Considering Compression Ratios

I continue to consider different ways of making the Mustang faster.  The challenge is that any performance improvement at this point involves replacing a relatively new part I installed with something better.  The gains are smaller without considering a larger engine.

If I went to a larger engine like a 347 or 363, I would need different heads that would work with a roller camshaft.  Bigger heads would have some form of improvement now so they would work for either option.  While I don't know that they offer a great deal of improvement in my current setup, I'm considering it and wanted to collect all the details I have on what different heads would do to my current compression ratio and if I switched to a larger engine later.

Looking through my original posts, I found the following detail on the original engine configuration.  If I plug it into an online calculator, the compression ratio is only 8.13 which does not seem right compared to the stock specs published online (9:1+):
    Cylinder Size: 4.040 x 2.87
    Deck Height: 7.365cc (.035" In Bore x 4.040 Bore))
    Gasket: 10.16cc (.047 x 4.10" Bore) (Fel-Pro 8548PT-2)
    Piston: 12cc Dish (Keith Black Silv-O-Lite 1157)

    CR 8.13 (w 55cc heads)

If I calculate where I am after the rebuild, the compression ratio is at 8.86 which is rather low.  I thought it was a little over 9:1 for some reason but don't see where my measurements are off.

    Cylinder Size: 4.040 x 2.87
    Deck Height: 0 (Zero Decked)
    Gasket: 10.16cc (.047 x 4.10" Bore) (Fel-Pro 9333PT1)
    Piston: 6.5cc (Keith Black KB115)

    CR 8.864 (w 60cc heads)    

The Summit website states that the compression ratio of the Dart 347 small block is 10:1 with a 58cc head.  The Summit site does not include a compression ratio spec for the Dart 363 but it does indicate the pistions are Mahl 93024485 with a 6.5 cc dish which would put the compression ratio at 10.7:1 with a 60cc head and 11:1 with a 58 cc head.  

The FelPro 10112 head gasket which compresses to .039.  The cc of the current FelPro 933PT1 is 10.169cc and the 10112 is 8.438 cc.  This has almost the same effect as dropping the head cc to 58.  This still only puts me at a 9.045:1 with the current setup.

If I use the FelPro 10112 and start to mill the head, I see the following impacts on the current setup:

58 cc = 9.266:1

56 cc = 9.5:1

According to a MotorTrend article I read, a change in 1 compression ratio is about a 3% change in power.  https://www.motortrend.com/news/0311em-power-squeeze/

My thought is that this really isn't worth the trouble.  I don't think the head would flow that much better and the compression ratio benefit is minimal.  The real difference is that I could have more than .550 lift and would be able to rev beyond 5500 rpm.

New Borla Pro XS Mufflers - Hoping to Eliminate Drone!

The current exhaust on the Mustang has a fair amount of drone on the highway.  I love the sound of the exhaust but when we take any type of road trip you can hardly hear the radio or have a conversation.  I've done what is possible with Dynamat and other stock style sound deadeners leaving the option of replacing exhaust components.  I've hesitated to this point as I hate to give up the current sound but I want it something that any member of my family would not hesitate to go for a long trip due to the drone.

Before replacing the exhaust, I attempted to use a decibel measuring application on my phone while driving around in the Mustang.  I expected to give me some objective measurement on how much (if any) the new exhaust is.  However, with idle, driving on the highway, driving at 2,000 under load, and going 60 with it in neutral the application measured the sound at a fairly consistent 75 db.  The only way I can explain the fairly consistent db is if it is just the certain frequency of the drone which is annoying.  

This past weekend I began the project of replacing my current Dynomax Super Turbo mufflers (Part# 17733) with a set of Borla Pro XS (Part# BOR-40358).  Removing the current exhaust with the rear axle in place was a challenge as the current mufflers were essentially crimped on by the exhaust clamps requiring much of it to be removed in large pieces.  I worked on it some Saturday morning and again this afternoon and everything is now apart.

Once it was apart, I noticed the Borla muffler inlet and outlet are actually a little larger than my 2.5" exhaust.  They slipped on rather loosely such that I really did not think a good seal would be possible.  I rented an exhaust expansion tool (EverTough 067097) from O'Reilly and used it to slowly open up the size of the exhaust pipes until the Borla mufflers slid on with a bit of resistance.  I then used it on the Dynomax mufflers to essentially create a dolly inside the muffler inlet and outlet so I could return them to a round shape so they could be used again if I desired.

The new Borla muffler is a straight through design which I hope does not make it incredibly loud.  

I shined a light down into the Dynomax muffler but it is a little hard to tell what exactly is going on inside.  The center inlet runs exhaust through a perforated tube and then to one side using a flow director at the opposite end of the case.  It seems to run in a large circle inside back around to the side where it has the offset exit.  Its hard to see how it is able to flow this way without the center inlet getting in the way of the exhaust exiting.  I searched for a picture of the internal design and found someone took one apart to find the following.  My case seems identical except perhaps a little longer.  

