79 minor repairs..need advice

Page 1 of 2  
Its getting to be that time of year when I start thinking of the things I wanna do to my 79 , take care of the items that need to be replaced/repaired..then theres the things I wanna do.
1) need to replace the window rubbers, and the t-top rubbers as they are either rotting or leaking. 2) stop them damn windows from rattling!!! anyone know how to put anti-vibration dampners in? Thats all I NEED to do..mechanicaly and body wise its awsome( cept fro the small rear tires which gets done regardless) I wanna get a little more power outta the l48 350..it has a mild cam , and aluminum intake, i wanna replace that weber carb with a holly 600( easier to adjust for sure) what else can be done without tearin the motor down?? It runs awsome now and dont leak/burn oil a bit so I dont wanna monkey it up but damn I wanna spin the tires in all 4 gears..lol Any advice from the pros would be appreciated:) TIA Larry in Va Beach
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

to
Vortec heads, headers, free-flow exhaust system with larger pipes, transmission kit? (Larger wheels? Just kidding.)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Larry & Michele wrote:

A 600 is a bit small for a 350, especially if it has any additional cam in it. You may want to look at a 750cfm with vacuum secondaries. The vacuum secondarys will all the engine to take all it needs without over carburation. When the vacuum drops off too much the secondaries stop opening. Works really well. Holley used to make 780 versions and I ran them alot on 350s.
Exhaust is important. nice big tubing, no sharp turns, etc...
What can gain you more than a lot of people think is... attention to detail. I use an engine analyzer with scope to make sure everything is working correctly together. For one... you would be surprised how much difference the spark plug and plug gaps can make a difference. Be sure the gap is EXACTLY the same for each plug. The gap determines how much voltage has to be on the coil before the spark will jump the gap. Well by changing that value you slightly change the timing of each cylinder (yes you do). Which can change the amount of power generated by individual cylinders slightly. With the scope I have verified this many many times. By measuring "dynamic compression" it will show. My scope allows me to electrically killing and individual cylinder and see the exact RPM drop. I then go to each cylinder and do that. If each cylinder is putting out the exact same amount of power, the the RPM drop will be the same. Just changing the plug gap will change this. Also be sure you have a really good set of spark plug wires. I prefer copper core with shielding instead of carbon core. The carbon core will break down over time and cause voltage drops. Use something like the Mallory H.E.I. (High Energy Ignition) Distributor. It has a really hot coil and works very well.
Some of these things don't sound like too much, but when everything comes together it can really make a difference. It's like building a race car... Once all the big things are done, the easiest way to remove an extra 100lbs is to find 100 places to remove a pound.
Just some hits.
Dennis
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
makes sense..i had thought of new ignition just because...i forgot to mention that it does have headers and flow master exhaust...i was told by my vette guy here that a 750 would be too big???hmmmmm.. its all them damn rear tires fault.....

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
A 750 may be a bit big for a completely stock 350 if the 750 has mechanical secondaries. The vacuum secondaries prevent the engine from getting more air than it can handle. At top RPM (6000 for an engine that has not been torn down and built for more) it will use more than 750cfm. However without a lot of work it will not handle a fully open 750 at lower RPMs and that will cause the car to "stumble" when the throttle is suddenly put to the floor. The vacuum secondaries will prevent all that by only opening as much as the engine needs. So at lower RPMs it will give say 600cfm if that's all that's needed and as the RPM goes higher and the car needs to breath more the secondarys will open as needed. There are a lot of people that preach the "Do not over carburate" and that's true, but under carburation is just as power robbing.
Dennis
Larry & Michele wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Dennis, just out of curiosity, are you an engine builder? Tuner? Technician? I'm just curious, because you seem to be offering a lot of knowledgeable, common-sense advice. I hang out with a lot of car guys and hear much discussion on performance tuning, etc. You have offered a lot of sound advice in your two responses in this string. Again, just curious.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
StingRay wrote:

I have been building and racing cars since I was 17 (many years ago). I have had cars in Car Craft and Hot Rod mag. Just out of High School I worked part time on a Top Fuel team (which is were I learned to pay attention to detail). Those cars are so close component wise that it's the little things on them that make or break the race. Now I'm an engineer on a Champ Car Atlantic team. So, yeah, I've been "around the track" a few times. After working on the TF team, we used to take our street cars to grudge night at the local drag strip. We had what was considered mild motors (we didn't get paid much back then) but everything was exactly matched to run together and tuned and tuned and tuned. Some of the guys with rich parents were showing up with these cars with all the fancy (and expensive) bolt on parts and we would beat them time after time (which really torqued them off). But they would for example have an tunnel ram with a 5000-7500 rpm power range and a cam that had a 3500-6000 rpm range and heads that were setup to flow at 8000 rpm and the rest of the engine built to spin at 6500 rpm.. and virtually no tuning. Very little maximum power overlap there. We hand picked all the parts that we did use to work as closely together as possible. Theirs looked meaner and sounded meaner... we won!
Oh well, just like life, it's the small simple things that make the difference.
Dennis
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Dennis, your short story does a lot to explain the great advice you have been offering. Your comments about mismatched components brought back a lot of memories over the years. There's nothing worse than hearing a blown Chevy dieseling & backfiring when you shut her down! Ouch!
Anyway, it's a pleasure to read your comments Dennis. I hope you're here for the long haul.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
The 600 will be more than enough for that smog era motor... Those heads won't flow enough to warrant a bigger carb.
Dennis Willson wrote:

