Need tuning help on 340

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midnight340 said:
I really appreciate all the response. And welcome any thoughts. I'm likely not too far off.

Tomorrow will check fuel pressure if I have to tape a gauge to the windshield.
(I am running 89 or 91 octane with no ethanol, so the pump says)

The only disadvantage to cold plugs is that I risk fouling, right? (But sure don't see any hint of that with the MSD box, even when I was at a much richer mix.)
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Call me if u`d like and maybe I can help ya out..............760-900-3895........Taking over the world one carb at a time...........ThumperCarbs............
 
AJ/FormS said:
It seems to me, if you can get the AFRs down at 12, your fuel system is keeping up.
The 160PSI is indicating a good Dcr, which the 218*cam is trying to achieve.
At 3450, 96 mph is pretty good for an LC 340 with a tiny 218 cam.
If your power-timing is down at 32* or less, to avoid detonation, that is hurting your mph.
What your tach at,crossing the line, and in what gear are you. That makes quite a difference.With a 218 cam you probably want to be trapping at 5400?Or less even. If you are winding it out too far, that could really be hurting you too..

But really , you need to figure out why 32* is detonating.
Are you running oxiginated gas?And what grade?

Heat is the number 1 cause of detonation.Or rather too much of it, in the chamber. Low Compression, open chamber heads, also have trouble with pressure spiking too early.

Ok something is not right here;
I plugged some numbers into the Wallace calculator,and I can't make the numbers come out with your inputs. This is what you supplied; 160psi, 218 cam,8.5 Scr.. No matter how I fudge the numbers, I can't make the 160 psi.
Can you be a little more specific as to the cam? What I need is the ICA; Intake Closing Angle, or an advertised intake duration plus I need the LDA;Lobe Displacement Angle.Then are you absolutely sure the cylinder pressure is 160psi, and that the 8.5Scr is accurate?
Sorry, I could not find the "BracketMaster on the Lunati Website.

I did manage to make it work with 10.5 SCr, a 66*ICA, and got about 165psi. This would be a 284/108 cam in at 104*. But the .050 on a 284 cam is more like 236 to 240;no where near 218*.In any case, this yields a Dcr of 8.23 which as you have discovered is too much for pump gas, and iron heads.
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I REALLY appreciate this post. And I'm sorry, I kinda missed it yesterday.

-I do still have the cam card if I can locate it. Also some of what you're saying is what has baffled me all along. I did cc the heads. But don't know exactly where the TRW 8.5 pistons ended up.
-(I couldn't find another timing light yesterday to double check mine, but will do so.)
-I'm pretty sure of the 160# as I wrote it all down carefully. I had one cylinder closer to 155 when I tested it but the rest were very equal.
-The detonation was not happening at 32*, but at 36-37*, then chasing numbers I leaned it more and saw it show up at around 34-35*

MPH at end of quarter: I got out my old time slips. It's usually pretty consistent at 95 mph or so, but on two high 13 runs the MPH #'s are 97.7 and 98.3. So I'm getting something out of the motor, but don't know how to figure DCR etc. Will look for more info.

As for shift points… I know things aren't ideal, but running 3.89 (Ford 9") and a 275/60 tire i usually shift at about 6200-6500, pushing it closer to 7,000 into drive as I'm almost to the finish when I have to get into drive. And yes, an earlier shift might be good. I've been running a mini-spool for several years, but am going to change that and am trying to figure out what I need to do gear-wise.

Before anything else I am re-jetting today. Haven't decided whether to take both the primary AND secondary jets up a step, or try going two steps on the secondaries. And I dropped the initial to 15* last night (which should land me around 30-31*…will check this)

My fastest times were with .116 jets in primaries, and .110's in secondaries. Trying to lean down the very, very rich idle and cruise I had, I've gotten too lean. Now need to fatten it up, I'm thinking I will go with reverse locations, .110's in front, and .116's where it really seems to need more fuel.

Back to locating the cam card for you...
 
AJ/FormS:
As noted in my last post, I found time slips at 97.7 and 98.3 mph. Also,
Here's a link to my cam card from Lunati:
http://www.lunatipower.com/CamSpecCard.aspx?partNumber=00042

My notes say that I did install at their suggested 5* advanced.
Also my heads cc'd at about 70.
The pistons are the L2385 at .030 over.
Pretty sure the head gaskets are Felpro .040"
The machine shop notes say the decks were squared, and the heads resurfaced.

