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Discussion Starter · #1 ·
This has been an interesting journey in understanding the relationship between transmission gear ratios, rear end gear ratio, and tire height. Build goal is a fun street car that can be daily driver during nice weather and will be comfortable on the long car club cruises at comfortable rpms and get decent gas milage but still get a bit of a jump off the line in street driving. Current thinking: 350 hp/400 tq sbc, 200r4 transmission, 3.73:1 rear ring and pinion gear (with a Detriot Truetrac limited slip) and 28 inch tires. If I understand this correctly, this will be the result.
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Please feel free to let me know if I have any of the above wrong.

My question is how does the specs for the torque converter fit into this equation? In doing a bit of reading, it appears that I should stick with a somewhat stock converter at about 1800rpm, maybe go a bit higher with a 2000 rpm torque converter but I want to make sure I understand the relationship between all of the components correctly. Any advice is greatly appreciated.
 

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Ryan
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Lots of variables here. Let’s assume you’re talking about a 350 small block with half way decent heads and a hydraulic flat tappet camshaft. Spread bore dual plane and a 600 carb. 350 hp and 400 tq will require a camshaft something the likes of 260ish advertised duration. 220 ish at .050” lift. That would pair nicely with a QUALITY converter in the 2000-2500 RPM range. A 2004r and 373s would be very nice for what you’re trying to accomplish. Since you’re using the 2004r, take advantage of a lockup converter.
 

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Ryan
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Discussion Starter · #5 ·
Look what I found. Exactly what I just described. Good luck.
That is awesome! Thank you. I have been collecting parts over the last two years and have UMI rear upper and lower trailing arms, QA-1 front and rear sway bars with QA-1 single adjustable stocker shocks, JEGS lowering springs, Richmond 3:73 ring and pinion gears and Eaton Detroit Truetrac limited slip differential so the next step is the 200r4. This has been a pandemic godsend for me and I think the result is going to be kick ass! Looking forward to a more "normal" year and lots of cruise nights and car shows in 2022!!
 

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Awesome. Looking forward to seeing the finished product.
 

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That is one of the easy motors to build or have built. Its a copy of the GM Ram Jet motor. I built one for my bracket truck and fun day driver. Truck was a 1990 GMC short box standard cab 2wd. Thing weighed 4462lbs and ran 14.52 at 97mph all day long. Had a th350 stock van converter and 3.73 gears with a 28 tall tire. Motor was a stock 1997 vortec 350 with the marine cam and 1.6 rockers and a carb and HEI. This is a full roller motor so no wiped out cam lobes. This cam can be had for as little a $50 form a marine motor or new for around $200 from summit or jegs. N0.14097395 Freshend junk yard 350 vortec motor form a 1996-2001 truck or van. Anyone can look up the specks and build it your self for under $400 to $600. Or just order the FI Ram Jet motor and have all the goodies or score a complete Ram Jet motor from a boat. Stand alone FI and 350hp and 400tq. Simple and cheap.
 

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Torque converters, for a performance car, belong in the same location as an auto tranny-------------------------IN THE RIVER!
 

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I'd go with a 25-3000 stall if you have lockup.
 

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Crazy Davies and his 67 with a Auto Trans & Trans Brake doing 60 Foots on 2 Wheels
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My Mechanics Auto Trans/Trans Brake SBC Car who Tunes the Carb on my 67
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My Street/Strip Auto Trans 67
Before Launching
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Foot Brake Launching at Idle eith a 3500 - 4500 Stall Converter
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You pick torque converters based on peak torque of your engine, which means your cam is critical in torque converter specs.
ABSOLUTELY CORRECT^^^ Your converter and stall speed RPM goals need to be dictated by your camshaft specs and where in the RPM scale your engine is making torque and power. Other than that, some transmissions use "Lock-up" type torque converters while some transmissions use non-lock-up converters. I would also highly recommend that you do not purchase a torque converter from any manufacture nor from any retailer that will sell you one with a generic off-the shelf stall speed RPM, rather than one who will have you either fill out a vehicle spec sheet, or will require you to call them so they can ask you questions about your vehicle specs, such as approximate vehicle weight, rear tire height, rear gear ratio, transmissions first gear ratio, and CAMSHAFT SPECS.

Let me explain that your stall speed RPM target/goal is based on the camshaft and where in the RPM powerband your engine makes it torque and power. However things like vehicle weight, rear gear choice, and transmission first gear ratio will effect how any given torque converter's stall speed RPM will come in at. That is why it can be very difficult to obtain the advertised stall speed RPM from an off the shelf torque converter with generic advertised stall speed RPM, since every vehicle combination is going to effect how the torque converter acts.

For instance: If you install a torque converter, (be that a cheapie or a high quality one) in your 3,800 LB car, and the stall RPM at full throttle comes in at 2,500 RPM and you decide that you want to make the car faster by stripping it down and you take the car down to a total vehicle weight of 3,200 LBS or less, without touching the torque converter, the resulting stall speed with the lighter vehicle weight is going to be a lesser RPM than 2,500 and if the lower stall speed RPM isn't a good match with the camshaft you're using, then the car will actually be slower off the starting line, or from a traffic light than it was when it was heavier.

Another thing about torque converters is that what's often not advertised is their "slippage percentage". This has nothing to do with the stall speed RPM, and has to do with how efficiently the converter operates. A low dollar cheap converter will usually have a slippage percentage of well above 10% and sometimes even over 15%. This is how much the converter slips at full throttle ABOVE the stall speed RPM. Many expensive high quality torque converter will have a slippage percentage of less than 7% and some even less than 5% regardless of the stall speed RPM chosen.

So to be clear on this slippage percentage thing, you can have a stall speed of 1,800 RPM or all the way up to 6,000 RPM but that doesn't have anything to do with how much slippage at full throttle the torque converter exhibits above the stall speed RPM. The slippage percentage as far as I know has mostly to do with non-lock-up torque converters though. If you opt for a cheap $250 to $300 torque converter, then you usually merely get what you pay for, (which isn't much). For a decent quality middle of the road converter, they usually cost in the $500 to $800 price range.

The two companies that I know of, (but not the only ones that are good I'm sure) that sell some good quality hi-perf torque converters are ATI Performance, (for non-lock up and lock up type converters) and Precision Industries, (for Lock-up type).

The factory stall speed RPM has nothing to do with the stall speed that your vehicle combination needs, UNLESS your camshaft specs and other vehicle specs are identical or VERY close to the factory specs. If for instance you choose a stall speed RPM that is too low for the camshaft and engine combination you have, your car might very well move like an old tired dog at full throttle from a dead stop such as when a traffic light turns green.
 
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