Worth the effort?

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71Duster

71Duster

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Basis of the question is after getting a 2nd and 3rd opinion my year old 3000rpm advertised.recomended convertor will only flash around 2500rpm and is the cause of my gutless off the line performance.

Now the 727 in the car is in good shape iternally BUT many of the holes in the case are helicoiled and it has developed a few leaks the last 2 years.

Now the driveshaft is a Bubba special that was cut down frm a Fury and needs to be retubed and balanced anyways.

So the question is: Is it worth the while to swap a 904 in place behind a moderate built 340 for street use? Its a full weight stock car with 3.55 Gears. Thinking the lower first gear might be nice on the street.
 
Not knowing what you currently have for a convertor...
Any convertor's stall speed will vary depending on engine's torque output, a car's weight, and the design and manufacturing of it. If an engine makes more or less power than the convertor manufacturer anticipated, or in terms of the lessor expensive units the car is lighter or heavier than the manufacturer's "average", the stall speeds will vary. Generally, the cheaper the convertor, the more likely it will be a little off from the advertised stall. So I would say don't feel too bad, and if you really want to see if the convertor's the culprit, look to the health and tune of the engine. Because if the engine's down on power or not what was anticipated, the convertor stall will be lower.
Now, as for opinions, I'd rather have a close-to-stock 727 behind a mild 340 in a street car. There are valid opinions about going faster, lighter, lower first gear, etc. But unless the 904 is getting gone through and upgraded to the 727 type high gear clutch drum, my opinion is to stay with the 727. If this was a race car and you planned to drop some coin on the swap, I would go 904 for the reasons I mentioned. But for what you have, I think the 727 is the best way to fly. I'd also make sure the engine is holding up it's end of the deal too.
 
It wasn't a bargin basement converter it's an SMR unit. The engine's state of tune is questionable because off the line the bog is terrible as is performance for the first few feet until you can get some rpm into it. It WILL NOT even spin a tire, I gave up and after getting a recomendation from a board member took it into a shop. The guy runs a funny car and seems decent and knowledgeable. He tuned on the carb a bit and is pointing at the converter being too tight for the lackluster performance off the line.
 
Besides tuning, did he do any diagnostics on the engine? Specifically cylinder pressures or leak downs? I've found some issues with cam degreeing, valvetrain geometry, timing, and ring issues on "great running" engines by doing those when other things were suspect. If the convertor is a good one (I'm not familiar with SMR but have heard the initials before) then I'd still be looking elsewhere before I threw money at the trans. A 340 in an A body should be able to spin the tires 1/2 way thru first totally stock with mild gears. If the response is slow, I'd be looking at cylinder pressures.
 
I would go with a 904 in a heartbeat if i were you.
There are lots of tips and upgrades you can do to make them very healthy for what your intended use is.....
Plus they are lighter and take less horsepower to run.
JMHO,
Go for it!
 
It's only pulling about 12" of vacuum so I am going to start with checking and re lashing all the valves.

Again I am going to do a compression test. The engine is only two years old and has run like this from day one. If the engine has issues I'm gonna be mad as hell as it'll be the 2nd time in this car.
 
Here are the specs on whats in the car, off the line performance has been dismal from day one, lays over with a nice bog. Hell I've even managed to get it to stall a few times. It's been tuned by me and my Dad-a mechanic of 30 plus years- The shop that built the engine used a 4 gas analyzer and the last guy which puts me here. I'm going to do some checks on the engine itself and see where that gets me. I have a growing urge to pull the plug but the way the car runs I couldn't even sell it for near whats into it so OI might as well spend more and fix it.

The distributor was curved by Daves Mopar so I know its done right. Base timing is 18deg all in mechanically around 2200-2500 with a total of 34deg. Now new this year is it pings on WOT for a breif moment not a thing was changed from last year to this and it pings with fresh tank of 91 octane.

650 Speed Demon mechanical secondaries, #66 Jet front #31 discharge nozzle #68 Jet in the rear with a #25 rear discharge nozzle on an edelbrock rpm intake

Stock J Heads 2.02 intake 1.60 exhaust and Crane Gold 1.5 ratio rocker arms.

3.55 gears and a 727 with 3000 stall from SMR, stage 2 shift kit from transgo.

