Upgrading my 340
- Thread starter Raul
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I think your main problem is with the ports... You have large port heads, small tube diameter headers, and what looks to be an edelbrock performer or performer RPM intake...
1st thing that I would do is to get the ports matched from the intake to the heads... At least a good gasket match port so the ports on the intake match the ports on the heads...
Then get larger diameter tube headers to let the exhaust flow a little better, either TTI or Dougs headers will work well...
You are loosing too much flow velocity with smaller ports in the intake than the head, it slows down the flow when it enters the head, then you have a restrictive exhaust to choke the flow...
An engine is an air pump, you need to balance the intake flow with the exhaust flow... If one is greater than the other, it becomes the bottle neck/restriction...
I would run an Edelbrock LD340 myself, as they are great street intakes...
Also, why a 1.90" exhaust valve and only 2.02" intake... You've opened up the exhaust valve .030" over the stock size on the exhaust and have the stock 2.02" intake valve....
Another way to increase idle vacuum is to get a set of Rhoades variable duration lifters... They bleed down at idle and make the cam tamer for better idle vacuum and quality, and more low and mid range power without sacrificing top end power... They pump up to full lift and duration by 3500 RPM... I've used them for years on street engines and had great success with them... they will give better idle vacuum, more low and mid range power, and increase MPG slightly - don't expect miracles...
Rhoades lifter main page:
Rhoads Lifters
Part number - you will need the 2018 lifter or the Vmax lifters 20108X - but should run adjustable rocker arms with the Vmax to get their full potential...
Part Numbers
Read the second article here on the "smart lifter" for more info...
Articles
Some people don't like the Rhoades lifters and may give me some crap for recommending them, but I like them and have used them for decades and run them for over 200,000 miles with no trouble... Let them bash away...
My blunt opinion is: you have too much head for a street motor.. A stock 340/360 head with a little porting and a good valve job will be fine for the street...
I would focus more on the ports right now than trying more intake and carb set-ups.... Study a little on fluid dynamics and you will understand what I'm talking about...
Too large of a port will be a sudden expansion and will slow down the air velocity in the port... Velocity is torque...
Port vacuum is determined by the diameter and length of the port... Too big of diameter will slow down the velocity... You have to match the ports for what you are going to do with the engine...
1st thing that I would do is to get the ports matched from the intake to the heads... At least a good gasket match port so the ports on the intake match the ports on the heads...
Then get larger diameter tube headers to let the exhaust flow a little better, either TTI or Dougs headers will work well...
You are loosing too much flow velocity with smaller ports in the intake than the head, it slows down the flow when it enters the head, then you have a restrictive exhaust to choke the flow...
An engine is an air pump, you need to balance the intake flow with the exhaust flow... If one is greater than the other, it becomes the bottle neck/restriction...
I would run an Edelbrock LD340 myself, as they are great street intakes...
Also, why a 1.90" exhaust valve and only 2.02" intake... You've opened up the exhaust valve .030" over the stock size on the exhaust and have the stock 2.02" intake valve....
Another way to increase idle vacuum is to get a set of Rhoades variable duration lifters... They bleed down at idle and make the cam tamer for better idle vacuum and quality, and more low and mid range power without sacrificing top end power... They pump up to full lift and duration by 3500 RPM... I've used them for years on street engines and had great success with them... they will give better idle vacuum, more low and mid range power, and increase MPG slightly - don't expect miracles...
Rhoades lifter main page:
Rhoads Lifters
Part number - you will need the 2018 lifter or the Vmax lifters 20108X - but should run adjustable rocker arms with the Vmax to get their full potential...
Part Numbers
Read the second article here on the "smart lifter" for more info...
Articles
Some people don't like the Rhoades lifters and may give me some crap for recommending them, but I like them and have used them for decades and run them for over 200,000 miles with no trouble... Let them bash away...
My blunt opinion is: you have too much head for a street motor.. A stock 340/360 head with a little porting and a good valve job will be fine for the street...
I would focus more on the ports right now than trying more intake and carb set-ups.... Study a little on fluid dynamics and you will understand what I'm talking about...
Too large of a port will be a sudden expansion and will slow down the air velocity in the port... Velocity is torque...
