427Hotrod

Thought this was very interesting data. Big cube, mild engine with headers vs manifolds.



http://www.chevelles.com/forums/showthread.php?t=842601


JIM

toobroketoretire

Thanks for finding and posting this information because I have been wanting to know the actual gain from running headers over the stock iron manifolds. Its good information but I want to know how well they would perform when mufflers are installed because we HAVE to run mufflers on the street.

DUB

YEAH...but did you look close at the read-out. The devil is in the details. Does not seem to be 'real world'. The coolant temp was rather LOW ...if you ask me. 138 degrees Fahrenheit.....that wont last long when being driven on the street.

I would love to see it at the temp the coolant usually is when driving it on the street and see if it changed the results.

...which is why you need to put your car on a chassis dyno and know exactly what is being put on the pavement. Basically anything else is a guesstimate.

And for what it is worth:
I often times get customers who want to get the MAX out of their engine.....and in doing so.... seem to never use it. And these are engine that are already quite impressive. They rarely are revving it up to where the power is....and spending a lot of $$$ to gain more HP and torque that seems to just sit there. I am sorry...when I am driving a car that is rather awesome in power...I can not feel the horsepower/torque gain when I am already being planted back in the seat BEFORE any improvements were made. Just 'saying'. There is a limit to what I personally feel is usable for the street.

But people can obviously do as they wish.

DUB

427Hotrod

Not really a big deal with the temp...the two tests were run at similar temps for consistency.

I think we're missing the point of the post...it wasn't about the peak power the engine made...it was about the difference in headers and manifolds throughout the curve. If you've got 60 more HP on the engine dyno...you're going to have more power to the wheels at whatever loss the drivetrain has. Doesn't matter...more power is more power.

Add mufflers? Depends on what mufflers you use. I have Pypes Race mufflers on mine with full exhaust out the back. It's quieter than the Flowmasters I had on it before. When it was naturally aspirated it ran just as fast capped up as it did uncapped. (9's@142mph). With the twin turbos it made just as much power capped up as it did uncapped...which REALLY surprised me since it makes 1140 RWHP with a mild tuneup.

When I dyno test I run it at various temps..but I can guarantee you I always test at low temps also as part of the series because when I go racing I pull to the line with low coolant temps and hot oil. I want to know what it's capable of. No doubt it will put out a little less as it warms up on the street...big deal....

This was a 600 HP big block...easily usable on the street especially with the RPM range it makes.

JIM

96 lt-4

There are more gains to be had with the headers.Look at the A/F readings.The headers are quite lean.With more fuel the numbers will go up.

HP Hunter

The numbers will usaully be higher when it gets hotter, its the way it works.

Harry

427Hotrod

Haven't spent much time on an engine dyno? Hot oil and cool temps will almost always pull some more power. Same at the track...it will run faster unless you have computer controls trying to hold it back.

Yes...thermodynamics says the hot cylinder makes more power....and if things are tuned that way for WOT long distance running...or even for low speed cruising...it would help.

But on a hard dyno pull or a standing start drag race it usually works the other way.

Within reason of course....50* coolant temp might not do so well...but probably because oil temp would be low too most likely. It's hard to get the two at opposite extremes. 130*-140* works well. 160* isn't bad...and we're not talking huge numbers either way...maybe 5-10 tops.

JIM

JIM

632C2

Based on this data, I can't see why anyone would run a set of cast iron exhaust manifolds!

Steve

DUB

if you are looking to get the MAX out of your engine...and a person plans on using it. I guess that is up to the person and what they want for whatever reason.

Putting headers on ...there is a 'trade off' because they usually require some modification to be used to get them in and all accessories to connect correctly. Depends on the engine....depends on the person who owns the car and what they want.

