408 vs 427 strokers

5.0Torx · Jan 28, 2008

hey all. i have a 68 mercurcy cougar that my brother and i are restoring. this is our first musclecar and we were thinking about doing a 351-based 427 stroker for it (reminiscent of the FEs). but all i ever hear about are 408s.

whats the difference and why do more people buy 408s than 427s?

TIA

skywalker · Jan 28, 2008

Price and reliability are a big part of it. Depending on the block, you may have to notch it for a 427 which brings up the price. $27 is also at the limit of the standard 351W block so if you are racing some reliability issues may come up. Also, most people simply don't need THAT much power.

5.0Torx · Jan 28, 2008

thanks for the reply.

which blocks need to be notched?

My bro and i just want an NA beast. we wont be putting a blower on it for 1200 hp or anything. i'd be happy with a 6000-6500 rpm shiftpoint and between 500 and 600 hp at the flywheel. Is the 427 going to do that ok? i'd pay a little extra for the extra cubes, just because. its not like 408 is small lol.

skywalker · Jan 28, 2008

500+ hp is very much possibly with a 427. Not sure which blocks need to be notched but i would say most. which if you are doing the build yourself isn't to be of a deal as you can just have it done when you get the cylinders bored.

rbohm · Jan 28, 2008

the current most common stroker kits for the 351w are the 393, the 408, and the 427. each of them has their advantages and disadvantages, and all will make about the same amount of power given the same modifications. the 427 is at the limit of displacement for the block. as for block notching, that depends on the parts selection as to whether or not notching is needed. the only way to know for sure is to mock up the assembly and notch as needed.

fastcoupe68 · Jan 28, 2008

You can always go with an aftermarket block and then you wont have to worry about reliability issues

5.0Torx · Jan 28, 2008

where do i get an aftermarket block?

skywalker · Jan 28, 2008

Summit, Jegs, Mustangs Unlimited, etc. Even with an after market block though, reliability isn't necessarily fixed. The reliability problems are due to the over-boring of the cylinders walls taking them to the limit. Some aftermarket blocks fix that issue (Dart comes to mind.)

SoCalCruising · Jan 29, 2008

If you get a Dart block, get the 4.125" bore and use a 4" stroke crank. That makes 427ci. With AFR 205s, you'll make 550hp with a modest cam. Put in a beefy cam and 600hp is in the mix. AFR 225s will make a bit more power, depending on whether or not your cam will make use of the extra airflow at high lift.

fastcoupe68 · Jan 29, 2008

skywalker said:
Summit, Jegs, Mustangs Unlimited, etc. Even with an after market block though, reliability isn't necessarily fixed. The reliability problems are due to the over-boring of the cylinders walls taking them to the limit. Some aftermarket blocks fix that issue (Dart comes to mind.)

With what he is trying to accomplish 500-600 hp, an aftermarket block wont have any reliability issues. Any block bored passed the manufacturers recomendations would def have reliability issues, be it Ford racing, Dart, World products. As long as you stay true to there rec your not going to have problems. There are also many other factors that cause reliability issues and that could take alot of typing if we were to get into those subjects.

skywalker · Jan 29, 2008

fastcoupe68 said:
With what he is trying to accomplish 500-600 hp, an aftermarket block wont have any reliability issues. Any block bored passed the manufacturers recomendations would def have reliability issues, be it Ford racing, Dart, World products. As long as you stay true to there rec your not going to have problems. There are also many other factors that cause reliability issues and that could take alot of typing if we were to get into those subjects.

I can't agree with that statement. Just because they say it is safe at a certain over-bore doesn't mean there is not diminished reliability. Of course, this is affected by compression ration, max rpm, etc. But regardless, the thinner those walls are, the more risk you run of disaster.

fastcoupe68 · Jan 29, 2008

skywalker said:
I can't agree with that statement. Just because they say it is safe at a certain over-bore doesn't mean there is not diminished reliability. Of course, this is affected by compression ration, max rpm, etc. But regardless, the thinner those walls are, the more risk you run of disaster.

You dont have to agree because i am sure you know more than the manufacturers' do so we'll leave it at that

fastcoupe68 · Jan 29, 2008

skywalker · Jan 29, 2008

fastcoupe68 said:
You dont have to agree because i am sure you know more than the manufacturers' do so we'll leave it at that

Look, you don't need to be a smart ass. I'm an engineer and I understand how specs are chosen. Anytime you bore over you start to reduce cylinder wall reliability. The max overbore is chosen through statistical analysis, stress testing et cetera, that says x% of the time as y rpm with z cylinder pressures from w compression ration at this cylinder wall will not fail. Do I know the exact percentage? No. But I can still tell you that within the manufacturer's recomended specs, the maximum overbore has the least reliability.

