StDomingos

As I getting ready to put my '81 away for the season I've been thinking about a few winter projects. One of those was the possibility of squeezing some more power out of the engine with a set of long lube headers, but I'm on the fence about whether the money spent would show any noticeable improvement.

Here is what I'm running at the moment;

Goodwrench 350 engine with Brodix IK180 heads, Comp XE256 cam, stock 1981 aluminum intake and quadrajet (from a '78). The transmission and rear end are stock (TH350c and 2.87 gears). The exhaust runs from the stock tubular manifolds into true duals with no cats.

The computer was removed long ago along with any smog gear. There is no emissions testing where I live. I figure my compression is about 8.5 to 1 (or a little bit more). The car is strictly street driven also.

So, with that setup do you think I'd notice any power improvement by switching to long tube headers?

71VetteLover

I suggest saving your money and install a TH700R4 with a set of 3.73 gears. With that combination you'll get the low end performance you want AND a comfortable 2000 rpm @ 60 mph.

cooper9811

71Vettelovers suggestion is pretty expensive, and while it would give you more bottom-end grunt, it would not do anything to improve overall power.

I don't know how much the 81 tubular manifolds flow. Headers might provide a minimal gain, but that's a pretty conservative cam with decent heads, so I tend to doubt you swill see a lot of gain in ability to breathe unless you go with another camshaft - it all has to work together.

Your cheapest seat-of-the-pants gain (with the current setup) will be had through an aggressive timing curve if you have not already done that. The timing sticky has several threads go over timing curves - here is a good overview:

https://www.corvetteforum.com/forums...long-post.html

Aside from that, what are your overall goals and budget for the car? Knowing that will help with any advise or suggestions.

Dynra Rockets

They don't flow any better than the earlier cast iron units. They were designed solely for weight reduction. I've read they support about 300 crank/260 rwhp. The tubes are tiny and the collector is junk from a flow standpoint.

jb78L-82

I would not with that cam which is basically the L-82 cam lift (,450/.460, duration 222, LSA114) with less duration pushing the power lower down the RPM which is where you want it with those lower numerical gear:


Brand:
COMP Cams


Manufacturer's Part Number:
12-256-4


Part Type:
Camshafts


Product Line:
COMP Cams Xtreme Energy Camshafts


Summit Racing Part Number:
CCA-12-256-4




UPC:
036584063278


Cam Style:
Hydraulic flat tappet


Basic Operating RPM Range:
1,200-5,200


Intake Duration at 050 inch Lift:
212


Exhaust Duration at 050 inch Lift:
218


Duration at 050 inch Lift:
212 int./218 exh.


Advertised Intake Duration:
256


Advertised Exhaust Duration:
268


Advertised Duration:
256 int./268 exh.


Intake Valve Lift with Factory Rocker Arm Ratio:
0.449 in.


Exhaust Valve Lift with Factory Rocker Arm Ratio:
0.456 in.


Valve Lift with Factory Rocker Arm Ratio:
0.449 int./0.456 exh.


Lobe Separation (degrees):
112


Computer-Controlled Compatible:
Yes


Grind Number:
CS XE256H-12

Long tubes will not do much for you in the lower revs but will help somewhat in the 3,500-5,200 RPM range...maybe 10-15 HP...the big gain for you is the true duals, freeflowing mufflers, and no cat.....which you already have.

On my rebuilt/upgraded 355 L-82 with AFR 180 64 CC CNC heads, Howards roller cam (.525/.525 lift, duration 219/225, LSA110) and 10.2:1 compression, I originally had 1 5/8 inch shorty headers which are bigger than the small primaries on the GM 81 manifold and switched this year to XS Power 1 7/8 inch LTH headers to take advantage of the tremendous breathing ability of the AFR heads:

https://www.google.com/search?q=XS+p...=1509361919741

I literally just looked and XS Power does NOT offer them any longer on their website.

After the switch this year, I did notice a dramatic change in the ability of the engine to pull from 3,000-6,000 RPM on my motor...it's VERY obvious!!!But my engine is very different from your lightly modified 81 motor

Rescue Rogers

Go to YouTube and lookup engine masters. They have all sorts of actual dyno comparisons.

I'm going with 2.5" collector rams horn to 2.5 sweet thunder side pipes. I'll lose horse power after 5500 to 6000 rpm but I'm using a mechanical lifter version of that cam listed above

AirBusPilot

Get them.

You’ll pick up power from idle, to redline. Figure 20-30hp.

mobird

I would get the headers.


I have a Goodwrench 350 as well, with Brodix IK200 heads and a Lunati 268 cam.


I would say your biggest problems for performance at the moment is your rear gears however. So maybe find some cheap longtube headers, and then invest in a better rear gear ratio.

