MSD ignition conversion on my '88 5th Ave

[AJ/FormS]

Wait, you have a 5.2 engine?
I am so busted,lol.
Good thing I prefaced my story in the very first sentence, to 8.0 !
And ended it with mentioning tight splits.

If it's passing power you need, um, 3.07s are not the right gears.
75mph will be 2929 in loc up. Kicking it down into1.54 second, the Rs will jump to 4737. This is way past the power peak, and so far into never-never land for a stock-cam teener that the car will do not much more than roar.
Perhaps you could look at this from a different angle. At what roadspeed do you want to begin your passing maneuver? and at what rpm should your teener be, to expedite this?
Lets say you wanted to begin the pass at 70mph, and the engine makes peak power at 3900. And you want that A999 to kick down one gear,into 1.54second, and you want to complete the pass at 80mph.
Firstly, determine the maximum rpm, say 4200, and the TC slip is say 5%
The gear ratio for this is;
(80mphx1056constant x1.54second)/(83rollout x4200/1.05slip)=2.55 .. So 2.45s are the closest ratio.
These will get you 70 at 3528 and 80 at 4032; perhaps a little on the low side, but the next ratio, the 2.73s are 11% higher so; 3931 and 4493, which IMO is too far past a 3900 peak.

Now, if you were to use the A904, and the tranny downshifted into 1.45second, then the right ratio would be
(80x1056x1.45)/(83x4200/1.05)= 2.71s, so 2.73s would be the ones. These will get you to 70mph at 3700 and 80 at 4230; very well centered around the 3900 power peak.

I like the 904/2.73s. Drove many many Mopes with these. Your rpm at 75 in Drive,will be about 2600 plus slip perhaps up to 2730. I would install a TC in the range of 2600 to 2800. Your car will have a completely different personality.

If you lived next door, I would loan you these items for a test-run,lol.

Be advised;
I guessed at the 3900 power peak. Yours might be lower. Or higher. IDK. Find out. Then just sub in a number that is about 5% higher, for your top speed rpm. The formula in blue will work for any numbers you sub into the right spot. I even guessed at the tire rollout of 83 inches. This is for a tire that is 26.4 tall, or a 205/70-15.

 

[MoparKidD-4]

I've got 28" tires so a bit different numbers but not much. I would imagine I don't need to downshift to pass if I'm cruising at 2900 RPM. Peak torque on this thing was rated at like 1800 RPM, maybe it'll be a tad higher with the dual exhaust and TQ added, no more than 2000? 2200? In 3rd gear cruising at that speed I'll have great response and if we say peak RPM is 4000 that puts top speed at only 110 mph, I bet it'll pull pretty hard going just from 3000-4000 RPM between 75 and 110 if I ever bothered to go that fast lol.

I still haven't installed a tach yet, I want to find out where valve float is wild guess is 4500 RPM? Anybody here tried it? Of course I haven't tried to hit valve float yet this engine runs too nicely to beat on...

EDIT: You mention stall converters, I have a 2600 RPM one that's going on the 904 in my Duster which will also be behind a 318 but with a Magnum top end and 226* @ .050" duration cam

 

[AJ/FormS]

