My '86 with a 700R4 has 45K miles and runs great, but I'd like a few more ponies under the hood. I installed a K&N air filter, Hypertech chip, Borla exhaust, and the throttle body air foil. The car is peppy but I'd like more street muscle, along with a husky exhaust rumble that speaks Bad Boy. The Borla's merely produce an irritating drone, and the idle is sissy.

My car is registered in Texas as an antique and therefore does not have to pass emission tests. This car is not a daily driver. In fact it has never been driven in the rain. I use it for show and go.

My questions:

1. What would be the effect of removing the catalytic converter? More hp, better rumble, error codes, etc?

2. My '60 270 hp 4-speed Vette with the Duntov cam had a nice rumble and idled a bit rough, the way I like it. Therefore, I'm thinking a performance cam might be an option provided it doesn't kill my budget by requiring a slew of other needed go parts - runners, headers, ported heads, etc. What cam/options do you guys recommend that would yield ~ 50 hp increase, along with that husky exhaust note that we all love.

3. Am I getting in over my head?

Jack

 

Taking the cats of my 87 soon, the biggest thing is the smell really, I don't think you'll notice a HP gain, but I got long tube headers so... believe me they're leaving. Get headers they will make the biggest difference on the l98, but the extra surface area creates extra heat, so be mindful. I'm removing the cats bc it's a performance weekend ride and i live in "lawless" Michigan!

 

Well, the Hyperjunk sticker is worth 20HP as is the K&N sticker and the airfoil sticker so there is 60HP right there which beats whatever your gain from the K&N and the exhaust and the Hyperjunk chip by 59-60HP. If you really want something, you should have installed headers and gotten a dyno tune at the very least. As to the idle, not much you can do about it since it is set from the factory at whatever it is unless you change your cam and have it reprogrammed for the ricer effect.

1. Nothing will happen other than more noise. BTDT and replaced the hollowed out cat with a real cat.

2. Intake and cam and dyno tune. Probably have to go through the valvetrain to make sure your springs are capable of supporting the higher lift cam. An easy $3K if you do the work yourself and get it dyno tuned.

3. Depends. How much work can you do and how much do you want to spend? Whatever it is you plan, double it. That will probably take care of the "while I am here" items.

 

Why do you say that? I don't know about you but in WI, the exhaust is behind me and I drive in the opposite direction of the exhaust pulse.

My TPIS headers and the extra heat that my 383 doesn't really fry stuff that isn't in direct contact so I have doubts that his setup will generate that much heat that it becomes a concern unless he is idling it all day long with the hood down and in really high temperatures.

 

OK, so I know everybody has an opinion but I did this procedure 5 years ago and documented the results specifically to debunk these myths. I posted my results here: https://www.corvetteforum.com/forums...h-numbers.html

And yes my catalytic was fine and passed an IM240 smog test before removing so it was not plugged or any of the other horse-puckey people like to tell you. These old style ceramic brick catalytics were restrictive - period. Not as bad as the 1970's era ones but still not like a high flow catalytic of today's standards. I had even larger improvements with my '87 GTA back in the day (20+ years ago) when I did it on there. At any rate there is significant HP to be had by doing this.

I also eventually replaced the front y-pipe with a catless y-pipe which also netted some gain. I then went all out and went to Super Comp Headers with 3 inch dual exhaust into an x-pipe and then out to the 2.5" Magnaflow mufflers. Don't do this unless your car is not a daily driver. With the Borla mufflers it might be OK but with the Magnaflows it is bad enough I wear ear plugs when driving to the different road course tracks around Colorado, but it does sound mean.

BTW, I still have the catless y-pipe and bypass pipe laying around the shed if you are interested as I have no more use for them.

Going the next step, the mini-ram plus LT4 hotcam combined with a decent exhaust completely changes the car and puts it more on par with early 90 ZR-1 standards, maybe a tick slower, but not by much. However, this requires new computer tuning and injectors. In my case I went the next step with AFR heads and the Holley HP controller, which I highly recommend as a kick-butt controller. The AFR heads are good as well, but I really need to up my cam size to take advantage of them.

--Calvin

 

Interesting read. I did a few back to back runs with and without the cat in the F-body that many swore gave gains. Absolutely nothing. I disconnect them at the point before it joins together

 

Your existing mods did probably just nothing for you in terms of speed.

