Thread: Detop swapping the GS???

I have a 99 regal GS that I drive to work (55 miles one way). I am going to start tuning for gas mileage and doing a few mods to help with mileage also. I don't need this car to be fast. I was thinking about swapping a L26 or L36 top end on to it. One thing I was also thinking is that the lower gear ratio would also help with gas mileage v.s. if I just had a normal NA car. What is your guys take on this and if there are any NA guys out there what are you getting for mileage?

The lower compression ratio of the L67 bottom end will lose you gas mileage cause you'll have no torque and have to rev the crap outta the motor

Try a 4.2 inch pulley and lots of tunning

Isn't the lower compression in the shape of the heads? Also where do you get a 4.2" pulley? If you are talking a SS kit my GS came s/c'd from the factory.

The higher the compression of an engine, the more efficient it is. This is why vehicles like the VW Jetta TDI or whatever it is get the mileage they do. They are diesel and have much higher compression.

Of course, with higher compression comes higher temps and the need for a higher octane fuel to ward off knock. Ideally you want a high compression motor that can run on the lowest possible octane.

I am not shooting for low compression? I am wanting to get rid of the s/c and gain the higher compression of the NA motor, maybe even more. My GS is bone stock and getting 24-26 highway. Are the pistons in a NA motor flat top, or is the shape of the bowl in the head different? Where do they get their higher compression? I am not really worried about loosing power, for power I have the other car in my sig. Another thing I plan to do is tune for a lower octane fuel because premium is over $4.20 a gal here. I guess this is just an idea for now but in theory you should be able to get better gas mileage with out the s/c.

What does the TDI run for a compression ratio? It pretty much has to be way higher than a gas engine just because it runs on diesel. Also isn't diesel way more efficient than gas anyways? So mix the power of a diesel with the light weight Jetta and you should get great mileage.

the block makes the compression ratio, not the heads. do like TDC was saying and throw a ton of timing at it during cruise. that will help out your mileage a lot.

Ok I guess all I was wondering is if the compression was different because of the head or piston. Are the pistons in the N/A cars flat top? I added a bunch of timing today so we will see how much better it gets.

BTW I also started to tune for 10% ethanol because it is $0.30 cheaper than premium here.

Originally Posted by Andrew_99GTP

Ok I guess all I was wondering is if the compression was different because of the head or piston.

The difference in compression between the L67/L32 and the L36/L26 is because of the crank, rods, and pistons. Not the heads, not the block. The heads between the two are identical except that the supercharged heads have an opening for fuel injectors.

I wouldn't do this. The L67 bottom end with no supercharger to support it is a dog. No get up and go.

Originally Posted by Sabrewings

The difference in compression between the L67/L32 and the L36/L26 is because of the crank, rods, and pistons. Not the heads, not the block. The heads between the two are identical except that the supercharged heads have an opening for fuel injectors.

I wouldn't do this. The L67 bottom end with no supercharger to support it is a dog. No get up and go.

I don't know if I explained this or not but if the difference in compression wasn't in the heads I was never going to do this. I don't want the low compression. If it the difference was in the heads then I would consider the swap. Don't the L67 and L36 have the same bore and stroke?

Ok thanks for letting be know.