karkrafter

I'd think you would gain 5-10HP up to about 4000 RPM and gradually more to redline. topping out at 20-25 HP gain probably at speeds you [we] probably don't often go...As far as factual data, tons of variables but I'll be I'm close if you google I'm sure you could find some comparos out there..


I spoke to a popular 383 builder and mentioned I didn't want to run headers ..he suggested his 435 HP estimate would be closer to 400 with 2.5 ram horns...

GUSTO14

When building the engine for my '63 Convertible, I spoke with the folks at Comp Cams a lot. Their assessment was that it should produce around 450 hp. They also said if I added headers, it would likely see an additional 100 hp.



I will be using 2 1/2" rams horns as I'm using sidepipes and it will see mostly street use. 100 hp seemed like rather a lot, however when it's complete I may take it to a chassis dyno to see how close it comes to their original assessment.

Good luck... GUSTO

65tripleblack

I'm surprised. I have Hedman sidepipe headers mounted to my aluminum angle plug heads and there's no problem.

Brzezinski does extrusion porting for pure stock cars. It helps quite a bit, but not as much as headers.

What displacement engine?
Cam specs?
Are the manifolds 2 1/2" or 2" ?
What size exhaust system and what mufflers?

Dr L-88

Sorry, I forgot to add to my original posting:

355 engine, 10:1 compression, mild hyd roller camshaft, 2.5 inch rams horn manifolds, 2.5 inch exhaust into factory N11 off road mufflers.

Thanks for everyone's input.

Rex

65tripleblack

Rex,
Depends on how badly you want headers, or not.
Mild engine build, small displacement should breathe just fine thru manifolds.
Brzezinski work is VERY pricey, and so used to get an "edge" in pure stock. IMHO not worth it for your intended use.
Best thing you can do with the stock manifolds is to port match them to your heads. If they are "D" ports, you'll see that a LOT of material can be removed.

65tripleblack

Here are mine

Dr L-88

Thanks again for everyone's input, it is much appreciated. At this point I am leaning toward just the stock manifolds (perhaps massaged a little)..................as the car will be street driven. It WAS raced in California many years ago with this FI setup. At that time it had a set of stock manifolds later replaced with a set of home made headers.

Induction has a lot of potential for incoming air flow.....................but probably a lot of potential for exhaust restriction too with stock manifolds. But as I said, it will be street driven, WHEN I do drive it.


Thanks,
Rex

wmf62

wow... sounds too good to be true....

Bill

karkrafter

What are the specs on this engine??? I want 450 HP with Mainifolds too!!

63 340HP

The 2.5 inch 901/902 ramshorns are some of the best flowing factory stock exhaust manifolds from mass production. The stock manifolds interior finish is fairly good. The main areas to enhance power is port match to achieve a reversion step from head to manifold, and to smooth out the flash in the collector and entry to the pipe or FI spacer (or heat riser valve). The D-port heads have a mismatch with stock manifolds that must be addressed by removing manifold material (and they will work with any vintage fuelie head).

I purchased the cnc ported reproduction manifolds while the stock manifolds were on the car. The cost was near the same as vintage 901/902 manifolds or headers. I wanted to work on them before installation and save my stock manifolds to display on my rebuilt original RE code engine. The external finish of the GM pieces is far superior to the Chinese castings.

The important internal areas to improve on the stock castings by port matching can be accomplished in a few hours by hand with a die grinder or vertical mill, and the 901/902 exterior finish is way better quality (the way to go, and in full support of your most recent post).

For giggles the following are power curve model comparisons of a SHP 327 with an LT1 cam, stock 1.94 valve 461/462 heads, and N11 exhaust, with stock port matched ramshorns, vs. cnc ported ramshorns, vs. 2"x38" tuned headers. The LTI cam design is biased to a broad mid-range torque curve and restricted exhaust. The point to bring this up is that the 2nd design off-road cam and more radical aftermarket cams will react to less restriction a little differently (more top end effect).

Notice the differences in power are much less than traditional wisdom (mostly because the stock 2.5" ramshorns are good).


