Increasing 3100 Efficiency

[rxkaffee]

This might be a little more on-topic in the performance forum, but I could not start a topic there, "Access denied", and asked for forum password again. However, I have no real desire to increase power output, but understand that most fuel economy increases come hand-in-hand with more low-rpm torque.

Since we're going to stick with a 3100 as a replacement engine for the Monte Carlo's blown motor, I'd like to see what I can do to improve efficiency a little while its out. It has been a while since I looked at the numbers, but from the factory this car is only rated at something like 25mpg.

I don't want to spend gobbs of money on this (no 500$+ custom headers). And I do want to keep the 3100 heads(for now atleast).

I have heard that some of the 3100 gen3's prior to `96 were non-roller rockers. This generation of Monte began production in 94 or 95, and we're not sure what year car this engine came out of. Is there any easy way to tell, without disassembly if this engine will have rollers?

Most intake track modifications are accompanied by a slight to moderate loss of air velocity and would likely be counter productive to my goals. I might get a little better mileage by replacing the factory paper filter with a same-style K&N.

I have looked at some lightweight valvetrain gear, but haven't found much. Mostly light lifters I believe they were, and pretty pricey at that. There used to be some torquer/fuel economy cams avail for some Chevys, but I think it was for SBC's in trucks. Couldn't find anything similar for these v6s.

A big help, I think, would be a stickshift. However it seems there has not been much luck putting a 5spd into the Monte Carlos.

There are ony two fairly solid ieas that I have on this.
1) Crank scraper
2) 5-angle valve job

The crank scraper should help reduce frictional losses and decrease the rotational mass a little, but I'm not expecting this to do a whole lot. A 5-angle valve job however, could help by as much as 10% I've read. It should help by increasing the air velocity during times of low valve lift. I was also thinking about having the combustion chamber gasket-matched. The hope is that this would reduce the chances of hotspots in the chamber, allowing me to run a more lean A/F ratio at some later date.

Any words of wisdom you guys 'n gals care to depart with?

[bszopi]

First, that is wierd that you got that error. Doesn't really make any sense, but oh well...

Next, $500 custom headers would be a DREAM!!! Just standard off the shelf headers for these engines are in the $900 price range (with ceramic coating), but they do provide a nice increase in power (~20hp).

As far as finding out about the roller rockers, its as simple as removing the 4 screws attaching the valve cover. That's really the only way to determine it, as some heads that had the notches for the rocker pedestals still got the ball and pivot rockers. And I wouldn't really consider taking off a valve cover "tearing into the engine".

A 5-angle valve job may provide a 10% increase on some other head, but not these. It will provide a slight increase, but port work and combustion chamber work is where you will see the gains.

[rxkaffee]

When you say ball and pivot, are you talking about the contact tip between rocker and valve, or how the rocker arm is mounted? I have never heard roller rockers referring to anything other than the tip.

[bszopi]

The pre-roller rockers were the old stamped steel pieces, and are mounted in a "ball and pivot" style:



The stock roller rockers are only roller fulcrum and not roller tip:

[rxkaffee]

wow, GREAT pictures!

Good to know that they all have the same tips. Are the pedistals interchangable between the roller and non roller heads? So that or ball/pivot aftermarket rockers can be used on newer heads.

What type of port work would be advantageous to increasing efficiency? It seems that the most common port modifications increase volume, but lower the air's velocity, causing power to be shifted higher into the RPM band.

=====EDIT====
Found the thread about putting roller-rockers into a non-roller head. But what about putting ball/pivot rockers into a roller head?

[87S10]

wow, GREAT pictures!

Good to know that they all have the same tips. Are the pedistals interchangable between the roller and non roller heads? So that or ball/pivot aftermarket rockers can be used on newer heads.

What type of port work would be advantageous to increasing efficiency? It seems that the most common port modifications increase volume, but lower the air's velocity, causing power to be shifted higher into the RPM band.

=====EDIT====
Found the thread about putting roller-rockers into a non-roller head. But what about putting ball/pivot rockers into a roller head?

When I was porting motorcycle heads for some flat track racers,I always applied a real rough barrier finish to the ports using 36 grit on aluminum to enhance turbulence for better homogenization of the fuel mixture which most of the time allows for a more complete combustion,end results more power requiring less fuel demands,better efficiency,at least that's what was relaid back to me from their re-jetting,maybe different with an auto,don't know.

[rxkaffee]

36 grit on aluminum to enhance turbulence for better homogenization

I've wondered about increasing port turbulance too. I'd think the biggest difference between this application, and your bike works would be the carb. I know that passage roughness is alot more significant in carb'd engines.

People still recomend against polishing intake ports on fuel injected cars though, so this might have some benefit to it.

But assuming there is no benefit... would there be any drawbacks to more turbulance while entering the combustion chamber though?

[Superdave]

When I was porting motorcycle heads for some flat track racers,I always applied a real rough barrier finish to the ports using 36 grit on aluminum to enhance turbulence for better homogenization of the fuel mixture which most of the time allows for a more complete combustion,end results more power requiring less fuel demands,better efficiency,at least that's what was relaid back to me from their re-jetting,maybe different with an auto,don't know.

I'm sure you ment Atomization.. not homogenization. homogenization refers to processing Milk.


It all depends on port shape and runner style but most of us who port these heads go no finer than 80 grit in the intake ports. I typically run 120 grit in the intake runners before the injectors.

[rxkaffee]

It all depends on port shape and runner style but most of us who port these heads go no finer than 80 grit in the intake ports. I typically run 120 grit in the intake runners before the injectors.

How does 80grit and 36grit compare to the stock finish on the 3100 heads? Is that more rough than the stock finish? I'm guessing these aluminum fellows are quite a bit more smooth inside than alot of the old cast iron stuff.

[robertisaar]

the aluminum is cast much smoother, there is no doubt about that, but even the finish left from 36 grit is a lot smoother than the casting, especially where the halves of the manifolds are fused(?) together, making a big ugly seam that fucks up everything...

[rxkaffee]

Better to have uniform finish roughness?

especially where the halves of the manifolds are fused(?) together, making a big ugly seam that fucks up everything...

So using rough grit would only increase turbulance in areas that would be ground down because of casting lines? No improvement over stock finish in terms of velocity and turbulance? Or would it be more advantageous to have a uniformly rough finish, even if its not able to be uber-rough?