--
Ric Seyler
Online Racing: RicSeyler
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
While it's true that he only needs 690 CFM (maybe more depending on the cam and exhaust) for that engine... It's better to go a little bigger than smaller as long as he uses vacuum secondaries. So if he uses a 600 then at is peak RPM he's 90 CFM short of what he needs, with the 750, he's giving the engine everything it needs, no more, no less. The engine will run fine with a 600, but just not put out everything it could. Smog or no Smog... a 350ci engine requires a certain CFM to effectively reach certain RPMs and depending on the volumetric efficiency it could take more (due to cam overlap and and the ability for the exhaust to scavenge).
Dennis
RicSeyler wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Those heads won't flow enough to warrant anything over 600cmf. He will have a lot more problems with getting it to idle properly, bogging down on tip in, fouling plugs, etc. Putting more fuel into a stream that will have no more volume or flow will just get the mixture rich, not more power. And can puddle fuel in the intake and can wash down the cylinder walls.
But hey he can go ahead and buy a 750 and monkey around with jets, the idle air circuit bleeds, the boosters, the powervalve, the secondaries diaphram spring and a bunch of dyno time to dial that carb in. Verses buying a 600 and read the plugs and change jets is even if that would be necessary..
Dennis Willson wrote:

--
Ric Seyler
Online Racing: RicSeyler
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Some people just don't really understand.... the idle circuits between the 600 and 750 are the same, no bogging down because of the vacuum secondaries, it's the airflow that puts fuel into the stream, if the carb was to big then it would put less fuel due to the reduced air speed through the venture. The setting on an out of the box street 750 with vacuum secondaries is for a mild engine with relatively small jets.
All your statements (except for the one about the diaphragm springs) are only true for the 750 double pump competition version.
The factory Q-Jet is actually much larger than 600, the one I run on my IROC tested at 800 CFM on the flow bench when I was setting it up.
I give up.... No wants to stop and think about how things work and why. I've done this a lot and for a long time and successfully.
RicSeyler wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Dennis Willson wrote:

Nice basic theory, but not true in application. If that was the case you could put a Dominator on a 4 banger, (it only draws the fuel it needs theory) You are missing the transition between the idle circuits and the main circuits.... that is where the tip in bog will come from. Plus bigger CMF carbs have bigger holes in the boosters, and some even have different style boosters, annular style, drop leg style, straight leg style. All have significant different effects on fuel metering.
And he will have to play with the air bleeds. i.e. That's why you can't just screw down the idle screw on an engine with a giant cam to get it to idle. It will transition into main circuits and excessively richen the mixture and sputter and foul the plugs.. That's specifically why the trick of drilling a very small hole in each of the primary butterflies came about. So you can back off the idle screw to get out of the main circuits and back into the idle circuits, while still allow sufficient airflow past the butterflies.

The wrong secondary diaphragm spring will also cause bog when using a "too large for the heads" carb.

The Q-Jet meters fuel differently and has a complete different idle circuit setup and design. It uses metering rods and power pistons & springs. And the transition circuits work differently. Apples and oranges.

I'm not trying to take away from your accomplishments, I'm just disagreeing about a little bigger is better than a little smaller, and specifically that era smog SB Chevy will benefit from a bigger than 600CMF Holly/Demon metered style carb. Plus you have to figure in to the equation, gearing, car weight, how much mechanical advance the distributor has, manual or auto, what stall converter if applicable, etc, etc.

--
Ric Seyler
Online Racing: RicSeyler
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
One of the best street carbs ever built was a Q-Jet. Unfortunately, you need to tune them to run on the street, not accept the factory setup, and most do not know how. There are cam kits for the rear air flap and spring kits so that it opens at different rates to change the performance. You can buy lots of different metering rods to get the gas you need. From the factory, they were set up to make mom & dad happy and get decent gas mileage. By 1979, they were all about gas mileage even though they were messing it up badly. The right flap cam and the right metering rods and you will see a great running carb. Plus you can change rods easily by removing the air cleaner to adjust to what you need.
Basically, Holley's vacuum secondaries tries to duplicate the engine-controlled metering that the Q-Jet does.
However, if you have a stick, you don't need a vacuum secondary Holley. That was designed to work with the automatics so as to not bog with the rpm drop in the shifts. The Q-Jet is variable fuel metering, not variable air flow like the Holley, and so it will function with the tick as well as the auto.
I'd drop an L82 cam or one similar in yours in an instant, unless you know what your cam is. You will be happy with a cam with .460 to .475 lift and about 260 deg duration. Not so crazy as to make low speed driving a pain, but yet it will give a wide power range and let you have fun around 4500 rpm or so. Many tell you to use an RV cam with a stick for low-end torque. That is fine if you have a truck and you want to pull a trailer, never going over 55, and never passing anyone. Most RV cams give power from 1000 rpm to 3500 rpm which means you cannot generate the power to the upshift point in an automatic and you really have no power with a stick if you are in a passing or highway acceleration mode. In fact, with a .460/260 dur cam, I pulled a 24 ft trailer quite well with a 350 and Turbo 400 and did it at speeds up to 80 mph. In a light vehicle like a Corvette, it gives you plenty of power without the hassle of a solid lifter like the LT1 cam.
Pull your door panels and you can get into much of the window area, at least as much as you will ever get. You should be able to see the cushions if there are any. The rubber strips on the top door opening will eliminate a lot of the rattle so be sure they are in good shape, too.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Tom in Missouri wrote:

