lowes-yellow77

Late nights after work

tracdogg2

Don't say that!

Torqued Off

We can put him on the Ignore List just as fast as we did last time.

HeadsU.P.

That looks awesome and then some. Quick questions:
That timing chain cover looks beefy. Will it clear your waterpump ok?
The vacuum ports off the intake will clear your secondary fuel bowl?

lowes-yellow77

The timing chain is the Cloyes 2 piece cover for roller cam, it states that it will clear but I have both a edelbrock high flow and a regular 400 one, I will update on this matter once I get one installed, the vacuum port clears fine, its further back then the picture makes it look.

71VetteLover

A HOT street engine may reach a 100% volumetric efficiency with open headers but the moment you push the exhaust gasses thru the restrictive exhaust pipes, mufflers, and tail pipes the volumetric efficiency drops FAST. Which is why a 600 cfm carburetor will easily supply enough air for any street 350" engine up to 7000 rpm.

I have a pretty hot 454" in my '71 and to see how far my 750 cfm Holley's vacuum secondaries open I put a little hairspring clip on my secondary lift rod. At 5500 rpm under a full throttle the lift rod still lacked about 1/4" of lifting all the way which would indicate about a 90% secondary opening. So if my 454" can't use all of my 750 cfm there would be no point in installing an 850 cfm.

A L-48 will achieve about 75% VE whereas an L-82 will achieve about 80% VE and an LT-1 will achieve about 85% VE and it's because of the exhaust system restriction that all street engines have to deal with.

71VetteLover

A 350" engine operating at a 100% VE will consume 175 cubic inches per revolution. A cubic foot contains 1728 cubic inches so you divide the 175 cubic inches by 1728 and you get .10127 cubic foot per revolution. Multiply that by 6000 rpm and you get 607.62 cfm. See how easy it is? Now factor in a GENEROUS 85% VE and you end up with a whopping 516.47 cfm at 6000 rpm. But it only gets worse because at 5000 rpm (where most automatics upshift at) it'll only consume 5/6 (83%) of that 607.62 or 428.67 cfm. Do you NOW see how pointless it is to run a 750 cfm carburetor on a 350" street engine pumping thru mufflers?

ctmccloskey

Hello there,
I built a fairly stout 427 for my 1968 L-71 Convertible but with more attention to good street-able manners than flat out racing.

I was told by some to use a smaller carburetor (650 DP) to keep the air speeds up for a good mixture at lower speeds. This worked fine until I went drag racing with my Corvette Buddies. The carburetor was clearly the limiting factor on my engine.

I then heard about A.E.D. Performance Company down near Richmond, Virginia from some local racers. I spent over an hour with one of their technical people sharing all the specs from my engine, and the car it was intended for.

After a couple weeks I received a box that had my new carburetor in it. I was nervous about setting it up properly so I called A.E.D.'s customer service and asked for help on where to start. I was told that they had "set it up" at their facility and all I had to do was "bolt it on". They told me that if it did not perform the way I expected that I could bring my car to their shop and they would set up my carb on my engine using their dyno at no cost to me.

This is what I call GREAT customer service! I had never been treated that way by any company who makes custom carburetors!

I bolted it on the car and it ran perfectly. I could not improve the tune if I tried. They had the jetting dead on for my application.

I then realized that there are people in the Carburetor industry who know the "science" behind these devices. No more guessing or formulas, just plain science.

I would recommend the people at A.E.D. to anybody who wanted a GREAT carburetor out of the box. I am sure there are other people out there who can provide this type of service but A.E.D. has a "Customer for life" in me!

I hope the next person who needs help with a carburetor gets treated this way. At A.E.D. Performance I know they will be! Good Luck and Happy Motoring/Racing!

JoeMinnesota

VERY nice looking setup, Lowes! Hey - If you have issues with a short water pump clearing that timing cover, definitely research some pump options. They do make some waterpump spacers in a few thicknesses, but if you go that route it leads to spacing out the crank pulley or damper, and then the alternator, and then the PS pump if you have one... don't ask me how I know. The retro rollers are nice, though, and rev fast!

Barry's70LT1

I very much disagree in using a 600 cfm carb. Yes, if you're NOT intending to rev beyond 4,500 - 5,000.

Real world..............
I have had a 750 DP Holley on mine for many years. Works great everywhere. Several years ago in an attempt to get better mileage, I installed a 600 vac sec Holley.

The performance was like I had attached a heavy travel trailer to the back. Took forever to get thru the gears.

That 600 lasted about 4 hours on there, and I then reinstalled the 750 and the performance was back.

DO NOT follow those calculators for a performance engine. They're OK for the family station wagon.

