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Stroke of crank for 1970 Trans Am Motor |
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Trader 
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Joined: May/15/2018 Location: Ontario Status: Offline Points: 6881 |
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 Posted: Jan/18/2022 at 7:55am |
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Have to de stroke the 3.28 crankshaft to 2.9x. Close by using the 1.88" and definitely using the 1.771" Honda journals. Chebby people are doing this. The race forums have people shifting at 9000+ RPM doing this and getting many years now on a crankshaft.
From a strength point of view, the smaller journal has less weight, less friction, can build a large radius ... These are high RPM engines, just like this build would be going after. Cannot get the 2.9x stroke with any other AMC Gen2/3 crankshaft. Edited by Trader - Jan/18/2022 at 8:00am |
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DragRacingSpirit
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Joined: May/27/2009 Location: Mo Status: Offline Points: 903 |
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Posted: Jan/18/2022 at 4:27pm |
Maybe on a 290 or 304 block with the valves seriously shrouded/notched for the bigger valve heads I would agree with your suggestion that the 304 heads are the best thing to work with. You take the larger bore block and put the same amount of time and and work with the larger valve iron head, by a competent head porter.....I would have to see it to believe it......i'm from Mo. As far as a comparison to an aluminum SR head, competently just cleaned up your not even close. As far a an SR ported to the max for a 7500rpm 426 or 434 with 260cc runners and 2.125-1.650 valves you would be lucky to hit 2/3 the numbers.
Edited by DragRacingSpirit - Jan/18/2022 at 4:29pm |
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Best 1/4 mile 8.99, 1/8 mile 5.71, 60 foot 1.27, no power adders
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Trader
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Posted: Jan/18/2022 at 5:31pm |
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True, was re-looking the numbers. The SR heads would be the best for this type of build if you could use aluminum heads.
Still, without all the information to duplicate a Trans Am motor, think building a test mule with a de-stroked 3.28 crankshaft and 343 or 360 block would be the way to start. Spending a lot of money on a billet crankshaft and not knowing exactly the best combination of piston/rod/head... would be stretching. You can design on paper all you want, but proof is in the actual results. Really depends on a budget and rules for the purpose. With unlimited resources you could make multiple billet crankshafts, custom/aftermarket rods and pistons and sell what you don't end up using. The 1.77 Honda rods can only get you down to 309.5 CI, offsetting could get you lower.
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Javelin_GT
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Posted: Jan/18/2022 at 5:35pm |
There is no guess work. Barry Allen has built 3 of these in recent years all running in vintage TA style cars. Call him and ask. Here is one of the price sheets.  Edited by Javelin_GT - Jan/18/2022 at 5:40pm |
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Hurst390
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Posted: Jan/18/2022 at 8:23pm |
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SC/Hurst Rambler
11.62 120 100% Street Legal |
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Trader
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Joined: May/15/2018 Location: Ontario Status: Offline Points: 6881 |
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Posted: Jan/18/2022 at 10:00pm |
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So if there are no secrets to this build, why not just build them?
Time and again there are requests for AMC forged crankshafts stock and different strokes and there are companies like this in the US that make them all the time: Since a 290-401 share almost every dimension but stroke/rod diameter and minor crankshaft flange you would think this easy. A few variable changes on the CNC and done. They make 3 or 4 different stroke 454 crankshafts under $2000. More for 350's and LS's for less money. Don't tell them you have sales for 20 4" stroke crankshafts, ask the price for producing strokes of 2.9", 3.44", 3.68" and 4". I know people would like more options, but start with 4 sizes that would sell and if there are enough sales, they will do custom strokes. And just use the 72 up crankshaft flange. You can have it machined later for the Gen2 flange. You could probably get a choice of 2.0944" or 2.2481" rod journal for no cost on any stroke. There seems the desire and a lot of people with money for this, just pick a company and go for it. |
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Javelin_GT
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Posted: Jan/18/2022 at 10:32pm |
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Bottom line....race engines cost money. Doesn't matter if its road racing, drag racing, circle track, or whatever. There are cheaper ways to build a period correct 5 liter Javelin engine. Model it after the 1968 Kaplan engine with a 290 block and crank and get some 304 heads instead of notching the block for bigger valves. You can buy SCAT or Molnar steel rods, order forged pistons, and run an R4B up top. These were also wetsump motors so get an oil pan from Aviaid or Canton. That would all be period correct and good to go in SVRA or most any other vintage group that runs TA cars. Or you if you have the means you can spend as much as you want on a custom crank, dry sump, and all other stuff money can buy. The engine is just the start. Suspension, brakes, transmission, etc all need to be worked out and again.....there are cheaper and more expensive ways of doing all that. Dont forget the cage.....road race cage is around $3000 depending on where you live. Oh and the fuel system will require an FIA approved fuel cell.....thats another $1000. There is lots more to consider when building a vintage race car beyond the engine. |
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Trader
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Posted: Jan/19/2022 at 10:00pm |
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Still stuck on the 6500 RPM with the cast crankshaft.
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Hurst390
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Posted: Jan/20/2022 at 8:29am |
You do realize there have been people attempt this already? You do realize there isnt enough people out there to support an AMC magazine? Let alone an AMC crank. Here is probably the money maker. Start a magazine of LS swaps into an AMC/Rambler. |
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SC/Hurst Rambler
11.62 120 100% Street Legal |
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DragRacingSpirit
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Posted: Jan/20/2022 at 3:58pm |
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Oh no not an LS.  You can buy parts for them at target or best buy.
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Best 1/4 mile 8.99, 1/8 mile 5.71, 60 foot 1.27, no power adders
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Trader wrote: