Critique my planned combo

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wildbill

wildbill

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Meridian, ID
I am currently building a 75 duster for bracket racing at Firebird raceway in Idaho (2700 foot elevation) - will not be street legal. Gutted with a single racing seat. 10 point mild steel cage already installed. Approx 3000 pound race weight? Hoping to run at least well into the 11s with this combo. Let me know if this sounds realistic before I go any further - only the short block is built at this point.

8.75 rear with 4.56 gears and a spool
Full manual 727 with transbrake
~3500 stall
360 - 0.030 over
KB 107 pistons (approx 0.005 in the hole)
0.026 Mopar performance head gaskets
IMM RHS heads with 62cc chambers
About 11:1 CR
Hughes or Comp pro magnum rockers (any suggestions which would be better?)
Lunati Voodoo solid cam (PN 30200742)
Advertised Duration (Int/Exh): 280/288
Duration @ .050 (Int/Exh): 251/259
Gross Valve Lift (Int/Exh): .566"/.586"
LSA/ICL: 110/106
Valve Lash (Int/Exh): .016"/.016"
RPM Range: 2800-7000
Edelbrock Victor intake
Holley 750 DP carb
100 horsepower nitrous system (if needed)
 
i would look at a 904 instead of the 727...giving away at least .15 and 2 mph...and the 904 does not explode.

And since it is a race only....more converter...4500 rpm.....

what size rear tires?
 
I knew I would forget something! Planning on 28 X 11.5 inch tires if they will fit without wheel well mods. I do have a 904 core that came with the car so maybe I should go with that instead.
 
I bracket race..and all I (we) use is 904s with transbrakes....simple trans...

28 inch tall tires fit...11.5 dont know if sure...
 
Sounds like the 904 is a better choice. I have a manual/automatic 904 in my 73 scamp. Have at least 100 mid 12 passes on it without problems. Maybe I should use a 28 X 10 or 28 X 10.5 tire just to be safe.
 
maybe some other will check in later with other tire combos....i am sure someone knows..
 
I don't see that the sub frames are tied.....if they aren't , do that.
I'd consider bracing the housing and adding a billet cap on the driver's side too. Not a bunch more to do for an 8 3/4 , but it will help it last.
Get the suspension to work.....this will pay off in both e.t. and consistency.
Make sure the front is free to move and use what has worked for others as a guide.
I picked up a tenth in our last car by copying a few stock eliminator tricks.....it was a Ford , but the principals are the same.
Six cylinder coil springs , ditch the sway bar , good shocks and a travel limiter up front.
Good shocks , clamp the leaf segments in front of the axle and adjust the snubber on the slapper bars to 3/4 below the spring eye......CalTracs are the rage now , and they obviously work.
 
tubtar said:
I don't see that the sub frames are tied.....if they aren't , do that.
I'd consider bracing the housing and adding a billet cap on the driver's side too. Not a bunch more to do for an 8 3/4 , but it will help it last.
Get the suspension to work.....this will pay off in both e.t. and consistency.
Make sure the front is free to move and use what has worked for others as a guide.
I picked up a tenth in our last car by copying a few stock eliminator tricks.....it was a Ford , but the principals are the same.
Six cylinder coil springs , ditch the sway bar , good shocks and a travel limiter up front.
Good shocks , clamp the leaf segments in front of the axle and adjust the snubber on the slapper bars to 3/4 below the spring eye......CalTracs are the rage now , and they obviously work.
Click to expand...

transbrake, 8 3/4 rear ??
 
The car does have subframe connectors installed (I forgot to mention that). I am planning on using Mopar SS springs and a pinion snubber. I have already purchased adjustable drag shocks. There are no sway bars. I have rebuilt the front end with aftermarket adjustable upper control arms. Still have the slant 6 torsion bars.

Should the 8 3/4 be OK at this level or do I need to consider a Dana 60?
 
8 3/4 will be okay.
I have well over 200 pass's on a 8 1/4 ear with just c-clip eliminators.
 
Where did you find C clip eliminators for an 8 1/4? I looked everywhere and couldn't find them. I run an 8 1/4 in my Scamp and would love to add them just to be safe.
 
I would use the tallest tire that will fit under that car, maybe a 29 or 30inches and add more gear to make up for it. With a 10pt cage and frame connectors your car is going to be very stiff, making you rely on your suspension. If its in your budget forget about the super stock springs and do an adjustable 4-link or at the very least by a set calvert springs and bars. They do work. I would look into getting weight off the front of the car, fiberglass hood and bumper. That will help weight transfer especially on stock front susension.

Firebird is a great track... Racing in the spring and fall and into the evening hours the track does get cold making hooking up in the later rounds very difficult. Its frustrating to spin a way your win!!

Keep in mind to the corrected altitude is almost never at 2700ft, maybe during the halloween classic. During the summer it easily hits 5-6 thousand feet. You can expect to slow down during the summer...

