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Old 09-09-2019, 08:22 PM
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383 stroker camshaft and compression ratio?

I need some help with my build. I'm a bit stuck on what to do next and what cam and compression ratio to run.



I'm trying to build a stroker 383. I want to put it in my 72 gmc truck. I'm aiming for a drag race truck now. I know I wont be going that fast with how much money I have but thats the direction im shooting for. I don't care about driveablility at all and Im going to make it for just drag racing and try to do upgrades over time.


I have recently purchased the following parts:

summit racing 1996-2000 4 bolt sbc gen-1 bare block. Its the 1 piece rear main. They did the following machine work: decked, line honed, bored & honed cylinders with torque plate to 4.03. They also said the deck heigh is not exact and that it is no less than 9.01.
I also purchased an eagle 3.75 stroker crank, cast steel. With all dimension being similar to the stock 350 and one peace rear main seal and internally balanced.
Then I got wiseco forged pistons. Made for 4.03 bore and the compression height is 1.425 with +7cc piston head volume.
I also got scat forged steel connecting rods that are clearanced for the stroker, with bushed small end.
I also got the main bearings and rod bearings, and dial bore guage set and micrometer.
I'm also running the blueprint cylinder heads https://blueprintengines.com/product...sembled-h8002k
They allow .575 lift and the chambers are 64 cc.

I'm putting a roller cam in this engine and IM not sure which one to get. So Im stuck on which cam and compression ratio to use. Note that this truck is heavy and Im using the sm 465 four speed tranny. After this engine build my next upgrade is a 5 speed. Also, I'm in the process of lightening the truck.

I know the cam specifications are dependent on these variables but for now I want the best cam for this set up and I can change some parts around later.

I want to run pump gas. I was thinking of running a compression ratio around 10.8 so I can run a big duration cam. The wiseco pistons I got say that the valve reliefs are extra deep or what ever for the valves to clear. Im looking for the most power on pump gas and no valve clearance issues, but Im not worried about road performance.

The block I got has an unknown deck height. But I know its no less than 9.01. My plan of action was to take it to the machine shop and have them measure my deck height. Once I have my deck height I can choose the compression ratio and cam. Is there any way to measure my own deck height? I'm just kinda lost on what to do next and I keep watching videos and reading articles.

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Old 09-09-2019, 10:10 PM
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All builds begin with the fuel used because the fuel determines the static compression ratio and the static compression ratio determines the cam. So what fuel are you planning to use? Yes, have a good shop measure the block deck height at all four corners of the block.

Last edited by techinspector1; 09-09-2019 at 10:34 PM.
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Old 09-10-2019, 08:00 AM
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You did say pump gas, so I assume pump premium.

Why would you buy pistons and then want to decide on compression ratio? Also you mentioned a balanced crank, but imply that you bought the rotating assembly piece-meal. Better to get a complete matched/balanced rotating assembly.

Blueprint 195 heads are not going to get you very far at the track. Why go to all the trouble of building a forged piston stroker motor for the drag strip and then put marginal heads on it. Get some good heads - the best ones you can afford. Profiler 210s or AFR 210s depending on your pocketbook. You won't be sorry.

Manual trans is not good for drag racing - only good for spinning street tires and breaking parts when you get a heavy vehicle to hook up. Automatic will require a good torque converter (not cheap). Rear end should have a full spool so not to break spider gears when the slicks hook.

You will not notice much difference in power between a 10.8:1 and 10.0:1 CR with a properly matched camshaft/heads.

Lots of things need decided and thought out before a camshaft is selected. How much is this vehicle going to weigh and what times/trap speeds do you intend to run? What RPMs will the engine be running at (before/after shifts). I don't think you are quite there yet, but there are a lot of people here that can help you when you can answer these questions.

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Old 09-10-2019, 10:04 AM
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90 percent of the power is in the cylinder head so spend everything you can there.
The heads will dictate much of the cam needed
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Old 09-10-2019, 11:27 AM
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Too many under optimized choices for a racer truck. But some of that depends on out for fun or out to win.

The pistons are for 5.7 inch rods, without putting Mallory metal in the crank this drives you to an externally balanced engine. This is OK on the street but for drag race rpms is hard on the center 3 mains as the shaft runs locally out of balance which puts a twist in the shaft that eats these bearings up fairly quickly. The 6 inch rod and piston almost always allows internal balance without having to add heavy metal in the counter weights. The 6 inch rod used a much shorter thus lighter piston which allows this. There is no such thing as a prebalanced crank unless you know the exact rod and piston weight it's balanced to, I'll explain why below.

