[KARGUY]

What is the maximum horsepower that can be obtained in a 461 with a 1 3/4 in header?
Engine specs are 461cubic inches, 310 cfm heads, 10-1 compression ratio.

Thanks for the info.
Karguy

[Ron H]

Which brand of heads? Intake? carb? Bore and stroke of engine? Cam? CSA and volume of heads?

[NHRASuperStock455SD]

First thing: chuck the small tube headers if this is a race car it will kill rpm which kills HP.

[pastry_chef]

http://forums.maxperformanceinc.com/....php?p=4361582

Unless your combo has changed from what you have listed above, you are fine with 1 3/4

There are MANY documented street/strip style Pontiac's that have run mid and low tens with 1 3/4 primaries.
Dave (torqjunki), Mike Davis, Kinsler back in 2003 (10.2 seconds) just to name a few.
Of These many DID the swap to larger tube and gained NOTHING!
Butler Performance selected 1 3/4 to run in Engine Masters for their 650 Horsepower Engine < no rule limited them from running a 2 inch primary, but they ran 1 3/4.

I can also show you a 3880 lbs Chevelle with pump gas 468 running 10.2 and has broken into the 9's also with 1 3/4 tubes. Also tried going larger, nada.

[pastry_chef]

Yet another back-2-back test 1 3/4 to 2 inch tubes,
very little as in less than 1 tenth - Summer 2008
-----------------------
Mark (70 lucerne lemans)

'68 Firebird 3100 lbs
'68 400 block .060
4.25 eagle crank
6.8 rods,SRP pistons
Comp 290b-6, 255/265 flat tappet around .600 lift with Harland Sharp 1.65 rockers
KRE 310 cfm 74 cc dports,
11.5-1 compression
Victor intake,1050 Dominator
Turbo 400 ,ATI 9" 4500 stall converter
Moser/Dana 60 rear with spool and 3.73 gears Hoosier 30x10.5 radial slicks

footbrake time 10.01@131
tbrake time on 9" tire 9.93@ 132


Some people just have a *thing* for BIG headers.
http://forums.maxperformanceinc.com/....php?p=4433348

455 .030 over
6X heads that flow 250 @ .5 lift
1.5 roller rockers, UD 280/288 H/O cam
2x4 Wenzler with 2 Holley 660's.
1 3/4 Hedman headers
3" exhaust exiting before rear wheels

Best 12.6039 @ 107.65
-----------------------------

Where is the bottleneck here??
Well, I would say he could use a bit more cam and lift, say hyd flat 234/244 -112 with 1.65 rockers. I would have replaced the converter as well.
1 3/4 header was NOT the issue...

[KARGUY]

Thanks to all who have replied. So I guess the answer is 650 horsepower.

Thanks again
Kg

[FBN Racing]

for what its worth

68 bird with driver 3050 pounds
60 over 455
410 gears
turbo 400 with brake
48 heads
big flat tappet cam
1 5/8 headers

9.98 in the 1/4

[Ron H]

You could make 700 or 400. It depends on the total package even with the 310 heads.

Headers can limit rpm as Lynn said which can limit HP.

I think it is naive to say a 461 can make 650 HP with a 1 3/4" header when there is a huge combo of parts not being talked about. The rest of the combo is more important since a 1 3/4" tube is not really "small".

[ponjohn]

Look in street section, there was a combo that was down on power with tri-y's. He then put on 2" and it picked up. He then bought new 13/4 for his specific car, it lost.

I'll see if I can find the thread.

[GTOLou]

Originally Posted by ponjohn

Look in street section, there was a combo that was down on power with tri-y's. He then put on 2" and it picked up. He then bought new 13/4 for his specific car, it lost.

I'll see if I can find the thread.

Wish I knew more about tri-y's?? Do they lose over conventional (decent quality) headers?

[ponjohn]

http://forums.maxperformanceinc.com/...highlight=Dyno

[David Holmberg]

Originally Posted by GTOLou

Wish I knew more about tri-y's?? Do they lose over conventional (decent quality) headers?

Not always, it depends on the combo. Normally they will pick up in the low and mid rpm range, and sometimes help higher too. It really just depends on what the motor needs.

[pastry_chef]

Originally Posted by Ron H

Headers can limit rpm as Lynn said which can limit HP.

I think it is naive to say a 461 can make 650 HP with a 1 3/4" header when there is a huge combo of parts not being talked about. The rest of the combo is more important since a 1 3/4" tube is not really "small".

In VERY general terms, yes combination is always important.

However to address the header size strictly on displacement and RPM

>>>
1.750" headers are fine for 461CID till 6600 rpm.
>>>

An exact statement that surprised me a little in its simplicity, but it came from a man who evaluates and engineers performance combinations every single day and he gets BIG BIG results!!! like scary.

I'm personally not a big fan of tri-Y.
As to the example performance gain or loss, I would suggest other factors such as primary and collector lengths played a larger role there.
Then tube and collector lengths are impacted by cam timing events and wave tuning.

