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long rod engines

05-01-2004, 08:45 PM
Hey guys,

I'm just about to begin the build up of a 420A.... anyhow, putting aside the 4g63 argument, I have some questions about stroker and long rod engines.

I am completely new to the idea of using a long rod or stroker motor. I know for the stroker that the cylinder is going to need to be bored out a bit, and that all the kit contents will need to be installed. But how reliable are stroker motors, and how much reworking of the fuel/timing curve am I going to need to do?

Also, with long rod motors, it seems that they do not need machining, but instead they use specialized pistons? to accomodate for the longer rods. Anyhow, what's the deal with these, are they any less reliable, are there problems with cam timing. I haven't read extensively yet, but it seems that they simply hold the piston at TDC longer to create more power......could this cause trouble with valve timing?

Interesting questions, if anyone has a good "general info" link on stroker/long rod engines, that'd be wonderful.

This engine, btw, is going to be turbocharged and running an extremely modified head (cams, springs, oversized valves, the works).

- Nathan

05-02-2004, 08:27 AM
the basic concept of the stroker kit is to lengthen the stroke of the piston causing more area inside the cylinder for the molecules of air and fuel to mix in return a bigger explosion in the combustion chamber that forces more power onto the piston making it move faster! i have heard from a lot of people that have put a stroker kit on there car whether it was turboed or not that the inprovement was so nice that they would never go back! it revs faster yet not as high, and for a turbo car there is basically no lag, if barely any at all! i was planning on doing the kit for my car over the winter but i got the GST and things just didnt workout for the whole stroker plan, oh well! just make sure you get lowered compression pistons like 8.5:1-9:1 if you are goin to run turbo... as for fuel and timing get a datalogger and AFC and that will help you out a lot! they have yet to come out with a DSMlink for the n/t motors and i doubt they will for awhile if they ever do... so go with pocketlogger or another source of datalogging cause you will need it! good luck man, take some pics and let us know how it turns out! :thumbsup:

05-02-2004, 12:03 PM
okay, and any word on the long rod setup? Since I like what I've read about the stroker......I would imagine it could rev just as high with fully balanced and forged internals, no? (Not to mention a fully built head with titanium valve springs/retainers, all new everything)?

- Nathan

05-02-2004, 12:15 PM
i havent really read into the long rod setup much so i couldnt really give to a straight answer except it seems like the same concept of the stroker... to make a larger stroke for better and more power. i'll read up on it and post up later what i found out!

05-02-2004, 12:23 PM
Stroker and long rod are two seperate things, and can be used together or seperately. The stroker just increases the stroke of the crank. It has a longer throw. This give you more displacement (doesnt need to be bored, thats just part of a normal rebuild), and you get more leverage on the crank for the same explosion/expansion force (longer lever at the crank). The piston will also be special. To use the 4g63/2.3 liter example, the stroke is 12mm longer. So the piston pin has to be moved up 6mm so the piston does get pushed through the head ;) The rods used are just plain stock 1g rods, or 1g upgraded rods. There is no change to the rods reqired. The downside is the rod ratio, its gets a bit worse. The rod gets more "sideways" which causes a number of problems, and this is why the revlimit is usually lowered a bit. Properly built though, they rev pretty damn high, magnus runs around 8500 rpm IIRC.

The long road motor requires custom rods and pistons, but not necessarily a change to the crank. The whole point is to make the rod angle less severe (less sideways) so it can rev higher safely. An example is a 4g64 type block with the smaller 2 liter 4g63 crank. Basically the opposite of a stroker. The result is a little extra displacement from the extra bore of the 2.4 liter block, but more importantly a much more favorable rod ratio. I dont doubt that the people shifting at 9500-10k rpm are using a destroked motor like this. If you search back for some of our discussions on the advantages of making power/tq at high rpm, you'll see the benefit in this.

05-03-2004, 02:31 PM
I hate to ask so many technical questions, but it seems like a few of you guys know your stuff when it comes to building motors - and when I'm coming from the honda world where people know one thing: engine swaps + small turbos.......that's a refreshing thing. I had some mechanical engineering friends explain the long rod thing to me and they basically said the same thing, better angle = better forces.

Anyhow, so with the long rod motor, the rev limit would likely need to be pushed back.....

Well, let me give you some numbers, and see what you make of the setup.

The stock bore/stroke of the 420A is 87.5 mm x 83 mm [3.44 in x 3.268 in]

The new rods would be 0.136 longer than stock.

So, assuming a balanced and blueprinted, fully rebuilt/forged bottom and top end..... would I still be able to rev up to 7200 rpm (stock red line), and perhaps further since I have simulated the engine and it seems that I'd be doing quite well up to 9000+rpm if I can get the motor to rev that high safely.

Also, when would a forged crankshaft be needed?

Thanks again for your time!

- Nathan

05-03-2004, 06:07 PM
7200rpm isn't that much. The stroker motor redlines are less than a normal or destroked motor, but still are like 8000.

I wouldn't worry about a new crank. I don't think the DSMers in the 9 second range have anything but OE crankshafts.

05-04-2004, 07:55 PM
what everyone said is very true. If you want to get an imense amout of motor knowledge go out and buy a book written by Smokey Yunick. He helped invent the Small Block Chevy and most of the rules in NASCAR came about becasue of him and his black and gold cars. Now alot of times whenI have suggested this his books people say that was all stuff from 20years ago and doesnt apply. Wrong. For some reason people think that four bangers work on a different set of rules than older V8's. they dont. It is all performance engine theory.

The one thing that always stuck out my head was to put the longest rod you could safly put in there. The reason for this is that it will keep the piston at the top of the boar for a bit longer than the standard rod. This will help with build cylinder pressure becasue it allows the the piston to reach a greater speed and suck in more air in per stroke. It also helps to get as much exhaust out as possible to get a nice fresh intake charge. Only other thing to worry about is wristpin height. If you get a stroker or a long rod kit make sure that the pins dont go up into the oil control ring. Alot of people have god luck like this but on a daily driver it just seems to be more prone to oil consumption. It will also lead to cracked ring lands especially in a high heat turbo application.


05-04-2004, 09:46 PM
Michael, I appreciate the recommendation and the information.

I will check out the book idea :).

- Nathan

05-05-2004, 12:50 AM
I agree, it seems like as time goe by I apply more and more old v8 knowledge to my motors. Much of it is the same. Just adjusted for boost. My current motor has the wrist pin in the oil control ring, and so far so good. But I would feel much better if that wasnt the case, and I think thi is the biggest advantage of doing the 2.4 liter block as opposed to the 2.3 conversion. Another thing poeple do is use hte 2.4 block, but still put the pin in the poil control ring. Now you get the extra stroke/displacemtn, and long rods. Rod ratio becomes more like the 2 liters. Marco is taking his 2.4Ls to 8500 rpm without problems. I dont think I'll be goingmuch over 8k any more. Rev limit is now set to 8250 and I shoot for 8k rpm shifts.

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