Another educational thread about Iron blocks..
Thread Starter
Joined: Nov 2001
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From: Valrico, Florida
Another educational thread about Iron blocks.. Some have asked me why I am going 408ci and not 427ci. It was explained to me once, but I cant explain it back to the individual asking? Something about oversquare motor? They also asked about how high a 408ci to 427ci Iron can be rev'd..? I have no clue.
Vince, you would need a 4.125 crank in an iron block to produce 427cubic inches. Several people have had bad luck running with that much stroke in these engines. Over stroking the motor also limits your RPMS as well. Its not a good idea. Im sure someone will chime in with a more scientific answer, but this gives you the jist of it.
Thread Starter
Joined: Nov 2001
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From: Valrico, Florida
Ron, I remember someone else on this board complaining about their old 427ci Iron block, but they complained more about the actual crank they purchased than giving a good detailed explaination on why this is not a good setup. Most talk about a 414ci Iron Block as well. In another post I read that the 427ci should make 15 to 20rwhp more than a 408ci and about the same amount of tq increase. MTI sells a 427ci Iron Block so I am sure it must be possible w/out issues, but there must be a ACTUAL downside to doing 427ci Iron.
The MTI427Roadster guy is the one who had problems. He had a bad crank and huge oil consumption issues.It was an MTI iron with a 4.125 crank. SPeak to Allan about it, hes not a big fan AT ALL of overstroking an engine. I think he can make the power you need out of the 408. 
Thread Starter
Joined: Nov 2001
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From: Valrico, Florida
Allan explained it to me a while ago, but my work laptop crashed and I could not recover my .pst file. If MTI has a issue with this motor they might want to give away a 408ci instead a 427ci Iron.. Now to the revving of these motors.. How high would say one of these motors go with a 232/236 lsa 114 cam or a 242/256 lsa 115?
Thread Starter
Joined: Nov 2001
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From: Valrico, Florida
Now the cams I mentioned are hypothetical. I am in full guess mode. My car is going to be a FAST street car with some giggle for the other FAST cars. Idle quality is not as important to me, but I do not want to idle at 1100rpm. I want the idle to be like the 232/236 lsa 114 I had in my 346ci. I had the idle set at 850rpm and the car never stalled. I have a M6 with 3.73's and the car just rode out. I broke the motor and I am upgrading to a bigger motor. I have not talked to Futral yet about cams, but I am sure he has something in mind.. 
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The only limitation with my 4.075 stroke is the hydralic cam. Lunati claims 9k rpms is possible, but not done because of valve float. Why rev a motor way past its power peak. I don't have oil consumtion or any other issues going over 4". I would stick with the 4" crank just because they are easy to come by, will be cheaper to balance, and have a better rod ratio. My idle is at 950 on an auto with 3800 stall and 242 .595 112lsa cam.
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Originally Posted by VINCE
Some have asked me why I am going 408ci and not 427ci. It was explained to me once, but I cant explain it back to the individual asking? Something about oversquare motor? They also asked about how high a 408ci to 427ci Iron can be rev'd..? I have no clue.
Oversquare means that your stroke is longer than your bore. A 4.125" crank would be needed to achieve 427 at the max bore of 4.060" that can be achieved on an iron block. Your 408 is at the recommended 4.030" with the recommended 4" crank.
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From: Bay Area, CA
414 CID = 4 inch stroke 4.060 bore, cylinder walls are kinda thin, I'd rather keep the extra meat there for strenth and let that motor have 250 shot! shoot if I were to start over, I would do a sqaure'd iron block 4 inch bore and stroke 402 CID and run 30 pounds!!! 
Originally Posted by VINCE
Some have asked me why I am going 408ci and not 427ci. It was explained to me once, but I cant explain it back to the individual asking? Something about oversquare motor? They also asked about how high a 408ci to 427ci Iron can be rev'd..? I have no clue.
Last edited by sr71bb; Dec 30, 2003 at 05:11 AM.
Thread Starter
Joined: Nov 2001
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From: Valrico, Florida
Originally Posted by Damian
Vince, Alan is gonna set you up RIGHT. Let him worry about all this stuff cause he knows. Good luck brother...
josh
josh
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Vince,
There is NOTHING wrong with running a 4.125 stroke and 4.035 bore in a street engine especially if you keep the revs below 7500rpm. There are race motors running 8500rpm without problems with a similar bore/stroke ratio.
I would be more concerned about running a hyd cam and also the oiling system above 7500rpm than the crank itself.
I believe there were a couple of reluctor wheel issues with certain 4.125 cranks. This may have been resolved or might still be an issue. AFAIK the lunati 4.125 cranks are fine.
Cheers,
Chris
ps- I would keep the bore around 4.035 even with sonic testing of the block. You will get several serviceable overbores/hones with the block at .035 over.
There is NOTHING wrong with running a 4.125 stroke and 4.035 bore in a street engine especially if you keep the revs below 7500rpm. There are race motors running 8500rpm without problems with a similar bore/stroke ratio.
I would be more concerned about running a hyd cam and also the oiling system above 7500rpm than the crank itself.
I believe there were a couple of reluctor wheel issues with certain 4.125 cranks. This may have been resolved or might still be an issue. AFAIK the lunati 4.125 cranks are fine.
Cheers,
Chris
ps- I would keep the bore around 4.035 even with sonic testing of the block. You will get several serviceable overbores/hones with the block at .035 over.
TECH Regular
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From: Spring Hill, TN
A decently built 427 can rev higher than the limitation that's placed on you by the LS6 intake manifold anyway. If you want to routinely rev above 7K then you'll need a different intake manifold with shorter runners (custom made?). So short of that there's no reason not to go 427 unless it's cost prohibitive. You'll have better torque and more overall power.
PS. in regard to the side-loads mentioned above, this can be mitigated with longer rods which can be accomplished with pistons that move the pin location higher up.
PS. in regard to the side-loads mentioned above, this can be mitigated with longer rods which can be accomplished with pistons that move the pin location higher up.
Thread Starter
Joined: Nov 2001
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From: Valrico, Florida
Originally Posted by LOnSLO
It's UNDERsquare that builders don't like. UNDERsquare motors have more stroke than bore. One good reason they don't like them, valve shrouding.