[pastry_chef]

Looking more closely at pggto's combo.
http://forums.maxperformanceinc.com/...d.php?t=699135

I know SD Dave's CNC Eheads exhaust port has really good CFM and then the Old Faithful Cam has a 9 degree split at .050 favoring the exhaust.
Might be the 1 7/8 primaries were over-scavenging in his combo... 2 inch would reduce that and make more HP.
Too bad it wasn't a Solid Roller.. could have run some Lash changes with the 1 7/8 tubes to test my assumption.

IMO no way 1 7/8 was choking 550 Horse.

[pastry_chef]

Another.

TIP and KRE Pump Gas Pounder
http://www.highperformancepontiac.co...h/viewall.html

463 Cubes
650.4 Horsepower @ 6,300 RPM

340-cfm, 74cc KRE aluminum D-ports
Compression 11.41

Comp Solid Roller
-----------------
Duration at 0.050
265/272-deg

Lift 0.691/0.691-in
Lobe Separation Angle 110-deg
Scorpion 1.6-ratio full roller

1050 Holley Dominator
Edelbrock Victor

Headers 1.75-in Hedman

[ponjohn]

Originally Posted by pastry_chef

Looking more closely at pggto's combo.
http://forums.maxperformanceinc.com/...d.php?t=699135

I know SD Dave's CNC Eheads exhaust port has really good CFM and then the Old Faithful Cam has a 9 degree split at .050 favoring the exhaust.
Might be the 1 7/8 primaries were over-scavenging in his combo... 2 inch would reduce that and make more HP.
Too bad it wasn't a Solid Roller.. could have run some Lash changes with the 1 7/8 tubes to test my assumption.

IMO no way 1 7/8 was choking 550 Horse.

With this logic are you saying that a smaller header (1 3/4) would have increased the over scavenging?

This is a really popular combo, it also sounds like even though the cam made good power with 2" headers AND the 2" is a band aid for a poorly chosen camshaft, correct? ( Or maybe there is a better camshaft choice)

[gearbanger]

He could still put some 1.65 rockers on the intake and see if it picks up. Wouldnt that boost the intake and let the exhaust have to work harder?

[pastry_chef]

Originally Posted by ponjohn

With this logic are you saying that a smaller header (1 3/4) would have increased the over scavenging?

This is a really popular combo, it also sounds like even though the cam made good power with 2" headers AND the 2" is a band aid for a poorly chosen camshaft, correct? ( Or maybe there is a better camshaft choice)

If an over-scavenge condition existed I believe 1 3/4 primary would make it worse for that combo, yes.

With everything ideal you desire a header that will scavenge (think velocity/small CSA) well but also handle exhaust demand (CFM/CSA). Basically correct range of velocity.
Too big header will slow velocity and reduce scavenge.

Over on Chevelles.com the Bowtie boys mainly have two very popular basic head choices
AFR 265 cc and Brodix 270 cc oval
The AFR line has a slightly raised exhaust port with improved exhaust CFM, the vast majority find the raised port to be no problem for header clearance in reality.

The Brodix uses OEM exhaust port height and much weaker exhaust CFM.
With about the same approx 340 inlet CFM both will make about the same power (650 plus), but require VERY different cams.
For general examples, say only 4 degree split @ .50 I to E for AFR, to maybe even duration I to E depending.
Generally speaking the Brodix MUST have minimum 12 degree split @ .050 to perform, I've seen one 427 dyno with 16 degree split @ .050 - the dyno showed great power and the cam was dead on.
displacement and peak RPM also comes into play for ideal split.
Big difference from "cookie cutter" off the shelf type cams.

Last I looked at some SD 310 cfm Eheads flow sheet exhaust CFM was VERY good so 9 degree split @ .050 sounds high to me.
Would be interesting to see how 4 deg split or even single pattern would fair.
With a solid you could band-aid loosen the exhaust lash (like reducing exhaust duration) and see what it did to the dyno power or track result.
There have been cases with tenths and several MPH gained teaking for a less than ideal cam.

[400 plus]

Originally Posted by pastry_chef

Another.

TIP and KRE Pump Gas Pounder
http://www.highperformancepontiac.co...h/viewall.html

463 Cubes
650.4 Horsepower @ 6,300 RPM

340-cfm, 74cc KRE aluminum D-ports
Compression 11.41

Comp Solid Roller
-----------------
Duration at 0.050
265/272-deg

Lift 0.691/0.691-in
Lobe Separation Angle 110-deg
Scorpion 1.6-ratio full roller

1050 Holley Dominator
Edelbrock Victor

Headers 1.75-in Hedman

GREAT article

[pastry_chef]

just comparing some numbers.
when you consider the difference in valve size looks to me the SD 310s more than hold their own in exhaust capability. Not sure if Dave uses a pipe or not.


AFR 265 Exhaust

1.880 valve
with pipe

.200 - 157
.300 - 195
.400 - 227
.500 - 253
.600 - 265

------------------------------

SD 310 CNC E-head Exhaust

1.77 Valve

.200 - 128.2
.300 - 178.3
.400 - 214.7
.500 - 237
.600 - 247.5