High altitude vs low altitude and affects on RPM range? - Ford Muscle Forums : Ford Muscle Cars Tech Forum
 
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post #1 of 12 (permalink) Old 08-18-2003, 04:41 PM Thread Starter
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High altitude vs low altitude and affects on RPM range?

What affect on the RPM range of the power band does altitude have if any? Does low altitude extend or raise the RPMs or is the RPM range the same? I know nitrous actually lowers the power band some and between 200-500RPM compared to not using nitrous on the same engine but low altitude would be much like using nitrous because of the added oxygen volume. I am curious so I can change my combo some when my car gets up here in NY from the 5600' altitude of Albuquerque's drag strip. I know my converter will loosen up about 300-500RPM and I can go with a Super Victor intake instead of the high velocity Vr Jr I have on there now but the RPM range of the different altitudes is what I'm interrested in now. 20% HP increase from Albq to this low altitude I fully expect. I also expected my converter to stall around 4000rpm up there and it wound up stalling at 4800rpms on the second weekend plus I expected a big hesitation stabbing the throttle from an idle with my 1050 dominator up there but on the contrary, it had awesome instant throttle response so..... I built the 392 to make a lot of torque down low because of the expectant tight 4000 stall and didn't hog out the heads or Vr Jr intake like I normally would have so to use this converter in low altitudes I need the Super Victor intake, more port work to the heads, and possibly larger cam with more intake duration and lift and less duration and lift for the exhaust. The headers and exhaust are big time overkill for this mild combo and it is way too big up at that high altitude but should be a better match at this low altitude. 1 7/8 - 2" step headers with 3 1/2" collectors and full 3 1/2" h-pipe and exhaust was meant for a big nitrous hit on a 400+cid 7500RPM small block I was going to build when I lived in Tulsa and fist moved to Albq but it has changed since then. I shifted at 6000RPM, 6500, 7000, and 7200RPM and no ET/MPH difference what-so-ever and I'm hoping it's because of the altitude, too large headers/exhaust at high altitude(not enough exhaust gas volume in thin air), ported Vr Jr intake too small, and lean carb combination. I did take it to 7800RPM but I felt it nose over some and lost over 2 tenths so I didn't do it anymore. I made one tuning change in the 2 weeks I had it running and that was adding #92 jets front and back from the #90s it had to start with and I dropped .18 off my ET from that one change the last day I raced it on Saturday. 30* total timing at 5600' altitude(easy to start with locked out advance). I had not bumped up the timing at all the whole time. I built it for low end power for a strong launch with expected 4000 stall and got a 4800 stall instead and an engine with no preferred RPM shift point. With the 4.30 gears I was crossing the line at 6100RPM but some software I tried said it will be 6600RPM down here which is near where peak HP on this engine should be(nitrous will bump up the stall much higher depending on what HP shot I go with if I even use nitrous this time). Any ideas or comments? She'll stall between 5000-5300RPM down here so I will be helping out the top end now. What will the altitude drop alone do to the RPM range? Any experience? I assume around 300-600' altitude down here.

The combo is:

12.5-13:1 392W w/cast pistons
moderately ported Windsor Sr heads(54cc chambers)
ported Vr Jr intake
256/266 at .050 solid roller, .656/.656", 108 ILC, 108 LCA
9375 1050 Dominator
28/10.5 ET Drags
4.30 gears
5000+ stall C4

I will get a 265/265 at .050" cam and 110-112LSA intalled at 108 ICL later with a Super Victor intake and porting the heads more or possibly going with some Vr Jr heads and heavily porting those. Possibly change to forged pistons if I really want to use more than a 175 horse shot of nitrous which I haven't decided on yet. I got a 500HP fogger off a 351W Vr Jr intake and it's asking me to put it on something almost every day but cast pistons keep me from doing it to the 392 but my 532 can handle it Ideas/comments/info is appreciated. This altitude thing has me off cue at the moment

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[ This Message was edited by: 89 coupe on 8/20/03 6:31am ]
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post #2 of 12 (permalink) Old 08-18-2003, 06:06 PM
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High altitude vs low altitude and affects on RPM range?