Your ETs can swing 2-4 tenths during the day out there, Get a weather station. I have a spare if your interested. Once the sun drops behind the stands in the evening everything changes, the track temp and corrected altitude.

Spend some money on valvetrain, springs, locks and retainers. Isky Super 7 "7degree" are nice highend pieces that you can rely on.

Don't waist your money on a shelf converter. Get a dyno sheet, car weight and order a custom built unit. Theres can be an easy 1/2 second to a full second on the right converter and it will more consistent. They can build it to handle the transbrake, weight of your car, A1 in vancouver,wa is great and they know mopars. Look into a mechanical diode sprag.

I would also consider an electric water pump, electric fans and a nice alum. radiator. That will allow you to cool the car between rounds.

A vacuum pump is another way to pickup another easy 2 tenths!!

You didn't metion exhaust but an open X-pipe after your headers picked me up another 3/4 of tenth.
 
Thanks for responses. All very good info. I will need to look into a custom converter.
 
The pinion snubber makes a nice door stop.
I am also using SS springs , but if I had the ability to start over , I would definitely go with CalTracs.
I am considering ladder bars now , because I still have the back seat in mine and don't want to cut it up any more.
An adjustable 4 link is the cat's fanny , but at the h.p. and e.t. levels you are looking at , I don't see it as must have.
A diet is as close to free gains you will ever get , and since it is gutted I'd commence to losing window regulators , lightening doors etc.
Glass hood is always a nice touch.....bumpers and deck lid......pretty soon you are knocking on 2800 lbs.
The Dana - 8 3/4 debate is a lively one.
I personally would do a 9" before a Dana because I have a lot of experience with them and like the versatility of ratio swaps etc.
What will kill the 8 3/4 fastest is a hard leaving HEAVY car.
Over 3000 lbs. , this becomes more of a concern.
Sub 1.50 60' launches happen all the time with light cars and 8 3/4 rear ends......but they are usually well prepped.
 
I agree with ditching the pinion snubber...If the SS springs are working properly, that pinion snubber will be doing nothing...Also, as great as caltracs are, it seems many get the SS springs to work well, so if you already have them I would try them first.

As for the engine combo, sounds good to me (I am no expert), but I will say you might pick up if you switch to a bigger carburetor...If you have any buddies willing to let you try say a 950HP carb on that after you get the 750 figured out just to see if it picks up with some fiddling, then you can know for sure if you want to step up to the larger carburetor.

At 3000lbs, with the right converter, I can't see high 11's even being an issue....faster should be cake I would think...and yes, if the car isn't painted or you don't care, I would fibreglass the hell outta it if its a race car...Still wish I had done a glass trunk lid on mine before I got the car painted
 
I have already purchased the SS springs. It is currently in primer with bodywork done. I will have to think about some fiberglass. Hood and bumpers? My plan had been to stick with the steel hood and use only the actual chrome part of the bumpers. I was going to fabricate some much lighter weight brackets for the stock bumpers and ditch all the heavy stock stuff.
 
wildbill said:
I have already purchased the SS springs. It is currently in primer with bodywork done. I will have to think about some fiberglass. Hood and bumpers? My plan had been to stick with the steel hood and use only the actual chrome part of the bumpers. I was going to fabricate some much lighter weight brackets for the stock bumpers and ditch all the heavy stock stuff.
Click to expand...

You could definitely do the bumper bracket lightening...check out moparts.com race section, there is a weight loss thread going on there right now, and I think on page 4 or 5 there are some pics of some bumper brackets lightened to hell and back to give you an idea
 
Your piston to head is too tight. My machinst and friend builds badass World of Outlaw motors and him and I have had this conversation and there is no reason to run the piston any tighter than .040. He has hundreds of dyno hours logged and there is no power made when having the quench tighter than .040 with a steel rod.I would also run a cometic head gasket just because 10 head bolts suck and the cometic will give you the best seal without worring about them blowing out. At .031 piston to head it is very likely that the piston will hit the head.

Rearview.jpg
 
wheelsup73 said:
Your piston to head is too tight. My machinst and friend builds badass World of Outlaw motors and him and I have had this conversation and there is no reason to run the piston any tighter than .040. He has hundreds of dyno hours logged and there is no power made when having the quench tighter than .040 with a steel rod.I would also run a cometic head gasket just because 10 head bolts suck and the cometic will give you the best seal without worring about them blowing out. At .031 piston to head it is very likely that the piston will hit the head.

Rearview.jpg
Click to expand...

I didn't even notice that in the original combo, very good point...I have never run tighter then .039" myself, but have read of others who ran .030" and less, and they had marks from the valves contacting the pistons in certain instances....better to be safe then sorry
 
I didn't think about that! I will have to use thicker head gaskets and lose some compression.
 
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