Sidepipe horsepower loss?

[rdc767]

Guys looking for some advice. I did a dyno run last week with less then stellar results. 295hp / 383cu/in sbf

Looking through my setup and I going to change a few things.

Port match the headers or at least work the welds and smooth them out.

Possible change the glasss packs out in the sidepipes or take them out.

Taller manifold (victor jr.) and port match the heads. Current is a low dual plane. Current carb is a Edelbrock 750 cfm

Don't really want to change out the cam. It has a hydraulic flat tappet with 500/520 lift. Heads are procomp aluminium 2.02/1.60 valve. Compression is around 10.5/1. Max timing was 36 degress. a/f ratio was a bit rich 12.5 to 1.


My question is can you go too large in the inside diameter of the glasspack? I was thinking of taking them out and just using a thin fiberglass sheet and metal screening. (dont care about noise). Aft of the collector is 3.5" I would use a 20" turnout the same size 3.5".

Is no restriction in the exhaust bad for HP? or the exhaust valves?

Thanks
Ron

[blykins]

You will make it infinitely louder if you keep reducing the amount of "stuff" that's inside of those pipes. It's not really the packing anyway, it's the ID of that hole going through the muffler.

However, restrictive sidepipes have been shown to take 100hp, so what do you do, right?

Sidepipe mufflers would be the easiest route probably.

I wouldn't swap the intake as a smaller inch motor wouldn't most likely gain a tad bit of power on the very top end, but lose a lot of low end and mid range power.

If I were going to get into the heads, I would swap brands altogether. The Procomp stuff flows like factory iron...very restrictive. You could pick up 50-75hp by going to a nice head like an AFR or Brodix.

[RICK LAKE]

rdc767 Ron Side pipes can cost from 0-60HP depending on the motor. 12.5 A/F is fine for WOT but not for cruising down the road. You want about 13.1-13.5 A/F. Exhaust is a black magic thing. You want just enough back pressure to help control heatout of the heads and not burn the exhaust valves. Back pressure you are looking for about 1-2 psi+ at Cruise speed of the car. This will jump to 3-5 psi under WOT. The motor doesn't live there all the time. If the car is going to be street and the size of your motor 2.5" in and outlets are fine. If you go to 3" the noise will increase and you will need ear plugs for any cruising. Race pipes are wide open side pipes. I have both. The less the back pressure the richer you should run the motor to prevent burnt valves. Open pipes will hurt bottom end power and only get small gains at 5,000 rpms and up. If this motor is built for torque, it will fall on it's face. If it's a high HP motor in the 5,000-6,500 rpm range than bigger is better. Just watch out of the noise police. Ps that ringing in your ear will stop after a couple of hours. At least the other half can holler at you and you will not hear a thing from the left side. As far as the other question, it's about matching parts. You need to find out where the power curve of the camshaft is and work from there. With the size of the motor a single plane torker manifold that is ported and flow checked would be the way to go. I would send this manifold to Joe. Craine and let him do his magic to balance out all ports and flow of the manifold. Some ports can be 5-30 cfm off other ports. This means less air and fuel getting into that cylinders. His work comes back looking like thing to be put under glass. There are small power gains too. Depending on manifold from 3-25 HP and a little less torque. keep this motor streetable. If you have the HP bug, build another motor and race pipes for the car. This way you always have a spare bullet for the car. Your motor is a 400+ HP motor, drivetrain drain is about 15-18% and side pipes another 10-30%. Re work exhaust and intake and retest. Good luck Rick L. One last note, (BIGGER IS NOT ALLWAYS BETTER, JUST BIGGER) this is for exhaust and tuning it.

[vector1]

you have a restriction somewhere, need more info. 750 carb would be on the small size imo. cam, what kind of power band are you looking for would determine intake. header pipe diameter, what do the heads flow. exhaust can have a big effect on hp, not only as a restriction but as a vacuum to pull intake charge into the combustion chamber to exceed the 100% volumetric efficiency thing.

[Dwight]

I have a 354 sbf with Ford Fuel injection. I had ProCom heads and dyno'ed about 320 rear wheel. I bought a pair of Keith Craft Brodix heads and one of his Custom Comp Cams to match my motor set up. I also installed a pair of Classic side pipes at the same time. Dyno'ed 402 rwhp and 416 rwtq.