As balance goes there is no such thing as buying balanced parts and ending up with a balanced crank assembly. The counterweights have to be modified to counter the weight of the specific rod and piston used. Different rods by type and manufacturer and the same goes for pistons have different weights that have to be specifically addressed in a balance shop. Crankshafts typically come with overbalanced counterweights that allow trimming their weight against any selected rod and piston combo by removing counterweight material. This is much less expensive than having to add heavy metal to the counterweights. This is drill and ream a hole in the steel counterweight then press in a heavy metal slug made of a tungsten alloy. This is expensive both in process and material cost.

Although rods and pistons are sold in 'balanced' sets what is actually meant by that is they are weight matched to some tolerance, usually a gram or two. This reduces the amount of material removal the balance shop needs to remove from the heavier pieces to match the lighter. For a competition engine 1 or 2 grams of separation is too much, the balance shop will get this into something more like .1 gram. Once these parts are equalized bob weights are prepared and assembled on the throws then the crank is spun to identify how much materialneeds to be removed (or added) from specific counter weights and where on the counterweights to bring the assembly into balance. There's a lot more to this, I'm just bouncing across the surface to save time.

Getting the crank assembly into internal balance allows the use of a neutral balanced damper which simplifies replacement if needed, with an external balanced crank the off balance damper is part of the balancing assembly, if it needs to be replaced the engine needs to be disassembled and completly rebalanced.

External balanced engines should use a high end damper like the Rattler as the lack of main bay to main bay balance adds a lot of harmonic twist to the crank to where when racing the much more improved damping capabilities of these high technology dampers really soaks up the twist moments running out the end of the shaft.

Your head selection would be OK for a street 383 motor, for a race motor not so much. I typically run 190 to 200 cc ports for street 350's. The 383 is happy with 200 to 220 on the street, for racing I look to 230 to 240 ports before taking the grinder to them.

Cam and compression walk together for best efficiency which is related to best power but not the same. You can run too much cam for the compression and still get plenty good power though not optimized but that will come with high fuel burn. For racing that isn't a big consequence, for a daily driver that's far from optimum in terms of fuel consumption and engine life. Racing with aluminum heads you can push the conventions to the high side which will better the power. This is something where you need to go to the online static/dynamic calculators with cam and compression specs and iterate their model to see what fits best.

Bogie
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Old 09-10-2019, 09:22 PM
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Thanks for the info! I'm trying to learn as much as possible. Looks like I'm just going to have a street motor for now because I don't know enough and have enough money. So I can throw out the idea of a pure drag racer. I'm in it for fun not to win and my main objective is to make it faster than it is right now. And I'm in it for the knowledge. I also want an engine that lasts a while. I definitely do not want an engine that doesn't last long.

I'm going to run 91 octane.

Pistons: I can send the pistons back if I need to but this is why I chose these pistons. With the pistons, rods, and cranks, my rotating assembly length is 9.0. And the pistons have a +7 volume. My block came machined with a minimum 9.01 deck. So I can deck the block to 9.0 giving me 0 clearance and a compression ratio of 10.86. I read a quench of .04 is good. So my quench would be the size of my compressed head gasket thickness.

Heads: I want to run these heads for now, and when I save up I can buy better ones

Crankshaft: I wasn't assuming it was a balanced assembly. I got each component of the rotating assembly because it allowed me to get what I wanted. I was able to choose the compression height of the piston and volume on top, stroker rods. I have also heard that they come not balanced very well. So I wasn't going to deal with that. My plan was to take my rotating assembly in to have it balanced. Thanks for the info on balancing! I have been watching and reading lots of stuff on it. I'm not to sure what they meant by internally balanced crankshaft when I purchased it. But I thought it was correct in some way so that it works out to be internally balanced by the machine shop. I found this on summit "Crankshafts are listed as internal or external balance. This doesn't mean it's already balanced. It just tells you how it's intended to be balanced. It must be checked with the specific piston and rod combination you use."
https://help.summitracing.com/app/an...ine-balance%3F
So I need to figure out the bob weight of the rotating pistons and rods and compare it to the bob weight of the crankshaft.

Rods: I read that to run a .04 quench area I need steel connecting rods. And its a good idea if my compression ratio is 10.86. I did not want the 6 inch rod because I read that it increases the dwell time, and it pushes the wrist pin into the ring pack making the top of the piston thinner? and then effects which cam I need more because it increases detonation or pressure. not sure? So I thought it was getting too complicated. But that is interesting that it makes it so you dont have to use mallory. Maybe I could have gotten a heavier crank too? I should have done more research trying to get all the parts to have a lower bob weight compared to the crankshaft initial bob weight. But I was limited to the parts for their dimensions and stuff so I thought I would just pay to have it balanced.