It runs a Hughes cam #heh2328al

111deg lobe seperation/installed centerline 108deg
intake lift .506/ exhaust .524

[email protected] Intake223deg/ Exhaust 228deg

Cam timing @ .050” Tappet Lift

Intake Opens: 3.5 Deg BTC
Exhaust Opens: 48 Deg BBC

Intake Closes: 39.5 Deg ABC
Exhaust Closes: 0 Deg ATC


Engine is .060 over with Keith Black Hypereutectic pistons on stock rods and a stock forged crank.

Ignition is an FBO box
 
Did a compression test tonight all the numbers look good.decent.

#1- 160psi, #3 - 170psi, #5 - 155psi, #7 - 155psi

#2- 175psi, #4 - 165psi, #6 - 165psi, #8 170psi

All tests done cold and dry. Going to get some more info before resetting the valve lash however.
 
I'd be pulling the cylinder head off and checking to see if the valves are leaking. 2,4,6,8 look great but the 1,3,5,7 are too much of a gap for my tastes.
 
The cam is too small, or you could look at it as the convertors is too big.

within 10 psi is fair, but 15 is showing something is off.

How old is this motor, did u build it yourself, and were the heads cc'd?

btw ...if its bogging, it may be because it has too much pump shot, and basically an out of tune carb
 
check the carb..see if the front squirter is squirting as soon as you touch the throttle....and as the rear throttle opens...make sure the squirter moves with it..

why #31 squirter in front ...and #25 in rear.....up the rear...squirter that is...
 
71Duster said:
Did a compression test tonight all the numbers look good.decent.

#1- 160psi, #3 - 170psi, #5 - 155psi, #7 - 155psi

#2- 175psi, #4 - 165psi, #6 - 165psi, #8 170psi

All tests done cold and dry. Going to get some more info before resetting the valve lash however.
Click to expand...

When you did the test was the carb wide open and all spark plugs out? I don't think you're going to find out anything major by checking the rocker settings. Being that this is a hydraulic cam if the settings are 2 loose then the valves will tap and too tight to the point that the lifter piston is at the bottom of it's travel I would expect a larger discrepancy in your cylinder pressures like 1 or more way low. The passenger side bank is within 10% so they're not bad.
So when you say you've got a bog what exactly are you doing. IE, are you going from idle to foot to the floor in one second.
 
Well all three shop have all said it is NOT the carb and all have tuned it with the same result.

The engine is 3 years old and only summer driven. It was built by a reputable local shop. The bill states it was blueprinted but unfortunatly they never gave me any of the internal numders.

All spark plugs where out with the throttle held wide open and turned over for an equal number of compression strokes.

When run off the line from and idle or held on the footbrake and given some rpm the car will lay over and do nothing could call it a massive hesitation before it slowly pics up and goes. If your cruiseing its no problem. This car will NOT do a burnout it will load up and push against the footbrake and do nothing, even if you let off the throttle it will not even chirp the tires.

All in all its a gutless wonder off the line. Great in the upper RPMS but thats it. I've had three different shops all recomended highly by others, all racers in there own right tune this car with the same result.

Last year I was told the convertor stalled too low -IE: 2600- So I sourced out a new SMR unit who recomended 3000rpm stall and thats what I bought swapped the convertor with no change in drive characteristics and a 2500rpm flash and once again I have been recomended to "change the stall" I've had the original 340 when tired in the car act this way, had a 360 built by a shop that had TONS of problems but also also bogged. Now the 340 rebuilt has the same issue.

Beyond all that with nothing changed over the winter then the balancer it pings under WOT off the line now. Fresh fuel etc and no change.
 
All things considered and with the existing drive train you should be able to melt down the tires off the line. Don't take offense to this but are you positive the rear end is 3.55, are you taken someones word for it or have you check it yourself.
 
demon seed said:
All things considered and with the existing drive train you should be able to melt down the tires off the line. Don't take offense to this but are you positive the rear end is 3.55, are you taken someones word for it or have you check it yourself.
Click to expand...

Yeah, but how big are the tires.

A 28'' will tame 3.55's down to 3.17's

All gear ratios are based on a 25'' tire.
 
What happens if you just go from idle, tap the gas, and then immediately floor it? Like you would if you were driving it with really low vacuum?

I don't know about their advice about getting bigger stall converters. I mean, there are MUCH bigger cams that only require a 2300-2400 stall, (A lunati voodoo cam I was looking at comes to mind.) Working with my friend on chevys, you don't normally use a 3000 stall in anything that isn't an absolutely off-the-rails built motor.