Rescue Rogers

You'll be wasting money if you're not living above 3500 rpm. Look at all the other improvements and do headers last

Matt81

I just installed a set of LTH from Hedman a little over a month ago. The thing I noticed most was how much quieter my engine ran. NOT what I was expecting. If the 81's came with the AIR tubes in the manifolds like my 78, good chance they could have small cracks in them. Turned out I was running with several small exhaust leaks.

Will second 71VetteLover suggestion on the overdrive. That was my winter project last year, swapping a TKO600 for the 4-speed BW unit. Totally changed the car, made it a lot more fun to drive. Took good advantage of the 3.73 rear gears too.

Not sure on the difficulty of the 700r4 swap, but can't imagine it would be much more difficult than the manual. In fact, probably lots easier since autos came with a removable crossmember. Certainly something you can do in your garage over the winter.

jb78L-82

I actually think you can get 20-30 from the exhaust alone. Here is why:

I did 233 RWHP with my OEM L-82 with no emissions, McJacks shorty headers, and 2.5 inch duals...everything else OEM (882 heads, L-82 cam etc). The stock L-82 did about 185 RWHP so the difference with the duals only and shorty's was 48 RWHP...mostly from the exhaust since McJacks are just a slightly better manifold than the Ramhorns. I originally had the Mcjacks on the rebuilt L-82 355 and switched to LTH headers this year and noticed zero change in power from off idle to 3,000 RPM versus the Mcjacks. The engine does pull MUCH harder from 3,500-6,000 RPM though with the LTH headers

Karol on this forum with a L-82 with 882 OEM heads, cam of unknown origin, and 2.5 duals only (no headers) did 248 RWHP on the same exact dyno. Difference of 63 RWHP...no headers. This year Karol put on the same LTH headers as on my L-82 355, and he has relayed that the off idle to 3,000 feels the same with slightly more HP from mid rpm to 6,000...his comment was 10-15 more hp.

I really do feel that on stock to slightly modified engines the real power gain is in the 2.5 duals with free flowing muffler. The LTH headers helped my 355 a LOT because of the roller cam and AFR heads with their tremendous airflow numbers.

jb78L-82

Funny you mentioned how quiet the LTH headers made your engine. I noticed the same on my L-82 355 when I put on the XS Power BIG tubed primaries. The engine is MUCH quieter than with the McJacks....
Not what I expected...it roars above 3,500-6,000 RPM but is a sleeper at lower revs...no one suspects the fury....

drwet

I have always found headers to be one of the most effective upgrades. At one time I would have said they are about the best bang for the buck out there, but that was when headers were cheap. No true anymore. Still a good upgrade. I have always been able to detect a significant performance improvement with headers. Don't care to speculate on exactly how many.

Matt81

Another unexpected outcome of the headers is my engine cools down much quicker when shut off. My set is thermal coated, so maybe that is why? Surprised me when I got in the car after parking for an hour and the temp gauge is back to about 100 degrees.

StDomingos

There are some good ideas in here.

71vettelover - I have thought of that exact swap for the future, but it would be a bit more coin than I could justify at his stage considering that I also wouldn't feel comfortable with my mechanical abilities to do this myself and would have to pay somebody.

Cooper9811 - I have already recurved the distributor. The intended use for the car is as a cruiser with an occasional bit of stop light to stop light fun. There isn't really a budget but I don't want to drop a few grand on a new transmission and rear gears. I guess I'd like to keep the spend under 1000.

The AIR tubes are long gone and welded closed, but the prospect of less under hood noise and heat from the long tube headers is appealing. I would certainly get ceramic coated headers if I pulled the trigger.

If I were to do the rear gears I think I would want to do the transmission at he same time to keep nice highway manners.

AirBusPilot

I switched from 1 5/8” tri Y headers to 1 7/8” full long tubes and it feels like it gained a ton of low end torque. It also stopped fouling plugs.

Our engines are different, mine made about 415 rwhp after the swap, and I have 415 ci.

There seems to be an incorrect line of thought that headers kill, or don’t add low speed torque, but as long as the primary tube size is close, you should have gains across the rpm band.

jcloving

I put long tube headers and 2.5in s/s exhaust on my stock L-48 and I immediately noticed a difference. I had the stock two into one with cat before I made the change. Someone above mentioned a 20-30hp gain. I would absolutely agree with that.

It sounds like you already have the heads, intake and cam. Headers will let that combo breathe like it should.

Do it.

Rescue Rogers

HEADS, CAM AND CARB.......

AirBusPilot

Just what I was saying, big gains in torque down low with long tubes, and superior power across the entire power band.

Rescue Rogers

rereading your initail post youre not going to get much from headers with 8.5:1 compression. I would look for some forged 10.5:1 pistons and good connectng rods. pull your motor apart, give it a good hone and throw new connecting rod bearings in it and put it back together, then you'll want headers and they will actually do something for you