5.0Torx · Jan 29, 2008

skywalker, its great to talk to a fellow engineer. im a junior at UM-Rolla and i follow right along with what youre saying. The truth of the matter is that both you and fastcoupe68 are right, just looking at it from different perspectives. I am fine with doing AFR 185s or 205s with a modest cam so that the shift-point is between 6000 and 6500. I want a real ground pounder with lots of torque down low. I know that, for that objective, deciding between a 408 and a 427 is like deciding between a sledgehammer and dynomatie for killing flies, but like i said earlier, i mainly just want the 427 so that i can say 427 lol. Im going to go check the bore sizes for the 408 and 427 stroker kits and decide what i think is best.

Of the two, which one would have a higher max engine speed? I want to cam it so that my shift-point is around 1000 rpm before the thing explodes.

thanks for the help guys. keep it civil.

PS will it fit in my cougar?

skywalker · Jan 29, 2008

Yes, It'll fit a cougar and I'm a senior at GaTech (senior whose remaining classes are all unrelated to my major

I was in no way saying that the 427 won't hold up: it will. But It has a much higher likelihood for failure than a 408. I've heard of several 427's blowing under heavy load at the track. But that likelihood goes down a lot with a Dart block or any block for that matter with a siamese bore.

Max rev depends on a lot of things:valve springs, cam, lifters (you'll get the best results from a solid roller, but they require more maintenance) the heads the carb. Typical small block should max out about 6500. With solid lifters and the right valve springs you can get that up to 8k.

enferno · Jan 29, 2008

you can get 600 hp no problem with a 408 NA

fastcoupe68 · Jan 29, 2008

skywalker said:
Look, you don't need to be a smart ass. I'm an engineer and I understand how specs are chosen. Anytime you bore over you start to reduce cylinder wall reliability. The max overbore is chosen through statistical analysis, stress testing et cetera, that says x% of the time as y rpm with z cylinder pressures from w compression ration at this cylinder wall will not fail. Do I know the exact percentage? No. But I can still tell you that within the manufacturer's recomended specs, the maximum overbore has the least reliability.

If were going to be like peacocks and show off our feathers then here we go
Not being a smart ass just speaking from 25 years of engine building experience, mainly automotive and marine racing engines, one year longer than you've been in existence
Lets concentrate on what his application is
A 500 to 600 hp 408 or 427, at this level a properly tuned Ford factory block can and will withstand the amount of horsepower level he desires ( I ran a 408 13-1 compression ratio, solid cam motor that made 578 flywheel horspower, shifting at 7200 rpms in a 66 stang for five years, ran the hell out of it at the drags every weekend and drove the car on the street alot. Never did I have a problem with reliability, never broke anything in the motor, ever!)
Now with an aftermarket block at the same level HP levels you basically with good internals, properly prepared have a bullet proof combo.
With a Dart block to make a 408 ci engine 4.00 stroke and a 4.030 bore the wall thickness in this block is so thick you will not and I repeat (will not) have a reliability issue.
427, 4.00 stroke and a 4.125 bore, the same holds true for this application.
Anything else I can help with, I'll be glad to assist

skywalker · Jan 29, 2008

You understand how to build an engine and have done so for 25 years. I fail to see how that changes how metal reacts to stress. And I said that using a Dart block fixes reliability issues and I also said that anytime you overbore you reduce reliability (true) and that you drastically reduce reliability at max over-bore (you do.)

fastcoupe68 · Jan 29, 2008

skywalker said:
Yes, It'll fit a cougar and I'm a senior at GaTech (senior whose remaining classes are all unrelated to my major

I was in no way saying that the 427 won't hold up: it will. But It has a much higher likelihood for failure than a 408. I've heard of several 427's blowing under heavy load at the track. But that likelihood goes down a lot with a Dart block or any block for that matter with a siamese bore.

Max rev depends on a lot of things:valve springs, cam, lifters (you'll get the best results from a solid roller, but they require more maintenance) the heads the carb. Typical small block should max out about 6500. With solid lifters and the right valve springs you can get that up to 8k.

I'm not trying to bust your B-lls but you have alot to learn! And leave the name calling on the playground, please

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