84ta406

iTrader: (6)

Dyno results comparing the two header sizes/brands. Interesting how the 1 3/4" required less timing to bring the HP back in the ballpark.

Tony @ Mamo Motorsports

This engine clearly liked the larger primary tubes.....as it should with this many cubes and a high flowing efficient set of heads and induction.

What's the most interesting is how much gain there is lower in the curve going against conventional Internet wisdom. Most would expect the higher peak numbers but claim the bottom will be softer with the larger tube header.

I have seen this many times including when I did the same test on my 383 in my C5. The gains in torque were more than the gain I saw in peak power and the car felt notably stronger when I rolled off the rollers with the larger tube headers and went for a rip.

The average power had increased significantly with the larger primary tube from the exact same vendor (ARH was used for both of the headers dumping into the exact same X-pipe and catback).

Good stuff....

Keep in mind though this is only a test of WOT conditions.

In part throttle operation there is a high likelihood the smaller primary would make the engine feel a little sharper because your moving a fraction of the air at that RPM and throttle position and the smaller primary pipes will keep the airspeed up during that type of driving condition.

-Tony

Double06

iTrader: (1)

I do not know much about the catherderal port exhaust and the ARH headers for this application - so I am going to use my LS7 as an example. On the LS7 the exhaust port if you use a 1.75 inch header (1.65 ID) it pinches it down from the exhaust port which may be like 1.75 inches across and is not round D shaped (1.50 inches high). So even though the flange may be stretched to fit the squarish D shape it pinches down very quickly to a 1.65 ID circle. Thus, the exhaust gasses are changing from D shape to a round shape within 1/2 and inch and does the 1 7/8 header kind of give it a better transition to do that. My question is part of this gain even down low the 1 7/8 or 1.77 ID tube just being a better fit for the exhaust port itself? Like you said defies the logic. As I said I do not know what the ports measure on the 235 cc head (which I assume the exhaust port is worked over) just relating to my LS7.

wannafbody

iTrader: (2)

This is why dyno results and butt dyno results sometimes don't match.

G Atsma

One's butt may fool one... THEN who is the butt?? LOL

jmilz28

iTrader: (13)

I think we have ALL been fooled by a butt once or twice...

FourG63 97GST

iTrader: (1)

bumping this up, @Tony @ Mamo Motorsports quick question, if this exact combo switched out the 103mm throttle body, for a 90mm. how much power do you think it'll lose in an apples to apples scenario? I'm essentially curious what the throttle body is worth on this combo

NAVYBLUE210

Based on my experience I will say 8-10 hp loss at most.
My 396" made 690 HP @ 7100-7300 RPM on the Westech Dyno with a 102 TB through 1 7/8" ARH LTs.
In my C5 on a hub dyno made 592 HP @ 6800 RPM with a Mamo ported 90 MM LS2 TB
through ARH 1 7/8 LTs & catted X pipe with 2 1/2" exit at the muffler end all the way back.
I expected 610+ given light clutch & diff. so estimate 18 -20 loss between 90 mm TB & 2 1/2" exhaust.
I think catted 2 1/2" exhaust Vs 3" reduced more than 90 mm TB.

Tony @ Mamo Motorsports

I would agree with Dan's (NavyBlue) assessment on the power difference.....no less than 5 and no more than 10 is what your likely to see with the larger TB

Cheers,
Tony

G Atsma

Which then makes one wonder if a 95 or 96mm would adequately feed this engine....

SlowTBSS

I wonder if that would change drivability? Opposite end of the spectrum but I do wish we could have tested a LSXhr on this but I suspect it doesn't pull enough RPM to make it worth while etc.

DualQuadDave

iTrader: (6)

Yep, I think the lsxhr would be a neat try. As much as everyone poo poos the Hi Ram, with a 4000+ converter, does the ultra lowend torque matter? At the same time, that 2.100 intake valve will hit max effort, but it would interesting to see how far it can go rpm/power wise on that ci. I'm in the works to do some 4.00bore experimenting soon. Also have a 4.155 bore mule that fell in my lap, so will be some interesting comparisons.

I have a theory on the whole throttle body sizing thing. Besides a venturi effect where basically you want the air path through the intake to be a decreasing radius funnel, I believe there is a time/fill effect happening as well that is directly effected by the air speed/air demand. There is a formula brewing in plenum size vs throttle opening + rpm/displacement and the differences come out more when you have a drastic difference in same engine combos of high airspeed vs low air speed/similar flow. In other words, an LS3 at 500whp gains nothing with a bigger TB, but the same motor w/ cathedral setup will pick up w/ a 102mm. To me, the gain is the fill demand of the intake plenum vs the cylinder downstroke. Plenum volume will effect it, obviously, but I am thinking of this in just regular available LS intakes/combos. Look at Jayyyw's combo, he cut his runner length in half.and from his numbers, midrange stayed the same. That's interesting.