71VetteLover

Here's a street engine carburetor sizing chart for 6000 rpm operation that I made many years ago that is within 1% of the carburetor manufacturer's recommendations. A very hot street engine like an LT-1 will seldom exceed an 85% volumetric efficiency because of the exhaust system restriction so if you use the 85% column you can't go wrong. For those 350" engines equipped with automatic transmissions that upshift around 5000 rpm the CFM requirement will be reduced by about 17% which would mean only 429 cfm at that 5000 rpm upshift. That's why the 600 cfm vacuum secondary Holleys and the 625 cfm AVS secondary Edelbrocks are the preferred sizes as they'll flow more than enough air but without being excessively large.

For open header drag and track racing applications where fuel mileage isn't a concern the next larger sizes of carburetors are often preferred because those engines often reach or exceed 7000 rpm.

lowes-yellow77

y`all do math very well, some of these formulas are on point for a perfectly stock engine, add after market goods and it throws off a major imbalance. if you have a ground pounding sbc chevy with 500 HP vs a 290 HP crate engine it is going to significantly change the fuel and air needs is all I`m going to add.


I learned one thing and I love learning even if its something I should have known so ill pass it on. The aluminum intake install states

"When you are fully prepared to install the intake manifold, apply a 1/4” wide bead of oil-resistant RTV-silicone sealant to the
front and rear block-sealing surfaces, making sure to overlap manifold gaskets at all four corners.Do not use the cork or
rubber end seal gaskets included in the gasket set. Apply a light film of RTV-silicone around the water passage
openings."

I never even thought to read them but was bored I have always used the cork or rubber gaskets from the intake set. I have never had a leak on the intake but I have found surface prep is key.

lowes-yellow77

I have looked into these but ran into what you mention all other components need a bump out as well

theandies

I do the same thing but I use a long screwdriver.
They do make automotive stethoscopes

lowes-yellow77

They are an unsung hero

71VetteLover

So you think the carburetor manufacturers and the factory engineers are wrong when they recommend 1-1/2 cfm per cubic inch? A mechanical secondary carburetor gives a false sense of "increased power" because of secondaries being prematurely opened when they'd normally be closed. But it's no different than putting your foot in deeper with a vacuum secondary carburetor because cfm is cfm regardless of how many barrels or style of secondary a carburetor has. If you put an 1000 cfm one barrel carburetor onto an average 350" engine it would feel REALLY powerful at small throttle openings just because of the larger bore that would pass so much air at a minimal throttle opening. But at only half throttle the engine would already be maxed out because it couldn't swallow any more air.

71VetteLover

Yep, and the chart takes the engine's level of performance into account. An L-48 would be about 75% efficient, an L-82 about 80% efficient, and an LT-1 about 85% efficient. It's the restrictive exhaust system that causes the reduction in volumetric efficiency in street engines at the higher rpm's and that's why street engines only require the smaller cfm carburetors. It's pointless to install a 750 cfm vacuum secondary carburetor on an 85% efficient 350" engine because the secondaries would only open about 10% at the very most; even at 6000 rpm because it would only be able to swallow 517 cfm at 6000 rpm. The primaries alone would provide 375 cfm (or 73%) of the 517 cfm needed and that's why the secondaries would barely open.

Excessively large carburetors will give a false sense of "increased power" because each degree of throttle opening provides more air than the same amount of throttle opening in a correctly-sized carburetor. But as the engine can only swallow a given amount of air at maximum power the larger carburetor doesn't provide any benefit other than bragging rights (or should I say bragging wrongs?).

lowes-yellow77

The waterpump clears, it is the Edelbrock high flow short pump. I figured I would share if someone is in the same both with the cloyes 2 piece timing cover.

71VetteLover

A two piece timing chain cover? So you can do a camshaft change without dropping the oil pan? You can also do it with the stock stamped steel timing chain cover by grinding a 15 degree angle onto the lip(s) of the oil seal reinforcement that goes up against the underside of the block (sorry I don't have a picture to show you).

Very few people know just low LITTLE air their street engines actually consume at wide open throttle and buy carburetors that are excessively large. A 350" engine may benefit from a 750 cfm carburetor on an engine dyno but when the engine is dropped into a car and the exhaust system is attached the volumetric efficiency is radically reduced to 85% or less efficiency The 85% column of the chart clearly shows the actual cfm the engine will consume at 6000 rpm but that figure needs to be reduced an additional 17% for engines with automatic transmissions that upshift at 5000 rpm. So a 350" engine with an automatic transmission ends up consuming a pathetic 404 cfm at 5000 rpm; far short of the 750 cfm the carburetor was rated for.

lowes-yellow77

The timing cover is designed for a retro roller cam setup and to make it easier for cam endplay.

https://www.summitracing.com/parts/clo-9-221