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I Need some more Umph

quickjagg

Well-known member
Joined
Feb 10, 2002
Messages
149
Location
Maine
Corvette
White 1981
I'm starting to get tierd at people laughing in my face when I tell them the stock hp rating for an 81, and was wondering what I could add for go faster parts. I'm plannning on buying a true dual exhaust, and headers, how much extra hp will this give me? (aprox.)

I was also wondering that since I don't have the stock carb, I have a 600cfm holly, would my hp still be 190? if not how much do you think I have? There isn't a dyno anywhere close by, so I can't check this stuff out =(.

One last thing, those chips for the ecm that give you hp, would I get the full 20 from one if my carb isn't hooked up to the ecm?

Thanks for the help! Sorry if questions like this have been asked before, but I'm feeling really lazy today =).

-Chris
 
Well, I can't offer you much help, as I sold my '81 before I was able to add more gopower. I asked, and did some searching for chips, and I found that they really didn't make that much difference.

There's a black '81 in my home town and he went with true dual exhaust, no cats, dual electric fan, aluminum radiator with better flow, and I think intake and carb and headers. He's not sure how much hp he gained, but he said it made quite a difference. He thinks he's now running 220-250 instead of the stock 190.

When you feel like it, run a search for engine topics ;) there's quite a few going right now I think.

hth.

-T Jay
 
just go with cam and heads. 1K will get you going pretty fast


Frank
 
IMHO, true duals with no cats would show a nice increase & might be the cheapest VS effective mod you could make... headers might only add a few more since your current engine is not producing many ponies anyway. I'd check your State laws and with other local rodders about modifying exhaust ... dunno what your state requires ... check before you go changing stuff/spending$ (exhaust or carb or distributor or 'puter).

Dunno if your distributor has a vacuum advance or not (I think original dist connected to 'puter that controlled timing. Maybe your dist could be recurved, but lotta guys go to the earlier vHEI w/ vac advance ... permits a range of timing mods/tuning which would help yours. Nice rebuilt vacuum advance HEI dist can be had for under a hundred. Understand original Qjet carb replaced by Holley ... and probably not affected by 'puter now.

With dual ex, another cam would help a great deal ... the stock one is no where near enough. A new mild cam with new lifters can be had for under a hundred.
JACK:gap
 
Chris,

I'm with Frank on this one. Your just spending money for almost imperceptible increases until you get a cam and heads. The cam being the most important part of making HP in an otherwise stock engine. If you do the cam, you'll have to do the chip to match it. The exhaust mods will help out a lot more with the cam.

To answer your original questions, Headers and exhuast, 20 to 30 Hp. The chip should work fine with your non-stock carb. The programing of the chip will change your ignition timing and would change the carb mixture a little if you had the stock one.

Steve
 
Chris,

You asked a question and you'd better get your brain ready for an overload of Corvette tuning knowledge.

These guys here in the forum really know their stuff!

I do believe that in one of the C3 threads, someone did mention that true dual exhaust was not street legal. And looking through the Eckler's catalog, they said that true dual was meant for off-road use only.

Someone please correct me if I'm wrong on that.
 
Yeah true duals on my 81 is for offroad only, but my uncle has a respect for older cars, and inspects them too =) since the nearest emmisons test is a long way away I don't need to get an emmisons sticker. I just have to make sure that it isn't too loud otherwise people may complain. However there are lots of people driving around with no cats, and no mufflers and havn't got into trouble for it yet. Thanks for the help guys! Any cam recomendations? And do I need to remove my motor to install one? How much do heads cost? I was hoping to not spend a whole lot, mb 1k tops.

Thanks again for the help!
 
The cam can be changed in the car, but it's easier if you pull the motor. If you don't want to spend the money on an engine lift ($200), then you can just forgo that expenditure. What numerical ratio of rear gear is in the differential? That makes a big difference as well, when it comes to launching from a standstill. Going too big though, will negatively affect your fuel consumption. Cost would depend on whether you do the work or not, but a guy around here does rear gear swaps for $400 or so.