So my plan of action would be get it decked to 9.00 and balance the rotating assembly?
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Old 09-10-2019, 10:33 PM
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I also don't know the answers to some of the questions.

I was thinking I could shift around 6,400 or what ever RPM makes me go faster.
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Old 09-11-2019, 07:29 AM
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Buy this. https://www.skipwhiteperformance.com...nk-rods_89381/

Add a Comp Cams XR276HR or Comp Cams XR282HR, an Air Gap manifold, and a 750 Holley/Quick Fuel 4-corner idle with vacuum secondaries. Use 1 3/4" headers.

Only thing holding you back will be your heads. You may need to change valve springs on these heads as AFAIK Blueprint heads come with valve springs that aren't really very strong.

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Old 09-11-2019, 08:00 AM
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Springs:
  • Spring Pressure Open: 295-305 @ 1.225
    Spring Pressure Closed: 115-125 @ 1.800
    Outside Diameter of Outer Spring (in): 1.437 in.
    Dual Valve Springs
    Chromemoly Retainers
    7 Degree Valve Locks
Looks like these springs are the same ones that AFR specs for Hydraulic flat tappet. https://www.airflowresearch.com/cont...spec-sheet.pdf
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Old 09-11-2019, 09:20 AM
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Quote:
Originally Posted by RobbyDD View Post
Thanks for the info! I'm trying to learn as much as possible. Looks like I'm just going to have a street motor for now because I don't know enough and have enough money. So I can throw out the idea of a pure drag racer. I'm in it for fun not to win and my main objective is to make it faster than it is right now. And I'm in it for the knowledge. I also want an engine that lasts a while. I definitely do not want an engine that doesn't last long.

I'm going to run 91 octane.


It's real hard to have fun when you're working on the engine all the time. You can't even work on the chassis or body when the engine keeps having issues so this is a real solid plan.

Pistons: I can send the pistons back if I need to but this is why I chose these pistons. With the pistons, rods, and cranks, my rotating assembly length is 9.0. And the pistons have a +7 volume. My block came machined with a minimum 9.01 deck. So I can deck the block to 9.0 giving me 0 clearance and a compression ratio of 10.86. I read a quench of .04 is good. So my quench would be the size of my compressed head gasket thickness.[/QUOTE]

You're not wrong, but too much internet garbage has led you astray somewhat. There's nothing wrong with a 9.010 deck. It gives you room for later rebuilds and the most important aspect is flatness and finish for head gasket sealing. An extra .010 isn't going to make a difference for what you're trying to do.

[/QUOTE]Heads: I want to run these heads for now, and when I save up I can buy better ones.[/QUOTE]

There are already better ones on the market for the the same money. You just need to keep shopping.

[/QUOTE]Crankshaft: I wasn't assuming it was a balanced assembly. I got each component of the rotating assembly because it allowed me to get what I wanted. I was able to choose the compression height of the piston and volume on top, stroker rods. I have also heard that they come not balanced very well. So I wasn't going to deal with that. My plan was to take my rotating assembly in to have it balanced. Thanks for the info on balancing! I have been watching and reading lots of stuff on it. I'm not to sure what they meant by internally balanced crankshaft when I purchased it. But I thought it was correct in some way so that it works out to be internally balanced by the machine shop. I found this on summit "Crankshafts are listed as internal or external balance. This doesn't mean it's already balanced. It just tells you how it's intended to be balanced. It must be checked with the specific piston and rod combination you use."
https://help.summitracing.com/app/an...ine-balance%3F
So I need to figure out the bob weight of the rotating pistons and rods and compare it to the bob weight of the crankshaft[/QUOTE]


That crank has a target bobweight of around 1850 grams.
Balancing is only around $200 and generally a good idea but keep in mind it's not a perfect science and a lot of assumptions are made that are debatable so again, for your intended goals with this, $200 is a good idea. Just don't get carried away wasting time looking for .5 grams. I'd shoot for something like 5 grams or less on the rods and 10 grams or less on the pistons.

Rods: I read that to run a .04 quench area I need steel connecting rods. And its a good idea if my compression ratio is 10.86. I did not want the 6 inch rod because I read that it increases the dwell time, and it pushes the wrist pin into the ring pack making the top of the piston thinner? and then effects which cam I need more because it increases detonation or pressure. not sure? So I thought it was getting too complicated. But that is interesting that it makes it so you dont have to use mallory. Maybe I could have gotten a heavier crank too? I should have done more research trying to get all the parts to have a lower bob weight compared to the crankshaft initial bob weight. But I was limited to the parts for their dimensions and stuff so I thought I would just pay to have it balanced.

