Desirable camshaft specifications

[Taylor95]

I'm looking around for a good camshaft that would help increase my fuel economy. I own a 97 XJ. I will be porting the exhaust ports on the head at the same time I do a camshaft swap. What sort of specs should I look for to get a more fuel efficient camshaft? Here's a stock replacement cam:
https://www.summitracing.com/parts/m...model/cherokee

and some other ones I found
Crower Level 2
https://www.summitracing.com/parts/c...ions/year/1997

Crower Level 4
https://www.summitracing.com/parts/c...ions/year/1997

Mopar
https://www.summitracing.com/parts/dcc-4529229

Howard Cams
https://www.summitracing.com/parts/hrs-320111-12

If you don't want to click through all those, just some general tips on what kind of cam I should get to maximize fuel efficiency would be great! Keep in mind that I will be porting the exhaust valves because they are too small on stock cylinder heads.

[Daschicken]

The only advice I can offer is the advice listed in the 65+ Efficiency mods.

[Ecky]

Referencing what Daschicken posted, I believe in an ideal world you'd want an adjustable cam. Advance the timing on it until you aren't getting any more power. Lower lift and duration cams (to my limited understanding) can be advanced further.

One can simulate the Atkinson cycle by increasing overlap of intake and exhaust significantly, at least at lower RPM. This is generally best paired with a huge increase in static compression ratio. I'm aware of some gasoline engines with static compression ratios as high as 16:1. The valve overlap decreases peak cylinder pressure to safe levels (e.g. 10:1), but you still get the wonderful (in this case) 16:1 expansion ratio, which greatly improves efficiency.

Someone please correct me if I'm off about this.

[Taylor95]

I have heard the same thing about increasing the static compression ratio with valve overlap--but would I still be able to use 87 octane fuel with such a high static compression ratio?

I believe that to be accurate. How would I adjust the settings to achieve that overlap though?

[Ecky]

I can't advise on how to do it specifically, but if done right you can run whatever fuel you'd like.

[arcosine]

Any performance cam will lower your gas mileage. (period) If you are going for economy and not performance than there is no need to port the heads, since economy driving is done at low RPMs and velocities are low. In fact trying to port the exhaust may destroy the anti flow back and scavenging that is inherent in most exhaust port designs. Just keep your old cam and that will save more money than any new cam will make up in mpg.

[arcosine]

Any performance cam will lower your gas mileage (period). If you are going for economy and not performance then there is no need to port the heads, since economy driving is done at low RPMs and velocities are low. In fact trying to port the exhaust may destroy the anti flow back and scavenging that is inherent in most exhaust port designs. Just keep your old cam and that will save more money than any new cam and porting will make up in mpg.

[Vekke]

I have done vast research over 1000 km just test driving and setups on tdi cam timing or torsion value as it is said on vag tdi. I made a custom program that injects same amount of fuel 16mg/stroke all the time for full rev range on a 1.4TDI which is 3 cylinder diesel engine. So its not exactly same amount of fuel if rpm rise there is more fuel injected per hour, but still its constant amount per stroke. If you would have level road for testing you would get even better results, but you have to use what you have.

Test road was 6,3 km long full of uphills and downhills and I doubled that for fine tuning. Just by changing the timing, meaning adjustable cam you are able to get 5-10% improvements on a diesel engine at least. Problems arise when you change your drivebelt it often does not go exactly same place.

I moved adjustment from -2,2 torsio to 2,2 which was best setup for this car and the time went from 267 seconds to 243 seconds and to back direction from 278s to 253s. I started the test from 70 km/h speed and put the pedal to the floor. This way car would accerelerate and the small differences in start speed would not have so big impact to end result.
-2,2 =12600m/267s+278s=12600m/545s=23,1 m/s--> 83,1 km/h avg speed car needs about 8,5 hp for this avg speed
2,2=12600m/243s+253s=12600m/496s=25,4m/s-->91,4 km/h avg speed car needs about 10,5 hp
During the testing top speed got 10 km/h higher from 105->115 km/h and car was able to keep much higher speeds at uphills and steady sections as well.

https://ecomodder.com/forum/tool-aer...ToStep=40-65-1

As you can see there is big differences out there you just need to dig them out in testing.

All those values were inside VW tolerance +-3,0 degrees for diesel engines!!!

1.4TDI Audi A2 can now drive on 6th gear from 75 km/h and before any ecu modifications limit was aroung 90-95 km/h speed range. 100km/h is about 1750rpm. Now I am able to go 80 pretty easily if there is no big uphills.

I did same testing also on 1.9tdi and results were pretty much the same, there drive speeds got higher so avg speed wise it was not so big high speed difference but energy consumption was higher at higher speeds...

Best torsion values were not same for different cars so you need to find out which is best setup for your car. Cheap and easy method would be to make a stopper under gas pedal or hand throttle to have always same throttle position on petrol or diesel car.

[Taylor95]

Originally Posted by arcosine

Any performance cam will lower your gas mileage (period). If you are going for economy and not performance then there is no need to port the heads, since economy driving is done at low RPMs and velocities are low. In fact trying to port the exhaust may destroy the anti flow back and scavenging that is inherent in most exhaust port designs. Just keep your old cam and that will save more money than any new cam and porting will make up in mpg.

I disagree with this. This is also a vehicle specific conversation so some experiences you may have will not hold true for a 4.0 jeep engine.

I do not plan on porting the intake valves. I Will port match those and do probably a mild port on the exhaust valves. If you look at a picture of the cylinder head, you will see how small the exhaust valves are in comparison to the intake valves.

I think many performance cams for the vehicle can increase gas mileage. Many Jeep owners want more low end power for rock crawling, and that low end power will increase fuel economy.

[Taylor95]

Originally Posted by Vekke

Just by changing the timing, meaning adjustable cam you are able to get 5-10% improvements on a diesel engine at least. Problems arise when you change your drivebelt it often does not go exactly same place.

I moved adjustment from -2,2 torsio to 2,2 which was best setup for this car and the time went from 267 seconds to 243 seconds and to back direction from 278s to 253s. I started the test from 70 km/h speed and put the pedal to the floor. This way car would accerelerate and the small differences in start speed would not have so big impact to end result.
-2,2 =12600m/267s+278s=12600m/545s=23,1 m/s--> 83,1 km/h avg speed car needs about 8,5 hp for this avg speed
2,2=12600m/243s+253s=12600m/496s=25,4m/s-->91,4 km/h avg speed car needs about 10,5 hp
During the testing top speed got 10 km/h higher from 105->115 km/h and car was able to keep much higher speeds at uphills and steady sections as well.

Thank you for sharing! I didn't that such a large difference could be made by adjusting the timing alone.