I would also look to an already proven package. Chris McDonald has stretched the importance of this when trying to get the most bang-for-the-buck. Edelbrock has some good packages, as well as Holley and other retailers. I think with the budget you have, you can still make some effective changes that will improve the performance of your Vette quite nicely. :D

--Bullitt
 
here what I went with, Im guessing Im around 350-400 hp and a big diffrence in performance

Heads Edelbrock Perfomer RPM 60899

Cam Comp Cams Extreme Enegry CL12-242-2

Timing Chain Cloyes ‘True’ Double Roller 220-9-3100

Water Pump Edelbrock Victor 8812

Carborator Edelbrock Performer 750 CFM 350-1411

Intake Manofold Edlebrock Performer 350-2101

Header’s Headman 68300

Rocker Arms Comp CamsMagnum 249-1412-16

Lifters Comp Cams High Energy 249-812-16

Pushrods Comp Cams Magnum 1010 Chrome Moly 249-7693-16

Ignition MSD Ignition 6A 6200

Head Gasket FEL-PRO Pre-Flattened Steel 1003

Exhaust Gasket FEL-PRO Pre-Flattened Steel 1405

Intake Gasket FEL-PRO Pre-Flattened Steel 1205

Mufflers Mil-City Twin Tip Performer Series 603922
 
I'd put your money in 9.5:1 pistons, 2:02 valves installed in your existing heads, carb calibration and recurve the distributor. Complete job with cam, lifters, heavy duty valve springs, rocker studs and balancing should be under 2500 if you do the assembly and calibrations yourself. Curve kit is less than 10 bucks at Summit. A Rochester calibration kit is about 100. The Holley is OK, but kiss the power valve goodbye the first time it backfires through the carb. I wouldn't bother with headers unless you are going over 375 horse, they are a pain because they leak or burn out rather quickly, and really won't do much for horsepower. Side pipes would be nice if you have the money! In Illinois we can get "collector" plates to avoid emission testing, but we are supposed to be using the car only for show or club events. Most cops won't bust you on this one, but could. Rear axle ratio has a lot to do with performance as well. Consider a 3:56 or 3:73. A 4:11 is good if you spend all your time on the drag strip. The 3:56 is a good all around gear. :)
 
BigFish,

How old does a car have to be to get those "collector plates"?

Are you talking about the tan colored plates with the little "AV"?
 
I believe the car must be at least 25 years old. The people at any testing station have the paperwork to register for those. :)
 
Ok Chris

You can change the cam with the block still in the car, but you have to gut pretty much gut the whole front end (radiator etc).

I have done some research on some packages. Holley has their systemax packages. The cost about, maybe a bit more, $1300 but give you everything you need for the top end (heads (aluminum), cam, lifters, timing chain,pushrods, intake etc.) Edelbrock has packages also but you have to make sure that your hood can clear the setup, as the performer rpm manifold WILL not clear. It probably runs about the same price. They both claim over 400hp/400ftlbs.

Can you do it yourself? That will save you some big bucks.

I asked about cams and heads on an earlier post, just look for it you will get some info. I am planning on going with a dual energy cam from comp cams and sportsman II heads. That cam provides good low end torque, "torque is king in the streets". I am shooting for over 400ftlbs of torque. The heads already have the 3 angle back cut, can hack .55" of lift have 2.02/1.6" valves. All you need to do is just port them. It will probably be cheaper to go with the systems holley and edelbrock have but I have future plans and this package is going to work for me. You need to set a goal and work towards it and figure out whats going to work for you.

DON'T use the stock heads. There is no point in putting any work into them. For the money you are going to spend its just better if you buy new heads. This is from experience! What I am refering to is new springs to handle the lift etc and any other machine work that is going to be involved. The sportsman II are bolt on heads, you might want to check out world products torqure heads, a bit cheaper.

If you do go through with it, after you remove the heads measure the distance from the top of the block while the piston is in the TDC position. Calculate the volumes, use this info to calculate the compression ratio. You also need the volume of the heads. This will also let you know what thickness of gasket you need to use for your desired compression ratio and quench area. 9.5 should be good enough, you could even go 10 with iron heads & 10.5 with aluminum.