Coil Spring Completion and Driver Upper Ball Joint Replacement

Today, I finished the replacement of the front coil springs by handling the driver side.  This included not only replacing the spring but also the upper ball joint.  

A few months ago, I decided I'd check the front suspension, make sure everything remained tight, and lubricate everything.  In the process, I learned of a slit in the driver side upper ball joint boot.  It was not horrible but it would certainly cause the ball joint to fail early.  

The ball joint replacement required that I grind off the rivets which held the original in place.  The new one is a Moog K8142 which bolts in place once the old one is removed.  The current upper control arm is a Moog unit so I thought I might be able to just replace the boot but the new one is held on by a trim ring while the original had a metal ring inside the boot which held it in place.  Regardless, the job is done and did not take too long.

If you look close, you can see the slit running from left to right on the top surface of the boot.

The new one bolted in place...

I then installed the new spring with the entire job requiring about 2 hours due to taking a leisurely pace with it all.  

I drove around the block some with the rear suspension bolts still just snug.  The front is now at 25 1/8" to the bottom of the fender which is a 1" increase over the 24 1/8" height before starting work.  I did not expect as much of an increase as I used the exact same springs and cut them exactly 5/8" higher.  Being longer, I expected the spring rate to be every so slightly less such that it would be between 1/2" and 5/8" higher.

The rear is still a bit of a mystery.  I'm still using the 1" lowering blocks and stock shackle with 5 leaf springs.  The passenger side is at 25 3/4" while the driver side is at 25 1/2" which has not settled much although I've not driven much either.  This is not much different than it was before switching but I'm completely full on gas which likely makes a bit of a difference.

I'm tempted to buy a set of .75 or .5 lowering blocks just to raise the rear a slight bit more.  I've not had the tire drag but then again I've not had many people in the car or the trunk full of gear for a road trip.  This would raise the rear to make it balance more with the front of the car.  I could also cut the front springs down just a bit more.

The best option would be to leave it alone for a bit now and drive it around some.  The front might settle some in the days to come.  It would be best to give it that opportunity before making any permanent change like cutting them.  If I were to do anything, I would try some different blocks to balance it out some for now as I wait to see if it changes over time.  

New Coil Springs - Passenger Side Done

I purchased a new set of front coil springs (NPD # 5310-8) and have been waiting to install them.  As a baseline, I measured the front suspension and the height to the bottom of the fender lip was 24 1/8"

I'm replacing my current springs with the exact same style I used before which are for a big block car.  The springs are rated at 428 lbs and set the ride height at 11.5" which is a little high.  I'll be cutting some off but not a full coil like I did with the last set.  My goal is to raise the front end by about half an inch which is not much and is a little picky.  However, now that I have raised the rear, the front will look rather strange unless I raise it at least a little.

I removed the passenger side coil spring and set it next to the new one.  I oriented them the same so it was each the height of the current spring on the new one.  I then measured up on the spring to the height that the overall spring height is 5/8" taller and cut both of the new ones there.  

I installed just the passenger side spring and went for a drive around the block.  The passenger side currently sits at 25 1/8" so I gained essentially an inch.  Trouble is that I know the raised height on one side is loading the other side of the suspension some.  If I move both up equally, perhaps this side drops more or perhaps it is actually shifting weight to the back some now.  It is hard to state.  I'm debating if I leave it alone or cut a little bit more off, install the driver side, and then pull the passenger side back out to fine tune it.

Since I had the measuring tape out, I measured the back and found the passenger side is at 26" and the driver side is at 25".  This is a little bewildering.  

When I installed the 1" lowering blocks, I drove around a bit to try to get the suspension to settle.  While I was out driving, I filled up with gas which was a bit of a mistake as it changed an extra variable.  When I made it home, I found the driver side was 1/2" lower than the passenger.  The blocks are exactly the same height so I figure it is something with the spring rates being slightly different or more gas weight on that side but none of it really makes any sense.  

As I said before, one of the many joys of working on a car with parts from China.  

New Rear Leaf Springs 3

I put on the 1" blocks on the rear suspension this morning.  Before driving, I quickly measured the passenger side and found it to be 26 1/8" which was about as expected as it was right about 27" before.  I then decided to go on a drive with the bolts just snug so it could settle.

While out, I completely filled the gas tank which was probably not the best decision for evaluating height changes.  When I returned, the passenger side was at 25 3/4" and the driver side was at 25 1/2".

Unfortunately, this means the driver side is back where it started at with the 4.5 mid eye springs.  That is a little surprising as that means the with the 1" blocks and a tank of gas that the driver side dropped 1.5 inches.  It is visible that one side is lower which is rather frustrating.  I keep throwing money at the problem but nothing sees to fix it.

I'm probably going to leave it for a bit now and come back to it later.