Take a guess where the bottle neck is!

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Lars

Lars

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Took my 70 to the track last October. Best time was a 14.34 @ 94 mph with a 2.2ish 60 foot. I was driving on Arizonian 235/70/15 street tires (yeah, truck tires) at 35 psi. The thing that got me was the engine fell on its face at 5K. So I'm thinking the bottleneck might be the carb, but I don't know for sure. Engine is a .030 360 with a Barry Grant Road Demon 625 on a Edelbrock Torker II intake (that seeps coolant), stock valve J heads (springs are matched to the cam), Comp cam 268XE (iirc) .471 int .480 exh, 224 duration 106 center line installed @ 105 degrees, KB HP116 pistons 10:1 compression (est), stock oiling system, Carter mechanical pump, stock fuel lines. I have a 650 DP that I can rebuild with a 750 body, and a NIB Edelbrock Air-gap intake on the shelf. The cam is rated to 6K iirc, and I doubt I'm at the limits of the heads just yet. So that leaves me looking at the carb, I have the tune spot on according to the plugs, so I'm guessing its an airflow problem.

Thoughts?
 
Are you spinning? What RPM are you shifting at? That seems like it could run mid 13's............... Hows your tranny?
 
dodgetkboy78 said:
Are you spinning? What RPM are you shifting at? That seems like it could run mid 13's............... Hows your tranny?
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Trans is solid, has a 3K stall converter. It's real lazy with the 3.23's though. I was shifting right before 5K, if I tried to pull it past 5K my times would suffer pretty bad. Tires couldn't get traction all the way through 2nd gear.
 
Really, I think your cam and heads wont build power MUCH past 5K.... But the tire spin could definatly slow you down a sec..........
 
Fell on it's face means that it won't pull any rpms past 5000. RIGHT???
Like the engine looses power?
In your second post you make it sound like it's spinning at the top of second gear because of to much power.
You have lost me here.:scratch:
 
It runs hard and then hits a brick wall at 5K. It just occurred to me that it could be the ignition box also. I had a bad one that wouldn't pull past 4K, maybe I have the same thing here, just at 5K. Oh, and Comp rates the cam to 6K iirc, I'll look it up here in a second.
 
What kind of ignition do you have? Is it MOPAR? If so, the reluctor clearance can cause a brick wall too..............
 
Yeah, Mopar electronic ignition throughout, I can't find the cam, I'll have to look for the cam card this weekend to be sure. Going off of memory, and it's been over three years since I stabbed that cam in.
 
I reckon a bigger carby....750cfm & the air-gap intake.....need to check that ignition system...hows the ign curve???
35psi....a bit high....try 25psi.....give a better launch.
 
I don't think it's your carb per say. I have a little more in my engine and run a 650 speed demon and I don't run out of carb. Could your floats be set to low? What size of fuel line are you using? Could your exhaust be causing a bottleneck?

Jack
 
The BG carb when compared apples to apples CFM-wise to a Holley 4150 (the 650 DP you have) is about a 720cfm. So I don't think it's the carb. Assuming the heads were done properly and the geometry is good, the valve job was good, etc... I'd be looking at the ignition. The MP distributors can be problems but that's what you have. What is the timing curve set up like? I'd replace the control box with a Standard Ignition LX-101 box. The MP orange box takes away timing above 4K rpm and have been problematic in the past. Also check your connections and make sure with the ignition key in the run position you have at least 9 volts at the coil positive post.
 
Just a stab in the dark, But could it be the fuel pump floating at high RPM's? My buddy had that problem in his El Camino...... I had a carter Mech also and switched it out and it seems to run better at higher rpms now with the elec.
 
If it starts to run ***ROUGH*** at 5000 rpms look at your ignition.

If the power falls off at 5000*** BUT THE ENGINE STILL RUNS SMOOTH***look at the carb.

> MAKE SURE YOUR FUEL AND AIR FILTER ARE IN GOOD SHAPE.<
GOOD LUCK:burnout:
 
It just falls on its face at 5K, like there is nothing left, pulls real hard all the way up to it. Been a while since I ran it up to 5K though, the track isn't close and with the 3.23's I really have to stretch it out to get to 5K and I kinda don't want to risk it on the street. The more I think about it the more I think it is the ignition. It is an older MP electronic conversion kit I bought back in like 99, that has the orange box. The fuel lines are stock 5/16's line. Could be the fuel pump. I've been wanting to convert over to an electric pump, but I just haven't been able to get to it. Filters are good, I changed the fuel filter recently when I was chasing a problem on it, and the air filter looks good.
 
Get rid of the orange box, and verify the coil's getting battery voltage minus 2-3. I've fixed older conversions whose connections were just not really good any more, or whose ballast resitor was replaced with something from a parts store that was a higher resistance so the coil was getting 6-7 volts. I don't beleive it's fuel related.
 