Port vacuum is determined by the diameter and length of the port... Too big of diameter will slow down the velocity... You have to match the ports for what you are going to do with the engine...
Road lifter I'm not a fan of but have never used them so there you go.
Personally i don't think he need a 1-3/4 header. A 1-5/8 would be fine......however, if that's what it takes to get the header tube of the ground......then do it!!! My first set of header were some blackjack header(yah i know i'm dating myself) and that one header tube smacked EVERYTHING! Got some Hooker Super Comp headers on. Three motors latter, am making enough power for the tube diameter.
Personally i don't think he need a 1-3/4 header. A 1-5/8 would be fine......however, if that's what it takes to get the header tube of the ground......then do it!!! My first set of header were some blackjack header(yah i know i'm dating myself) and that one header tube smacked EVERYTHING! Got some Hooker Super Comp headers on. Three motors latter, am making enough power for the tube diameter.
Raul
Well-Known Member
I runon my street tires...BF Goodrich 245 R 14's I believe I had them down to 22lbs for traction. I thought my exhaust valves were 1.9's . Aren't the 340-X heads 1.9's with 2.02 intakes?
Raul
Well-Known Member
Bottom end is a stock rebuild except for camshaft, and hydraulic roller lifters top end I gt bigger ported heads and did the matchup of opening the ports on the intake to match the head port openings.
Raul
Well-Known Member
then I do have 1.60 exhaust valves. Appreciate all the info, but again, I do not wish to pull and open the motor up for modifications. I'm open to hear about header sizes, types, brands as well as tuning aspects and intake modifications as I first had interest in deciphering between a fuel injection system over a six pak which I thought would give me a tremendous amount of acceleration and torque. I've been hearing thata 750CFM well tuned could give 10-15 horsepower and the AIRGAP EDELBROCK Intake would also put more power to my engine and that I might be suffocating it with 1 1/2" header pipes
SLOPAR72
Well-Known Member
Oh this one is above my paygrade.... Good luck OP....
JW
JW
nm9stheham
Well-Known Member
Well, if you can find the piston info on the build info, that would be imporant to complete the picture of what you have. The reason I question that it is a 'stock' 340 bottom end is that the stock 340 pistons stick up about .018" above the deck. The Speedmaster heads with 64 cc chambers (assuming that is what they are) are closed chamber heads. You would need a thick head gasket to keep the heads' closed chamber area far enough from the pistons to keep them from hitting each other; a standard Felpro head gasket would juuuust be barely enough and we don't know that it was used or something different or thicker....or thinner, in which case you may be skirting disaster.
I don't want you to rebuild your bottom end, but we really SHOULD get a handle on what you have for compression ratio and that is all in the pistons and head gaskets and head volume. At least I think we know the head you have at this point.
One of your posts seems to indicate that this engine has to rev out before it starts making good HP; one cause of this is a combination of too much cam with too little compression ratio. So that is why the bottom end details are needed to make a complete picture of what you have.
I know you would like a list of things to just change but no one here is going to be able to help you do anything for certain, but just take random shots at this or that change without complete info. We are getting some info but not all so the help is going to be limited as to how accurate it will be.
Got any pix of inside the valve cover? Or under the intake manifold?
RAMM
Well-Known Member
What does it crank? PSI?
A 750 MIGHT give you 4 more HP but what you are after is torque.
A six-pack won't do anything for acceleration--it's only a 340 with a 3.31 stroke.
Without the advantage of a torque converter you are at the mercy of your engine and are clawing for every pound feet of torque. 340's are NOT a torquey engine and it looks like you have one of those "Mutha Thumpr" cams which are garbage BTW.
There is no single bolt on that is going to give you what you are after. Try a 4 hole tapered spacer, make sure your timing curve is doing what it is supposed to. Try more timing everywhere unless you hear pinging and experience hard starting, engine run on etc.. Try 18 initial timing, 36 total all in by 3500 rpm +/- 2 deg. Just unplug vacuum for now. You could pick up some serious mid range power if your timing isn't close but this will not get you the major torque production you seek. J.Rob
nm9stheham
Well-Known Member
I always forget: the cranking PSI is a great indicator of the dynamic compression ratio, which is where I've been wanting to get to with the piston info. And it helps with the interaction between cam and compression. RAMM asks you a very good question, OP.