Yes, the Q-Jet can work really well. I have one sitting on top of my 87 IROC's supercharger. You are also correct that it's more complicated to setup. However it doesn't need as much constant touchup after you get it right to keep everything OK as come carbs.
Another reason for the vacuum secondaries is because at full throttle the engine can't really use all 750CFM and that would cause the airflow to slow down which will cause a decrease in power. The vacuum secondaries will prevent this. Also for someone that really know how to drive and can really feel the car and has the self control to only give as much throttle as needed you can go with a large completely mechanical carb... This is not your average on even slightly above average driver.
Yes I know if it's a manual you downshift... but there's no RPM that his engine can safely reach that will use all 750CFM and considering how mild is engine is, it will bog if he suddenly went to full throttle. If he's going to go manual secondaries he should go to the 600. It will still have slightly reduced power at high RPM, but will have more midrange than a 750 manual secondary.
Dennis
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
This is a multi-part message in MIME format. --------------060102050205090604000202 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit
That motor doesn't have the flow for any mid-high RPM cam, a "RV" Cam would be the only way to go.
Tom in Missouri wrote:

--
Ric Seyler
Online Racing: RicSeyler
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
That '79 engine should be running the 462624 head.
462624.....75-86...350/400......76cc chamber, 1.72/1.5, 1.94/1.5 or 2.02/1.6 valves
Now if it is running the 1.72/1.5 valves, then flow would be below 4000 rpm mostly likely. The 1.94/1.5 are more likely and should let him run up to around 5000-5500 max. That would work with the L82 or similar cam. My tech book on the engine components stops at '77 so I'm not sure of the valve size on the '79 L48 and L82. The '77 used the 333882 head and it ran the 1.94/1.5 on the L48 and the 2.02/1.6 on the L82 and odds are the 462624 heads were set the same way.
And I have run cams with .460 lift and 260 dur with the 1.94/1.5 -882 heads and it was quite fun.
A friend and former Chevy test engineer says this is the same line of thinking GM has done in their latest truck engines, ignoring the traditional RV cam for cams that put the power up the range a bit.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
This is a multi-part message in MIME format. --------------070105040806010407060503 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit
2.02 intakes on a '79?? The low compression, old tech smog heads needed velocity not volume for atomization among other things. I'd be surprised if that engine had that big of an intake valve. But I've been surprised too many time to remember... :-)
Tom in Missouri wrote:

--
Ric Seyler
Online Racing: RicSeyler
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Well Ric, they had a 2.02 on the L82 at least up to '77 and it was as smogged as they get through then. I see no reason to think they removed the 2.02 valves, especially since hp increased in '78 and in '79
Part of the reason is that the L82 had a either a 6000 or 6500 redline, I don't remember. To run that speed, you pump that much volume and you need those valves.
You could be relating to the mid '80s with the TPI engines, which although they produced more power, they were usually redlined around 5500 and used the 1.94/1.5 valves like the L48.
And as to power, while it is easy to say they were dogs, because they didn't burn rubber like the previous years, the horsepower is more of a surprise than you would think.
Year L48/L82 1973 190/250 1974 195/250 1975 165/205 1976 180/210 1977 180/210 1978 185/220 1979 195/225 1980 190/230 After this, there were no L48/L82 but the horsepower is similar:
1981 190 1982 200 1984 205 1985 230 1986 230/235 ah 1987 240 1988 240/245 cp
Remember, the '84's brag line was "Life Begins at 150" and they did that with 205 hp, 10 hp more than the '79 L48 and 20 hp less than the '79 L82. Or even more ironic, the same hp as the '75 L82.
The '85 went to 230 hp or 5 hp more than the '79 L82.
And realistically, these are stock configurations. Most of these cars in any year could gain 5 hp with a muffler change or more. Typical tweaks of air cleaners, mufflers, lack of catalytic converters, carb adjusts, timing changes, and such could pull an extra 15 or 20 hp pretty quickly.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
'It runs awsome now and dont leak/burn oil a bit so I dont wanna monkey it up but damn I wanna spin the tires in all 4 gears..lol'
REPLY: An impossibility with an L48 ...at least from typical add on's. You need to understand, that, the 1979 corvette was intended to be a cruiser and not a 0-60 car.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

    Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.