So my plan of action would be get it decked to 9.00 and balance the rotating assembly?[/QUOTE]


Again, the internet has you filled with knowledge that misplaced.
A long rods does what you read, a long rod can change the needed cam specs, and even changes how the head performs. What YOU need to looking at is the main goal of lightening the pistons so the crank can be balanced internally.

You have too keep in mind what your trying to do and the cost and value of the time and knowledge of what your trying to do. You don't need to worry about minor things on a street or track fun toy if it the cost doesn't net you anything. Keep it within the application at hand.
For example, I would buy a custom cam for everything because for the extra $50, the HP to $$ ratio favors it in all engines even if it's just a grocery getter. However a $2500 set of ultralight dyers rods and $2500 38lb Wineburg crank in the same grocery doesn't make sense by dollars or functionality.
It's a balance game between picking quality parts that get the job done and expense plus the tolerances needed to get there.
The internet has you chasing .0001 and .5 grams and all that in 400hp engine but when .001 and 5 grams is plenty close enough in realty to net the same goals, .0001 is a waste of time and effort and expense trying to hold on to something that just doesn't have the impact.
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Old 09-11-2019, 11:53 AM
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Originally Posted by techinspector1 View Post
All builds begin with the fuel used because the fuel determines the static compression ratio and the static compression ratio determines the cam. So what fuel are you planning to use? Yes, have a good shop measure the block deck height at all four corners of the block.
The 1968 SB Chevrolet 350 CI engine in my 1962 Bel Air was rebuilt in 1969 with forged flat top pistons and 64 cc 1962 double hump heads, for 10.3:1 compression ratio, with about 170 lb cranking cylinder pressure. Until about 1990, the 350 ci engine ran excellent on 92 octane premium pump gas, according to the original owner.

I bought the 1962 Chevrolet Bel Air three years ago. I must use five gallons of VP, C-12 108 octane racing fuel and fifteen gallons of 92 octane premium pump gas at every fill up in order to avoid detonation. In the future, I expect to use more VP 108 octane racing fuel and less premium pump gas.

Pump gasoline has got worse over the years and it is not getting any better.

Keep that in mind when you choose the heads and the camshaft. A compression ratio of 9.5:1 is considered high by today’s standards.
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Old 09-11-2019, 12:06 PM
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Keep that in mind when you choose the heads and the camshaft. A compression ratio of 9.5:1 is considered high by today’s standards.
Only if you use old, iron heads from the previous century. Today's modern engines typically use new-fangled aluminum cylinder heads, and roller camshafts. 9.5:1 is easy to manage, and most people would add a full point of compression (10.5:1) for a performance/race oriented engine, and do it on 93 octane pump gas. With modern ignition components, aluminum heads, proper oiling control and a camshaft with modern lobes and beehive springs to match.
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Old 09-12-2019, 04:04 AM
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you are building this truck bass ackwards and will burn a tonne of money to be disappointed in the performance gained.
Start with the truck
set diff up for maximum traction and weight transfer. Build/buy transmission that is your final choice. TKO 600 might live. Get some racing tires. Use a cheapo/stock engine (3500)
put a cam in it (cheap solid lifter) that will take you to 5500 rpm

get lots of track time
get more track time
Plan the replacement engine as a drop in for a year in the future
probably a 540/auto
get to the track
learn to drive
make it reliable
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Old 09-12-2019, 02:35 PM
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Originally Posted by 2001Blazer4x4 View Post
Buy this. https://www.skipwhiteperformance.com...nk-rods_89381/

Add a Comp Cams XR276HR or Comp Cams XR282HR, an Air Gap manifold, and a 750 Holley/Quick Fuel 4-corner idle with vacuum secondaries. Use 1 3/4" headers.

Only thing holding you back will be your heads. You may need to change valve springs on these heads as AFAIK Blueprint heads come with valve springs that aren't really very strong.
I forgot to mention that I already purchased these heads a couple months ago so Im stuck with them for a while. In six months I will get some more money to get big heads.
What valve springs are reccomended?
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Old 09-12-2019, 02:55 PM
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Originally Posted by johnsongrass1 View Post

It's real hard to have fun when you're working on the engine all the time. You can't even work on the chassis or body when the engine keeps having issues so this is a real solid plan.

