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Does anyone here have time slips of their before and after exhaust modifications? I don't think the 2-1-2 is all that terrible. To the OP, a new monolithic catalytic converter will probably free up 15-20 HP.
Somewhere in time I have a post of 0-60 times using a G-tech. I tried to look it up, but ran out of time.
I think I started around 7.1 sec with a well-tuned but stock GW350 (L-48 for all intents and purposes) and was down to 6.6/6.7 with 1 5/8" headers. 6.2 with true dual catted 2.5s and the same headers. Dropped into mid 5s after heads/cam.
Somewhere in time I have a post of 0-60 times using a G-tech. I tried to look it up, but ran out of time.
I think I started around 7.1 sec with a well-tuned but stock GW350 (L-48 for all intents and purposes) and was down to 6.6/6.7 with 1 5/8" headers. 6.2 with true dual catted 2.5s and the same headers. Dropped into mid 5s after heads/cam.
Thank you Shark. This is good information and very helpful to forum members. A one second improvement in 0-60 time with headers and a dual exhaust with cats is excellent! I've got my 82 Crossfire down to a 14.906 or a DA corrected 14.618 in the 1/4 with just headers, tune, and a 2-1-2 exhaust system with a (magnaflow) single cat. To the OP, take note.
Last edited by Fly skids up!; Jan 4, 2022 at 08:01 PM.
Thanks for the info TL79C3 What did you do with the heat riser? Also, is there a clearance issue with the speedometer cable and the driver side pipe?
Thanks
Budryzer,
I used the stock manifolds, with new ss 2.5 down pipes and was able to keep the heat riser. I wanted to keep as stock as possible (other than the duel exhaust) and use the same carb and choke set up. I had no clearance issues with speedo cable. I cannot be happier with the installation and the awsome sound. All said and done I was into for about $900.00
Thanks TL79C3. Thats exactly the same scenario for me. Thanks for the info
Fly skids up: Shark Racer dropped .9 of a second on his 0-60 with just headers and duals! Pretty remarkable.
BTW, Skids are for kids LOL I'm a retired Chinook IP
Budryzer,
I used the stock manifolds, with new ss 2.5 down pipes and was able to keep the heat riser. I wanted to keep as stock as possible (other than the duel exhaust) and use the same carb and choke set up. I had no clearance issues with speedo cable. I cannot be happier with the installation and the awsome sound. All said and done I was into for about $900.00
Where did you buy your exhaust from? You already gave me the part number but when I looked at the image for the kit, it looked like it was for headers???
I purchased it at Jegs. part #958-SCC10S $758.99 the S at the ends stands for Street Pro Muffler or an R would be race pro. Both are the same price. Street Pro is louder of the 2 then there is one that is even louder. The down pipe is DCC10S $141.99.The exhaust system was complete with tips, band clamps, and hangers.
I purchased it at Jegs. part #958-SCC10S $758.99 the S at the ends stands for Street Pro Muffler or an R would be race pro. Both are the same price. Street Pro is louder of the 2 then there is one that is even louder. The down pipe is DCC10S $141.99.The exhaust system was complete with tips, band clamps, and hangers.
I would never spend $800 on an exhaust and not install ceramic coated long tube headers.......they work and go together. The increase in both over the stock system is staggering......
It will also support future mods......
There are several people here that preach manifolds and I am not one of them......the pathetic 2" outlet rams horn manifold is barely capable of handling a stock 250 horse engine.......1000cc motorcycles have bigger downpipes......
If you have to have manifolds....use the 64-65 327/365 2.5" outlet manifolds and the mandrel bent Corvette Central down pipes......
fyio.. that heat riser IMO is a waste. My choke maybe adds 2 minutes to come off high idle and even recent below freezing temps..it gets hot without it, and always has a restriction and risk of failure..
about 1 minute in is choke hot air https://www.corvetteforum.com/forums...d-to-warm.html
I like OEM too.. and quite frankly would love headers too.. but for me and a packed 79 ac engine compartment. not enough squeeze at this time., can always add later.
too bad Allens is no longer..i think i am all in from manifolds back including spacer for heat riser ~ 550 bucks. and walmart mufflers dynomax were 200 of that.. ss band clamps at RA are cheap and high quality,
Thanks for the input Jebby, however my goal wasn't to ad HP as much a improve exhaust note. Even though I am fully aware that headers would also improve on the exhaust music and add a few more ponies. My concern about headers are first extra heat under the hood ( I know ceramic coated dissipates heat well) and I was concerned about busting bolts off on the head trying to remove the old manifolds. And that is not a war I was willing to battle at this time. The old system came out fairly easy and the new one went in just as well. And I couldn't be happier with the results.
Ceramic coating doesn't dissipate heat. It insulates, such that the hot exhaust leaves your engine bay. With a properly tuned engine, ceramic coated headers can reduce under hood, and in-car, temps. Side pipes work even better for keeping your feet cool.
Put you money where your mouth is. Show proof ....dyno sheets before and after of the 50-80 HP gain on a stock 1979 5.7 by solely installing dual exhaust.
Seriously? You think we all run to a dyno everytime we do a mod on our cars? We get on this board to share real life experiences and try to help one another out.
I Know my 77 came with the same super restrictive exhaust.
Changing it out was by far the biggest improvement in power I have ever done to my car. Tons of threads on this forum on this topic over the years. We are not talking about talking off a decent system for a slightly better one.
We are talking about taking off totally choking garbage and putting on something that will let your car breathe.
Here's a quote from a thread that's also running right now.
Do your homework, I'm really just trying to help.
That's 90 HP. with timing, exhaust and removal of some smog.
No one on here is trying to mislead you.
fyio.. that heat riser IMO is a waste. My choke maybe adds 2 minutes to come off high idle and even recent below freezing temps..it gets hot without it, and always has a restriction and risk of failure..
about 1 minute in is choke hot air https://www.corvetteforum.com/forums...d-to-warm.html
I like OEM too.. and quite frankly would love headers too.. but for me and a packed 79 ac engine compartment. not enough squeeze at this time., can always add later.
too bad Allens is no longer..i think i am all in from manifolds back including spacer for heat riser ~ 550 bucks. and walmart mufflers dynomax were 200 of that.. ss band clamps at RA are cheap and high quality,
Is Allens still selling systems? You mention they are no longer????
From: Into the Mystic And yet, despite the look on my face, you're still talking TN
St. Jude Donor '09 thru '25
I would also look at Corvette Central, they have a true dual system with Magnaflow mufflers. They are not loud at idle, no drone at speed but you definitely hear them when you stick your foot in it.
I would also look at Corvette Central, they have a true dual system with Magnaflow mufflers. They are not loud at idle, no drone at speed but you definitely hear them when you stick your foot in it.
This. I first was looking for an Allen's system for my car, but have also come to the conclusion that they went belly-up. No response from them directly and all their resellers are out of stock on everything from them.
I went with the dual Magnaflow system from Corvette Central on my 1980 and I am pleased. Not quite as loud as I wanted, but it is still a 1000% improvement over the stock soda straw system. No cruising drone, adds some presence/rumble at idle, and comes to life when you feed it onions. Thread here.
Test run fly-by clip after install...
I'm not being mislead!! I'm just simply pointing out that it is Impossible to gain 90HP by a simple exhaust system upgrade!! As your post even supports my statement....
" an increase at the crank to 315 with the mods I pointed out... (exhaust system upgrade and curve the timing) 235 at the tires".... OK.....so a stock 1979 l82 produces 225HP that is only a 10HP gain. It is literally impossible to gain 90HP with simple bolt on mods on an 8.9-1 compression engine.