Can you tell me approximately what compression/DCR all this might suggest?
 
where are the piston in relationship to the deck....down how far down>?

need that to cal compression...
 
70aarcuda said:
where are the piston in relationship to the deck....down how far down>?

need that to cal compression...
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That's the one number I'm missing without pulling a head. Kicked myself forever over not checking that when I screwed the motor together!!! Or if I did I haven't found the number. I have about 55,000 miles on it since. Just put it on the strip a few times the last 4-5 years.

Local strip (hour and 1/2 away) opens May 7, so may get over there for some testing.
 
SLOPAR72 said:
This thing is lean..... My last ownership of an A Body in the late 80's had a nice small block in it and I really struggled with making decent time slips.... The fuel pressure gauge on the Cowl was a turning point for me when I installed it. Details I don't remember so much but not too long after that I had 11 second time slips.... It is worth having one even if only temporary....

JW
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Mandatory for properly tuning any carb............too much pressure or too little can cause troubles...............Taking over the world one carb at a time.........ThumperCarbs.......
 
comp. distance on the L2385F is equal to the stock low comp. 340 at 1.740", and deck being cut pistons are down about .080", and pistons are forged with 2 valve reliefs at 3cc total. so comp ratio is about 8.1:1
 
Dropped timing back 2 more degrees from last time. Increased the jetting in primaries AND secondaries. To .110 and .113, installed a fresh NGK BPR8ES and made a WOT run through the gears, shut it down, pulled the plug.

(Had a fuel pressure gauge taped to the windshield, and it held 6# until the very end and started to drop just a bit.)

My timing light showed 15* initial, and 30* total. Ran strong and felt good. But the plug was completely clean at the base of the porcelain (magnified with lighted otoscope) and the strap burned almost the the plug body. No darkening or color showing anywhere on the porcelain.

I will re-check my balancer against TDC (again) tomorrow, and will get another timing light. This is driving me crazy, trying to understand all this.

I can try upping the jets to .116 in the secondaries (12% fat according to Edelbrock) and my A/F numbers are now in the 12's mostly in normal driving. Some 13.5 mid-range, with the .110 primary jets. (4% lean according to Edelbrock) My idle is in the 12's with the idle screws only a bit under 3/4 out.

Here are photos of the plug from the run today: (NGK BPR8ES)
 

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have you run racing gas in it as a test for pinging, it sound like low octane fuel, my blazer must run 91, in the spring because of the winter blends with warm days. normal fuel is 87 rest of year and it shows up on the top end of the rpm band.
 
midnight340 said:
I run 91 octane (no ethanol.)
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Put some fuel in it until you get some color up the porcelain. I hate the coating on those NGK's because it is different on the race plugs. The race plug is easier to read. I'd forget the ground wire until you get some fuel into. Stop worrying about what number of jet and needle you are running. It is application specific.
 
yellow rose said:
Put some fuel in it until you get some color up the porcelain. I hate the coating on those NGK's because it is different on the race plugs. The race plug is easier to read. I'd forget the ground wire until you get some fuel into. Stop worrying about what number of jet and needle you are running. It is application specific.
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Thanks. I'll do that.
At one point I was jetted just a bit richer (one step front and back) and had a bad bog off the line, and I thought it was from being too rich. I leaned it back to about where it is now and it ran the best times.
But I've changed my fuel system, distributor, etc. since then.
 
Get the idle set up properly and work UP from that foundation.
 
crackedback said:
Get the idle set up properly and work UP from that foundation.
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I have some frustration there as well.

It's idling now with A/F in the 12's now, if I lean it down with jetting so it will idle in the 13-14 range then I can't get enough fuel for "power" mode. I already am running a 75/37 rod which is the thinnest "power" rod Edelbrock makes, and the largest idle/cruise rod that they make.

It has the "plain" 8" springs (strongest in Edelbrock's spring kit) and it is in the top hole on the accelerator pump.

I keep thinking I'm missing something here. It wants almost no fuel at idle, and a quite a bit in midrange, and a whole lot WOT.