Raul, unless the headers were specific for a 273/318 app, they are most likely off the shelf 1 5/8" jobs. You do not need more header than that to go faster than you are, I did a
set of T/A heads on an AAR 'cuda, 340 6pak, Mopar's 292/.508 purple shaft, cc'd @9.69:1 compression. These were not "all out" ported by any means, the car is full-on street
& the only change at the track was bolting on the slicks. With a 9.5" converter &727 trans the car has gone a best ET(I believe 4:30's)of 12.35, & a best MPH(4:10's) of 109.
On a set of off the shelf Heddman 1 5/8" jobs, 3" pipes & muffs, dumping in frt. of the axle. Your ride should be lighter, & that cam should have more torque, the stock T/A rockers
on that 'cuda were only netting .475-.480" lift worst to best. I would check Your timing curve & jetting & go from there.....
set of T/A heads on an AAR 'cuda, 340 6pak, Mopar's 292/.508 purple shaft, cc'd @9.69:1 compression. These were not "all out" ported by any means, the car is full-on street
& the only change at the track was bolting on the slicks. With a 9.5" converter &727 trans the car has gone a best ET(I believe 4:30's)of 12.35, & a best MPH(4:10's) of 109.
On a set of off the shelf Heddman 1 5/8" jobs, 3" pipes & muffs, dumping in frt. of the axle. Your ride should be lighter, & that cam should have more torque, the stock T/A rockers
on that 'cuda were only netting .475-.480" lift worst to best. I would check Your timing curve & jetting & go from there.....
Raul
Well-Known Member
Hmmm, The Compression Ratio is 10.5:1....Sorry, No Pics of under intake or inside valve cover...
Raul
Well-Known Member
Advance the timing to where it just starts to ping? or not allowing any ping, in any gear? I remember in the past when it pinged in 4th gear (with my 4-spd) it would stop by downshifting, or if the load was not great. With the current 5spd it doesn't ping at all, even under a heavy load.
I would also confirm that the camshaft is indeed where they say they installed it 3deg advanced, not just "the card recommended it & we picked the closest keyway & put it
together". i hate to be that cynical, but I check everything that I don't do Myself, hell I even triple check Myself!!!
together". i hate to be that cynical, but I check everything that I don't do Myself, hell I even triple check Myself!!!
That's the next question, what rockers are You using, & what is the preload they set the lifters at....
Just from bits and pieces of articles I've read plus playing with software dyno.
Someone with a dyno should be able to back it up. If you put an engine on where the dyno verifies it's using eg.. 600 cfms when you bolt on different carbs say 550, 650, 750 etc.. the engines vacuum should change to a value where each carb would become a 600 cfm.
I just found this article I skimmed through it's basically saying what I'm saying.
How Big A Carb Do You Need?
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I'm having problems wih the page loading. It keeps resetting. But I think I read enough to understand what you mean. I think this boils down to just how much the engine is eating rather than carb size. I do not see a carb as a limitation as you putt unless it is pulling to much vacuum under load. (W.O.T.) IIRC, (LOL there....) a bigger carb is needed if it is pulling .7 or .5 on the vacuum gauge at WOT.
Considering carbs are rated at a vacuum draw of a set amount, how often does the carb pull that much vacuum? It varies as you stated and I agree. But it is the overall size of the carb that has to be choosen for the intended purpose at hand. To this end, not to add to the mix, but, this is the reason I like certain carbs for certain jobs. In example, the TQ or AVS for a dual purpose machine. Holley's for a race effort. The Holley has many different cfm sizes available to suite the need. The TQ is super flexible and the AVS only has a few sizes. So a short coming is hard to avoid sometimes, cfm wise. Theres worse things ..... than a carb to small.