There is a little more to it, pay attention to the details!! Do a lot of research and reading. Be patient, I am learning this lesson right now!!:eyerole

I am sure there is a lot more info other people will post that might help you out. I am in the same position, this is what I have found.

Hope this helps.


Frank
 
If you want to stay under $1k, I would suggest looking into a set of Vortec heads. They are extremely cheap (a little over $400 for the pair) but their performance potential is very impressive. While you're at it, you could add a new intake (you'll need a new Vortec-style one for the heads anyway) and a cam, and still have about $200 left out of your $1k budget to handle any chip-burning costs and perhaps some sort of exhaust modification.

Good luck.
 
There are hidden costs with those Vortech heads.

1. For starters you have to get center bolt covers.
2. Dont have to but, need to get the heads machined for screw in studs not pressed. Especially it you are running a high lift.
3.You are going to need to get new rockers for them of you change the studs. Something about those self aligning rockers (please help on this one)
4. Very limited on how much power you can get out of them
5. I think, I could be wrong, cannot improve on flow. At least very little


in the end you are going to pay the same for a set of high performance heads.

please if anybody sees or knows otherwise please post.

Frank
 
i just posted this post about people that are looking for more HP by doing either or all of, cam, header, intake, and throttle body, (basic upper end) Click Here

You have to be carefull like sscam69 touched on. Mostly when you see a cheap hi hp set of heads in a magazine or something they are BARE meaning no valve train and it would negate the heads by putting your stock stuff in ( if the valves fit ) Most full assembled heads cost around 800-1500 depending on aluminum or not....these cost can get way higher when you talk about porting and polishing basic race prep heads. but for stock heads i would suggest porting polishing and like i said in the other post punch out your lil intake valve to a 2.02 and a exhaust to a 1.60 a good machine/speed shop can do this reletivily cheap (under a grand give or take a bill) while your at it get your inake and exhaust atleast ported and you can polish yourself on those with a drummel polishing wheel if you know what your doing (pretty easy) but leave the heads for the big boys :D

Good Luck!

Gawd i need to save some loot i want 1600 bucks or so to spend in upgrades :) then the mini ram.....hehe i'd be happy :D
 
IMHO, off-the-shelf chips produce limited and, at best, minimal results. And a custom-burned chip is just that ... made just for an engine's specific mods/configuration ... likely you'd need to have another chip burned each & every time you might make a major mod change. IF, repeat IF your smog laws/inspection/UNCLE/testing situation will permit, I'd suggest dumping your computer and your computer-controlled distributor. For about what an off-the-shelf chip sells for new (maybe even less), you can buy a very nice rebuilt vac-advance HEI distributor (i.e. Accel pn 59107 or pn 9107) that already has a nice performance curve (Accels & SOME others include an array of springs, weights, and adjustable vac can) that can be readily tuned for virtually any future mod. Such a performance HEI dist will permit you to set ignition timing curve virtually any way you want ... regardless of virtually any possible mods ... you can make appropriate timing changes to essentially stock motor (that'll really help) ... and as you add mods/change octane ... all this without need of chip/additional chip(s). You may be pleasantly surprised how a performance ignition curve will wake up an otherwise stock motor ... especially carbed motors produced after about 1970. If under 11:1 cr on pump gas you will not NEED any hot coil, hot module, MSD box etc ... stock coil & module with fresh, quality wires & plugs'll be plenty.

You've already got the Holley carb ... add a "power valve protector" kit (about $10) and freshen & tune it to suit.

After you've addressed the ignition & fuel ... go ahead & add duals, cam, gears, heads, pistons, stroker etc ... even a big block ... then you can tune for each mod or combo thereof with a fully-adjustable vac-advance HEI dist and freshened, tuneable Holley ... without any chips. BTW, if a blower's in the cards, a vac-can HEI probably won't fit. Just my .02.
JACK:gap
 
The first mode of an older style HEI is a good one and there must be loads in the junkyard, it will give you a reasonable improvement when matched up even just with a fairly mild cam and a good exhaust. Changing the cam in the car is not a problem I have done it twice. The main problem with the original 81 motor is its low compression and good heads can go some way towards helping this without going to the expence of pistons. I have and Airgap intake and it did fit under the hood albeit with a very thin filter element and a drop base. I changed to the scoop to get some nice cool fresh air into the engine.