Pistons: I can send the pistons back if I need to but this is why I chose these pistons. With the pistons, rods, and cranks, my rotating assembly length is 9.0. And the pistons have a +7 volume. My block came machined with a minimum 9.01 deck. So I can deck the block to 9.0 giving me 0 clearance and a compression ratio of 10.86. I read a quench of .04 is good. So my quench would be the size of my compressed head gasket thickness.


You're not wrong, but too much internet garbage has led you astray somewhat. There's nothing wrong with a 9.010 deck. It gives you room for later rebuilds and the most important aspect is flatness and finish for head gasket sealing. An extra .010 isn't going to make a difference for what you're trying to do.

[/QUOTE]Heads: I want to run these heads for now, and when I save up I can buy better ones.[/QUOTE]

There are already better ones on the market for the the same money. You just need to keep shopping.

[/QUOTE]Crankshaft: I wasn't assuming it was a balanced assembly. I got each component of the rotating assembly because it allowed me to get what I wanted. I was able to choose the compression height of the piston and volume on top, stroker rods. I have also heard that they come not balanced very well. So I wasn't going to deal with that. My plan was to take my rotating assembly in to have it balanced. Thanks for the info on balancing! I have been watching and reading lots of stuff on it. I'm not to sure what they meant by internally balanced crankshaft when I purchased it. But I thought it was correct in some way so that it works out to be internally balanced by the machine shop. I found this on summit "Crankshafts are listed as internal or external balance. This doesn't mean it's already balanced. It just tells you how it's intended to be balanced. It must be checked with the specific piston and rod combination you use."
https://help.summitracing.com/app/an...ine-balance%3F
So I need to figure out the bob weight of the rotating pistons and rods and compare it to the bob weight of the crankshaft[/QUOTE]


That crank has a target bobweight of around 1850 grams.
Balancing is only around $200 and generally a good idea but keep in mind it's not a perfect science and a lot of assumptions are made that are debatable so again, for your intended goals with this, $200 is a good idea. Just don't get carried away wasting time looking for .5 grams. I'd shoot for something like 5 grams or less on the rods and 10 grams or less on the pistons.

Rods: I read that to run a .04 quench area I need steel connecting rods. And its a good idea if my compression ratio is 10.86. I did not want the 6 inch rod because I read that it increases the dwell time, and it pushes the wrist pin into the ring pack making the top of the piston thinner? and then effects which cam I need more because it increases detonation or pressure. not sure? So I thought it was getting too complicated. But that is interesting that it makes it so you dont have to use mallory. Maybe I could have gotten a heavier crank too? I should have done more research trying to get all the parts to have a lower bob weight compared to the crankshaft initial bob weight. But I was limited to the parts for their dimensions and stuff so I thought I would just pay to have it balanced.

So my plan of action would be get it decked to 9.00 and balance the rotating assembly?[/QUOTE]


Again, the internet has you filled with knowledge that misplaced.
A long rods does what you read, a long rod can change the needed cam specs, and even changes how the head performs. What YOU need to looking at is the main goal of lightening the pistons so the crank can be balanced internally.

You have too keep in mind what your trying to do and the cost and value of the time and knowledge of what your trying to do. You don't need to worry about minor things on a street or track fun toy if it the cost doesn't net you anything. Keep it within the application at hand.
For example, I would buy a custom cam for everything because for the extra $50, the HP to $$ ratio favors it in all engines even if it's just a grocery getter. However a $2500 set of ultralight dyers rods and $2500 38lb Wineburg crank in the same grocery doesn't make sense by dollars or functionality.
It's a balance game between picking quality parts that get the job done and expense plus the tolerances needed to get there.
The internet has you chasing .0001 and .5 grams and all that in 400hp engine but when .001 and 5 grams is plenty close enough in realty to net the same goals, .0001 is a waste of time and effort and expense trying to hold on to something that just doesn't have the impact.[/QUOTE]

Makes sense thanks! The next issue is I don't know where to spend the money for the ratio of money to power. I thought I was being cheap so far and building a basic engine. The parts I got were only a couple hundred more over cast parts. I got forged piston, and rods and steel crank because I was thinking about parts that last and it lets me build more power later on without worry about weak parts. Maybe I'm over doing it but I have have had a piston come apart in a two stroke dirt bike and start coming out the exhaust.

I have spent about 3000 on the long block.
Since the engine is already decked, I'm going to install the rotating assembly to measure the clearance just so I know my compression ratio and call it good. I want to leave some room to rebuild it again down the road too. And if it doesn't matter that much for my power level I'm all for it because I want to save money and put it where it counts like you were discussing. I have always skimped out on engines and stuff so I wanted to do it right this time and spend the extra money so I can have something I like.
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