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
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
Just some hits.
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.....
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.
Larry & Michele wrote:
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.
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
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.
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).
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:
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
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.
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
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.
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
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.
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.
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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:
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
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.
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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:
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
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.
After this, there were no L48/L82 but the horsepower is similar:
1986 230/235 ah
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.
'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.
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