Flywheel weight determination UPDATE

[pontiacgp]

I don't mean to swim upstream against popular opinion but i don't believe that a 4 lb difference in flywheel weight will make a drastic difference in first gear take off

you're right but he currently has a 16 lbs flywheel so that makes it around a 9 lbs difference

 

[DRIVEN]

Agreed on both counts. Street cars don't like light flywheels. Period. Not only will the heavier flywheel help take off much easier, it'll run smoother as well just due to inertia. That may or may not be noticeable.
On the fuel system, there may be some tuning to do there too. In my experience EFI is a little more forgiving on the calculator rule than a carb would be.
Id suggest starting with the flywheel. If that doesn't cure it, substitute a carb with known jetting. Whatever you do, do it in stages so you know what helps and hurts. Don't throw a bunch of parts at it all at once. And please update the thread to keep us posted. Might just help someone else out in the future.
Good luck.

 

[Mike T]

Pontiacgp - Missed the 16 lb flywheel weight somehow. I completely agree that 9 lbs would make a difference. I have read that the benefits of a heavier flywheel are not linear. You lose some of the benefit as the weight of the flywheel is offset by the horsepower loss to spin the extra weight. However, the difference in rotating mass between a 16 lb and a 30 lb flywheel would be substantial and I would agree, have an effect on getting the car moving. Especially since the hydraulic systems don't really weigh anything on the "pressure plate side".

Driven - You are right, the newer EFIs are pretty forgiving. My point was that the short stroke and relatively narrow bore of the 327 require high velocity flow as the mechanism to pack as much air/fuel into the cylinder bores as possible on each intake stroke. (Unless you use a Huffer) The large openings of an 800 cfm EFI plate will reduce the intake air velocity and consequently the air volume pulled into the engine on each intake stroke. Its not the adjustment of the fuel that might be a problem but the the fact that, because of the set size of the intake openings in the plate that I think might be a problem. Less fuel charge, less power, less performance.

 

[1983calais]

I don't mean to swim upstream against popular opinion but i don't believe that a 4 lb difference in flywheel weight will make a drastic difference in first gear take off. Between gear shifts and when you get off the throttle, maybe but not from takeoff. The 327 was all about hp not torque. In order to achieve the best possible hp curve, the engine has to have high air/fuel velocity. Unless I'm missing something, the Holley Sniper 4bbl EFI is rated at 800 cfm, way, way to high for a 327 unless you built it out of some monster expensive internals. (cam, valves, etc.)

The air/fuel ratio that promotes good cylinder burn, flame propagation and power is around 14.7 parts air to 1 part fuel, or very close. In order to stay in that neighborhood, the 327 at 7,000 rpm has a theoretical air capacity of 621 cfm. That's at 100% volumetric efficiency. For a "street" modified engine the maximum cfm rating drops to 540 cfm (+/-) (*click on image below) (stoichiometric air–fuel mixture is about 14.7:1)

If you have the 4 bbl Sniper, I don't think the 327 can keep the air/fuel velocity high enough when pulling it through the big 800 cfm bores. Remember, the EFI doesn't use vacuum to meter in fuel, so you are probably running real rich, especially at low rpm. I would be willing to bet that if you ran the engine at idle for about five minutes and then pulled the EFI, you would find gas puddled in the bottom of the manifold plenum. The rich mix and low air fuel velocity would make for very, very weak performance, especially to get a 4,000 lb +/- car moving from a dead stop.

Borrow a 650 cfm - bbl from someone with 60-64 jets and i think the 327 would wake up. Just a thought.
View attachment 85312

Thanks for the input. I thought about the same thing with the EFI but the computer is supposed to monitor the air/fuel ratio and keep it around 13:1 - 15:1. It monitors the fuel through the o2 sensor in the header collector. The sniper system is designed to support up to 600 hp. My engine is only about 400 hp. I will be going from a 16 lb flywheel to a 26 lb flywheel. Adding 10 pounds should help my problem. Will it fix it entirely? I hope so but only one way to find out. I appreciate all the info and welcome any other opinions and knowledge. I never claimed to be an expert at this but I enjoy learning and listening to further my knowledge of this great hobby.

 

[1983calais]

Pontiacgp - Missed the 16 lb flywheel weight somehow. I completely agree that 9 lbs would make a difference. I have read that the benefits of a heavier flywheel are not linear. You lose some of the benefit as the weight of the flywheel is offset by the horsepower loss to spin the extra weight. However, the difference in rotating mass between a 16 lb and a 30 lb flywheel would be substantial and I would agree, have an effect on getting the car moving. Especially since the hydraulic systems don't really weigh anything on the "pressure plate side".

Driven - You are right, the newer EFIs are pretty forgiving. My point was that the short stroke and relatively narrow bore of the 327 require high velocity flow as the mechanism to pack as much air/fuel into the cylinder bores as possible on each intake stroke. (Unless you use a Huffer) The large openings of an 800 cfm EFI plate will reduce the intake air velocity and consequently the air volume pulled into the engine on each intake stroke. Its not the adjustment of the fuel that might be a problem but the the fact that, because of the set size of the intake openings in the plate that I think might be a problem. Less fuel charge, less power, less performance.

Ok, so if the bore of the sniper system is to big for the 327 what about a spacer that reduces the bore? The velocity is the speed the air is forced in. I realize this may reduce volume ( amount of air). I'm not an expert at this so I'm explaining it how I understand also. But that would reduce the big bore so in theory this may work? I just don't want to take it off and stick it on the shelf after all the money I have spent on it and the fuel pump, fuel fittings and fuel line. I am going to order the flywheel this week and hopefully next week I can get everything put back together and have some results. Thanks to all of you for the help.

 

[Mike T]

Ok, so if the bore of the sniper system is to big for the 327 what about a spacer that reduces the bore? The velocity is the speed the air is forced in. I realize this may reduce volume ( amount of air). I'm not an expert at this so I'm explaining it how I understand also. But that would reduce the big bore so in theory this may work? I just don't want to take it off and stick it on the shelf after all the money I have spent on it and the fuel pump, fuel fittings and fuel line. I am going to order the flywheel this week and hopefully next week I can get everything put back together and have some results. Thanks to all of you for the help.

 

[1983calais]

Didn't catch that MikeT.

 

[Mike T]

Looking at a couple of things about your situation but have somewhere to go now. Have to reply later tonight.
What kind of intake will you be running and describe your exhaust system, including pipe size.

 

[1983calais]

Looking at a couple of things about your situation but have somewhere to go now. Have to reply later tonight.
What kind of intake will you be running and describe your exhaust system, including pipe size.

Edelbrock performer intake, 2.5 inch exhaust with x pipe, long tube headers 1.5 inch , 492 heads, 2.02 int

 

[Mike T]

Edelbrock performer intake, 2.5 inch exhaust with x pipe, long tube headers 1.5 inch , 492 heads, 2.02 int

I may end up eating a little crow tomorrow. Can you sent me your cam specs and is it hydraulic, flat tappet or roller?