Corked with N11 & undercar 2.5 inch exhaust (below, top is stock port matched 901/902, midle is CNC ported ramshorns, and bottom 2"x38" tube headers):




Open exhaust, no restriction (below, as before, top is stock port matched 901/902, middle is CNC ported ramshorns, and bottom 2"x38" tube headers):



In all comparisons the headers improve mid-range torque. The differences in torque and power are near zero, splitting hairs for most drivers.

A more radical cam, like the 2nd design GM off-road cam and typical catalog choices with tight lobe displacement angles, will benefit from significantly more midrange torque improvement from headers because that is where the 240-260 ft/sec exhaust charge momentum usually occurs to help extract exhaust gas from the back of the valve, to improve the VE enhancement from valve overlap by drawing more air across the chamber when both valves are open (you can exploit the improved exhaust head pipe tuning rather than design for the restriction of a full exhaust).

With a corked street exhaust, a cam optimized optimized for a wide torque bandwidth typically needs less overlap, the reason for the revised factory GM LT1 and L82 cams and the current LSX series cams that utilize wider LCA's (one of the goals for the 357 engine with the Brezezinski manifolds in my photos, that still output over 420hp and 430tq with the 3.48" stroke).

You should be happy with stock manifolds port matched to the heads.

PAmotorman

some lawn mower and chain saw plugs are the shorty type so check around at a mower supply place

MikeM

Don't you think 2" tubes on those headers are a little extreme for a SBC street engine? That can kill power. I can't see any header manufacturer recommending that for a street engine built to those specs. Any specs probably.

Most street headers for 350 ci/less SBC's used to be 1 5/8" for good reason. It's best to look at your exhaust as a complete systems package with the engine specs and expected usage of the engine.

One size does not fit all.

Stingxray

OK Angle plug heads = performance // Cast Iron Exhaust =not so much

I have SBC AFR 227 Angle plug heads with these OBX Stainless hedders. Now I was thinking about going to Sidepipes whitch means these could be Forsale. I can postphotos if you like .


http://www.ebay.com/itm/63-82-Chevy-...5T0EXF&vxp=mtr

TCracingCA

Same here! Shorty plugs, but I stud the headers also and run copper gaskets, so I can side them back some after breaking apart the side exhaust flange in 5 minutes!

I do have a set of 1-7/8 Hedmans that go under the car, on one car that are clearanced for angle plugs. Those were discontinued, but the best Corvette header setup that Hedman used to sale! Because I wouldn't mind finding another setup, I am not going to share that part number! But 1-7/8 is a little too much for most of the engines guys have on here! The 1-5/8 marry better for stock to a certain level, and then the 1-3/4 are a nice beautiful compromise to about the 450hp level, helping the lower end somewhat.

You should cam, port and tune for whatever headers you decide to run! Marry it all together!

Hey did you leave the 140 cam inside that thing?????

63 340HP

MikeM,

I agree with you from a practical standpoint, and from a systems design aspect, 2" headers are way overkill. A good 1 5/8 header will enhance the torque more below 4000 rpm where most people run their SBC. Less total tq & hp, but more where most people operate their engine.

The 2" head pipe is what the engine optimization program recommends, with cautions (what most discussions dismiss). From personal experience, a head pipe ID 125% larger than the exhaust valve head diameter typically loses average power and ET on full body cars (a 1 7/8" ID rule-of-thumb limit for a 1.5" valve). Bigger valves and more displacement/airflow benefit from larger head pipes.

Ramshorns are far from consistent in ID like a tube header, and model between a stock 1.71" ID to a CNC ported 1.82" ID. Your experience with a 1.675 OD header (~1.5 ID) exploits the benefits of the consistent tube flow over the rough texture and larger irregular average diameter of ramshorns (streamlining wins every time, what you recommend works).

I also agree with your point of a total systems approach, and further, to the need to understand how one change impacts other attributes. This is why identifying the heads and cam are important when discussing what works (why I try to be descriptive, but not excessive to the point of boredom, when presenting model and actual dynamometer run data).