Comments inside the quote

I've got 28" tires so a bit different numbers but not much.5.6% for all numbers. This IS a lot,being about equal to one rear gear size. EG it will make a 2.94 feel like a 2.76. I would imagine I don't need to downshift to pass if I'm cruising at 2900 RPM. At 70mph with 2.2 or 2.45 rear gears,you will have to downshift out of Drive and into Second. With the 3.07s and 28s your rpm in Drive/loc-up, at 70mph, will be about 2580.Passing will be ok if you don't mind measuring acceleration with a sundial. Peak torque on this thing was rated at like 1800 RPM, well firstly your 5.9 is not a deisel!, and secondly torque is not what helps your car to pass at 70mph.You need torque times rpm,otherwise known as horsepower. Power comes with rpm. But rpm requires the valve-timing to come along with it, and the reason is that the stock valve-timing rapidly chokes the ability of the engine to pull in air. It's always about the air. ALWAYS.
Look at any dyno print-out. Notice the torque curve falls away as the power continues to climb. At the torque peak the engine is DONE! But the RPM X TORQUE/5250 continues to build horsepower, until either the engine can no longer pull in more air,or,she suffers a mechanical failure.
imaybe it'll be a tad higher with the dual exhaust and TQ added, no more than 2000? 2200? I doubt it; neither of these will change anything at 2000/2200rpm In 3rd gear cruising at that speed I'll have great response no you won't; unless you are now talking about the 3.07s. It will be better than 2.2s or 2.45s for sure, but 2200 will be about 60mph. So if you begin your pass at 60@2200, you better haul out that sundial again. and if we say peak RPM is 4000 that puts top speed at only 110 mph, I bet it'll pull pretty hard going just from 3000-4000 RPM No it won't, it will be sucked out, just as it is today, the faster you go the worse it will be, cuz now your engine is dividing it's power between the chassis and wind resistance. Which will very rapidly win, cuz wind resistance increases as the square of the speed. In other words, if you double the speed it will take 2squared times as much power to buck that wind. If you triple the speed, it will take 3squared times as much power.Ergo, IF it takes 45 hp to buck wind with your car at 55 mph, it will take 2squared times as much power at 110mph,or 180hp;JUST TO BUCK THE WIND. between 75 and 110 if I ever bothered to go that fast lol.

I still haven't installed a tach yet, I want to find out where valve float is wild guess is 4500 RPM?Old tired LAs won't go that high.There is almost no closed seat pressure left, as the valves bang up into the heads.I wouldn't go looking for valve-float on purpose! Anybody here tried it? Of course I haven't tried to hit valve float yet this engine runs too nicely to beat on... On fresh LA teener heads, 360-2bbl valve springs took my 73 teener to 5000 plus regularly. With a 9.73 or greater starter gear and a 2800TC it was a blast, with the stock shortblock, plus bolt-ons,NO CAM,lol. It didn't pull up there anymore but that's ok, it had reached the speed-limit by 4200 in second. A998 and 3.55s

EDIT: You mention stall converters, I have a 2600 RPM one that's going on the 904 in my Duster which will also be behind a 318 but with a Magnum top end and 226* @ .050" duration cam This could be a good combo if the Dcr has been addressed; That is a fun sized cam, really almost too big for even a pumped up teener. If the compression has not been pumped up, then the low-end will be lazy, and you will need a lot more TC on the start line, and a starter gear closer to 10 or 11.......but I guess you will find that out for yourself.

I know I'm being hard on you, perhaps even to the point of being a dick, but; I think you have your own ideas, and I think you are gonna try them no matter what I,a stranger,or anyone else, says. OK, I get that. Since you are rich enough to have two projects on the go, I guess you are rich enough to do things twice. That is how we learn,doing things over when they don't work out the first time. That is how I learned! I did a lot of things many times,even.
Except the compression. I bumped it up to 11.3 on day one, and it was a winner.
I never did learn how to make KD for my kids,tho.

 

[Aspen500]

LOL, would have cost somewhat less to build my Aspen if I hadn't ended up having to do some things twice, or even three times due to a stupid mistake, an amateur mistake due to inexperience (paint), not knowing, wrong parts selection, etc...........Comes with the territory.

 

[MoparKidD-4]

Comments inside the quote


I know I'm being hard on you, perhaps even to the point of being a dick, but; I think you have your own ideas, and I think you are gonna try them no matter what I,a stranger,or anyone else, says. OK, I get that. Since you are rich enough to have two projects on the go, I guess you are rich enough to do things twice. That is how we learn,doing things over when they don't work out the first time. That is how I learned! I did a lot of things many times,even.
Except the compression. I bumped it up to 11.3 on day one, and it was a winner.
I never did learn how to make KD for my kids,tho.