I've run without the secondaries and can get fairly close on idle/cruise (13's) but I have to stay "8% lean" and then get 15-16 or even higher A/F with some throttle which seems a bit on the lean side. (with "plain" heaviest springs) Then when I hook up the secondaries it's hard to get enough fuel.

Apparently it needs very small primaries and very big secondaries??

Time for a Thermoquad? (Won't fit my LD340, though) O:)
 
It's at 15* initial and likes 20+ initial, of course it's going to be fat at idle.

Give it the initial timing it wants, set the idle mixture screws and move up the food chain from there.

You will get stacking issues when the idle is off. It's fat, so the accelerator pump doesn't need to be where it should be. AP can be lean so you don't have an off idle rich stumble (fat idle covers this) and on up the circuits.

Get the base circuit correct, so that the additional circuits work, providing the required fuel that they are supposed to give it.
 
midnight340 said:
Dropped timing back 2 more degrees from last time. Increased the jetting in primaries AND secondaries. To .110 and .113, installed a fresh NGK BPR8ES and made a WOT run through the gears, shut it down, pulled the plug.

(Had a fuel pressure gauge taped to the windshield, and it held 6# until the very end and started to drop just a bit.)

My timing light showed 15* initial, and 30* total. Ran strong and felt good. But the plug was completely clean at the base of the porcelain (magnified with lighted otoscope) and the strap burned almost the the plug body. No darkening or color showing anywhere on the porcelain.

I will re-check my balancer against TDC (again) tomorrow, and will get another timing light. This is driving me crazy, trying to understand all this.

I can try upping the jets to .116 in the secondaries (12% fat according to Edelbrock) and my A/F numbers are now in the 12's mostly in normal driving. Some 13.5 mid-range, with the .110 primary jets. (4% lean according to Edelbrock) My idle is in the 12's with the idle screws only a bit under 3/4 out.

Here are photos of the plug from the run today: (NGK BPR8ES)
Click to expand...

That ground strap looks hot and your gauge seems wacked cos it looks like you pulled it out of the box. Get a Holley and your problems will be solved............Taking over the world one carb at a time.......ThumperCarbs..............
 
crackedback said:
It's at 15* initial and likes 20+ initial, of course it's going to be fat at idle.

Give it the initial timing it wants, set the idle mixture screws and move up the food chain from there.

You will get stacking issues when the idle is off. It's fat, so the accelerator pump doesn't need to be where it should be. AP can be lean so you don't have an off idle rich stumble (fat idle covers this) and on up the circuits.

Get the base circuit correct, so that the additional circuits work, providing the required fuel that they are supposed to give it.
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I appreciate the input. I've learned a lot doing this, but can't always get the bits of info organized logically. But what you say makes good sense.

I'll get the 10* bushing ordered today for the MSD. And order some more jets so I have what I need when I get there.
 
midnight340 said:
I'm really surprised I haven't heard this before now!! O:)
(…and it HAS occurred to me.)
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Simply the best style carb made...................If e-brocks were that great, you`d see em on every car at the track.................Taking over the world one carb at a time.......ThumperCarbs.......
 
I dont think you can read the plug from 1 quick pass usually takes 3-4 before you start seeing color.
 
all carbs have jets and mixture screws and a vacuum based enrichment etc. NHRA super stock cars run 9 sec. 1/4 times with Carters and Holleys and Rochesters and Autolites. what is your vacuum at idle? hang with it, quality takes time
 
Marcohotrod said:
all carbs have jets and mixture screws and a vacuum based enrichment etc. NHRA super stock cars run 9 sec. 1/4 times with Carters and Holleys and Rochesters and Autolites. what is your vacuum at idle? hang with it, quality takes time
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Yeah, I'm pretty committed to getting this carb right. I think people like Holleys because they get tinkered with till they make power. Edelbrocks usually get bolted on and run with little more than a rod change. Or so it seems to me.

I had the vacuum up to a good 14" at one point. More like 13 now. And thanks for the encouragement. I'll get it eventually.
 
joec said:
I dont think you can read the plug from 1 quick pass usually takes 3-4 before you start seeing color.
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I had wondered about this, whether i should put several passes on the plug first.

I am fortunate as they just built a new interchange about two miles from me, and just past it I'm in the countryside. A quick right turn and I'm on a 2-lane seldom used side road where I can see anyone coming from either direction. Over 1/4 mile straight away. Nice.:burnout:
 
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