Port your plenum,take screens out of the MAF and also remove the stock rings in your runners. Vids on Youtube to show you how


Get a 2 1/2 inch front y pipe and run a straight pipe replacing the car for now. get an AFPR and wake fuel pressure up by 5 pounds as your next wallet mod.

How fast do you want the car to go and how much do you want to spend?

 

Lightening the wallet was what they do.

Not sure I would want to remove the screen. It's not like the MAF is restrictive at that level. IF I were to remove the screen, it could change the characteristics so I'd wait for a tune before I do that. Not sure about the AFPR either. ECM will probably reduce the injector pulse width to compensate once it finds out.

 

Remove the air foil, junk.
Hypercrap is also junk, but if you already have it, might as well leave it.
Borla and K&N is fine.

Removal of the main cat will give around 10-15hp on an L98 engine. Removing it will not generate a SES light. Removing the EGR will and has to be either wired up to spoof it (search the EGR Diode trick) or with a custom chip.

86E has weak '624 iron heads, they won't let you do much. 86L '128 aluminum heads are a bit better. Determine which you have. If you want 50 hp you will have to make a change here.

You will also have to port out the intake to flow the air, or buy a new larger base/runners.

A reasonable cam in the range of 210/210@050" would give you smiles. I would not bother with anything smaller, and anything bigger requires more thought. Then you would have to have a custom chip done, replacing the hypercrap.

So its not as easy as swapping out the camshaft and being done.

 

Seriously? That is a lot. Never tried on mine but the F-body didn't run any faster with that which is what I find amazing. Unless the cat is clogged, that is. : I know hollowed out cat vs Random Tech cat didn't seem to yield much when my buddy tried it on his car. We took out my hollowed out one and he installed it and later the RT cat on the strip. Automatic so that takes out the driver error some.

 

Hi Calvin,
I'm interested in the Y-pipe and bypass pipe. Let me know more.

Jack_Hutchison@comcast.net

 

Thanks for the reply.

I'm leaning toward the Hooker 2149HKR headers. I have the aluminum heads on my '86L ride with auto tranny. Do you know if they'll fit properly without modifications?

I'm considering a 226/226 @ 0.5" life Crane 100082 flat tappet cam with lifters designed to fit auto tranny with 3000+ converter. This cam requires valve spring replacement. What do you recommend for springs?

I want an idle that is a little rough, a great sound with the headers, and a few more ponys. Will this cam be acceptable? Anything better?

Jack

 

It probably would fit but if it were me, I'd like to ceramic coat them for corrosion resistance. Not sure how good their material is but it's probably cheap. Put a set on another car and plug access was a nightmare.

Pretty high stall. Is that what the cam suggestions is?

I would suspect that you might have to get it dyno-tuned to run properly and to give you the rice effects you want. Check out who can do it before you start your project

 

2149s come ceramic coated already, they will fit and are what many here use.

226/226 is too big for a TPI 350 engine, it is a midrange cam, your intake cannot feed that camshaft. This would be a mismatched combination. Also, the heads are probably not going to flow enough to get power with it, '128s are nicer than 624s but they need portwork to flow.

I would go smaller and tighten up the LSA if you want to have it choppy at idle. Bear in mind that you will still require intake modifications.

I would not recommend ever going to 3000rpm TC on an L98, your stock transmission is 2000rpm in 86, leave it alone. You need to open the powerband to higher RPM before going that route. As long as you keep a TPI-style intake on it, you do not need 3000rpm TCs.

You will not be happy with the combination you have here, its not set up correctly.

 

I thought that it has fitment issues with the plugs and engine mounts? Or am I reading something wrong? How is the changing of the plugs?

 

I would say one of the best mods I have done was a good set of Long Tube Headers. I removed the cats and made it true dual. The mufflers are your choice in sound. You will notice a difference with just doing the headers. If want more...cam, heads, intake, tune, etc.

 

Dump that factory cam and get a tune. Your exhaust note will be bold.
And dumping the cat (unless its plugged) will change nothing.

 

Once you do headers, intake and cam, you have to do a tune. I had an L98 F-body that was noticeably better than stock but until we had Lingenfelter do a tune, it didn't run right.

 

Thanks for the response, but you lost me on the 128s/624s and LSA. Can you explain this in layman's terms?

What Crane or other cam would you advise for a little choppy idle, and what intake mods would be required, if any?

Jack

 

A couple people have used Accel shorty plugs with one or two plugs causing the issue, and the only other consistent issue I've heard is that the Y pipe does not always want to fit.

I see no reason to discourage him from using them.