Considering carbs are rated at a vacuum draw of a set amount, how often does the carb pull that much vacuum? It varies as you stated and I agree. But it is the overall size of the carb that has to be choosen for the intended purpose at hand. To this end, not to add to the mix, but, this is the reason I like certain carbs for certain jobs. In example, the TQ or AVS for a dual purpose machine. Holley's for a race effort. The Holley has many different cfm sizes available to suite the need. The TQ is super flexible and the AVS only has a few sizes. So a short coming is hard to avoid sometimes, cfm wise. Theres worse things ..... than a carb to small.
I think the easiest way too explain how I see it is.
1st is we know carbs need some vacuum level to operate but for the sake of this discussion lets say they don't for a second. So then we would want zero restriction from our carb which would be zero vacuum at WOT any bigger wouldn't offer anything more since the carb has no restriction in this case.
So for this case say a 1050 cfm carb offer zero restriction and has zero vacuum at WOT on our imaginary engine.
Since we do need some vacuum to operate were gonna need to run a smaller carb. And as we go smaller and smaller the carb cost us hp over the 1050 because or restriction.
So only want to go small enough that the carb can operate. Since a daily driver, street strip and race car have different requirements the size will be different for each. But from what I understand the sweet spot for a hot street or street strip engine is a vacuum level of .08" to 1". In this case probably a 750-850 carb.
2nd since the smaller the carb gets we give up hp over the 1050. So different size carb will make the engines air flow needs vary slightly but for this discussion let's say it don't ando for our imaginary engine say it needs 550 cfms of actual air flow not carb size. And the formula cid x rpm ÷ 3456 does estimate the engines actually consumption pretty well. Now no matter what carb you run the engine will pull 550 cfm through it. So theoretically if you put a 550 cfm carb on it. It should pull a vacuum of 1.5" which is a fine choice if you don't mind leaving power on the table.
But most will think that this is the correct choice cause our engine needs 550 cfms and the carb is 550 cfm a no brainer. But what we don't realize that a 750 cfm carb at around .09" of vacuum is also a 550 cfm carb. And a 850 cfm carb at even less vacuum is a 550 cfm carb. No matter what carb you put on this engine the vacuum should change to make them all flow 550 cfms.
So really the right carb for the job should be the biggest carb that full fills all the engine requirements.
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The underlined; YES! But only top end power. Or via the formula, a whole lot from mid way to the top.
The bold type; Not exactly. The carb is still the carb at it's rating. The engine is pulling or consuming that 550cfm. So the carb is not smaller, just not used to it's fullest. Down grading the carb cfm size (850 to 550) is IMO a wrong way to state it and go about writing about. This wold just confuse people. It is not accurate.
The italic; YES! Because the engine is only consuming that much. But where it happens should change, slightly. Nothing to argue over. The bigger the throttle bores the less velocity.
One last thing, a carb doesn't need vacuum. The air rushing through the venturi(s) is ether done by vacuum OR the atomshpereic pressure. OR turbo/supercharger. Fuel is drawn out from the carb from the air rushing past the fuel openings in the carb.
Even though I will never happen the easiest solution would if the carb companies measured at a vacuum level the correspond with real world requirements like 0.8" - 1".
So a 750 would now be rated 550 and a 650 would around 500.
So a 750 would now be rated 550 and a 650 would around 500.
Sorry, but vacuum is always the delta value between atmosphere & the lack of it wherever it is being monitored, pressure drop means there is a vacuum. W/o it no fuel is going to
flow, which is why the venturi exists, to create a local pressure drop(vacuum) that will pull fuel out & recover most of the mass air flow. And as has been documented by many,
the wet flow rating at 1.5"Hg advertised can be all over the place side by side other carbs, so choosing between diff. models & brands...........????? It comes down to actual carb
capacity, & what min. depression You want at max RPM, 273 said it right. Turbos etc. are simply raising atmosphere to much higher levels.
Killer;
Then if you are correct, then explain forced induction relative to vacuum.
You can't and therefore your wrong.
Carbs do not work on vacuum alone.
A forced induction is pressuring the engine. Above and below the carb. It is the air flow going past the carb gas ports in this manor. Not vacuum.
Then if you are correct, then explain forced induction relative to vacuum.
You can't and therefore your wrong.
Carbs do not work on vacuum alone.
A forced induction is pressuring the engine. Above and below the carb. It is the air flow going past the carb gas ports in this manor. Not vacuum.
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