The side pipes are 3" inside diameter and 4" longer than my old 24" x 2 1/2" I.D. pipes. The old side pipes had the louvers turned backward and I installed the new ones with the louvers turn forward. Quieter now.

Heads, cam and exhaust system, making good power for a small block.

I told Keith I wanted a street motor not a drag racing motor. I'm making 350 tq at 2500 rpms.
Fuel ratio at 12.5
Dwight

[Dwight]

Classic Chambered Exhaust Inc. - Home Page

[rdc767]

Well I think I found some of my problems. I surprise It ran as well as it did.




Must lay off the adult beverage when dropping the intake on.

Thanks for the advice. I'm going to flange aft of the collector (3.5" with 3 bolt) to be able to make quick changes to the turnout. Low restrictive and be able to switch to the stock glasspack I have now.

Still contemplating the manifold change Airgap or torker II ?

[DAVID GAGNARD]

Just my opinion, an Edlebrock Air Gap would be a good choice and so would a Holley 750 double pumper, The Edlebrock carbs are not know for good performance unless someone that really knows what there are doing goes thru one, still, an out of the box Holley 750 DP would be better.....
So would a side pipe change.....

David

[Jeff Frigo]

Originally Posted by RICK LAKE

rdc767 Ron Side pipes can cost from 0-60HP depending on the motor. 12.5 A/F is fine for WOT but not for cruising down the road. You want about 13.1-13.5 A/F. Exhaust is a black magic thing. You want just enough back pressure to help control heatout of the heads and not burn the exhaust valves. Back pressure you are looking for about 1-2 psi+ at Cruise speed of the car. This will jump to 3-5 psi under WOT. The motor doesn't live there all the time. If the car is going to be street and the size of your motor 2.5" in and outlets are fine. If you go to 3" the noise will increase and you will need ear plugs for any cruising. Race pipes are wide open side pipes. I have both. The less the back pressure the richer you should run the motor to prevent burnt valves. Open pipes will hurt bottom end power and only get small gains at 5,000 rpms and up. If this motor is built for torque, it will fall on it's face. If it's a high HP motor in the 5,000-6,500 rpm range than bigger is better. Just watch out of the noise police. Ps that ringing in your ear will stop after a couple of hours. At least the other half can holler at you and you will not hear a thing from the left side. As far as the other question, it's about matching parts. You need to find out where the power curve of the camshaft is and work from there. With the size of the motor a single plane torker manifold that is ported and flow checked would be the way to go. I would send this manifold to Joe. Craine and let him do his magic to balance out all ports and flow of the manifold. Some ports can be 5-30 cfm off other ports. This means less air and fuel getting into that cylinders. His work comes back looking like thing to be put under glass. There are small power gains too. Depending on manifold from 3-25 HP and a little less torque. keep this motor streetable. If you have the HP bug, build another motor and race pipes for the car. This way you always have a spare bullet for the car. Your motor is a 400+ HP motor, drivetrain drain is about 15-18% and side pipes another 10-30%. Re work exhaust and intake and retest. Good luck Rick L. One last note, (BIGGER IS NOT ALLWAYS BETTER, JUST BIGGER) this is for exhaust and tuning it.

Rick:

Great job, I am taking my car to the dyno next week with my new Howe 3002 3-2/3" mufflers. There is a seat of the pants difference. I will post the numbers.

[Rare Iron]

Remember, engine must be able to exhale properly. Build power up at the engine, it must be able to get out downstream without excessive backpressure. Right diameter = flow velocity. "Stock" type mufflers with under a 2" flowpath going through them is just idiotic. I wouldn't run that diameter on a '67 Mustang 289 2bbl.

-Eric

[Rick Parker]

It looks like you found part of your problem, but everything must work in unison. Primary pipes must be taken into consideration too. Many of the component supplied and used on these engines and cars were intended for their original displacement and although increasing the displacement WILL increase the overall performance all the components on both sides of the valve seat must be reevaluated for their flow potential and capacity. Only with everything properly sized can you expect blistering performance from any engine. Good luck

[RET_COP]

Dwight, nice HP increase. Any idea how much HP gain came from the head/cam swap vs the exhaust.
I did the windsor sr. to KC brodix head with flat cam to Jones roller cam swap, but kept my 2 1/2 ID reversed louver exhaust. I figured 60 to 70 gain. It sure feels it across the rpm range.
Lou

[Dwight]

I don't think I gain a lot with the exhaust changes most of it was the heads.