The sky is the limit if you have the money and I would also recommend going with a "kit" of matched componants although the Edelbrock RPM set up is just a bit to much for a daily driver.

Here`s an interesting article on setting up the older HEI ignitions and you`ll be surprised at the improvement over the original set-up.

HEI SETUP FOR PERFORMANCE
written by Damon Nickles

--------------------------------------------------------------------------------
This article deals primarily with older-style non-computer controlled HEI distributors. This is becuase there is so much performance left in them vs. stock AND since many people have ditched the computer in their 3rd gen cars and gone with a totally non-computer controlled engine. Please note: All carbureted V8 Fbodies since 1981 came from the factory stock with a computer controlled, internal coil HEI distributor. Most Fuel Injected 3rd gen V8s use a modified version of the HEI known as a “divorced coil HEI” (not dealt with here).
A word first about those internal coil computer controlled HEI distributors: Computer controlled versions work basically the same as the old non-computer versions except that they don't have any mechanical advance mechanisms inside them- the ECM determines the advance curve electronically. There is NO WAY to change the advance curve of a computer-controlled HEI distributor- timing is controlled ENTIRELY by the ECM’s programming! The only change you can make in the advance curve, other than buying an aftermarket performance chip for the ECM, is to manually advance the base timing (usually worth a little HP by itself). Check your GM service manual for the correct way to set the base timing for your particular engine/year. If you have a computer controlled distributor in your car right now you can’t do much to increase performance other than to make sure it is correctly communicating with your car’s ECM and upgrade the coil to a better unit. This is not a bad thing- it leaves funds available for parts that WILL make the car faster!

DON’T USE A COMPUTER CONTROLLED DISTRIBUTOR IF YOU HAVE DITCHED THE ECM OR ARE RUNNING WITHOUT ONE!!!! You will get NO ignition timing advance AT ALL from the computer-controlled distributor plus lousy performance and lousy mileage. If you have disconnected the 4-wire ECM connector going in the side of the distributor or the wiring between the ECM and the distributor is damaged you will, again, get no advance (and a check engine light) Yes, you can remove a non-computer controlled HEI and drop an old-style mechanical advance distributor in its place- it will physically bolt right in. But it will cause the ECM to throw a code because the ECM looks to make sure the computer-controlled portion of the distributor is out there every time you start the engine. Once you begin to take things out of the ECM’s control you pretty much have to go all the way with it- replace both the computer-controlled distributor, the computer controlled carb (Qjet) and deactivate the check engine light.

That being said, the NON-computer controlled HEI can be made into a great distributor for a street or street/strip car. Its simple, easy to tune, and plenty powerful to light off any naturally aspirated engine up to 7000 RPMs if properly equipped.

Let's start with the coil. Its located on top of the distributor between the plug wire towers under a plastic cover. It's the "engine" that makes the sparks. Stock its capable of about 35,000 volts and so-so total spark energy. Its fine for a naturally aspirated street motor that rarely sees the high side of 5000 RPMs. It will provide the energy to jump a plug gap of .040-.045 with no problem in these applications.

You can upgrade the coil with an Accell or MSD replacement coil that will jump the voltage up to about 42,000 volts and total spark energy will also jump about 10-15%. There are even hotter coils than this from Accell, MSD and others that will give you the same 42,000 volts but a LOT more total spark energy (like 50% more). Either one of these “super high output” coils is a worthwhile upgrade for a hot street motor- you'll get better response and HP especially at higher RPMs where the stock one hits a kind of "wall". A new coil is also a lot cheaper than a complete MSD ignition amplifier setup and at least 95% as effective at making HP in most naturally aspirated applications (the MSD will still give you slightly better mileage & emissions due to it’s multi-strike spark capability below 3000 RPMs). With either hotter coil you can open the gap up to .045-.050 for just a smidge more HP. There are 2 different versions of the HEI coil and you need to make sure you get the right one. The only external difference is that one has red and white power leads, the other has red and yellow power leads. You will need to know which one of these you have stock to order up the appropriate aftermarket upgraded coil.

