Choosing header size / style 400SBC Camaro

M

mtrhead

Member
My build viewtopic.php?f=69&t=3024 is progressing
I've aquired 4.155 Block, 210 70cc Pro-filer Heads, STR 10 Cross Ram, 3.8 stroke Crower ultra light crank, Crower 6" rods, 11-1 Mahle Pistons. I have not choosen the mechanical cam yet. Roller or Solid. Either way its for street use just like my original post. TKO600 with a 3.90 gear

I'm onto wanting 4-2-1 headers. http://www.perfweldheaders.com/camaronovaheader.html
However they very pricey. Instead Im leaning towards MUSCLEMAXX DRAG 67-69 CAMARO SBC 1 5/8 - 1 3/4 W/O COLLECTOR COATED http://www.afabcorp.com/AFCO_Dynatech_U ... 7_69Camaro

I would then purchase a merge collector or fab in my own 4-2-1 onto a set of standard cheaper headers. My question is should I go for 1.625 primaries or 1.75" for street use? I've read over 50 posts you put up on header design. I think for street use I want the highest velocity and these 1.65 stepped to 1.75 seem about right then run a 4-2-1 flowmaster collector or equivalent merge collector. Ot I will go with a Merge collector even if I buy $99 headers and fab them in myself.
That maybe the best way to go?
 
obviously your cam choice will require the cam timing be selected to allow use of available octane fuel, and that 11:1 compression will also be factors here, and for a street car the large port heads and intake design will limit your off idle performance, a bit so youll want to concentrate on building almost all your power in the 3000rpm plus rpm band, and the 3.90:1 rear gear will keep you in the mid to upper rpms, much of the time.
you don,t want to restrict the exhaust port placing a header primary entrance any smaller than the exhaust port exit dimensions but theres only small gains in the upper rpms placing a larger pipe, than the exhaust port exit dimensions on the head, personally given the components listed Id select a decent set of factory headers and modify them by cutting off the collector, and welding on the 4-2-1 collector of your choice, after calculating the required length, and using the car to mock up the resulting header clearances. with the components youve listed Id select the larger diam primaries in most cases simply because your using components designed for 3000rpm and over and any minimal loss in off idle torque with the slightly smaller primary's will be all be meaningless



the links below contain a great deal of useful info

cams

viewtopic.php?f=52&t=1070

viewtopic.php?f=52&t=480

viewtopic.php?f=52&t=727

viewtopic.php?f=53&t=726&p=8809&hilit=quench+squish#p8809





headers
viewtopic.php?f=56&t=185

viewtopic.php?f=56&t=3155

viewtopic.php?f=56&t=1303

viewtopic.php?f=56&t=2870

viewtopic.php?f=56&t=260
 
Here is what Crower recommended Mechanical Roller peak power 6500 rpm custom grind
.610 lift (1.5) rockers
243 Intake @50
255 Intake @50
112 C/L for 128 110 C/L for 4625
Install 108 LS 4732 Firing order

Also, I've read until I hurt on headers.

I have about 4 I'm eyeing all DYNATECH's which get great reviews on the boards.

1 5/8 step 1 3/4 2.5 collectors
1 5/8 step 1 3/4 3.0 collectors
1 3/4 step 1 7/8 2.5 collectors
1 3/4 step 1 7/8 3.0 collectors

I was leaning towards the first and running 3" dual out the rear and the expansion from the 2.5 to 3 would somewhat replicate a merge.
 
Dynatech recommends the 1.75 to 1.87 versions. They sell a version without collectors and I can add
merge collectors but now we are talking more money.

My investigations say 10-15hp by all these special collector means up top not in the mid for the street. I think the easiest and probably all around good runner for a 550-585hp SBC would be the the 1 3/4 to 1 7/8 version with the 3" Collector?
 
With that cam selection,Crowers trying to maximize the mid rpm torque and that's a very valid approach but youll be running close to the detonation limits on dynamic compression, if you get any crap gas, the extra duration , of the cam(s) I selected will partly compensate by reducing mid and low rpm cylinder pressure, but sacrifice some mid rpm tq doing so, but with that rear gear ratio,compression and displacement with a manual transmission I don,t think thats a bad exchange for the extra detonation resistance
 
They also spec'd out a cam for 7000 rpm max

252 intake 260 exhaust everything else the same. The other cam offered more "snap" as he put it.

I understand what you mean about dynamic compression. Cylinder pressure will be higher due to the shorter duration and same compression (static) and C/L specs.

How much power would I be leaving on the table by going with a flat tappet (non-roller) mechanical?
I can save $750 at least.

The reason I thought more on the other cam is the "chugging" and lack of torq I've had in the past once I've gotten into the 250-260 duration on the street.

Do you think 1.75 - 1.87 3" collectors will be fine?
 
" a cam with 252 intake 260 exhaust everything else the same," cam on a 112 lsa would be a good compromise

the header size should be fine as long as the primary's are at least 36" in length, info below may help

http://www.pontiacracing.net/js_header_length1.htm

http://www.carcraft.com/techarticles/11 ... ndex2.html

http://www.mandrel-bends.com/catalog/

http://www.burnsstainless.com/mergecollectorsmain.aspx

http://www.stahlheaders.com/Frame%20Flanges.htm

http://victorylibrary.com/mopar/header-tech-c.htm

flo-c158218234.jpg


flo-c134218234_w.jpg

http://www.summitracing.com/parts/FLO-C134218234/

http://www.summitracing.com/parts/HED-14044/
hed-14044_w.jpg
 
Ok - I will lean towards the bigger cam.