Dwight

[Bill E]

We went to a 4" elbows a long time ago and a removable muffler that can be tuned to the engine. Every engine likes to see deferent configuration to work at the performance level the owner wont's to see. You have to remember House power numbers sale engines but torque is what you feel. Rick You save me a lot of typing.

[madmaxx]

You need to use intake gaskets with a metal liner. That is gasket squirm not miss installation . I forget the fel pro number. If you used the same gaskets it will happen again.

[Dwight]

the best gasket I have found is Cometic


never failed me like the Fel Pro.

Dwight

[tirod]

Well, there's something to be said for paying attention to details.

If this is a 383 stroker, a set of 195cc to 205 intake runner heads would be a better fit.

As for needing a bit of back pressure, some reading on cam theory suggests what is really going on might be related to too much overlap or duration. Engines don't need backpressure, we're trying to get them to do the opposite. That's what you pay for with $800 racing headers - the harmonic waves actually create a vacuum in the chamber that literally pulls the intake charge thru. If it's on a low profile cross over manifold, it will only starve one of the other four cylinders it's hooked up with. An open plenum will allow it to suck any other chamber with it's valves open on the opposite side. Things are that complicated. So the intake, cam, and headers are dynamically connected.

On the exhaust, too big is a guarantee of no velocity, and that's where aftermarket headers are generally weak. You need velocity to get the tuning, and if the exhaust pulse dumps into an effectively open chamber, then it can't develop a reversion wave to pull the intake charge in. A properly made set of smoothly flowing headers a size too small will almost always make more horsepower than some made too big.

How those headers are joined is another detail - look down them and see if the merges are tapered and have long tails in the center, or simply cut off and filled with a square blank. Further, are the merges in the 15 - 20 degree range, or steeper? Plus, after the merge, is the pipe the appropriate size? Again, a 2 1/2 collector sounds small, but it generally will make more hp than a 3" badly done. How long that collector is, plus the transition to the muffler is also important. And despite what I was told years ago by Hot Rod Magazine, glass packs properly fitted and sized do NOT mean a hp loss.

Frankly, I think this a a classic example of how the whole "blame the headers" camp of thinking has grown. I certainly do think many of them could be better made - and right now, if you didn't pay more than $400 for them, you aren't getting quality headers. You are just getting what you paid for, some tubes welded up. On the other hand, having made the decision to value engineer the headers, the decision making about other components of the motor and how they are assembled becomes a factor. As illustrated.

Motors can't just be screwed together, if it was that easy, then we'd all be getting figures like the high dollar crate motors 475 hp from a 383, guaranteed. Building hp from engines is a lot of choosing certain parts, and then knowing what other parts are immediately not usable, regardless of our affection to do so. That means the cam is on the table, and not considering it and reevaluating it's fitness a potential mistake. If it's got the wrong LCA or isn't timed optimally, throw it in the trash. It could be costing 60 hp, too. That's been proven more than once.

Engine building is about pumping - get the intake, heads, and cam working, then work on the exhaust to help. It's not wrong to look at it the other way, but if the back calculating shows the cam is all wrong, do you leave it? Don't box yourself in a corner.

[rdc767]

Well
Done some work. Basically just changing the manifold. I port matched the headers to the exhaust ports.

And opened the intake manifold to the heads. Went victor Jr. I know the rpm range run isn't ideal but it looks just cool. I really dont notice any loss of torque on the low end but as the rpm hit 3000 it takes off like a rocket.


I installed a 3 bolt flange to the stock exhaust. I going to experiment with different side pipes.



Going to try to make my own glass packs. Havent tried them yet. Opening is appox. 3" the old sidepipes 2"

[JBCOBRA]

Have you tried a different air filter?

[JBCOBRA]

These guys are awesome to deal with too.
Just get one of their HO series carbs.
AED Performance Racing Carburetors, Holley Carburetors, and Performance Holley Carburetor Parts