I don't think you're being a dick but there are important points I make sure to put in my responses that you sometimes miss, no offense. Regarding this 5th Avenue I'm just doing what I can with what I can find for cheap. I spent a month or so browsing eBay and searching for ring & pinion gearsets for an 8 1/4"; the vast majority were 3.55 or numerically higher ratio. And the "oddball" ones like 2.76, 2.94, 3.21, etc. were way overpriced. 3.07 was the only "tall" ratio for the 8 1/4" I could find for a decent price. I might spend $150 on a 4-bbl intake I might not need, I'm OK with that; the carb needs to be replaced so if I have a spare TQ lying around why not upgrade it to a 4-barrel instead of spending money on a new 2-barrel (with very limited choices btw)? I bought this car for $700 and so far have spent about $200 on the rear axle swap, just need the spring perches welded and a bearing and seal kit. I don't think you realize quite how cheap all of this is, it's kind of the reason I'm not "taking it slow" and planning things down to the T, I'm not worried about having to do things over because the current performance state of the car sucks so bad it'll be really hard (impossible?) to make it worse than it already is.

If I'm using the Wallace Racing calculator correctly I will be able to hit 70 MPH in 2nd gear with the 3.07s and those 28" tires at 4000 RPM. I don't try to pass people at max effort past 70 MPH anyway that's close to fast enough; when I want to pass people hard is when I'm stuck going 60 MPH in a 75 zone. Anyway I'm not worried about a 0.3x ratio mismatch on my rear gears, it's not enough to make me go and search high and low for some 2.76s when I have 3.07s sitting on my bench.

Who knows maybe I won't be satisfied with the stock power anyway and I'll end up putting in a cam like this Voodoo Hydraulic Roller Cam - Chrysler 273-360 (W/ Long Snout) 264/270 - Lunati Power

 

[AJ/FormS]

Ok, I hear ya.

If you start the pass at 60 with 3.07s,28 inch tires,and in second gear; it looks like this
(60 x1056x3.07x1.54)/88 x1.05=about 3400rpm.
This is a pretty good place to start from. If you do the maneuver right,you may be able to slingshot past the tardy-car. But by 75, your rpm will be 4255, and I think the teener will long ago have stopped pulling, and is now just roaring. But if you let her shift into Drive at say 70, the Rs will drop to 2600. It may be that at 2600 the teener will have the same power(climbing) as it has at 4255(decaying rapidly),IDK, so a shift would help nothing. In this case, if the 4bbl was wide-open, the extra 12 to 18 hp, could be of some benifit.
And as you say, if the carb is shot anyway, then a swap to 4bbl makes perfect sense.
Whatever you do, DO NOT expect a cam to improve things anywhere but at above the torque peak and reving pretty good.And DO expect a power loss below that same torque peak. A cam is like a see-saw; you are always trading power below the pivot-point, for power above it. And the pivot point tends to climb with every cam change. So the bigger the cam swap, the bigger the trade.And if the support works do not keep pace with the swap, then all falls into the potty. Supportworks starts with keeping the Dcr up, and includes things like headers/free-flowing exhaust, induction,ignition,cooling, and especially the TC and gearing. These all have to be carefully co-ordinated as the cam continues to get bigger. Eventually as the cam gets maxed out for street, the power-band becomes pretty narrow, and is all concentrated at high rpms, sometimes, or often, to the complete sacrifice of power at the lower rpms. This makes a great drag-rac engine, but it makes a lousy streeter.
Now I'm saying that,that is the direction you are headed in, only that you need to be aware of what up-camming tends to do.
In your case the powerband is totally mismatched to the tranny and the gears and the application, so a cam may be in your future. But when that day comes, the compression will have to be bumped, so now it becomes a multi-dollar deal. And then ciomes the matching TC, to that new cam, and probably fifferent gears again. So now the multi-dollar deal becomes a mega-multi-dollar deal.
Everybody who ever hopped up a car goes thru this, and the list of dissappointed hotrodders, who didn't bring along the supportworks is very long indeed.
In your case;
I highly recommend to not swap out the teener cam. If you need more power, find a bigger engine.