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Old 05-21-2012, 04:28 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, 09:00 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, 08:19 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/

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Old 05-22-2012, 12:20 PM
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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, 03:03 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, 05:25 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, 05:45 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, 06:57 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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Old 05-22-2012, 07:25 PM
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Facinating read from everyone. Been 30 years or more since I drag raced. Just curious what does "back halfing" mean? sorry to break up the thread.
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Old 05-22-2012, 11:13 PM
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Very briefly it's installing a different rear end suspension (and often a different rear end and housing), and crossmembers, etc. to help handling and/or traction. It may be a 4-link, or ladder bar (shown), or some other set-up. Usually includes a roll bar or cage to tie the chassis together along w/connections between the front and rear on cars with subframes/unibodies.

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Old 05-23-2012, 07:49 AM
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Quote:
Originally Posted by cobalt327
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...
Yeah, money,
I just replaced the trans with one that has a TCI reverse manual VB and all good clutches and stuff, got it for a little more than I was planning on spending for a manual VB and a deep pan, and it has both. The TCI trans I was running before has had chronic leaks, and running an JW UltraBell, the pump bolts don't seem to want to stay tight. As I get time and money, I am going to go through that trans, replace the case if necessary, and build it for a brake. Finding sponsorship would speed up a lot of these plans, and I've got some folks interested in doing so, but "the time isn't quite right just yet".
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