aklim

I think the Greenie Weenie groups aren't that powerful in OH so he might be able to get away with a set of LT headers without the AIR stuff and clean up the engine bay with a pulley.

tequilaboy

Here's an article with some test data comparing the L98 manifolds to long tubes:

https://www.hotrod.com/articles/pit-...-money-street/

Gains would likely be even less with a stock L98 catalytic converter and cat-back exhaust and tpi. You can draw your own conclusions.

sb66

were your hetman headers #63448 or 68446 by chance?

thanks

Sean

sb66

yes the greenie weenie groups do not reside near me - I even checked a few of the southern-ish states my wife thinks she may want to move to some day - if I take the smog stuff off - I do not want to have to try to put it back on

sb66

there were some gains - if I read that right - but they seemed to be less than 10hp - I guess I thought it might be more. I realize it will be a cumulative affect with several other changes and that seems to be when more power will come (cam, heads and headers) does that sound right?

thanks

Sean

cv67

Yup. More you have the more you get, it all adds up.

aklim

Chalk it to rust. All my smog stuff rusted and fell off I was so sad

aklim

You can imagine 10hp but I doubt you will be so sensitive that you can distinguish between 240 and 250hp.

The mods allow the other mods to function as a system. World's best heads and crappy intake doesn't help. I'd find a tuner and discuss it with him first but I'd do intake and headers and cam then tune. If I skip anything in that group it would be the cam

ctmccloskey

Hello again, SB66
I apologize as the headers that I have are for the Big Block Corvettes. I have a 427 in my 1968 C3 and it uses the #68096 long tube headers by Hedman. They do make long tube headers for the C4's and I trust their quality. Call them if you have any questions, they have been very helpful to me in the past.
Good Luck with your Corvette!

Mike Holmen

The old stock (GM) computer crappy and out of date, difficult to tune. Yes is can be done, but why bother.

The newer GM computer (anybodies aftermarket fuel injection systems) you can do anything you want or will dream about down the road. There are a bunch systems out there you can do tune it in your own garage. Yes lots guys hate self tuning systems, but what ever.

aklim

In 85 it is rather lacking in the amenities so rewire jobs may be OK for self tuning

Mike Holmen

Well said buddy. Must be one of the best things about an LS swap for me, now I can do run ever parts combo/engine I want now. Been even thinking about rewiring the entire car with a modern wiring harness, just fix a bunch of those old GM wiring harness gremlins.

My guess those long tube gains would be felt above 4500 rpm's, my car lives under 3000 rpm 95% of the time. If its a track car, probably a decent mod, why bother for a daily driver probably over kill.

aklim

I have always wanted to see a shootout between self tuning vs dyno tuning.

I felt like there was a difference before 4500 in the F-body but I also had a super ram intake so hard to say

tdereggi

You got to really think about what your goals are, Three of the first mods I did on my 85 were 2.5" CAT back, Replaced CAT with a pipe, added TPIS headers. Although I am happy with my mods for my road map long term goals, Im not sure Id do it again the same for a stock 85. The stock exaust diameter is already adequate for a stock engine. Larger diameter front pipes aren't always better,and can actually reduce performance, if its more than the engine needs for flow. (reduces velocity and suction). My vette sounded just fine stock. And with Borla, no cat, and headers, I could barely carry a conversation on in the cockpit. And having a high fidelity radio became pointless. Very soon after I put my CAT on again, to make the noise level tolerable. The CAT significantly reduces exaust volume and evens out the sounds from the headers a bit. Note that larger pipes will lower the exaust tone/note. The exaust mods made very little noticeable difference in performance at stock engine, but what it did do is drastically change the sound. Everybody hears you coming, and they know its you. The Borla really does sound bad ***. Just under stand that you are accomplishing bad *** sound. The muffler tips and headers also looked bad ***. But Increasing Car performance is achieved by upgrading multiple components as a matched set. When you start increasing size of intake manifolds., heads and cams, the upgraded exaust will complement that. So an upgraded exaust is something you can do in advance of other mods, if you only have cash to do one at a time. But the performance is noticed after more of the mods are also completed. Sure you might see 15 HP increase on a dyno when you upgrade the exaust by itself, Im not saying it doesn't add performance. Im just saying, is it felt and noticeable as much as the sound change? If you put the $2000 it would have cost for headers and a cat back system towards a better cam or downpayment for a supercharger, you would achieve much better performance gains. And then after, you'd have a good reason to want to save up to add headers to compliment the more powerful engine system. regarding the actually dual muffler link you asked about specifically.... its only 2-1/4" each, but that is all you need for a stock L98. The goal of that dual exaust would be to remove flow restrictions in the pipes where they transition to one pipe into the CAT and back to 2 pipes out of the CAT. If youre on a limited budget, That would be a very affordable and clean improvement over stock, if you don't need to stay emmissions legal, and your existing stock mufflers are in good shape. . But using a CAT back with larger rear pipes instead has additional advantages. I cost justified the higher price because I had mufflers that were rusting out also needing replaced. The idea is to create a lower pressure area in the rear, so the gases will move faster out from higher pressure front pipes out the exaust. Sorta creates a little pull. The other advantage of the CAT back system is you don't throw away the investment when you decide its time for headers. and if you want to toy with removing the CAT, using a cat delete pipe in place of cat, allows you to swap back and forth quickly when you need to go through emmissions testing.

sb66

money aside for a moment - how difficult is a project like that - because it sounds intimidating

Mike Holmen

Not bad at all, its just four-five wires to connect, one to 12v power, one to ground chassis, one to engine ground, one to a switched on power (key), one to the fuel pump, tach hook-up.
Of course depends on what you exact kit you buy, but its pretty straight forward. I'm not even a chevy guy and never done an LS swap before. The LS engine will drop in where ever the SBC was.

Benefits, you get in-cab adjustable cooling fans (two), of course more wires. coil packs (in-cab adjustable timing), in-cab adjustable fuel curves. Adjustable idle (in-cab). Live in-cab data display and even data recording. Modern knock sensors that actually work. I re-used my digi dash, but have a oil pressure and coolant temp on autometer gauges on my pillar.

and I hate wiring...I wouldn't go back. I have a 24X crank sensor, rear cam sensor (LS1), 2005 vette coil packs, 2012 LS3 injectors. These old cars the worst thing to re-wiring the car is getting everything out of the car. My interior needs a re-fresh anyways. I want to modernize my interior with heated/cooled/powered seat out a C6 or C7 vette, so everything has to come out.

sb66

thanks - this just applies to the ls engine?

sb66

thanks

yes I believe the outlay of cash will only allow for one thing at a time -
originally that is what I was trying to get at - I have to put new intake gaskets on to fix a leak - so I am obligated to that and any other mild changes regarding the immediate area. I came across the exhaust and thought that might be a step one -
but I am learning quite a bit from this thread and some of my original ideas that would have helped down the road may or may not be worth it in the end. I had noticed the exhaust getting a little louder and I do not know how old it is - It is some kind of aftermarket, mufflers/tips all in one.
I wondered if a more open cat with a more open after cat exhaust would free anything up? then when/if I add headers, I can still use cat back - does that make any sense?

I know the more sensible way may be to go headers and all - at the moment I am not as sure as I once was. In the end this is a street car that I would like to see have a little more pep in its step - but I realize it is also a 30+ year old roadster.

aklim

So figure out what intake you want based on the recommendations of the tuner who will tune it after you get to say the intake and headers
That or bring them a pile of parts and have them try to make it work

wardie

My firiend bought window supports they went bad in two months and Corvette Mods not only won't honor any warranty then won't respond in an email. Just sayin'