Compression

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Oct 17, 2018 | 10:43 PM

#16

85e150

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Quote:

Originally Posted by 71 F250

Hi 85, I honestly don't know how to start a thread. Since you are a moderator you can help me. Thanks.

Go up to the top of the page and click on "FE & FT Big.....".

Now you are in the forum, instead of an individual thread.

Look to the left side just above where the thread titles appear, and find a yellowish box labeld "New Thread".

Good luck!

Oct 19, 2018 | 11:42 AM

#17

69cj

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From: Middle Tn.

Stock 428cj's are 10:6 to 1. They will run on premium pump if you don't go crazy on the timing.

Oct 20, 2018 | 09:19 AM

#18

71 F250

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From: Divide, CO

cam selection at altitude

Quote:

Originally Posted by 69cj

Stock 428cj's are 10:6 to 1. They will run on premium pump if you don't go crazy on the timing.

I've done some more research and have found out that at high altitude DCR, what the compression acts like is reduced at altitude. I live at 9k in Colorado. At my altitude a 9.5 CR by the math works more like a 8.0 -8.5 CR with the thin air. I spoke with techs at Howard's Cams and Lunati and gathered that a moderate duration and 110 LSA will help build cylinder pressure and limit low RPM bleed off. I think I will be getting a Howard's 250931-10 cam; it is 215/215 and 520/520 on a 110 LSA to meet my goals. I will also ask the advice of the engine shop/builder here in Colorado Springs as he has built engines for the Pikes Peak Hill Climb. They run from about 10k to 14,110 at the peak; that is a fun day of racing to watch with a lot of different classes.

Oct 20, 2018 | 07:49 PM

#19

baddad457

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From: south louisiana

Quote:

Originally Posted by 71 F250

That's why the octane rating up there at the pumps is reduced vs sea level. I still think an even wider LSA would do you better.

Oct 20, 2018 | 10:29 PM

#20

71 F250

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Joined: Apr 2011

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From: Divide, CO

Thanks for all the input, I am told that a tighter LSA will increase cylinder pressure making up for some of the lost compression from altitude. That was what a Howards Cams tech said when I asked about my 9k residence. I am open to hearing all input and experience. Thanks, Kent

Oct 21, 2018 | 06:44 AM

#21

baddad457

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From: south louisiana

Quote:

Originally Posted by 71 F250

A wider LSA will increase cylinder pressure. 110 is on the low end for this. As a general rule, narrowing the LSA increases the overlap between the intake and exhaust, allowing scavenging at lower rpms. That reduces cylinder pressure..

Oct 21, 2018 | 10:56 AM

#22

71 F250

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Joined: Apr 2011

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From: Divide, CO

i have been looking a lot at cam selection and it is confusing. I have a comp cams XE256 cam with 212/219 and 487/493 lift on a 110LSA. I'm looking at other possible choices:
Howards 206/220 486/495 115 LSA
Howards 209/209 490/490 111 LSA
Howards 213/213 502/502 111 LSA
Howards 215/215 520/520 110 LSA
Lunati 210/210 508/508 110LSA

The listed power band on the cam I have is 1000-5200, the similar Howards cam on a 115 LSA is narrower at 1100-4200. I have the NP 435 granny tranny, 3.7 gears and dual exhaust in the mix also. The Lunati cam's power band is also 1000-5000 with of course more lift to get more fuel in. The other cam's power band starts a bit later around 1400 RPM or so. How much would I gain from the 115 LSA cam? If getting another I'm leaning to the Lunati

Oct 21, 2018 | 07:40 PM

#23

baddad457

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From: south louisiana

I would bet on the 115* LSA cam, but ask your friend who does the Pikes Peak run. Let me know what he says, I'm curious to see if I'm right. Ford's small block F4TE cam has a wide LSA (116*) and it builds more cylinder pressure. I've run it in a carbed Exploder 5.0 and with a 9 to 1 CR it would ping in summer when you bumped the timing to anything above 12* BTC on 87 octane fuel (at sea level) It has virtually no overlap . RPM range also depends on heads and intake, not just the cam specs alone.

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Oct 22, 2018 | 11:28 AM

#24

71 F250

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Joined: Apr 2011

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From: Divide, CO

What do you think caused the pinging, I want to avoid that

Oct 22, 2018 | 05:45 PM

#25

71 F250

Cross-Country

Joined: Apr 2011

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From: Divide, CO

I'm thinking if the 115 LSA cam is recommended I'd just get a cam dowel pin set to adjust the valve timing a bit. I just found a Lunati cam that looks like the best bet yet I think. It is their 10330700 cam 800-5000 power range, 207/213 duration @.050, 503/524 lift on a 112 LSA. The describe as their best low end torque cam and great for pick ups. I will ask the machine shop though for their input.