Another slow 340

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Duster346

Duster346

Chris Andrews
Joined
Nov 13, 2004
Messages
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Location
Castle Rock, CO
Hello friends! Some may have read about the Leadfoot Rally Duster build here.

We put a 340 into a '73 Duster, and it's a pooch. Engine was built 10 years ago, but not wanting to put another motor in the machine shop at the time, we decided to use the 340 for the Leadfoot Rally. When we drag raced the car for the compeitition, it only went a 15.08 at 91 mph best (4800 feet). It did go 130mph on the front strait of the road course.

I'm looking to get the car into the high 13's to race in the Fall Series here in Denver (plan to drive it to the track). I have SS springs, drag race torsion bars (to replace the 383 bars), and either 3.91 or 4.11 gears (to replace the 3.23's). Ordered a 10 inch MP 2800-3000 converter to replace the stock one. Got a 750 HP main body to replace the 650 dbl. pumper.

I fear the MP 509/292 cam (yeah I know, but it was built 10 years ago .. haha) and probably the intake might be costing power. But would like your opinions--comp cam & air-gap?? Here's the combo:

'71 340 .040 over 346cid
KB hyper pistons aprox. 10.25:1 compression
360 J heads 2.02/1.60, bowl blended & port matched (no flow #'s)
M1 single plane intake--too much for this little motor I'm thinking
Hooker super comp headers (1 5/8"), dynomax bullets with turndowns
Mechanical 120gph pump
MP dizzy, msd coil and wires, orange box (have MSD 6al on hand here).
Race built 904 trans, reverse manual valve body (about the only thing that works good on the car .. haha)
I figure the thing can't weigh more than 3000lbs.

I don't currently have a tach in the car, but at about 80-90mph it'll misfire pretty bad. Thing makes alot of noise, which is cool and all, but it's a dog. I'm used to ten second 440's ... 8)

TIA for any advice!

lfr_duster_028.jpg
 
So are you saying you run a 15.08 with the above combo?

You are barley running faster than a low compression, small valve, stock 73 340.
 
Yes sir!

The 15.08 was with no track prep, spinning the street tires (275/40/17) for 80 feet, and at 4800 feet elevation--about 6000 ft density altitude that day.

Up here we lose .8-1 second of ET opposed to the folks that race at sea level. Even the birds walk, up here. :-D

I'm also going to put a 28 inch tall ET street on it for some hook. I'd be really embarassed if this thing can't get into the high 13's ... (low 13/high 12 at sea level).

My old b'cuda (440) went low 10's at 130 with iron heads ...
 
That thing should trap well over 100 mph, I'd start with compression/leakdown tests, if it's popping you might have 1 or 2 bad/sticking valves,broken/misadjusted rocker arm, bad lifter, bent pushrod? an engine scanner would help tell you if the ignition is doing it's job too. The 3.23 gears aren't helping much either. Good luck!
 
With a sticky tire, that combo should work. My old 360 combo (very similar) had the MP 509 cam and 4:10 gear...it ran mid 13's at Bandimere. Good luck with you combo.
 
Chris,

I'm running 10.2:1 with a Lunati 60401 cam (213 @ .050) cam here and have no problems with detonation in a 5600 lb full time 4WD truck w 3.55 gears and 33x12.5 tires. There is no air here, lol! With that big of a cam, you need way more compression and a more agressive profile cam. We also need to check out your advance curve.

Please bud, let me help. I'd be happy to meet you at your shop and let you drive my truck. Let's go for a blast. Heck, I want you check out the tranny perfomance anyway. It's awesome thanks to your advice!

Most people don't understand that we have no air here, it's natures "anti-supercharger" :)
 
flyfish said:
With a sticky tire, that combo should work. My old 360 combo (very similar) had the MP 509 cam and 4:10 gear...it ran mid 13's at Bandimere. Good luck with you combo.
Click to expand...

Hey fly, what mph were you running at those times?
 
My 340 Dart with a 214/224 cam, LD340, 750 vac sec, MSD, headers and 3.91's ran over 100 mph in Vegas.

IMO, you'll need more converter than 3000 with that cam/intake combo.
 