I do not know details of the OP's 355 other than posted in this thread. He asked, and I presented my experience and what I learned regarding ramshorn manifolds. I assume most people are like you and will question specifics, promoting good follow up dialog to give other readers a better understanding of the systems assumptions and reasoning.

The graphs I presented were from my work on 327 & 350 engines with ramshorn manifolds, for reference comparison between the manifold and headers as identified. Some people might try to read more into the message than the facts as presented and suffer personally (and other peoples "feelings" are not under my control other than motivating add disclaimers like this paragraph).

EDIT:

MikeM, you got me thinking. I ran a model run with the 327 as described above, comparing just the change from stock port matched ramshorns to 1 5/8 x 38 headers. The area of improvement is mid-range torque and power. There is a little loss at top end, but the average power increase far exceeds the loss (confirming your recommendation for improvement in the rpm range where most people drive).

SWCDuke

Case in point: '65 L-79, rebuilt, .030" overbore with massaged OE heads, 10.35 measured CR, and LT-1 cam... tested on a lab dyno with both headers and manifolds (with the OE front exhaust pipes) exiting into the dyno cell 3" exhaust system with no mufflers.

The four-into-one headers were 1 5/8" OD, small for this engine's output, which was making about 360 (honest) SAE gross HP at 6500 and 330 lb-ft gross torque at 4500. The headers made about 8 percent more peak torque, but only about 3 percent more peak power due to the too-small tubes.

Even the efficient Corvette OE exhaust system, which generates about 3 psi back pressure at this power level would reduce the above improvements by about half in the car.

This project was thoroughly documented here on the CF about ten years ago. Search for threads started by "Dave McDufford" is you want to see all the details.

Also, you need a healthy overlap cam to get any improvement. Installing headers on a 327/300 won't do jack because of the low overlap and might even lose top end power because each cylinder's exhaust gas has to traverse about three feet of small tubing rather than being immediately dumped into 2-2.5" pipes.

My Cosworth Vega's bye-wye OE header with 1 5/8" OD 20" long primaries and same OD 14" downpipes may may make a bit more peak torque and top end power than with a well designed streamlined manifold, but it also has a shallow but long "hole" in the torque curve from about 2500-4000, which is right in the normal road driving operating range. Cams are reindexed to eliminate the waaaay excessive OE overlap to about the same as the L-79 cam.

In "track trim" with open exhaust it makes 122 SAE corrected RWHP at 6500 and is flat to 7000 (110 net at the flywheel OE rating), which is as high as I rev it, and peak torque is at 5000. The engine is all stock internally (8.2:1 measured CR) except for the reindexed cams. In absolutely showroom stock trim with the catalyst and restrictive exhaust system they're only good for about 95 SAE corrected RWHP, so my basically stock engine makes about 28 percent more power primarily by bypassing the restrictive "bead-bed" cat and very resrtrictive OE exhaust system.

A streamlined manifold would eliminate that hole (which is typical of most header installations). It might cost a little top end power and peak torque, but I'd rather have more torque/power where it spends 99 percent of it's operating time.

IMO headers are a waste on any reasonable road engine unless you plan on doing some serious racing with open exhaust, but not all manifolds are equal. The Corvette "ram horn" and OE Corvette big block manifolds are very efficient.

The 10 HP difference between the '70 Corvette LT-1 (370 gross) and same year Z-28 LT-1 (360 gross) was the less efficient "log" manifolds used on the F-body chassis.

Duke

stratplus

This is the hedman that I am using.

babbah

Headers YES!!!! Performance increase

63Corvette

A radical camshaft (think L-88) REQUIRES headers.....period!
My 1969 L-88 picked up 110 horsepower at the wheels with ONLY headers and rejet (leaner) of the carb. For STREET engines, headers are never required....except for bling

vetrod62

The same header I run on my 395 inch engine. A great header for an engine with good heads, bigger cam and RPMs. Fits well, Nice open port from the flange to the tube. I rev mine to 7500 all gears.

To bad they discontinued it about 5 years ago.