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Old 05-21-2012, 03:28 PM
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Vega Bracket car: Disappointing ETs...down on power from where it should be...

355, .275 dome hypers, Eagle 4340 crank and 5.7 h-beams, Crower 00426 solid roller, (250/252@.050", .570/.584, 112 LSA), Pro Topline 220 cc heads (67 cc chambers, similar to the current RHS 220 cc Pro Actions), Bowtie Vic Jr. intake, 750 DP (currently on E85, but had the same characteristics on 60/40 Pump gas/Terragon 110). The car weighs 2450, has a 9", 4.30 gears, 29.5 x 10.5Ws on 12" Weld Pro Stars, TH350, JW 5000 stall converter. Best ET to date with the current combo is 6.95 at 97~98 mph, finally got it down to a consistent 1.5 60', but I figured this combo should be in the 1.4xs - 6.50s range. I know the heads and cam aren't great for this motor, needs more cam and less head, but is that really killing the power that badly? I can only foot brake to about 3200 on the line, (S10 brakes up front, Ford Explorer brakes in the rear, stock master) stops GREAT though. Any ideas for me??? I'd like to find somebody to swap me some ***************, but none have popped up as yet.....

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Old 05-21-2012, 08:00 PM
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tire size

You need low gears with a tall wide tire. If the car is not back halved. You are probably spinning your tires and that is the cause of the poor 60' time.

Try lowering your tire pressure to 7 lbs. it will give you a larger foot print. If 60' goes up you found your culprit. there are several things you can do to help 60 foot without back halfing car.
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Old 05-22-2012, 07:19 AM
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It is 4 linked with coil-overs, as I said it weighs 2450 ready to race,

It does spin a tiny bit, but not much. I hit it with about a 60 shot of juice and it went 6.57 @107, 1.44 60', yanking the front tires for at least 20'. I'm fairly certain it's a mismatched combo problem, definitely not a chassis problem.

There are some videos of the car here: http://www.youtube.com/user/MrRickracer?feature=mhee before, and after the back half.

Lots of build pics and some video here too as well: http://s68.photobucket.com/albums/i4...half%20Begins/

Last edited by Rickracer; 05-22-2012 at 07:30 AM.
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Old 05-22-2012, 08:58 AM
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If you always run 1/8th mile you could use a lot more gear.

Foot brake launch:
When you stage and launch the car try not loading the engine against
the converter. launch from as low a stage rpm as possible
(locked timing) say 1200 rpm.

With more gear you could use more cam duration. ( horsepower)
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Old 05-22-2012, 11:20 AM
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What rpm do you shift at?
What converter is in it?

If its 2450 lbs it's not making a whole lot of power. Maybe 350-375 at the wheels. Something isn't right for sure.

How is the tune on it?
How do the plugs look?
What heat range for the plugs?
Tighten up the lash a little bit, and if it picks up power you could have went a little hotter with the cam.
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Old 05-22-2012, 12:30 PM
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From my calcs you don;t have near enough gear in the car even for the 1/4 mile.
You are not reving it near high enough.

Foot brake stall means nothing expecially on a light car with marginal brake power.

Launch the car from near idle stage and watch the tach flash on launch.
This is the real converter stall.
The converter will work much better this way. and even better with more gear in the car.
get some 4.88's

Last edited by F-BIRD'88; 05-22-2012 at 12:35 PM.
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Old 05-22-2012, 02:03 PM
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Quote:
Originally Posted by joelster
What rpm do you shift at?
What converter is in it?

If its 2450 lbs it's not making a whole lot of power. Maybe 350-375 at the wheels. Something isn't right for sure.

How is the tune on it?
How do the plugs look?
What heat range for the plugs?
Tighten up the lash a little bit, and if it picks up power you could have went a little hotter with the cam.
I have shifted everywhere from 7200 to 6000, it seems to run about the same ET whether I shift at 6000 or 7000 so I shift at 6000. I had a borrowed TCI 5200-6000 8", now I've got a JW in there that is about the same. The tune is pretty close, it MPHs best @42 on E85, drops a MPH or more from that @40 or 44. The tune isn't off much if at all, I've jetted where it is now by MPH. The plugs tell me it could use a little more timing, but the MPH falls off. The lash is .004" tighter than Crower recommends already, I've run it looser (spec), and tighter (.008"), not much difference. .600 is about max lift I can run with the heads, valves and springs the way they are now, I could cut the spring seats a bit deeper, but I doubt it's worth the trouble with these heads. More duration would make more power, but I don't think it would help my 60', and I feel like that's what's hurting my ETs the worst right now.

Quote:
Originally Posted by F-BIRD'88
From my calcs you don;t have near enough gear in the car even for the 1/4 mile.
You are not reving it near high enough.

Foot brake stall means nothing expecially on a light car with marginal brake power.

Launch the car from near idle stage and watch the tach flash on launch.
This is the real converter stall.
The converter will work much better this way. and even better with more gear in the car.
get some 4.88's
It's 60's the best stalling it as high as I can on the line. I MUCH prefer to do it the way you recommend, but between the lazy bottom end and the gear, it just won't 60' worth crap like that. I think a 4.88 gear, maybe even more, would help quite a bit. I was running a 4.88 with a 28" tire before the back half, and it went a best of 6.90 with fairly consistent 7.0xs, and high 1.5 to mid 1.6 60's, shifting at about 6800 and going through about 7000.
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Old 05-22-2012, 04:13 PM
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Don;t get all wrapped up with 60ft times.

The track is 660ft long.

You are getting paid for ET and reaction time and getting there before the other guy does , not 60ft times.

