FunTA
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Posts: 9
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Post by FunTA on Sept 17, 2006 17:38:45 GMT -5
I would like some guidance concerning my set-up. I have a 3300lb P/U with a 421SBC. The motor has CFM ported AFR210's and a hydraulic roller cam (242/252 .525/.540 lift LSA112) and NX plate. I just jetted the plate with a 150shot and took my first passes. The motor really seems to like the nitrous. I ran 10.23/132+ 1st pass and followed it with 2 more 10.23-10.25. The problem is I'm hitting the rev. limiter at 7500rpm before I clear the traps.
I was wondering if I need to change my converter or just go to a steeper gear. I'm running a Th350 w/3500 converter, 4.30 gears and a 31"tall tire. I calculate that at 7500RPM I should be running 160mph. But I'm only going 132-133. This is a difference of ~18%. Does this mean my converter has excessive slippage?
Or should I just go to 4.11 gears? My 60' is 1.43 so I hate to hurt it with a steeper gear but if that's what it takes I'll give it a try.
My Hyd. roller just isn't made for that RPM. I need help but want to make the right change. Would someone make a suggestion? Converter or gears.
BTW thanks to Mike I picked up .3 on motor with the port job.
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Post by bigjimzlll on Sept 17, 2006 18:01:03 GMT -5
What are you going on motor alone? Is this going to be a dedicated N20 ride? As you know N20 likes to have a load. What's the converter stalling at now? My 406 67 truck runs 10.90's 1.51 60' on motor alone with a 8" converter with 4.86's and a 32" tire. I am going to spray it next month, but I'm sure I will blow through the converter.
I assume with the 112 LSA it is a dedicated N20 ride, In that case a 9" converter and 4.10s would be the ticket.
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FunTA
New Member
Posts: 9
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Post by FunTA on Sept 17, 2006 18:37:14 GMT -5
Runs 11.20's on the motor passes but that's with the timing down at 30deg. I don't make a lot of motor passes. Just enough to make sure the motors good before spraying it.
I'm running a Trans.Spec. 10" converter. The converter supposed to stall 3500 but on spray I really don't know. I guess I need more info. I'm just wondering if the converter is just too loose?
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Post by us7race on Sept 17, 2006 19:30:49 GMT -5
Do you have a trans brake? If so you can pull the RPM chip out engage the Transbrake and mash the throttle to the floor to see the true stall of the converter with your motor, I don't think it is recommended to spray it while doing this though.. Sounds like alot of slippage to me mine slips about 12% but it is a 1/8th mile converter..so it's a bit looser. If you have a new converter built in the future check out... www.edgeracingconverters.comThat is where I had mine built and it has been flawless for 2 years with and without N2O . Most or all of their's are 9.5". |
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FunTA
New Member
Posts: 9
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Post by FunTA on Sept 17, 2006 19:45:54 GMT -5
Don't have a trans brake. Foot brake only. I've heard guys recommend Coan and Yank. I'll give the guys at Edge Racing a call.
Thanks.
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Post by Mike Stark on Sept 19, 2006 7:47:51 GMT -5
You'll never see 160 MPH at that RPM. The math doesn't account for weight, drag, etc. The only way to measure converter slip is to monitor driveshaft RPM in relation to engine speed. I would drop to a 4.10. This will help to make the converter a bit more efficient as well. Should put you down around 7200-7300 RPM.
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FunTA
New Member
Posts: 9
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Post by FunTA on Sept 19, 2006 11:28:37 GMT -5
Yeah Mike. I know 160 is unrealistic. I'm just saying it appears Iv'e got excessive slippage and I may be driving through the converter. I spoke to several converter manufacturers (Trans spec., Yank, Precision Ind, and Edge racing). they say the converter I've got isn't a good match to my set-up.
All of them suggested the same basic change. 9.5" Converter with ~4000RPM stall.
Also, 4.11 gears are on order.
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Post by 67RS502 on Sept 19, 2006 16:24:58 GMT -5
What do you shift it at? is it still makin power at 7500?
What mph at the 1/8?
You may wann a stick a 390gear in it if you plan on spraying it.
What kinda springs to get the hyd. roller to go 7500? Comp cam or Lunati?
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FunTA
New Member
Posts: 9
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Post by FunTA on Sept 19, 2006 23:01:04 GMT -5
I don't know why or how the little motor makes that much RPM. But it sure pulls hard to 7000. I don't know the manufacturer on the springs. I think they have a seat pressure of ~135lbs. Mike setup the heads for me when I had them ported.
The cam and lifters are Lunati. 300/310 adv., 242/252 @ .50, 112 LSA. Lift is only .525/540". I have a set of 1.6 rockers to try when I get this RPM thing under control. The cam is real tame and the truck drives around with no problem. BTW since I couldn't find off the shelf headers for a Mazda PU, I mod. a set of 1 5/8" primary Camaro headers. They should be way to small for this set-up but what can I say.
My shift light is set at 6400 but probably the actual shift pt. is a little higher.
I'm taking you guy's suggestions. I'm trying a set of 4.11 gears and a new converter to try and lower the RPM some.
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Post by 67RS502 on Sept 21, 2006 11:55:49 GMT -5
Mazda p/u, I would have thought it would be about 3000lbs, like my Luv truck. Them 1 5/8" are better then what I've got - 1 5/8" block huggers (smaller then the exh. ports), when I uncapped it, it didnt pick up jack... gonna have some 1 3/4" full lenght made.
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FunTA
New Member
Posts: 9
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Post by FunTA on Sept 21, 2006 16:42:05 GMT -5
The little P/U weighs alot more than perople think. I just put it on the scales last week and it weighs 3100+20lbs for me.
I hope to have a set of headers fab'd up this winter. The front suspension is a torsion bar type and it makes fitting headers a b****. Haven't decided on size yet. Maybe 1 7/8 or maybe a stepped headers to help with fitment. Any suggestions are welcome.
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