For blown or nitroused applications I always recommend an MSD (or equivalent) ignition amplifier box setup. You can do it with a stock HEI + hi-po coil but you'll likely have to close the gap way down (.030-.035) to make it work well.

THE ADVANCE SETUP: Centrifugal and vacuum advance (non-computer controlled distributors ONLY!):

Centrifugal advance assy. on the HEI is pretty darned good. The stock weights and advance plate are perfectly acceptable for all but the highest HP/RPM engines. Centrifugal advance is used to advance engine ignition timing relative to an engine’s RPM. With more RPMs, more advance is needed- UP TO A POINT (more on that later). ALL stock HEIs that were installed in V8s are designed to have a total centrifugal advance of 20 degrees, +-1 degree due to production line tolerances. This is as measured at the crankshaft (10 at the cam).

The HEI’s centrifugal advance is susceptible to old age, though. Typically the centrifugal advance weights wear their pivot holes into an "oval" or eat a trench into their pivot pins OR BOTH. This is bad and no attempt to change the advance curve should be made on a distributor that suffers from these problems- fix it first or get another HEI to start improvements on (I can buy them for $20 a piece in decent shape at local junkyards- just make sure you are getting the right one for your engine- they were used on ALL makes of GM V8s and all look very similar). Also, the centrifugal advance plate (that pivots around the main distributor shaft as the centrifual advance moves it), near the top of the distributor shaft sometimes gets gummed up and sorta "sticky," slowing the advance curve and generally preventing the centrifugal advance assembly from working correctly. If your centrifugal advance doesn't "snap" back when you twist the rotor with your hand and let it go then you have this problem. You need to pull the distributor shaft apart and clean everything out, especially up top, before you proceed with upgrades.

The stock HEI also uses a vacuum advance canister to further advance engine timing. Vacuum advance’s purpose is to compensate for and engine’s LOAD. Manifold vacuum is an excellent indicator of an engine’s load. A lightly loaded engine can tolerate more spark advance than a heavily loaded one for better fuel economy, emissions, and to keep the tip of the plug hot enough to keep it from fouling with combustion contaminants. The centrifugal and vacuum advance work together, but independent of each other, each adding its appropriate amount of timing advance, to supply the correct TOTAL spark advance to the engine under all RPM/engine load conditions.

Tuning for performance (changing the advance curve):

1. Centrifugal: Stock the advance mechanism is pretty good but the stock springs are usually way too strong, causing the advance curve to come in too slowly, if it ever gets fully advanced at all. All you need are the right springs and the right initial advance setting. Most Small Block Chevys like about 32-38 degrees total advance at WOT. Since we know already that the HEI has 20 built into the stock mechanism the first thing we need to do is set the initial advance correctly- that means you need an intial advance between 12 and 18 degrees (you might want to retard it 2-4 degrees for daily street use just to build in a little safety margin).

Now all we need to do is make sure the centrifugal advance comes in at the right RATE- relative to engine RPM. You want it "all in" by about 2800-3200 RPMs for a typical street performance motor. (Additional advance above this RPM point is neither needed or wanted- increased turbulence in the combustion chamber offsets the need for further ignition advance beyond this RPM level) You do this by changing the centrifugal advance springs to lighter ones. IF you use the Crane advance kit like I do you are looking to install one Blue (heavy) spring and one Silver one (medium). These springs are located directly under the rotor and are easy to remove/replace by hand or with needle-nose pliers. These springs will give you an advance curve that starts at about 800 RPM and ends at 2800. If you don't have the Crane kit then install whatever springs you have and check the advance curve with a dial-back timing light (or use a “timing tape” wrapped around your harmonic balancer) and a tachometer, swapping springs until you get it close to these specs. It doesn't matter if the springs are not "matched" side to side- you can install one heavy one and one light one and it will work fine. Please note that getting the advance in sooner does NOT build peak HP, but it does build quite a bit of bottom end torque. This mod will have you grinning ear-to-ear with the nice seat-of-your-pants improvement!