You do not need more valve lift than .600". But more duration and a LSA change will help. Especially with more gear and engine rpm.

Loading up on the converter when staging actually scrubbs off launch force.
ya it tends to make the car more consistant (especially if the track traction is marginal) , but indicates the traction-chassis setup needs work. 4 link bars, tire pressure.

More gear ratio often makes the chassis and tires "load" much better at the line.
Plants the tires much better and keeps them planted. Now the tires can take a harder launch. (launch at or near idle)

You will be using more of the available engine power band over the whole length of the track. (A lower ET) And the converter will function a lot better with more gear.

What is the compression ratio of your motor?

how is the cam you got, installed? Cam phasing..... intake C/L or intake valve closing point @ .050"

Did you try moving it around a bit to see how the engine likes it.
A 112 LSA cam is a bit unusual for this combo. N/A

4.30's and a 112LSA cam is more optimized to a nitrous combo than N/A

I;d go with 106LSA 100 to 104 in C/L
if the cr is 11:1 or more I"D get a new cam with 260-265@.050" in 265 275ex on a 106 or 108LSA, in at 100 to 104 but with the same valve lift. or close to it. The engine will respond much more to a duration change than a lift change.

And get some 4.88's reguardless.

Nitrous and naturely aspired require two different gear ratios.
Having two sets of slicks (tall and short) is the easy way.
a 2" difference in tire height actual(Measured) is about right.

Last edited by F-BIRD'88; 05-22-2012 at 04:25 PM.
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Old 05-22-2012, 04:25 PM
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It's around 11:1, I got this motor pretty much as it is and just freshened it up, (had a wiped cam when I got it), so I just went through and freshened it up, switched to a roller cam, and upgraded the heads to match the new roller valvetrain. I didn't have the money to change much other than that, so I didn't really check piston volumes, compression/deck height and all that, kinda wish I had now. I know more compression would help, lower LCA and more duration would help as well. I think I can safely get these chambers down from 67 ccs to about 62 by flat milling, and I'm definitely planning on a gear, I was leaning toward a 4.56, but I think I'll go along with your 4.88 suggestion, I know it worked good enough before with less tire. (9x28 Hoosiers) I could even make it through the 1/4 mile if I took the 7200 rev chip out of the 6AL, it would go through about 7300~7400.

Wow, you were editing at the same time I was posting. The cam is installed straight up.
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Old 05-22-2012, 04:29 PM
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Quote:
Originally Posted by Rickracer
It's around 11:1, I got this motor pretty much as it is and just freshened it up, (wiped a cam), so I just went through and freshened it up, switched to a roller cam, and upgraded the heads to match the new roller valvetrain. I didn't have the money to change much other than that, so I didn't really check piston volumes, compression/deck height and all that, kinda wish I had now. I know more compression would help, lower LCA and more duration would help as well. I think I can safely get these chambers down from 67 ccs to about 62 by flat milling, and I'm definitely planning on a gear, I was leaning toward a 4.56, but I think I'll go along with your 4.88 suggestion, I know it worked good enough before with less tire. (9x28 Hoosiers) I could even make it through the 1/4 mile if I took the 7200 rev chip out of the 6AL, it would go through about 7300~7400.

Yup,

if you were to measure actual PTV clearance now and in/ex valve open @TDC you could calc-figure out how much you can mill the heads and increase the cam duration and overlap for the new cam.
and not smack the pistons.

On a SBC all the .600" to .630" lift roller cams tend to be very easy to live with.
There are tons of durations available in these .400" or .420" roller lobes to choose from.

Tuo you should be buzzing it past 7000rpm in the traps for max performance either way. ( more gear)

Last edited by F-BIRD'88; 05-22-2012 at 04:36 PM.
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Old 05-22-2012, 04:45 PM
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The reason I didn't go higher with the compression before was that I was running pump gas with tight valve lash. My machinist convinced me to go back to Crower's spec, and the cranking compression jumped from about 200 to 235, and I didn't want to risk hurting it so I started running 60/40 pump93/110 Terragon. Now I'm on the corn, so more compression is a GOOD thing,
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Old 05-22-2012, 04:50 PM
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If the cam is now "straight up" 112 in C/L 112 LSA and you want to play with it
move it to a 102 intake C/L and then work back 2deg at a time.


When advancing the cam the intake valve gets closer to the piston @TDC
(to check for PTV clearance move the cam to a 100 in C/L and 0lash the valves
rotate the crank by hand 2 turns, if it turns, its good. then move it to 102 and start testing)
the sweet spot should be in the 102 to 109 in C/L zone.

The engine will show you what is best (ET slip)
I think that will help. I know 4.88's will help.

The carb may benefit from slight High speed air bleed +/- adjustment too.
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Old 05-22-2012, 04:53 PM
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Quote:
Originally Posted by Rickracer
The reason I didn't go higher with the compression before was that I was running pump gas with tight valve lash. My machinist convinced me to go back to Crower's spec, and the cranking compression jumped from about 200 to 235, and I didn't want to risk hurting it so I started running 60/40 pump93/110 Terragon. Now I'm on the corn, so more compression is a GOOD thing,
ya pump gas has its limits for sure.
It can get real expensive, real fast, exploring the limits of the laws of physics.
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Old 05-22-2012, 04:58 PM
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Wouldn't be the first time back halfing the car actually slowed it down.
I'm not that suprised.
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Old 05-22-2012, 05:57 PM
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Any reason you're not using a transbrake? If your not traction limited it'll help the 60' and that helps the ET more than just the reduction in 60' time...
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