Also, On the headers..almost all 1.75 headers available off the shelf have shorter than 36" primaries. I don't know what the Dynatech's are. I will call tomorrow.
 
I look forward to your thoughts on this. I called almost every shop that makes headers for 69 Camaro's
Lemons, Stahl, Hooker, Dynatech, Eds, Hedman, Dougs, and a few others.

All have a primary length from 24" to 30" with 30" ish being the general max I found. Now the Camaro has been around for 43 years now and the small block forever. Not one shop had anything close to 36". I did confirm with exhaust calculators in you postings that with my heads, cam choice and around 6500 rpm that indead the answer is 34-36" depending on RPM. Jump 500 they go shorter by about 2"

So why in the world are all these headers so short? Stahl wouldn't actually tell me but they did confirm that its shorter than 36" I needed to call back, they do have different versions

To make sure I'm measuring correctly. the lenght of the 1.75" tube? not to the end of the collector!

only ONE shop offered to sell me extenders and work with me on what my desire was and I'm getting extensions and slip on collectors.
 
almost all header manufacturers need and do find a compromise between building the best possible headers , with the widest potential power band,and the most cost effective design they can build that still functions reasonably well, and fits as many similar applications as possible, and while a longer header tends to produce more low and mid rpm power, the ratio of power gains are reasonably small compared to the added expense of building true custom headers that fit, each possible application, due to clearances, and additional materials, and producing a header that may only fit a single year , with a single engine or type of cylinder heads,or maybe only limited to several years of production, and the cost difference between lets say a 32" and a 36 " header primary design, limiting the market potential, makes producing headers with the ideal measurements cost prohibitive.
the the additional gains are there to be had, but unless your willing to build a custom design that may only fit a few cars, and are looking for every possible gain, it may not be worth the extra effort, if it costs you an additional $200-$300 dollars to build a header that produces an extra 10-15 ft lbs of torque ,(or in some cases noticeably more) most header manufacturers would much rather opt for a less expensive option

there ARE EXCEPTIONS
Headers.jpg


and some simple fabrication work to graft on collectors like these
flo-c158218234.jpg


to common headers like these
hok-2456-1hkr_w.jpg

usually results in gains in performance, at a reasonable cost to the few guys willing to take that extra effort


read this linked thread
viewtopic.php?f=56&t=3155
 
I have a cam with the 4-7 firing order swap. If I was to build 4-2-1's (headers) which cylinders do I pair?

I do know that THIS combo doesn't like 4-7 swap from a test. 13 / 57 28 / 64
This was from an actual test of a set of 4-2-1's

I've found 3 different donor headers that all merge differently that I can use for the surrogate.
 
v8-firing-flowchart.png


viewtopic.php?f=56&t=2537

viewtopic.php?f=56&t=1503&p=3419&hilit=coke+can#p3419

you normally try to pair cylinders that are 360 degrees later, in the firing order to maximize the blow down time in the header primary tubes, to maximize the low pressure in the collectors and minimize restriction to flow, if your limited to matching tubes from only one bank, or cylinder head try to match the cylinder firing further apart in the firing order, naturally this may not be the easy route to use designing headers when engine bay and frame clearance issues are taken into account, and one reason theres few commercial headers that maximize the engines exhaust scavenging, to maximize the cylinder filling and extend the power band to its full potential

theres a great deal of info on the site about selecting or building headers, but one major factor is that a NON-RESTRICTIVE exhaust system MUST be installed with ANY HEADERS to allow them to work correctly. for headers to work correctly they require an exhaust pulse to allow its inertial energy to drag the following charge along with it out the exhaust.
if you can,t visualize that it might help to find a 3 ft long section of 2.5" pvc pipe and wrap a bit of tape around a full coke can so it slides easily thru the PVC, pipe but fills its interior diam., now place the pipe horizontally insert the coke can and drop the opposite end strait down while you hold your hand over the end the coke can was inserted into, as the mass of the coke can falls you'll feel air dragged with it , the same basic thing happens with an exhaust pulse, its mass is far less but its traveling much much faster, and depending on the rpm and displacement it does generate significant energy that can be used to draw the next intake runners charge into the cylinder as it draws out the next exhaust charge during the cams overlap duration (LOOK INTO CAM TIMING)
keep in mind the LENGTH of the header tube effects the rpm levels and energy transferred as it takes time for that mass of hot exhaust gas to travel thru the primary tube, naturally a longer distance tends to require a longer time and the longer duration tends to impart a longer and stronger negative pressure wave to assist the next pulse IF ITS TIMED CORRECTLY and the header primary tube is the correct diam. and length for the engines displacement,compression, cam timing, and several other factors, but again, it works far more effectively if the exhaust system is a low restriction design that doesn,t reduce the scavenging effect of the pulse waves, and the tubing is long enough to work effectively

normal firing order
1-8-4-3-6-5-7-2

normal ideal paired runners

1-6
2-3
4-7
5-8


4/7 swap firing order
1-8-7-3-6-5-4-2

normal ideal paired runners

1-6
2-3
7-4
5-8
 
Fully understand - I was surprised at the length of these from Burns in your link viewtopic.php?f=56&t=2537 Short primaries before the 2-1

I'm going to start with 38" primaries and a merge collector. Then play with 2-1


Here are the type of pipes I make fully waterjacketed (Jetski) - its all about open duration, transferport timing, and desired HIT / RPM. bigger is NOT always better in the header and stinger size! 4 strokes are a whole different animal I'm learning
 

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This style header now is common place for 4 stroke dirt bikes. It came around in the Pro ranks a couple of years ago now its standard in the aftermarket.
 

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