I changed out the headers from Hooker 1 3/4" to Dynatech 1 3/4" stepped to 1 7/8". I did not get a retune yet but am putting a cam in the car in a week anyhow. I can't imagine this header change necessitating a complete retune. Anyhow, the car lost 51 horsepower peak and basically that much across the entire RPM range. It also lost 57 on the torque side at peak and a like amount across the board. The curves look almost identical when laid over each other but the horsepower and torque are just way lower. Can this header have caused this or should I be looking elsewhere for my lost 50 horsepower? Any ideas appreciated at this point. Thanks.

 

Does the transmission feel okay?? Almost sounds like the trans could be slipping, causing you to lose power to the wheels. Its harder to tell with a stall converter, since you're used to slippage, but its a good possibility. I'd check there first.

Second thing I'd check is the headers. Are they defective, perhaps a piece of metal jammed in one of the header pipes, or a protrusion into the pipe somewhere??

Perhaps you could switch back to the other set (yea I know its a lot of work), and see of your power goes back up. If it does, you've narrowed the problem down to the headers, and you can go from there.

 

The last time you were on the dyno was your converter locked verses not being locked this time. That could make a big difference depending on how efficent your converter is.

 

Sounds like too my header primary to me. Let us know about the converter.

The GOOD news is, IF it's too much primary (which I think it is) when you do a set of ported heads and cam the car should jump in production.

 

Thanks for the ideas so far. Let me add a little more. Both pulls were on the same dyno with the converter locked to take the converter flash out of the curve. The transmission is dead solid with no slip at all. I guess this is both good news and bad news. The header primary tube size is exactly the same as before for about a foot off the head (1 3/4") so I'd really be surprised if this is the culprit. I expected to lose possibly a few ponies down low and pick up 2-3 up top. I'm down almost 50 horsepower at every RPM from 3000 on up to the peak which is at exactly the same RPM as before BTW. The new headers look perfect with nothing inside them at all. Funny thing is that the old set of Hooker headers were far from perfect with big globs of crap on the inside of the front tube on each header where the hole for the AIR fitting was welded up. Old headers have already been picked up. I did not dyno before and after the Hooker headers vs stock manifolds but I picked up .3 and 3 MPH in the 1/8th so I know they added big power vs the stock manifolds. I'm actually down a lot now as compared to having the stock manifolds and exhaust. I'm also getting some popping/snapping out the exhaust upon initial acceleration but it seems to clear up after a second or so. Anybody think maybe I cracked a spark plug putting them back in and I'm dropping a cylinder completetly during the dyno pull? The shop that did the header install did the dyno pull for me. They're going to check the plugs/wires tomorrow (which have less than 500 miles on them) to see if maybe the problem lies there. Something not right is definitely going on here. If changing to the Dynatech headers which I thought to be an upgrade is what's causing this power loss I've got to relearn everything I've leared about high performance cars over the last 40 years or so. I'll check back in on this thread for any more helpful ideas and will surely post up if I find out anything stupid has happened. Thanks in advance for any help with this.

 

Have them check to make sure you didn't burn through your O2 wiring harness.

 

Go over all of your spark plugs/wires/O2 sensor wires/etc. That pretty much sounds like you are down a cylinder or something...does it feel 50 HP slower?

 

Same here. Sometimes plug wires are not on right or sensors get messed up. Do you have an SES light or anything?

 

What did the A/F look like on the new runs? If it was good, and the car runs OK, take it to the track. Thats where the truth lies, assuming you have numbers from before the swap.

 

Definitely sounds like a dead cylinder, I don't see any other reasons mentioned that will cause you a 50hp loss. Let us know what you find out!

 

Hmmm as they mentioned start with ignition stuff & O2 sensor wires then go with CR test buddy !!

peace

 

Definitely a dead cylinder. Look for an unplugged injector plug or unplugged coil pack or spark plug. Hey, it happens.

 

Dynatechs on my car lost big power too
Not nearly as much as u but they came off right away,went back to my Hookers..

 

I made like 460/410 through dynatecs and loved them all the way. Dont see any problem there. I also dont see why you even bothered to switch.

 

Cracked a plug during install

 

Does your Dynatech headers have the slip-on collectors? If so, that could be a problem. It could be pulling fresh air into your collectors and throwing your O2 sensors off causing your car to run rich therefore losing power (been there, done that). Just something to think about....

 

dead cylinder

 

I vote for cracked plug too. I did one during my header install. It was cracked on the body and you couldn't even tell without taking it out.

-Geoff

 

I called up Ron @ Vengeance today and asked him what he thought. He's doing the cam swap for me next Wednesday so I wanted to keep him up on things. He said to throw my MSD wires as far into the woods as I could and put some stock wires back on. They're a real PITA to put on and keep on anyhow. This sucker has got to be dropping a cylinder under WOT on the dyno. It will barely spin the tires on the street so it's definitely down on power. It's not the dyno lying to me. I'm changing the plug wires out and putting in new plugs as well in case one got cracked. I'm getting some new plug wires from the dealer to make sure I get some original ones so it's going to take until Friday to get them in. Ron seemed to think that the headers I have now are worth some measurable power once the new cam goes in vs the Hookers. I trust his judgement. I changed out to these headers because I wanted them for the 408 that's ultimately destined to go in the car. I would never have swapped headers if I intended to stay 346 cubic inches. I'll post back up hopefully Friday with the results but it's got to be something stupid like I suspected. Thanks everyone for your help. You can always count on getting help on this site.

 

Good advise. I won't even install MSD's. There is no way you'd lose 50rwhp with those headers.I go with 1 cylinder not firing too.