inch merge collectors and think it turned out to be the perfect choice. That said, I have a much heavier car. It will run 10.20’s at 3350 give or take fuel load(15 gallon cell)
Regards collectors, long time ago I went from a 3 inch collector to a 3.5 inch collector or a very well sorted, healthy W5 roller stroker.
I saw zero going to the bigger collector.
Click to expand...
The cars roughly 3100 with driver. Thank you, kindly!
 
i ran 9's with 1-5/8'' headers at 355''

i did end up building 1-3/4'' stepped to 1-7/8'' fender exit for the same 355'', i used schoenfeld merge collectors. when i switched to the W8 engine i used a bit bigger pipe, 1-7/8'' stepped to 2'' with schoenfeld merge collectors again.
 
I talked to a few very smart engineers builders and they suggested the merge collectors and that’s what I went with.
They also said don’t worry about the length of the pipes. Just get the merge collectors.

As you can see my headers are short but didn’t affect my performance.
First engine is the 414” W8 and the second is the 355” W2.

IMG_1381.jpeg


IMG_0330.png
 
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On our Superstock 340s the merged collectors added
around 6 to 7 HP.

The ones we used were about $350.00 and it is up to you
if that investment is worth it to you for the power gain.
They are not a "Silver Bullet".


My .02 = for Free!
 
9secRR said:
i ran 9's with 1-5/8'' headers at 355''

i did end up building 1-3/4'' stepped to 1-7/8'' fender exit for the same 355'', i used schoenfeld merge collectors. when i switched to the W8 engine i used a bit bigger pipe, 1-7/8'' stepped to 2'' with schoenfeld merge collectors again.
Click to expand...
looks like the step occurs around 16-18"
Thanks!
 
9secRR said:
i ran 9's with 1-5/8'' headers at 355''

i did end up building 1-3/4'' stepped to 1-7/8'' fender exit for the same 355'', i used schoenfeld merge collectors. when i switched to the W8 engine i used a bit bigger pipe, 1-7/8'' stepped to 2'' with schoenfeld merge collectors again.
Click to expand...
In fairness, your car is very light.
I had 1 5/8 headers on mine, I think they will support 525-550 horse. And that amount of power will run 9’s easily at 2600-2700 pounds.
A stroker will like bigger tubes, mine sure did, I had a large gain when I made the swap, if you remember. At that point I did just the header swap, nothing else, it showed 35-40 horse on the time slip
 
These are the stainless ones I bought. They were a pretty penny, but everybody I talked to said these folks absolutely know what they are doing.
They made quite a difference on my car, and could suppprt more power than I am making, easily.

MOPAR A-BODY SMALL BLOCK 1968-1976
 
B3422w5 said:
In fairness, your car is very light.
I had 1 5/8 headers on mine, I think they will support 525-550 horse. And that amount of power will run 9’s easily at 2600-2700 pounds.
A stroker will like bigger tubes, mine sure did, I had a large gain when I made the swap, if you remember. At that point I did just the header swap, nothing else, it showed 35-40 horse on the time slip
Click to expand...
2700 lbs. the 1-5/8” were LA truck headers so the ports didn’t line up well on the W2 heads but it worked. I figure the 355” is in the 560-580 hp range.
 
9secRR said:
i ran 9's with 1-5/8'' headers at 355''

i did end up building 1-3/4'' stepped to 1-7/8'' fender exit for the same 355'', i used schoenfeld merge collectors. when i switched to the W8 engine i used a bit bigger pipe, 1-7/8'' stepped to 2'' with schoenfeld merge collectors again.
Click to expand...
Do you have an idea of primary length?
Thanks!
9secRR said:
These are the headers on my friends Daytona. 416” W9’s.

View attachment 1716432009

View attachment 1716432010
Click to expand...
Wicked looking collector!
 
this is the primary tube length for the set of W2 headers. 1-3/4'' stepped to 1-7/8''. car ran 9.70 @ 137 with these headers.

#1 step at 10'', total is 24'' #2 step at 9'', total is 24''
#3 step at 8'', total is 19'' #4 step at 7'', total is 21''
#5 step at 9'', total is 19'' #6 step at 9'', total is 18''
#7 step at 6'', total is 19'' #8 step at 7'', total is 19''
 
9secRR said:
this is the primary tube length for the set of W2 headers. 1-3/4'' stepped to 1-7/8''. car ran 9.70 @ 137 with these headers.

#1 step at 10'', total is 24'' #2 step at 9'', total is 24''
#3 step at 8'', total is 19'' #4 step at 7'', total is 21''
#5 step at 9'', total is 19'' #6 step at 9'', total is 18''
#7 step at 6'', total is 19'' #8 step at 7'', total is 19''
Click to expand...
Thank you, Sir.
 

9secRR said:
i'm picking up my friends daytona tomorrow to do some work on it. i can take a few pics for you if you like?
Click to expand...
I appreciate that. I scalloped the motor plate and used shorty block huggers merging a 2 1/2 collector to 3" exhaust in order to shake out the project. The car seems like it takes too long to spin up until it gets into the midrange of second gear, which I attribute to the short primaries and 110 lsa cam 246/254 @.05. I had a 105 lsa 251/251 that I should have ran, but went with best combo I could come up with when the car was re-assembled in small block form. The ground clearance is non existent: roughly 4 1/2" from the bottom of the 2x3 tube on the left, and we were hauling with an open trailer which increased the ground clearance issue.

If you look, the inner fender well was hacked out for fender well headers when the previous owner ran a BB Mopar. The tubes were roughly 22-24" x 2" tube and then the collector is fairly large, possibly 4".

After scoping the project out, it appears, 22-24" primaries running into a proper merge collector out the fender is doable. There's no hope for under chasses headers because of the kick panel unibody torque box: see the lift holding the car up.

IMG_3411.jpeg


IMG_3412.jpeg


IMG_3413.jpeg


IMG_3415.jpeg
 
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Their is a program called Pipe Max. I'm sure some of our members have it. You plug in your engine stats and it'll tell you the preferred primary tube diameter, primary length, collector diameter and collector length. Vic Bloomer specked mine.
 
i tried to post pics of the headers in the daytona but it says to big to upload? never had that problem before.

the step is 11''-13'' and total length 23''-24''. 1-7/8'' to 2''
 
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