Perhaps consider a vacuum-secondary carburetor, I haven't worked with mechanical secondary carbs, but I've been warned away from using them because of these kinds of problems.
 
It's a 255/60/15 rear tire which works out around 26" if I rememebr correctly.

Even from a slow roll and into WOT the engine will still lay over. I bought the gears new as 3.55's and cruiseing on the highway at 60mph rpms are around 2800.

The only constant with all these builds has been the carb and I've pointed my finger at it too and also assumed my tune may be off which is whey I actually paid someone for their opinion but no one seems to want to condem the carb.

I thought a vacuum secondary might be the answer but thats a whole other can of worms on here. Mechanical vs Vacuum. If I knew for sure or had a really good backign I'd buy a proform or quickfuel, even a street avenger but I just don't know before I spend more money.
 
Have you taken a peek under the timing cover to see if the cam is installed where it should be? Low vacuum, dead bottom end, fine at high revs, with everything else being right sounds like the cam's retarded more than it should be. Though this is more pronounced than I've encountered, perhaps it's off a tooth? That'd also explain why it's been that way since you first got it.
 
Quote/ I bought the gears new as 3.55's and cruiseing on the highway at 60mph rpms are around 2800.

Yea that's about right, my 3.91's are running 3000 at 60mph with 255x60-15's. The dia. on the 255 is 27.1" also.

I'm starting to lean towards cam timing also, that cam is advertised at exhaust fully closed at TDC. You could pull the drivers tappet cover and eye no.1 exhaust to just closed then look at your TDC mark on dampener to chain case to see if they line up. Maybe she's out by 10 deg. or some ungodly number. Maybe who built that engine advanced her (or I could be bass ackwards) to far to give you a little more vacuum at idle, who knows.
Failing that I'd see if you can wangle another 650 DP'r out of a friend and try that. I've got an old 750 vacuum secondary on the shelf but that ain't going to help ya.
 
Most if not all the time, gotta make room for the freak chance it isn't, but every v8 I have build 'quite a few' the cam timing is advanced beyond the advertised when just setting it dot to dot on the timing gears.

I have to always retard the cam to get it installed straight up tdc.

My 340 required 6* retard to get it 2* advance.
My 410 needed about 4-6* retarded as well to get it straight up '110*'

Now....hughes cams come with around 4*advance built into them, think about that.
 
Good suggeston, I have the valve cover off already when I was looking at the rockers on the driver's side. Hughes website says all their cams are built with a 3deg advance so even if they lined it up dot to dot and it was bang on by chance it'd be thre deg advanced. Maybe the engine shop was trying to take the 3 deg of advance out?

I'd love to borrow a carb but unfortunatly I don't know many guys in the car hobby. I had been a member of the Edmonton Mopar Club for awhile but being 28yrs old at most of the guys in their 40's and up they had little interest in talking/teaching a younger guy. Most where content to bench race/bench tune for you. All talk about what I should do and should buy but when it came tme to roll up sleeves I was the only one there.

I know one member on the board that has a few carbs buts he's a few hours away and usually pretty busy.

Here's the link to my Phtobucket album
http://s1216.photobucket.com/albums/dd361/Corey_1982/

It's listed in the sub albums as 340 spark plugs
 
71Duster said:
Good suggeston, I have the valve cover off already when I was looking at the rockers on the driver's side. Hughes website says all their cams are built with a 3deg advance so even if they lined it up dot to dot and it was bang on by chance it'd be thre deg advanced. Maybe the engine shop was trying to take the 3 deg of advance out?

I'd love to borrow a carb but unfortunatly I don't know many guys in the car hobby. I had been a member of the Edmonton Mopar Club for awhile but being 28yrs old at most of the guys in their 40's and up they had little interest in talking/teaching a younger guy. Most where content to bench race/bench tune for you. All talk about what I should do and should buy but when it came tme to roll up sleeves I was the only one there.

I know one member on the board that has a few carbs buts he's a few hours away and usually pretty busy.

Here's the link to my Phtobucket album
http://s1216.photobucket.com/albums/dd361/Corey_1982/

It's listed in the sub albums as 340 spark plugs
Click to expand...
I would plug the power valves if you haven't and jet up about 8 sizes where you do plug them and I can almost guarentee she'll turn into a monster.
 
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