Normal compression on a T... high altitude makes a difference?
 

Hi:

Today we checked compression on my 1923 model T. Pistons 1 and 2 showed 40 lbs both cold or hot, while pistons 3 and 4 showed 35 pounds cold and 40 hot. Is this normal?

I live at an altitude of 1.5 miles, if that makes any difference.

Thanks!
Victor

Re: Normal compression on a T... high altitude makes a difference?
 

You might try finding a conversion chart that tell you the differences. 35 and 40 at sea level would be on the low side, maybe time for rings and valve job. The 2ed entry on the jeep forum gives a conversion chart.

From a jeep forum;
http://www.jeepforum.com/forum/f8/at...esting-722504/

General Google search;
https://www.google.com/search?newwin...w=1280&bih=844

Re: Normal compression on a T... high altitude makes a difference?
 

Thanks!

So, according to a table I found at your links:

Compression Test Altitude Compensation Factors

Altitude Factor
500 0.987
1500 0.960
2500 0.933
3500 0.907
4500 0.880
5500 0.853
6500 0.826
7500 0.800
8500 0.773

If I live at around 6000 feet, if I understand correctly I would have a factor of 0.840, which would mean that my engine at sea level when hot would now have 47 lbs of compression.

What is the compression it is supossed to have at sea level? I want to find out how far I am from what my engine should have...

Thanks,
Victor

Re: Normal compression on a T... high altitude makes a difference?
 

Around 50-55 range for a stock engine in good shape at about sea level.

Re: Normal compression on a T... high altitude makes a difference?
 

So, if my equivalent at sea level is 47 pounds and a good engine should be 50-55... should I really be considering doing rings or valves?

I don't want to question an expert's opinion, just wanting to learn if doing it would mean a noticeable increase in power.

Thanks!
victor

Re: Normal compression on a T... high altitude makes a difference?
 

By the way, here is a link to a small video of my T, driven by my son. I believe you will notice no smoke, which makes me doubt my rings are too worn... but the thing I measured compression for is because I find the car with a lack of power, particularly when going un any small incline or hill... in low gear, no problem at all, but in high, it will not have power to negotiate the incline...

Here is the video:

https://www.youtube.com/watch?v=gDDgcx0sqRM

Thanks,

victor

Re: Normal compression on a T... high altitude makes a difference?
 

Your altitude of 10,000 feet makes a big difference in the car's performance. Your cold cranking pressure measurements (not compression) are normal for that altitude. As you have demonstrated, the cold cranking pressure is down 20% compared to what would be normal at sea level.

You should install a high compression cylinder head, available from any of the T part vendors. Then your car will perform better.

Re: Normal compression on a T... high altitude makes a difference?
 

Thanks! I will look into that. I have talked with my friend that knows T's down here and he suggested starting with changing transmission bands to Kevlar, as the car has a hard time breaking and the high speed is far from outstanding... I will see how much that improves the car's movement, and if not I will consider the high compression head and doing valves and rings.

Victor

Re: Normal compression on a T... high altitude makes a difference?
 

The bands do not have anything to do with high speed (direct drive). Braking, reverse, and low speed yes. If they are adjusted too tight they can make the car overheat and accelerate slowly.

Re: Normal compression on a T... high altitude makes a difference?
 

Mmmm... that's a tough blow. I was hoping it could have to do something with the lack of power in high. Anyhow I am going to order the Kevlar bands as the car right now brakes almost nothing.

And I will have to look carefully into determining wether I need to do the engine or not. What puzzles me is that the engine is not smoking...

One question which has nothing to do with it, but perhaps I will save everybody reading a new post if I can find the answer here: Were T's in 1922 supposed to have the rubber pedal covers?

Thanks!
Victor

Re: Normal compression on a T... high altitude makes a difference?
 

Re: Normal compression on a T... high altitude makes a difference?
 

5 Lbs. is a jump for a low comp. engine but it's there so it's probably the result of expansion/heat. Rings do this but if a short warm-up evens it out just drive. As to the performance issue: long dragged out inclines are not what the T wants on a good day. There might not be much you can do without spending $. Re-build, high comp head, on & on. 40 isn't the best but not worst either. I'm saying a re-build might not be worth the $ performance wise.

Re: Normal compression on a T... high altitude makes a difference?
 

OK: Compression test is normal for your altitude, so even a complete engine rebuild will not help the low power situation. In fact, it will make it worse for awhile as a rebuilt engine will have significantly more internal friction, and any power gained will be lost. You can advance the timing more at high altitudes to somewhat compensate for the slower burning fuel mixture, and you need to lean out the fuel mixture to somewhat compensate for the reduced oxygen level reaching the cylinders.
BUT, you cannot get around the need for more compression! Best advice is a high compression head.

Re: Normal compression on a T... high altitude makes a difference?
 

A high compression head is the best bang for the buck performance wise.It really wakes up a model T.

Re: Normal compression on a T... high altitude makes a difference?
 

I don't like the rubber pedal covers. They tend to turn hard after a year or so, then they won't stay on the pedals. I just toss them in the trash because they just get in the way of driving the car.

Re: Normal compression on a T... high altitude makes a difference?
 

Well.. $400 for a high compression head sounds like quite a bit... and it will give you 7 additional HP, so it is interesting, but I don't think it would make a HUGE difference. Anyhow it sounds like a good possibility. I will go over the suggestions with my mechanic and see what he thinks...

And also, since mine is the only T I have driven, I will visit a friend that has a couple and ask him to let me drive them and compare. If there is not much of a difference, the most likely thing to happen is that the car would remain as it is. After all, one does not buy a model T because it is a fast or very enjoyable car! :)

I don't like the rubber pedals either, so I am glad they were not origianal equipment. Glad I asked before I bought a set just because I though they could be correct.

Thanks for all the help
victor

Re: Normal compression on a T... high altitude makes a difference?
 

Rule of thumb is a 3% horsepower loss for every 1000 ft. gain in altitude so if you are at approx. 8,000 ft. you are down to about 15 HP, maybe less. A high compression head probably won't add 7 HP at your altitude; maybe more like 5. So the head will give you back what was lost to altitude, putting you around the original 20-22 HP. That's about a 25% increase. That's a lot!

Re: Normal compression on a T... high altitude makes a difference?
 

Well... looking at it that way, YES, 25% is a lot of increase! I will seriously consider it. I guess the $400 investment is really worth it.

Thanks!
victor

Re: Normal compression on a T... high altitude makes a difference?
 

"Not a enjoyable car" Not so!! The model T is one of the best driving old cars,not fast,but can be!They are one of the easiest to drive, most reliable,and most enjoyable cars I have owned! Phil

Re: Normal compression on a T... high altitude makes a difference?
 

Well Phil, I said "After all, one does not buy a model T because it is a fast or very enjoyable car!", but I have to say, I agree with you, it is a nice little car and it moves fairly well... in fact I am amazed of it's turn radious, the little space it takes in the garage and it's fairly brisky moves, almost like a go-kart, but I still get scared of the brakes every time I need to stop!

Once I change transmission bands I am sure I will gain more confidence with it and enjoy it more.

Thanks!
victor