Yep, you really need a better converter. I don't think the stock converter stalls at over 1500 rpm. Gears will help too.

13.8 @ 103

Stock heads
Stock manifold
Stock Thermoquad
.508 cam
Headers
A/C
P2020797.jpg
 
ramcharger said:
Hey fly, what mph were you running at those times?
Click to expand...

Oh...it’s been a while, and 99% of the time I ran the car on the bottle at Bandimere. If I remember correctly it was running about 13.8-13.5 @ 103-105 naturally aspirated...depending on how bad the air was that day. That was why I ran the bottle all the time...it made the car very consistent 11.1's @ 122 mph on a 180 shot no matter how bad the air got. It’s nice to bring your own atmosphere when you race in Colorado:toothy10:.
 
Get 4.10+ gears to start, bump the intial timing up as high as it'll start with and limit the total to around 30*-34* all in at 1800-2200rpm.
Then get a 2800-3000 stall converter.

Just a start.

I don't like that cam for what you are doing.
 
flyfish said:
It’s nice to bring your own atmosphere when you race in Colorado:toothy10:.
Click to expand...

It's dang near mandatory, lol!:read2: Thanks for the info on your times. :)

Chris,
Have you done a cranking compression check yet?

Wild&crazy,
I agree, I don't like that cam for this particular purpose either.
 
get rid of that orange box and go with the crome one i think youl get rid of the mis fire in the higher rpm range.
 
Jeff, I'll let you know but I don't think I'll be able to make it up there Friday--we'll see.

Joe, flyfish, and all, thanks a bunch for your advice, ideas, and opinions.

The first fall race is a week from today (Sept. 13). I ordered a 3800-4000 9.5" converter from Lenny @ Ultimate last Friday.

My plan is to install the converter, MSD 6al, and probably a 4.11 or 4.30 gear (if I have time). Also going to bolt on the ET Streets.

We'll see what she does, and I'll be sure to post results in this thread. I think we'll have some time (couple weeks) until the second race, so I can upgrade during that time also.

Thanks again,

Chris
 
I think the air, and the gears are your main killers there.... that and spinning the tires lol.

Already sounds like you got a good plan worked out, I think you'll do fine.

Just for reference, almost an identical combo (Duster, 340, 10.25:1, M1 intake, 509 cams, J 2.02 heads) ran 13.4, with a 3500 stall converter.... but that was at sea level
 
not bashing the car or anything like that, I'm just not that good at this but I would have thought at sea level with that setup it would be closer to the 12's. Maybe someone should school me. LOL
 
68fastback said:
not bashing the car or anything like that, I'm just not that good at this but I would have thought at sea level with that setup it would be closer to the 12's. Maybe someone should school me. LOL
Click to expand...

You're right. At the time we didn't know how long the motor was together, or been run etc.... It eventually spun a rod bearing. We replaced it with a 380hp crate and it ran 12.8's with everything else the same. And I think the cars are closer to 3400 with driver etc, but I could be wrong.
 
I like the sound of that, im putting together a 360 and aiming for the 12's. It made me nervous to here the other numbers. But like I said, Im new to the putting together a track engine. Thank you.
 
Duster346, Any Updates???
 
I'm running pretty much the same combo with a 360. Never ran it in the 1/4 but it did run 7.90's in the 1/8 which is a low 12 sec 1/4. I'm running the mopar 292-509 cam. About 9.5 to 1 compression. Weiand Stealth intake, with a 750 holley. I know that timing will really kill a motor, when I started racing it, it had a 850 demon on it and I was running about 41' timing, and it was running 8.30's when I put the smaller carb on it and played around with the timing it really picked up, I'm running about 35' timing now.
 
It's been since the early 70's but in Denver i always ran a taller gear in the Dana and dropped 4 hole sizes in the carb jets. We also dropped the front spring perch down two inches. Our standard set up for mile high air. AHRA GT-1 Dodge Demon

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Timing is everything. Check to make sure your timing isn't jumping around. I had trouble with the MP dist. Switched to the MSD PRO Billet SOOOOO much better.

What plugs are you running? and what do they look like
How old is the fuel filter?
 
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