give me an exact rpm of peak hp

or a really good estimate

and i'll calculate all header/pipe dimensions for you

then you can measure the choices and see if they fall in these specs


my posts were just trying to show you its possible to make either of those header choices work fairly well , if you modify total exhaust length to fall in one of the best negative wave lengths


your 400 cid +.040 is really close to 406 combo in my surburban
same 270 he cam
1 5/8 headers
420 hp
will look up dyno data and post

 

well for the short time i had it drivable i was using cheap black jack headers that were too close to the plugs, and i kept burning the plug wires. i believe the headers were 28" long with a 3 inch collector and were 1 5/8" . I only had it up to 5500 RPM but seemed to be still pulling. i don't think that it would really pull much beyond here though. if i can have it pull hard up to 5000-5250 RPM i would be happy(with new header set up). torque seemed to be peaking out around 3500-4000. I was also using a stealth manifold at the time. my header selection is VERY limited because its going into a 3rd GEN F body. i have 2 selection from the Super Comps, 1 3/4 or 1 1/2. its going to be a street car so mid range is what i'm really concerned with, but also would like to keep "some" sort of fuel milage. so this has me thinking about teh 1 1/2" headers too. where ground clearance is minimal could i get away with 2 1/4" mandrel bent tubing for teh exhuast, or should i just use the 2 1/2" . Thanks for all the info and help.

 

suburban engine
419.0 HP @ 5000 both at 600 Rpm/Sec acceleration test rate
450.7 TQ @ 4300
------------------------------------------
Note=> would show approx 439.0 HP and 465.7 TQ
if dyno test were non-acceleration steady-state dyno tests

4.155 x 3.750 406 cid
Holley 600 cfm double pumper 65 jets
10.128 measured CR Exxon 93 prem
35.5 deg BTDC
SBC #487x castings 2.080/1.600 242 cfm Int / 225 cfm Exh
bowl-ported

stock GM oil pan, harmonic balancer, Pink pressed-pin Z-28 5.700 rods, Speed Pro flat top pistons +.030

CompCams 270 HE .470/.470 224/224 110 on 106.75
202.5 deg duration @ .100
175.0 @ .200
134.0 @ .300
84.0 @ .400
176 cranking psi

RPM Vac inches Hg
600 11.5"
800 15.6
1420 18.7
2120 21.6
2660 21.5
2760 21.5

computer predicted headers
1.587 dia x 47.2 best length or 24.8 2nd best length
2.962 dia collector x 14.1 best 28.2 inches 2nd best
56.0 3rd best 113.0 4th best

actual headers on dyno
1 5/8 dia unequal lengths from 24.0 to 37.5 longest primary
3.000 collector x 13.5
best dyno tested collector length 13.5 inches
96 percent accuracy of predicted value

 

old Baja Race SBC 355 cid
Comp Cams 252/258 .672/.672 106 centers on 107.1 CL

1 3/4 dia x 26 inches long


7.000 inch Collector--------22.000 inch collector
RPM-----HP----Ve% -------- HP------ Ve%
3500--229.6--79.4-------- 205.9---74.5
3750--243.1---77.7--------244.3---76.4
4000--254.1---76.3------- 282.0---80.8
4250--292.4--79.7-------- 320.4---89.1
4500--331.4--86.0---------357.4---93.6
4750--377.9--94.2-------- 386.2----96.6
5000--402.0--98.3-------- 405.6---100.3
5250--424.3--99.5-------- 429.8---101.3
5500--445.2--101.8-------452.4---102.9
5750--454.1--102.4------- 465.2---103.3
6000--478.4---102.9-------477.9---103.7
6250--490.6--103.4--------490.1---103.6
6500--493.9--102.2--------497.5--102.5

notice wave effects can be monitored by Air Turbine
showing up in Ve %

also notice 7.000 inch collector at start catches part of negative wave at beginning of test , then catches postive wave , especially at 4250 where there is 10.0 percent loss in Ve and 28.0 HP LOSS
as well


but at 4250 to 6500 the longer 22.000" collector
has negative wave occuring over greater rpm range

resulting in more HP/Torque

the primary pipes were TOO SHORT , but were customers headers he had that fitted chassis..so to make work, the 22 inch collector helped out the TOO SHORT primaries

 

Chevy 355 cid

3-Step Header design

1 3/4 , 1 7/8, 2 inch x 34 inches long Primaries

Collector= 3x11" ---3x15"------3.5x11------3.5x27
RPM---HP-----Ve-----HP----Ve-----HP---Ve---HP-----Ve
4000-270.4-87.6--285.9-97.4---224.5-76.6---300.9-97.5
4250-318.9-93.1--333.2-99.8---274.2-82.8----322.5-95.8
4500-357.6-100.9--361.3-103.1--339.8-96.4--352.3-98.2
4750-401.4-108.3--392.8-107.3--387.2-105.3--394.9-106.4
5000-424.6-111.2--414.9-110.3--422.3-110.4--425.6-112.8
5250-451.5-113.7--452.4-114.7--449.3-113.4---453.9-115.0
5500-481.9-115.5--477.5-115.4--476.1-115.5--470.4-114.4
5750-492.6-114.1--492.3-114.3--489.9-114.7--492.1-114.5
6000-506.2-113.9--497.9-113.0--498.1-112.8---497.4-113.8
6250-521.8-112.9--511.0-112.7--516.6-113.1---513.4-113.2
6500-516.5-109.8--515.5-110.7--510.1-111.0--514.4-111.5
6750-524.1-108.0--516.4-107.6--504.1-106.3--500.2-107.5
7000-512.3-104.6--502.2-104.8---507.1-104.4--504.3-104.7
7250-515.5-99.8---503.3-101.2----507.3-100.5--508.7-102.0
7500-491.0-98.1--497.2-98.3-----489.5-97.3--489.2-98.4

dyno tests with different diameter collectors and lengths
effects on HP and Ve %
effects of negative and positive waves

notice "TREMENDOUS" 76.4 HP Loss at 4000 RPMs between
3.5 dia x 11 -VS- 3.5 dia x 27 inch

when there is a lot of TIME at lower RPM ranges and collector diameter is TOO LARGE for particular RPM
header can loose a tremendous amount of Torque/HP

but can also be helped a great deal with tuned collector length
as in 3.5 x 27 inch collector causing Negative wave to be helpful
during overlap period