DUB

toobroketoretire

I have never run headers and probably never will because cast iron manifolds are so much more durable and long-lasting. Yes, long tube headers will produce more torque but by the time that increased torque gets eaten up with drive train losses and exhaust restrictions the gain isn't worth the expense. And then there's the increased engine compartment heat that shortens the life of all plastic and rubber components and adds to the interior heat.

I want to see chassis dyno tests showing the differences between cast iron manifolds and headers when using stock or near stock mufflers to get a real world comparison.

DUB

Not arguing with you or missing the point. I get that and understand that....and yes I know about the loss throguh the drive train.....and YES...I know there will be an improvement....logic simply confirms that if you can get the exhaust out of the engine in a good manner...you power will increase. Obviously this depends on variables that I know you are aware of. Because BIGGER is better to a point....because if BIGGER is better than there would be people throwing on 6" pipes under their car for exhaust.

Which is why I would have liked to see what the numbers would have been at street driving coolant temps. I understand if this engine was a drag engine only...then the numbers would reflect how it would be for it in its 'real world' scenario of usage.


I understand...once again...why you dyno where you do in regards to coolant temp. I get that...really I do.

But when I am having Corvettes dyno'd....becasue they are usually a street car...having it be at the operating temp so the results are what they are can be shown. YES...some pulls are made when we get it to the 140-160 degree Fahrenheit range to see what is going on and compare it to when it is at 195-210 degrees.

The main reason...when the Corvette is dyno'd before the exhaust or modification has been performed and we have baseline data.....then it is dyno'd again to see what is going on. This is also depending on if the owner is all caught up in the numbers of what the engine will do....and IF the money they just spent for this modification actually was cost effective or not. Spending $100 and getting 30 HP increase is a good thing (for example)...but spending $1000 and gaining 20 HP...might not be to some people.

DUB

fishslayer143

[QUOTE=DUB;1591280715. Spending $100 and getting 30 HP increase is a good thing (for example)...but spending $1000 and gaining 20 HP...might not be to some people.

DUB[/QUOTE]

zwede

Here you go. 71 Corvette LS5 454 4-speed. Dynoed on a dynojet chassis dyno.

Stock except Torker II intake, Holley 750 VS. Comp cams hydraulic flat tappet cam 219/229.

Red run: Stock exhaust manifolds.
Blue run: Hooker super comp 1 7/8" primary full length headers.

Both runs were with full exhaust, stock configuration under car pipes 2.5". Same mufflers.

mrichi

You have to be high in the rev range to get the full advantage of headers

Who's driving their 454 Vette at 5,000 to 6,000 rpm constantly

Little Mouse

Someone spends $800.00 on a hydraulic roller cam and its related parts for more power over a flat tappet and piece of mind longevity. Then they want those nice $1500.00 AFR heads. Then stick exhaust manifolds on there new 383 build. That would be very foolish. For most a ceramic coated header can be bought for less then $500.00 that gets rid of any temp under hood concerns. Were not living in the 1970s anymore.


If all you want to do is stick a small cam in your dead stock l 48 for a little more power then your not after much power anyway. Then you would have a valid reason not to use headers.

Little Mouse

headers improve things everywhere big time especially on any BBC.

ajrothm

Look at the dyno chart Zwede posted.... almost 80lbs tq more at 3500 with headers... That's a huge gain right above freeway speeds... That's huge...

Lots of members here are sadly mistaken about headers and the performance they offer over manifolds.

Shark Racer

If you bought a Corvette to putt around between 1500 and 3000 RPM you really shouldn't be diving too deep into the performance modification pool.

If you like to mat the throttle at all, headers are the biggest bang-for-buck outside of proper fuel and spark tuning.

Little Mouse

Look at the graph Zwede put up and its on a chassis dyno. At 2400 rpm on up big power improvements. That"s very usable power on your street car.

DUB

100%.

or... when a person has a Corvette that is blowing smoke...and you can manually spin the engine easily by using the alternator belt and it has no ring drag when it is not running...and they want to put headers on it to give it more power and better sound....

DUB