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Transmission ratio with 2165 engine

Willy PWilly P
I need some wisdom on the ramifications of using a 4.12 stock IRS trans with a 2165 CB Performance engine in my Roadster. I am thinking that a stock transmission will present two issues. One is the 4.12 ratio will be turning the engine at 4000 RPM at 70 MPH approximately. Aside from the sound of the engine being more pleasant to cruise at lower RPM, what are the effects of this RPM level on the 2165 engine? I cruise my 1600 engine at 4000 RPM/70+ MPH and experience no oil temp problems and a stock beetle can cruise all day at 70 MPH. Is cruising with the big engine at 4000 RPM detrimental to the engine? I would think that with the counterweighted crank,better rods,beefier valve train components,of the big motor that the 4000 RPM cruise would not be a problem. Also the cooling air flow at 4000 would be removing heat better than at 3500 RPM. The other issue is transmission wear/ strength. Will my stock trans last with the greater HP/Torque? Should I just get a beefed up 3.88 trans when I do my engine swap? I never drive over 80 MPH and cruise at 70-75. My current trans would give good performance in hilly /twistie roads that I like to run the car on. Any input is appreciated.
1959 Intermeccanica(Roadster)
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Willy PWilly P
I need some wisdom on the ramifications of using a 4.12 stock IRS trans with a 2165 CB Performance engine in my Roadster. I am thinking that a stock transmission will present two issues. One is the 4.12 ratio will be turning the engine at 4000 RPM at 70 MPH approximately. Aside from the sound of the engine being more pleasant to cruise at lower RPM, what are the effects of this RPM level on the 2165 engine? I cruise my 1600 engine at 4000 RPM/70+ MPH and experience no oil temp problems and a stock beetle can cruise all day at 70 MPH. Is cruising with the big engine at 4000 RPM detrimental to the engine? I would think that with the counterweighted crank,better rods,beefier valve train components,of the big motor that the 4000 RPM cruise would not be a problem. Also the cooling air flow at 4000 would be removing heat better than at 3500 RPM. The other issue is transmission wear/ strength. Will my stock trans last with the greater HP/Torque? Should I just get a beefed up 3.88 trans when I do my engine swap? I never drive over 80 MPH and cruise at 70-75. My current trans would give good performance in hilly /twistie roads that I like to run the car on. Any input is appreciated.
FM Former Member
A 2165 will produce more heat at any given engine speed more than your stock 1600.

Stroke is longer, piston diameter is greater, 100 more HP and with that in mind, you're trying to cool a huge engine with stock cooling components.

Sure, more RPM's means more cooling but more RPM's also means more heat so at some point, the heat produced is greater than the cooling system can handle.

I think I'd probably go with a 3.88 or, if you can find one, a 3.44 ring and pinion.

With a 4.12 R & P and a 2165cc engine, you will accelerate through the gears much faster and as a result, you'll be shifting more often.

If your intent is to race 1/8 or 1/4 mile drags then leave the 4.12 if it's to cruise then think about a 3.88 or 3.44.

In regards to the strength of your stock transaxle. It will work provided you take care of it but you're putting quite a load on parts made for 53 HP.

If you decide to get a new transaxle then go for welded gears, side plates, super dif's etc etc.
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