We just had a guy race the IHRA race here from Denver(Bandimere) & he was amazed at our crap track. He was saying (when his engine took a dump) that he usually runs about 6500 there & when he got here he went up 8 jet sizes & was going 1800 on his healthy SBC. I think you'll pick up about 500-1000 RPM from the info I saw on his laptop & his converter loosened up by 1000 rpm. You could go ask the guy at the shop we were at, I bet he knows more than us both




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post #3 of 12 (permalink) Old 08-18-2003, 06:14 PM Thread Starter
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High altitude vs low altitude and affects on RPM range?

I sure hope so. It freaked me out when there was no ET/MPH difference between shifting at all those different RPMs when I know it should make peak power somewhere around 6500-6800RPM. The torque and response at that high altitude was great though

Kent

392W/C4 - Cast pistons, iron heads, stock suspension pig
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post #4 of 12 (permalink) Old 08-19-2003, 01:32 PM Thread Starter
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High altitude vs low altitude and affects on RPM range?

John Urist hasn't run a carb in probably 5 years now so he couldn't offer much help. He has been Turbo'd and injected since just after I moved there when the Victor heads just came out and he was one of the first to get a set. That was when he was on the bottle with a carb and running 9.0s. Now he has forgot a lot about that combo. You saw his car......he has gone in the low 7.70s now with those true 28x10.5 tires. That car works! It slips and slides at Albq Dragway though so no full passes under full throttle there.

Kent

392W/C4 - Cast pistons, iron heads, stock suspension pig
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post #5 of 12 (permalink) Old 08-19-2003, 01:51 PM
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High altitude vs low altitude and affects on RPM range?

I wish I knew where he was gonna be when he travels, wuold LOVE to see that car at Dallas or Houston





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post #6 of 12 (permalink) Old 08-19-2003, 02:50 PM Thread Starter
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High altitude vs low altitude and affects on RPM range?

Give him a call and find out where and when he's going near the Oklahoma area. His number is in the magazines. I don't have his number with me now otherwise I'd give it to you. You liked his shop and the cars there huh?

Kent

392W/C4 - Cast pistons, iron heads, stock suspension pig
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post #7 of 12 (permalink) Old 08-19-2003, 04:21 PM
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High altitude vs low altitude and affects on RPM range?

hey mister ny its to bad i didnt get to whip your but befor you left but good luck out there ill e you some pics of the new toys i got a smokeing deal on some new jahns pistons and alum. rods for my fe so im going to put that in the 65 mustang and see if it will pull 9s with that solid roller i have im going to the track this weekend to try to blow the cleavland so i can put a real motor in it like a 514 with scj heads .
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post #8 of 12 (permalink) Old 08-19-2003, 06:54 PM Thread Starter
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High altitude vs low altitude and affects on RPM range?

Somehow I don't think you'll hurt the Cleveland unless you miss a shift and have no rev limiter or the oiling system wasn't modified. I know you'd like a SCJ head 514 but that's expensive if starting from scratch. Give the Cleveland a chance and try a bottle on it if not quick enough. Nitrous is the great and wonderful "fix all". Have fun this weekend and do post the results

Kent

392W/C4 - Cast pistons, iron heads, stock suspension pig
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post #9 of 12 (permalink) Old 08-19-2003, 09:10 PM
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High altitude vs low altitude and affects on RPM range?

i put the bottle on for just in case so well see. let me know how the tracks are over there i was over at johns house the other day and he is slowly convencing me to put a turbo on one of my cars.
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post #10 of 12 (permalink) Old 08-20-2003, 11:57 AM Thread Starter
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High altitude vs low altitude and affects on RPM range?

John Urist is right in everything he tells you about a turbo. The easiest way to make power and is much less stressful on the engine than making much less HP with nitrous. Smooth power transitions(no sudden spikes in power), no bottles to refill, no stress on the front of your crank like a blower produces and no funky harmonics caused by a blower. Also a serious turbo car is very drivable. Put a carb enclosure on and run a HP Holley with a turbo and you'll be handing out the ass woopins

Kent

392W/C4 - Cast pistons, iron heads, stock suspension pig
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post #11 of 12 (permalink) Old 08-20-2003, 12:12 PM
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High altitude vs low altitude and affects on RPM range?

I went to the steel yard & got some aluminum to make the bonnet for the F-100. Gonna use a BT 2 four intake & a pair of T04's...




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post #12 of 12 (permalink) Old 08-20-2003, 01:08 PM Thread Starter
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High altitude vs low altitude and affects on RPM range?

Gonna make a BIIIIG 2-4 bonnet huh?

Kent

392W/C4 - Cast pistons, iron heads, stock suspension pig
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