Performance difference between manifolds and headers?

[68CST327]

In a few weeks I think I'll be ready to head to the muffler shop and replace my broken old single muffler and rusted leaky tubing. I'll be getting a dual pipe setup, with an H-pipe, and probably Flowmaster 40's or maybe Dynomax's, but I'm really debating whether I should just bite the bullet and have a nice set of headers installed at the same time or not. Right now I'm running stock ram's horns.

I've also been intrigued by the Corvette 2.5" manifolds. How much power do they make over stock ram's horns? How are they comparable to headers? From what I've read, headers sound like a pain in the @$$, yet they produce dramatically more power (debatable I'm sure).

Desktop Dyno 2000 claims an increase of over 50 horsepower on a 327 when using headers as opposed to manifolds. Is this accurate?

[DanoDMano]

Got a guy here at Boeing with a '68 1/2ton w/ corvette ram horns and flowmasters.
It sounds real sweet to me!!!

[Jackal2k9]

honestly i liked the ease of use of ramshorns over headers they never leaked. but m header4s sound WAY smoother and much better tone. with a pretty good power increase in my stock 94' small block.

[DanoDMano]

I went with a set of hedmans, an h-pipe, and magnaflows.
After retorqeing a few times I have no leaks, and the Magnaflows rumble real nice!!!

[71Seth]

I have always heard that DD overrated all there hp and tq. #'s. Can anyone verify this????? I kinda wonder if my #'s are right?

As for headers i've never had stock manifolds on a sb. My 71 has hedman headers on it(about $110 from JEGS)They went on very easily and have gave no problems, just keep them tight. Warm up the engine and tighten the bolts, let it cool down check then and do it again. Becarfull if your running aluminum heads as they tend to make bolt break off when hot. If you do this a couple of times, and check them at every oil change you should have little trouble. I wish I had spent the extra $ and got the shinny ones though. just my .02 good luck
seth

[mikep]

I'm not so sure they overrate much. Its just a simple spreadsheet program based upon mathematical constants. If you have a few known variables such as exact cylinder head flow rates and cam profiles along with compression ratios etc and you run those numbers through the program at the end of the process you will come out with an answer. Its doesnt look like simple math but thats all it is. Ive compared quite a few known buildups using out of the box parts and the numbers DD2000 generated were nearly the same as the numbers published by the engine builders. the trick is you have to know the cylinder head flow rates and you have to be honest about what they are. A lot of actual flow info is available now to the general public that wasnt 10 years ago and that goes into the equation.

[Durney]

Most inexpensive software can be either right on or not even in the ballpark (+/- 100 hp). DD and most other claim to be a "copy" of the wave cycle analysis but in fact are a poor excuse. If you want to see a wave cycle analysis enigine simulation run expect it to take up to an hour or two to formulate the potential pulse variables (GM's software reportedly runs for a LONG time for each detail). Use these for what they are , a tool to help you understand how one change might affect another but dont think it necessarily close. Performance trends does have a FAR superior sofware ( I think the mail order sells the better version) and we occasionally would run it in comparison to our actual Dyno and even it could get stumped... but it was aslo occasionally within 3%. Alll professional software will need more input than you have access to.

hope this helps - SG

[69 Short Fleet]

I would leave ythe ram horns on for now, as far as headers go it is possible to loose horsepower if this upgrade is done by its self alone (ie. without doing a carb, and or intake upgrade with your headers). A good rule of thumb is whatever you do to one side of the head or heads you should do to the other. The "H" or "X" pipe method is a really good idea as Dano mentioned, I know a guy who just had his done and it made a noticable difference especially in the bottom and mid range as this method equalizes backpressure. I'm not a mechanic, and these are just my opinions!! Nice to see another member on the board, take care Doug

[Mike C]

Power gains based on a mod is a bogus claim unless ALL factors are included. For example:

My Jimmy broke the timing chain on the original motor while I was in college. I had no $, but I had a built 327. .030 over 4 bolt block, '69 large journal crank, forged flat tops, 186 heads, Crane 284/.480 cam, LT-1 intake, 780 Holley. So I dropped it in the Jimmy with the trucks ram horns and 2" singel exhaust. It ran OK, but not like it did in my Camaro. 6 months later, I added headers and 2 1/4" exhaust. Holy Crap! Probably picked up 80 hp and 50lb ft. Pulled nearly 1000 rpm more than before. Obviously, it was completely plugged up. It was way too much cam for a granny gear 4 speed, howerve. The 284 gave way to a 266, the LT-1 intake became a Weiand 8004 and the 780 Holley a Q-jet. It ran really well with the changes. I lost the headers and went to the 'vette rams horns and 2 1/2" exhaust about 4 years ago. It makes more low end torque than the headers, but the same top end. Power does fall off above 4500 or so, but that is to be expected with the cam and it did the same with the headers.

I like the rams horns from the 'vette a lot, and will put a modified set in my '64 when it gets its new 355.

[GreenMystChevy]

As already mentioned, it is possible to lose power with headers but that is usually not the case. Pipe diameter is crucial so that there is enough backpressure. Headers allow the motor to breathe just like K&N and their infamous filters.

I don't know how headers fit on these trucks because I have never tried but a lot of people don't like to hassle with clearence issues and potential starter problems from the heat. I personally am willing to sacrifice my effort for the extra power.

I just know that I put headers on my BB Chevelle and man o man is there a seat of the pants feel. Now just for a cam and re-jet of the carb

[68CST327]

bump...

[Ackattack]

IMO headers are the way to go. I really don't have any problems with them. When you get them, just be sure to get a starter heat shield...taht will save you a lot of hassle....they're like $20 from jegs.