2. Vacuum advance: Stock cans typically provide 22-24 degrees of advance. This is WAY WAY WAY too much if you have recurved the centrifugal and initial advance as described above. You will get "3 rocks in a coffee can" kinda detonation.

Can you just leave it unplugged? Yes. Your highway mileage will be off by about 5MPG and your plugs will load up with crud within just a few thousand miles. For a race car or a weekend street/strip can this is probably no big deal. For a daily-driver street car, forget it.

Vacuum advance for the street: You want about 12 (crankshaft) degrees total vacuum advance if you run WITHOUT a functional EGR system, 16 degrees if you run WITH a functional EGR system. Regardless, you want it to come in between about 5 and 15 inches of manifold vacuum. I have found the most expedient solution to be the Crane advance kit once more. Install their can with about 9 turns (tighter than the loosest setting) on the adjustable advance can spring. IMPORTANT!- Also, use the little "lockout" cam that comes with the Crane vacuum advance to lock out AS MUCH ADVANCE AS POSSIBLE. This will still leave you with about 12 degrees of available vacuum advance. If you set it with 2 notches LESS lockout than the maximum you will end up with about 16 degrees available vacuum advance- perfect for those of you running a functional EGR system valve.

So your “typical” advance curve will look something like this:

14 degrees initial advance + 20 degrees centrifugal + 16 degrees vacuum adv. = 50 degrees total

If you are in the 45-55 degrees range for total advance you’re in the ballpark. Each engine is a little different and what works for your engine might be a little different than what works for someone else’s.

That's about it for distributor setup. You're ready to rock and roll. Now all you have to do is install it correctly and plug everything in correctly. Here's a few tips:

Number 1 plug wire should be at the front of the distributor just to the driver’s side of centerline. The vacuum advance can should be pointing roughly at the passenger side front tire. If that's not your #1 plug wire, or your vacuum can is pointed in a weird direction then you have the distributor installed off by a few teeth. It won't hurt performance if timing is still set correctly but plug wire routing gets a bit messy.

The vacuum advance can should be plugged into a "ported" vacuum source on the carb. This is a vacuum port on the carb that provides NO vacuum at curb idle. When the throttle is opened past idle the vacuum kicks in and starts your advance curve for cruising/part throttle.

WATCH YOUR IDLE RPMS WHILE YOU SET INITIAL ADVANCE TIMING!!! You note that the centrifugal advance curve that I recommended above starts at about 800 RPMs. If you try to set your initial timing with the engine idling ABOVE this RPM point you will NEVER get a true initial advance reading since the centrifugal with be partially advanced at that point! Set it with the idle temporarily slowed WAY down if you have to but DO IT RIGHT!

A final word about that HEI "module:" Lotsa mystery around this little "thingamajig." This is just the little electronic brain located on the floor of the distributor housing with 4 wires going into it (2 per side). All it does is read the magnetic pickup signal from the magnetic pickup assy. around the distributor shaft and then using this reference signal, tell the coil when to fire and with how much "dwell". I always recommend a good stock GM module, not a parts-store cheapie. No reason to go crazy and get one of those $70 “super-high output modules here”- I have tried them and they do nothing for performance. But get a genuine GM one. Stock GM modules incorporate what they call a "variable dwell" circuit that reduces dwell at lower RPMs to keep the coil from over-saturating. This is good for sharp performance and long coil life. Some parts-store modules don't have this circuitry in them.
 
Thanks John

/ JOHN (JHL) ... HEI SETUP FOR PERFORMANCE written by Damon Nickles

John:
GREAT ARTICLE:BOW! Goes straight to the heart of what I'm trying to convey to Chris. Do you have a link to where Mr. Nickles might post such articles/tips? BTW, how's that q'master clutch working out for you? Thanks!
JACK:gap
 
Stick a new motor in it.
There's a lot of cheap engines for sale that were removed from junks. (eg. LS1's, LT1's, L98...)
Something like that will get you going for a long time and with moderate performance, and good mpg
Paul
 

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