 

The exhaust port on your heads seems to flow VERY well!!!!!
How much do you think i'm going to give up if i run the 1 1/2" Super comps? if i could gain more average torque below 4000 RPM i think it would be worth losing 15-20 HP on top. For the street its more fun to have more torque than top end HP, and it more economical.
I had contacted David Vizard about my combo and he said by changing the LSA to 106 from 110 i SHOULD pick up around 25-30 lbs more torque in the mid range IF i had an excellent exhaust system with near Zero back pressure, this is the reason for special ordering the cam.
So if this was your combo and given the options for headers what would you chose? keep in mind i don't have a dyno to test this stuff or lots of cash-o-la to spend on a mistake. i would preffer 1 5/8 but my choice is either 1 1/2 or 1 3/4. unless you know of other headers that would fit these SR heads(straight plug) and would work in the 3rd gen. thanks Tom.

 

the reason for the good exhaust flow was ;

single pattern lobes
and
pulling dragster trailer with suburban thru mufflers
would have more load for any given rpm


1 5/8 would be best

go with 1 1/2 headers for 4000 rpms and lower torque

1 3/4 headers would work too high for you

 

Well, i just couldn't pass it up. I found a set of good used Hooker Super Comps 1 3/4" on E-Bay for $225 including shipping!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
I guess it'll give me room to grow in the future. Now i just have to figure out how to route the exhaust under the car.
would it be easy to weld in Anti-reversion cones in the primaries, or maybe better said this way; do you know of weld in AR cones that would go in the primaries by the header flanges?Thanks!

 

I luv wen thredz git teknakawl

Thanks to those that have answered my previous questions.
My last set of assumptions have been buried in the data.

Here's an excerpt of my post on page 5. As always T.I.A.!!!:


For those that have read the book, he often inserts roman numerals
mid scentence in parenthesis, but I can't seem to figure out what
it means?

IE: Further experiments (XVI) show the effect of...

Is this pointing to a footnote, or is it some sort of engineering script, etc.?

He also mentions the term, "touring engine". Is that just a label
for a non-performance grocery-getter?

Lastly, page 34 shows graphs of exhaust pressure vs. piston position.

Looking at any single graph:

Are those graphs snap shots of the exhaust pressure during an
acceleration period between 1000-3000 RPM

or

Is it a snap shot of ONE cycle of combustion at a steady RPM?

The reason I question this is because it's an average pressure
representation.

 

OK , say if i wanted to get creative and make the 1 3/4 primary tubes work on my 408 sm blk with a 5750 power peak, how long would the primaries have to be, to be optimum?
I found a primary tube calculator but it didn't seem to work to reason. just for the heack of it i tried 1 1/2 primaries and it said they should be 57.4" long! and the 1 3/4 should be 42" long! that almost sounds backwards.
i got the calculator here:
http://www.grapeaperacing.com/GrapeA...ustheaders.cfm

 

408TA

my program came up with ;

1.751 Primary dia (1 3/4 closest) x 36.9 inches to 39.4 inches

3.269 Collector (3 inch closest) x 21.2 to 26.2 inches length

Collectors tune in at ;

5.9
11.8
23.7
47
95 inches

H-Pipe= locations= 5.9,11.8,23.7

X-pipe = 47.4

headers should work from 4250 to 6050 rpms

with possible loss in Torque from 1603 to 3103 rpms occuring from Positive wave occuring if total exhaust system length is
not one of the 5.9,11.8,23.7,47, or 95 lengths

thats what i come up with

you can try headerdesign.com

but the best method is to get on an engine dyno and find lengths
or just try this out at drag strip

 

 

i took the old copy of that book and used a 1.000" inch dial caliper to divide all Smith's graphs into finer grid details

(hoping the publisher did a proper job in replication of originals)

you could get a little more info out of book doing the same

its old data but still relevant

5000 rpms is highest i think he has data/tests for on intake side
but it gives you good basics

 

This thread is goign to go on fore ever!
heres my next question(s). on tuning the intake side: if you run an inclosed air cleaner and fresh air ducts, would the length of the ducts be used to tune the intake side. I would think yes, but if your using 4 inch(dia.) pipe for ducting would that be too big for wave tuning.

 

MaxRace, have you ever played around with Terminator boxes? And would they go at the "tuned in" lengths that you described.
I checked out that web site you sent me too, i think its great! But acording to that calculator, 90% of everybody is running too big of a primary!!!!!!!!, but form the info i've seen form it the primary lengths don't seem to come close to what is being maufactured for us.
would a merge collector help me out or should i just look into lengthening the primaries. the headers are only 28"long! i would have to add another 10" to them so they'll be tuned.
is there a company out there that sells a form cut to fit slip on primary tubes/collector?
I have a mig welder and i'm halfway decent at welding so doing this wouldn't be to big a deal for me.