Well let's start with the specs:

406ci
Hydraulic roller cam 230/236 .510/.520 112LSA
AFR 195 heads
10.5 compression
RPM Air-gap manifold
750 Edelbrock carb vacuum secondaries
1 5/8 shorty headers with 2.5 inch Y-pipe very restrcitive exhaust.

Alright its in my 83 Camaro w /T-56 Stage 3 Kevlar STAR clutch and 3.42's out back.

ON street tires it ran 13.5 @ 109 on a 2.4 60' time

Then I dynoed it yesterday:

320 hp and 380 torque at the wheels.

I was expecting more. I wanted to get this baseline then do these mods and see what I gained:
Victor Jr. Single plane port matched to 1205 gasket.
Hooker LT's with true dual dumps in front of rear tires.
and posibly a bigger carb.

How Much could I expect from those things? MY exhaust is very restrictive after the 2.5 inch Y-pipe it goes into a single piece of 2.5 where the cat should be then goes up to 3" I think that may be hurting me significantly. DOes anyone think I need a bigger cam? thanks I just to someone I can talk to that knows engines and can bounce ideas off me.

 

Yes the exhaust is a major restriction.
No you don't need a bigger cam.

Ya do need better tires.

Forget the dual exhaust.

A set of 1-3/4" shorties or long tubes with a nice mergeing
custom made y pipe into a big *** main pipe with a big ***
hi flow muffler behind the axle is better on a third gen.

big *** ='s 3.5" or bigger.

Uncork the headers and redyno it. You'll see.

 

I would go dual exhaust if emissions aren't a concern.
And get rid of those 1 5/8 headers.

 

How was your air fuel ratios on the dyno.

Was it starving for fuel? Borderline? May need to go up in Neadle and seat size and or fuel pressure on that Edelbrock.

The Vic JR will make alittle more peak hp, but stick with the Dual plane if ya can. It is a much sweeter street intake. Is it port matched?

You have enough head flow on that 406 to benefit from a bigger carb. (on the dual plane) Like a 950 cfm holley. Can you get something like that to try?

 

First thing that stuck out to me is the carb. And of course the exhaust, but I would try a double pumper, whole lot more repsonse. Not sure about the HP but you WILL tell a difference!

 

The air fuel was good. A little rich but good none the less. The Air-gap is not port-matched it is quite a bit smaller. I was going to port it myself but I thought I remember reading something like the walls on the inside of the intake can't be smooth because it will hurt air/ fuel mixing. Edelbrock sells a Victor Jr. that is port matched to my heads I was thinking about getting that. It makes plenty of low end. so if I gave up a little to gain top end I wouldn't mind. I was also thinking of a bigger carb but don't want to go too big.

I already have the Hooker LT's. Just haven't put them in yet. I am going to a dual 2.5 exhaust because it will be cheaper and I don't drive the car all that much anyways.

 

work on traction. a 1.9 60ft should put you well into the 12's. you could probably get better than that with that engine though.

 

I would forget the "true duals". Lots of maze, very little cheese.

Changing the cam & carb won't help your traction. There's a half second you leave on the table, right there.

Changing the carb & cam won't fix the exhaust, which right now is having to shove a fire hose load through a piece of drinking straw.

I think you should leave the engine alone until you get the rest of the car sorted out. My gut feel is that with suspension work and a real exhaust, you'll pick up around .8 sec with the rest of the motor as it is.

Get a set of 1¾" headers, a Y-pipe to at least 3", and a test tube (after all you should verify the need to REPLACE THE CATALYTIC CONVERTER ) of at least 3"; and figure out what your suspension needs to hook up what you've already got. That short time is terrible, you're getting drilled at the line by people with stock 305 TBI auto 2.73 cars. .1 sec off of 60' = .1 sec off of ET, i.e. maximum possible payoff.

For comparison, my 400 with the same cam except on its stock LSA, a Performer NOT RPM intake, Holley 800 spreadbore, double-hump heads, TES, stock HO exhaust including cat, & stock HO air cleaner, did 284 RWHP & 373 RW ft-lbs. Your car should be able to spank my junkyard head numbers like a red-headed stepchild, much more than it is.

 

I'd port match that airgap RPM intake first. It' a good powerfull
design with lots of street flexability. Like any other intake
it will work much better when port matched to your heads.
You can step up the carb size on a dual plane on a healthy
motor like yours to good effect.
You can't really mess it up. Just don't polish your work.
cutters and 40grit sandrolls is just right. lots of WD-40.
We picked up 30 some dyno HP on a healthy 350 just by port matching the performer RPM intake to Dart sportmans so I'm sure there is power there.