I have a similar set-up with my 340, it runs out on top end also, but I currently have an Edelbrock 750 verses your 625 Barry Grant. I only bought my car this summer, so I have no idea on the times it would run.

You make no mention of your exhaust system, mine has stock manifolds (of unknown vintage) and a stock dual exhaust system other than Flowmaster mufflers.

I am switching to an Edbrock Performer PRM intake (the price was right otherwise I would have gone with the Air Gap). I have headers coming and plan on redoing the exhaust pipes also this winter.

And as the cam goes, mine is similar to yours...I am swapping in a Comp Cams "274" when I paint my engine bay.

I would beef up your fuel lines to 3/8" and double check your fuel pump is working properly.

And I would say you need more gear in the rear...I have a 3.91 in mine...that should wake things up a bit.

My 2 cents,
Paul
 
1972DusterPaul said:
I have a similar set-up with my 340, it runs out on top end also, but I currently have an Edelbrock 750 verses your 625 Barry Grant. I only bought my car this summer, so I have no idea on the times it would run.

You make no mention of your exhaust system, mine has stock manifolds (of unknown vintage) and a stock dual exhaust system other than Flowmaster mufflers.

I am switching to an Edbrock Performer PRM intake (the price was right otherwise I would have gone with the Air Gap). I have headers coming and plan on redoing the exhaust pipes also this winter.

And as the cam goes, mine is similar to yours...I am swapping in a Comp Cams "274" when I paint my engine bay.

I would beef up your fuel lines to 3/8" and double check your fuel pump is working properly.

And I would say you need more gear in the rear...I have a 3.91 in mine...that should wake things up a bit.

My 2 cents,
Paul
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I have long tubes on it, and a full 2.5" system with a pair of chambered mufflers. I had 4.10's in it when I first set it up and it was really alive even with the 28" tires I had on it. Since I went to the 3.23's it just lost all its guts. I'm working up a plan to wake it back up again. I want to ditch the cheap highway tires and put a pair of 26" drag radials in the back, I also want to pull the 727 and put my old 904 back in it, the 904 is lighter, fits better, and always shifted good. Just the front seal was bad on it, so it leaked from the front pump a lot (it could be the pump leaking for all I know, I don't know much about transmissions). I'd also like to pull the SG/3.23's and put my 4.10's with the Detroit locker back in it. Then install that Airgap I have to finish it off. I think, if the engine can work with that converter in the 904 (its an old factory 360 converter) and I can get traction I wager I can pick up a second or better in the 1/4.
 
moper said:
Get rid of the orange box, and verify the coil's getting battery voltage minus 2-3. I've fixed older conversions whose connections were just not really good any more, or whose ballast resitor was replaced with something from a parts store that was a higher resistance so the coil was getting 6-7 volts. I don't beleive it's fuel related.
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I'll check it again, but iirc it was within that range the last time I looked at it. The car seems runs real clean, it sure could be that box letting me down. I should pull the plugs also. It doesn't idle as nice as it used to, but then again, it is hard to get a consistent idle setting with the Lokar throttle/kickdown setup I have on it (I prefer factory stuff). Putting the factory linkage back on it is also part of my plan.
 
what about valve springs?

adjustable rockers or non adjustable rockers?

do you know how much preload you have on the hydraulic lifters?
 
70aarcuda said:
what about valve springs?

adjustable rockers or non adjustable rockers?

do you know how much preload you have on the hydraulic lifters?
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Springs are matched to the cam, rockers are factory stock. I have no idea about the pre-load.
 
how many miles on the springs...and where they set up correctly as far as seat pressure and height?

just thinks to look at.........
 
70aarcuda said:
how many miles on the springs...and where they set up correctly as far as seat pressure and height?

just thinks to look at.........
Click to expand...

They were originally setup by a good machinist years ago, I can't remember the details though. They have about 20K highway miles on them.
 
Yeah, I had valve float make a car fall flat on it's face. Stiffer woke it up.
If you are sure you still have fuel pressure, look into that. Back in 1970, I had a Duster 318, 3 sp manual, open 3.23, f70x 14 tires. Ran 16.80. Slapper bars to even traction, 16.60. Holley 500 cfm 2 bbl, 18.5., but started falling at rpms. Installed stiffer than factory springs, as I could feel, and see tach not going up. valve float, I thought.
After that, 16.20's.
 
green1 said:
Yeah, I had valve float make a car fall flat on it's face. Stiffer woke it up.
If you are sure you still have fuel pressure, look into that. Back in 1970, I had a Duster 318, 3 sp manual, open 3.23, f70x 14 tires. Ran 16.80. Slapper bars to even traction, 16.60. Holley 500 cfm 2 bbl, 18.5., but started falling at rpms. Installed stiffer than factory springs, as I could feel, and see tach not going up. valve float, I thought.
After that, 16.20's.
Click to expand...

Did it make any abnormal sounds? I don't think I've ever experienced valve float, so I'm not really sure what to look for.
 
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