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-   -   When stroking a 351w, do i have to change the top end too? (http://mustangforums.com/forum/classic-mustangs-tech/710851-when-stroking-a-351w-do-i-have-to-change-the-top-end-too.html)

Steffan 06-12-2014 07:22 AM

When stroking a 351w, do i have to change the top end too?
 
I kind of didn't get this question answered in a previous post, so i think a new post wouldn't hurt:

If i stroke my 351w, do i have to make any changes to the top end too?

The reason why i'm asking is because i might end up doing the top end first, and then stroke it later if the top end alone does not provide the power i want (reason: budget)

I am planning on putting the following on the top end:

Edelbrock #2090
Edelbrock #97453
Comp Cams Ultra Pro Magnum Rocker Arms #1632-16
Edelbrock #9656


If i install those parts (feel free to speak up if you think those parts don't fit together), can i then stroke it to 393 or 408 later without having to make any changes to the parts on the top end again? It seems like waste of money to me if i have to modify the top end 2 times.

Steffan 06-12-2014 07:23 AM

Side note:
I know i can get more power when i stroke the engine to 393 or 408 at the same time i change the top end. But that will break my budget so i have to choose from bottom or top end, and the top end seems like the easiest way to get more power.

racer_dave 06-12-2014 07:49 AM

So, I didn't really get into this because it was kind of a general question... but here goes...

Like I said before- an engine is nothing more than an air pump If you stroke the engine(add cubic inches) and push more air then then you have to increase the air going in and increase the air going out. Increasing air going in means you have to evaluate the carb size, intake, valves, heads and cam(intake). they all have to balance out otherwise it's like pouring water into a funnel, you'll get a restriction. As soon as you get a restriction then all your money and time went down the drain because you'll lose horsepower.

Once you get all the air into the engine then you have to get it out as well. Which means you have to evaluate the cam(exhaust), heads, valves, headers, collectors, mufflers. And again, if you get a restriction then you'll lose performance.

Last you have to consider what is happening not just at full throttle but also at low and mid throttle. So you can't just go bigger on everything because that may slow down airflow at low throttle and mid throttle, which is where most cars spend their time. Moving air through the engine requires volume AND velocity. Get the ports too big and you gain volume but lose velocity. Make them too small and you gain velocity but lose volume. It has to be balanced. Most cars spend very little time at wide open throttle, and with 450HP I doubt you'll ever be there for more than a few seconds at a time.

So while its easy to say 'do I have to xxxxxx' the answer is that everything needs to be evaluated from the bottom to the top. If you don't then sure the engine will run and make more power than stock, but it won't be everything it can be and you'll lose power that was there for the taking if parts were chosen correctly. That's why I seriously suggested getting an already built motor. If you aren't understanding how all this works together then you'll have a tough time choosing components to build it up on your own.

barnett468 06-12-2014 09:15 AM

Quote:

Originally Posted by Steffan (Post 8397633)
Side note:
I know i can get more power when i stroke the engine to 393 or 408 at the same time i change the top end. But that will break my budget so i have to choose from bottom or top end, and the top end seems like the easiest way to get more power.

heads can be bought with different size combustion chambers. you need the right size for your eng. . if you buy the right size for a 351 they will be too small for a 392 or 410. . you can buy heads that have lower compression now but will have enough when you stroke it but it will not run as well as it coud now. .mi

69mach1377 06-12-2014 10:32 AM

Quote:

Originally Posted by Steffan (Post 8397631)
If i stroke my 351w, do i have to make any changes to the top end too?

Yes, otherwise you won't take much advantage of the extra cubes.

racer_dave 06-12-2014 10:51 AM

"But that will break my budget so i have to choose from bottom or top end, and the top end seems like the easiest way to get more power."

New cam, new heads, possibly intake as well. If you choose right you can make a bunch of power. If your budget is limited do those first and drive it. Then see if you want more later. Don't forget to get the distributor curved. Getting it done right can gain you some good horsepower and it's cheap. If in doubt what to order call the manufacturers, they will help. Start with choosing the heads, then the cam and intake. Tell each one how you'll be driving the car. Be honest with them and they will get you the best part to fit your need.

barnett468 06-12-2014 12:41 PM

if you have stock pistons the bigger valves in your new heads might hit the pistons.

if you have stock pistons the extra hp might break the pistons or the rod bolts.

can't have your cake and eat it too. going fast costs money. there is no such thing as cheap reliable hp.


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