 

Here is an indication of just how bad your traction situation is
and how much it is killing your et from what you should be doing with not an ounce more hp.

Multiply your et by your MPH.....

13.50 x 109 =1471.5 This is an efficentcy factor.
If your car was biting, your et and mph would multiply out to
between 1320's to 1400.

Even a dead stock chassis with some decent tires should
be at 1375 to 1400 efficentcy factor or ya better go home.

Take 1375 and divide by your MPH... ya get

1375 /109mph = 12.61 Thats what ya should be et-ing at.

1400 / 109= 12.84 Worst case.
remember that is without any more horepower.

When ya get this car sorted out your going to have a terror.

The dual exhaust is a bad idea. And will not save you any money.

I know this because I have dual exhaust. 2.5" welded mandral bent custom ganged dual tweeked turbo mufflers and the whole 9 yards. It works great,, has loads of ground clearance. BUT rattles cause there simply is not enough room. Peroid ZIP.
A well done 2 into 1 big pipe with 1 big muffler at the back
exhaust system gives up nothing ,, fits the friKKen car!!! and is actually cheaper. Flow master makes a muffler that supports over 800 hp.... 1 muffler 800hp...... that all the muffler you and I need combined.

Many others with faster cars than mine will tell ya the same thing.

 

I was going to do something like this:
https://www.thirdgen.org/techbb2/sho...hreadid=126944

I just don't want to spend the cash on a Mufflex catback 3.5 catback I could do that cheapy dual alot cheaper and easier IMO.

RB83L69 I don't have a cat. But right before the catback becomes 3" there is a little section about a foot in length where it just a single piece of 2.5".

The Mufflex Y-pipe would be a great idea except I have a Spohn tranny X-member. SO it would hit it. Do you guys think I could cut the Mufflex pipe down to size? Shorten it before it gets to the crossmember? Does anyone have a pic of one on the ground or anyhting?

 

OH yeah I forgot to mention I have a full Spohn suspension, SFC's, LCA's, Panhard bar, etc. NExt year when I get my 12-bolt I am going to buy some ET streets but as for now I don't want to blow my rearend.

 

Do you have the LCA lowering brackets? What does the car do at the line that makes it take so long to get going?

You might be able to notch the crossmember for the Y-pipe, if it's not too much interference. Personally I think as long as there's at least ¼" of vertical material left, it's plenty; after all, the factory thing it's replacing is only a piece of sheet metal.

I don't think there's going to be anything cheap about doing duals, if you want any ground clearance at all; unless you work at a muffler shop and can do it yourself. If you have to pay somebody to make something, pay them to make as large a single exhaust as they can make.

I was joking about the test tube... do you recall when cats first came out, and you could buy the tube in a box. The way they skirted the law about just removing the cat (this was of course before emissions inspection was common, and the law only prohibited outright removal) was that it was marketed as a "test" tube, to compare against your cat; I guess if the car ran better (it alwasy did, since those were teh days when nothing but the bed of pellets was available) then your cat was bad. Anyway, that's what they said on the box: in letters so small you could hardly read them "verify the need" and then in letters that covered the whole rest of the box "to replace your catalytic converter". At the time I worked in a place that carried them, and I still have one I use on a car from those days. I knid of wish I still had the box; it was a real hoot.

 

Trying not to incinerate the tires. Its either completely burn through 1st gear or bog it a little so you can get something out of it. I don't have the lowering brackets.

I talked to Steve SPohn about notching the crossmember and he said it was a bad idea because the torque arm mounts to the crossmember. He said it is like that for strength.

 

I wouldn't buy the mufflex stuff either. It is over priced and like you said. Won't fit your car.

You can pay some one the build you a good exhaust system.
If you could see mine you'd know that I mean.

The trans crossmember is notched a little and the pipes
snug right up there nice. Not like that Getto rigged pic.
The only part I'm going to change is to get rid of the twin pipes under the car and over the axle (passenger side).
A flowmaster merge Y pipe and a 3.5" main pipe will flow more air and fit no problem. A Flowmaster "Shootout muffer"
will flow all the air I'll ever need.
I seen it on another car at the track one day and talked to the guy. I asked him if it was a Mufflex system. He said don't even go there. He got a shop to do it in Toronto. He did it for less money than I did mine for. His main pipe was stainless too.

