Bob Turner

I came to the realization last night that the reason this motor is NOT performing up to par is the exhaust.

Here is what I am running:

Sandeson SHORTIE headers--- 1 7/8" tube

These 1 7/8" tubes flow into the 3" collector and then REDUCED down to a 2" pipe running to a 12" glasspack and then to the Eckler's stock looking side pipes......

Based on this description, do you guys think I am restricting the exhaust too much???? I do!! It seems that the car doesn't have the power it should. Granted, I still need to have a dyno shop set up the timing/carb but I can't even light up the tires with a 2.77 first gear and 3.08 rear!! :mad And this is a BIG BLOCK!!! :mad


The specs on the motor are:

454 .030"
Comp Cams XE274H 230/236 .553"/.555" 110
9.3 to one
Harland Sharp roller rocker arms
Demon 850
Performer RPM intake
049 heads 2.19/1.88" mild pocket porting

This motor, according to a Chevy High Performance article, should put out 480 hp/ 507 lbs.............

Opinions??????????????????????


Bob :cheers:




[Modified by Bob Turner, 6:58 PM 7/25/2003]

427Hotrod

Big time choking it!!

I'm not a fan of the shorty headers, but I think the pipe/mufflers are the worst.

I'd get a set of full length 2" headers and use AT LEAST 2.5" (MUCH preferably 3") pipes to some straight through mufflers, NOT regular 'ole glasspacks, use some Dynomax 3" bullets or some Borlas if you feel richer.


If you really want to use the shorties, I'd plumb 3" pipe to them and run that all the way to mufflers.


But there still seems to be something else wrong.....you should be able to wear out a set of tires pretty easily! That's not a real radical cam, but you don't have a lot of compression either. What's timing at? Set it up to around 36-38* total and shoot for 20-22* initial at idle. Might take a little tweeking inside dist. to do it, but that's what it will take to make it rock!


JIM

Brettmc

:iagree:
Shorty headers are still *kinda* restrictive. Why not longtubes? As above, timing could also play a role in the prob. How's the carb? Running rich will really kill hp. None of the above factors, by themselves, should keep you from roasting the hides. You prolly have all 3 workin against you to make the prob that bad. Lars has a a good paper on Demon tuning. My combo is not right by any means...yet....but I can still roast em in 1st and keep em spinning in 2nd till the side to side arcs get too wide and I chicken out on the throttle. :yesnod: :yesnod:

Brett :thumbs:

Bob Turner

Thanks 427HOTROD.....

I have been considering giving up the sidepipes and doing the exhaust right..... I will miss the look of them. And. the ease of pulling out the transmission without the exhaust in the way.... my record is 75 minutes!! But since performance is the goal, I will have to sacrifice.


Bob


[Modified by Bob Turner, 8:06 AM 7/23/2003]

Jughead

Bob, have you considered Hooker sidemounts?

sray454

Why not stop guessing and simply and temporily disconnect your exhaust downstream of the headers. Wouldn't this give you an indication of motor vs. exhaust woes ... ?

Bob Turner

Hi Len,

That's a possibility! I will have to look into their full length headers/sidemount pipes.

I have heard that these can be restrictive as well but I have heard about the JCL baffles that may help in this area.....

Decisions, decisions!!

Bob

mayberg

Stock exhaust for a 74 rat motor was 2.5 inches.

I don't spin tires as well now that I have new rubber, but they'll still spin. The '84 vintage tires spun quite easily.

Marks69BB

Bob - Either undercar as others have recommended above or get the Hookers (2 1/8" primaries into a 4" pipe :D ) if you can't live without the sidepipes and are cautious about burns. What would I do? Hooker sipepipes every time! Don't forget to NOT use the Hooker inserts; use the JCLs or I have a cheaper, IMO better sounding alternative (if you are interested just drop me an email). Even with your current setup you should be roasting tires so something is wrong. I had undercar exhaust with hooker SC headers with 1 7/8" primaries into a 3" collector down to 2 1/2" pipe into restrictive chambered pipes and could still burn the tires in first & second gears! The dyno pulls should tell you alot about what's wrong. Also, this may sound stupid but make sure the secondaries are opening all the way and that the throttle linkage at the carb goes the full range and is not restricted. Good luck with it! :cheers:

chewy

On a motor with 049 heads an 1 7/8s header is not your problem. There are people who have gone real fast with an 1 3/4 header and oval port heads. The 2in exhaust is a real problem but like has been said I think there is something else wrong. You should have enough low speed torque to fry the tires at will. Go back and check your tuneup closely.

Jughead

Hi Bob.
That's the path I'm heading down. :D Jet-hot quoted me $878 + shipping, w/o inserts. Was going with JCL spirals.


[Modified by 1970 Stingray, 5:20 AM 7/24/2003]

Chuck Harmon

:iagree:

Restricted or not, you should be able to melt those tires!

Chuck

467-Ratman

Bob, Check out Sandersons web site, they have a very interesting article about bigger is not always better, at least in headers! I have a set of Sanderson block huggers on my rat with 2.5 inch pipes back to Flowmasters. My motor rocks from the moment you hit the gas. I would say go with the bigger pipes and a good muffler, like Flowmaster and you will be happy. Your right though, any BB should be able to fry the tires for sure!!!!! :cheers:

Bob Turner

467 Ratman-

I think you are right here. I got the idea from your buildup to buy these headers, so I will keep them and have a shop weld in a 2.5" system all the way back with a crossover... I will now look at different mufflers.

I will go and read that Sanderson article now...

Bob :cool:

427Hotrod

If you are going to install new pipes all the way back on a big block, seriously consider installing 3". They will fit if the muffler guy is good. 2.5" will work well up to around 500 hp maybe, but that's pushing it especially if you run reasonable mufflers.

It doesn't cost much more, and in some cases it's actually quieter with larger pipe.


JIM

68427

I ran sandersons with 505ci and same 049 heads with big valves, a mechanical roller cam. first with a dual-plane intake, then with a single-plane. I used 2 1/2" mandrel bent pipes to Dynomax Ultraflows. With 3.08 gears this thing smoked the rear tires all through first gear.

I think your small 2" pipes with the horribly restrictive glass packs are hurting your performance. Also, while your head mods make those heads outflow stockers, at low lift the bigger valves don't work as well. I think a larger cam and single-plane intake would help.

Good luck. IMO the best thing about the sandersons is the increased ground clearance - you can run the car lower.

Bob Turner

sray454,

You're right. But I think that if I am going to do the exhaust anyway and get rid of some of the restrictions I have created, I will just wait on it. I am in the process of finding a dyno shop around here that can set this thing up once the exhaust is done....

Bob :cheers:

Bob Turner

Yeah, the Sandersons will allow me to keep the car at it's current "lowered" height and not worry clearance. I think I will keep them and run 2.5" all the way back.......

Bob

Chuck Harmon

Bob,

If you are going to run underneath, how about the 3" oval pipes behind the headers? You get the clearance of 2" pipes with 28% more flow than 2.5".

Chuck

norvalwilhelm

I just reworked the crossmember holes to allow me to go underneath or sort of through and run a 3 inch stainless exhaust without any problems with clearance.