markiemyster

I've been thinking of sending my 2" exhaust manifolds out to be reskinned. I've seen pictures of other folks and it sure would make my engine look better.

The thing is I was thinking of buying an old pair on ebay and having them done over so I don't have my 65 out of commision while the originals are out being redone for who knows how long.
Now my question: I now have 2" manifolds with a 2 1/2" exhaust system. I realize I would need to change the front of the exhaust to eliminate the reducer if I switch to the 2 1/2" manifold but would it be worth it in performance? Would I notice enough difference in HP to make it worth while?

Thanks, Mark

67-427ci

You could sand blast your present manifolds and paint them with POR-15 Factory Manifold Gray Hi-Temp paint. That's what I did and they came out looking great. It is an easy weekend job. If you do that, after the paint is dry, bake it in the oven for 1 hour at 350*. That will harden the paint prior to reinstalling the manifolds. Cost is about $20.00 for the paint.
Roy

dmentzer

I did exactly as 67-427ci did to his manifolds on my small block. Sand blast, clean real good, and paint. I installed on the car and left the engine heat cure them. Going on 9 months and they still look as good as they did when I first painted them.

66since71

Mark, Opinion here on the forum seems to be that the 2 1/2" rams horns are as good as headers. Apparently there is an issue about getting poor Chinese reproductions, so be careful.

devildog

Mark,

I run a 283 that has been overside a couple of times thru the years. I recently put the 2.5 manifolds on it. I REALLY had a BIG increase in low end torque.

I bought a pair of the chinese manifolds for about $80 each, sprayed the high temp gray paint and let the engine cure. Chinese fit good and no problems. Saved the original manifolds for the next generation to worry about.

Runs great and looks great for $200 bucks

wmf62

my 'Chinese' manifolds work great too....
Bill

aaronz28

only up to a point... on a 300 hp motor?.. sure I'd agree there,

but the 350 and 365hp motors will definatly be better with headers ...

wesmigletz

The 2 1/2" GM Manifolds are still out there for a reasonable price. I picked-up a 901 and a 902 manifold two weeks ago at Pomona for $180 for the pair. They look like they never been on a car.

markiemyster

Thanks guys, It sounds like switching to the 2 1/2" manifolds is worth the extra $$.
How would that effect the timing, carb adjustments, etc. Would they all stay the same. As you might be able to tell I'm not a real gearhead just a wanabee.

Thanks again, Mark

ptwohey

Mark, Interesting that you ask about the tune up with the exhaust change and I'm curious about the feedback. I switched my '70 LT1 to headers and something seems to be wrong now. It would not run well with original spec's so I tried advancing the timing and used a vacuum gauge to adjust the carb. I don't get a ping usually but it does run super hot that then the pinging starts. Also, just during a mild cruising speed, I feel the car is bucking. Another "not a totally gear head" wondering what to do.
PS..local tune up shop suggested I put it on the computer but couldn't find where to plug it in!

wmf62

if it is "bucking" (surging), it's probably too lean.
Bill

zim64

I would agree, fatten up the mains about 6 sizes, and the secondary (jets or plates?) if jets go up about 4 sizes.

devildog

Do not worry about being a non-gearhead, that is part of the fun to lelarn and understand. If you timed and used vacuum gage, you are no novice. However, please put some data in your personal profile; it is easier to make suggestions and heck of a lot more intersting.

First do not touch the carb until you know where your ignition is...very rare that these old carb engines are too lean. Go to the start of this C1-C2 forum and under the FAQ look at ignition. Read Lars stuff and then look a the other ignition stuff.

Get that understood,and we can help get those tires lit-up more than you ever imagined.

aaronz28

it is a well known fact that when you switch to hearders, you have to fatten the carb up to compensate...the fact that you are getting hot would also indicate a lean condition.

i'd like to know the rest of your setup and we can mostlikely help.

true about the ignition... make sure that is ok.
LT1 like 36 full advance and as much initial as it will take and still give a smooth start. get light springs in the distributor to make tht full advance come on about 2500 rpm... she'll love that.


if all that is set, and you still have the problem... which you likely will, you'll need to go up about 6 jet sizes. and possibly need more squirter size.

what carb you running?

thanks and good luck

Aaron
thanks

aaron