Find a place that welds/ makes truck exhaust. They have the pipe in stock and the know how. The corner Muffler Shop is a joke. Leave them to what they are good at. _________...
The after market ready made stuff is way over priced.

 

I would get the ET. Streets now. If the 7.5" axle is going to break,
then it's going to break.

We've put more power thru these 7.5" rear ends on sticky tires
then you want to know about. Nitrous, Big Blocks, real healthy small blocks.

One axle failure. Don't you think all that wild wheelspin
is hard on the driveline?

Wheel hop is what's hard on a stock rear end. It's like hitting the trans brake again and again.

Your car will be much safer with the ET streets. At least it will
go where you steer it.

You're much more likely to smoke the transmission.

 

http://www.ls1tech.com/ubb/cgi-bin/u...24;t=004024;p=

That is a Dr. Gas universal dual kit but I don't think it will clear the front sub-frame on a 3rd gen.

 

I think its not your main concern, but that cam will definently hold you back. Look at what guys are running with 350's set up like yours, and youll see that your cam is real close to what the have. Id say more cam...not a **** load more, just more.

 

1. that is a 4th gen fbody. They are different from the trans
crossmember forward. So It won't fit your car even without
frame conectors.
2. There are no mufflers.
3. Check the bends in the pipe. (compression bends)

4. If you can weld that stuff up, You can do an exhaust system right yourself.

 

Have you dialed in your distributor? My car gained a whole lot of power by recurving the distributor. My guess on your dyno pulls is that it isn't tuned right. By that I mean timing and air fuel ratio. You say your carb is tuned so check the timing. Try to get 36 degrees in by 3000 RPM. Also what is your base timing?

For the track time you will need traction. I know this sounds like a broken record but you need some tires. Also, you have full spohn suspension like I do and am getting 1.6 60' times with a 350 and some juice. If you have LCA relocation brackets try putting them in different holes. Believe it or not my car is quicker off the line by not using the relocation brackets at all. My car is also an 83 Z-28. I put v6 rear springs in the rear and it helped my 60' times.

Are your secondaries opening up too late by chance? Oh, I use a stock 7.5" rear and stock axles on slicks and haven't broke the axles yet.

 

This pic is a third gen.

Althou the main pipe in the pic is too small and the Y is not a merge
collector, this basic layout shows what you should consider for your car. A proper venturii style merged Y collector into 1 big main pipe will have the same function as the X pipe.

You can buy the merge collector from flowmaster or
Burns Stainless.
By the time you've mucked up a getto rigged dual system on your car, you could fabricate or have fabricated this system which will exhaust out the rear, sound great, not rattle, not scrape on ever bump, get ya past a cop, and support all the horspower you'll likely ever make.

Some things are just worth doing right.
With all the other good expensive parts on your car, I just don't buy into the I can't afford it story.

 

.....

 

Althou its not done on this car, the crossmember flanges
where the two pipes pass under, can be notched with a cutting torch and grinder. This allows you to snug the pipes up closer
and gains almost 1" more ground clearance.
This is the way to do LT header exhaust system on a third gen.

 

My exhaust is the exact same way as that. I thought someone took a picture of the underside of my car. The cutouts are in the same place and everything.

 

I am not going to say that you can't have a single exhaust that will support good power, because you can, but if you are going to do run it like that which you basically will have to because of the hooker lt's then I dont see any reason for him to not run duals if thats what he wants. The lowest point would probably be where the pipes run under the crosmember depending on placement and type of mufflers. You can route the duals over the rear axle on his car also. I have measured it out and even with me in the hatch of my car(I am not a small guy either) my friend measured a 4" gap on the smaller side to run the pipe for. I believe that it is the fuel injected cars that lack the room because of the gas tank or something because on his car which was an 89 iroc there was not clearance for a pipe to exit on the other side. My car is an 85 t/a that had the lg4 stock by the way. I think you will also get a better sound from duals, so I think that in his situation, it just depends on what he wants to do, and what kind of mufflers he plans on running. I have dynomax bullets so I dont really have to worry about muffler clearance to much myself though.

Ben

 

That exhaust loke nice but it would never fly with my crossmember. I was planning on making a Dual exhaust out of Spintechs oval tubing. 3" oval tubing routed around the crossmember into SPintech mufflers.

 

just my two cents, but my engine was a pooch until i realized the carb had a secondary lockout that didn't let the secondaries open until the choke flap was ENTIRELY open....made me run 15.5, now i'm in the 13's.