Similar builds

[blykins]

I personally wouldn't run valve sizes that big on a 428 bore or a 260 bore anyway.  Way more than what's necessary to make power.  Shrouding would be a big issue.

[My427stang]

I personally wouldn't run valve sizes that big on a 428 bore or a 260 bore anyway.  Way more than what's necessary to make power.  Shrouding would be a big issue.

Great point, I didn't either on those runs, I was going to add some other some points this morning too

1 - In both cases I used valves that were usable in the small bore.  My thought was to see what the sims did with just bore and stroke.  Knowing the big valves would hit, especially on the FE, I didn't even consider them

2 - The FEs in the Camquest and the Pipemax are not the same.  It was late and I didn't feel like entering all the data in.  I just used 2 builds from the Camquest package, made sure they made sense, and changed bore and stroke.  For Pipemax, I used my all iron stroker build from last year, which was pretty close in the forecast numbers.  Then changed bore and stroke. FWIW, Pipemax  it the HP peak almost spot on for best and average based on our testing but torque was higher in the real engine. 

[Gaugster]

Here's a nice clip that gets into some of the nitty gritty about bore vs stroke. Kind of a tangent but.... A different perspective on things too. Generalization are sometimes the pitfall of a project but I totally get how those old wives tales make there way into shop talk.

https://youtu.be/UV3RwBPqznU

[DubyaTF]

   Interesting stuff to think about from all. As a novice at best, I see the building method as a chosen path to the same result. Large cubic inches vs large amounts of RPM and some variations of both on the extreme end of performance.

   I don't know if anyone else has seen or heard of it but the "valve-less" 302 built by Coates International (I think) that was an experimental engine using OHC style setup with ball valves machined into the cams to eliminate the poppet valve, pushrods, valves etc. Supposedly that engine would spin at 10,000 rpm with stock rotating assembly because the non-existent valve train restrictions. I only bring this up because how a traditional cam basically stops working at a certain rpm and the engine is done making power and torque.

   Not only that but NASCAR builds are relatively mild as far as bore and stroke but specifically built for rpm. There's plenty of video of these engines on a Spintron winging 11,000 or 12,000 rpm without parts failures.

   Again, I'm just a grease slinger and I got bit by the FE bug so this has been pretty cool to read and think about future builds.

      ***EDIT- I found the link for Coates-
        http://www.coatesengine.com/csrv-system.html

[frnkeore]

I personally wouldn't run valve sizes that big on a 428 bore or a 260 bore anyway.  Way more than what's necessary to make power.  Shrouding would be a big issue.

This was the question:

My question is as follows if a pair of engines were comparably built meaning same heads, cam, compression ratio and bolt on components would a 427 be much more powerful than a 428?

The answer will be yes, mostly because of the shrouding issue. That is why I offered the comparison builds. I'm not even sure that they (428 & 260) could be put together w/o notching the bores but, they are diffinitly possible.

[jwrmach1]

I ran into a guy at a dragstrip over 35 years ago that had two cars he ran regularly.  A 67 427 Fairlane and a 1969 428 CJ Cobra.  Something that has stuck with me all these years was his comment that both cars ran indentical times.
JWR

[blykins]

I personally wouldn't run valve sizes that big on a 428 bore or a 260 bore anyway.  Way more than what's necessary to make power.  Shrouding would be a big issue.

This was the question:

My question is as follows if a pair of engines were comparably built meaning same heads, cam, compression ratio and bolt on components would a 427 be much more powerful than a 428?

The answer will be yes, mostly because of the shrouding issue. That is why I offered the comparison builds. I'm not even sure that they (428 & 260) could be put together w/o notching the bores but, they are diffinitly possible.

Well yeah, but there should have been an understanding that you don't try to cram stuff in there that's not logical.   Obviously the 427 will make more power since the valves will be hitting the cylinder walls in the 428. 

[1968galaxie]

Well yeah, but there should have been an understanding that you don't try to cram stuff in there that's not logical.   Obviously the 427 will make more power since the valves will be hitting the cylinder walls in the 428.

Interesting "thinking" experiment.
Are cubic inches - large bore, short stroke - or small bore, long stroke equal as far as making power?
At lower rpm where there is no valve size limitation to power produced - they can make very similar power.
When smaller bore starts to impact air flow - the larger bore engine combination starts to look better and better.


Just my opinion.

[frnkeore]

Well yeah, but there should have been an understanding that you don't try to cram stuff in there that's not logical.   Obviously the 427 will make more power since the valves will be hitting the cylinder walls in the 428. 

It is totally logical to put 2.25 x 1.74 valves in a 427, right? If you can't do that with a 390/428, then the bigger bore makes more HP, correct?

Regarding same for same, with smaller valves, the math gives the edge to the smaller rod/stroke ratio (cyl filling after TDC), i.e. 6.488 rod x 4.375 stroke (1.483) than say the 368 Linc/Merc, 7.065 x 3.66 (1.93). How much difference it will actually make on a dyno, I can not say but, I've played with it in a dyno sim that I have and it made 1.5 hp, for the lower ratio, for SB engines I've run but, at lower rpm, like under 2500 rpm, the higher ratio made about 1 more HP. The difference is so small that it would be VERY hard to find on a real dyno.

I like long rods though and for even 5, maybe even 10 hp difference, I'll take the long rod, for it's reduce friction and stress.

[blykins]

Well yeah, but there should have been an understanding that you don't try to cram stuff in there that's not logical.   Obviously the 427 will make more power since the valves will be hitting the cylinder walls in the 428. 

It is totally logical to put 2.25 x 1.74 valves in a 427, right? If you can't do that with a 390/428, then the bigger bore makes more HP, correct?

No, not necessarily.  Why do you think a bigger valve will always make more horsepower?  Not true. 

[frnkeore]

Brent, I know that you know better than your trying to portray. A 2.09 valve, will not flow the same air as a 2.25 valve, you know that, right. Air mixed atomized fuel = HP, right?

Now then, if your talking about something other than max HP, you have a point but, as far as I can tell, the question was as stated and indicated (as I saw it) the potential for max hp.

All things being equal, that 2.25 valve, unshrouded, will create more hp than the 2.09 valve, as the flow demand increases. Not only that but, depending on the ports design (ability to keep velocity up) it can out do the smaller valve in the lower range, too. You know that, I know you do.

[blykins]

Brent, I know that you know better than your trying to portray. A 2.09 valve, will not flow the same air as a 2.25 valve, you know that, right. Air mixed atomized fuel = HP, right?

Now then, if your talking about something other than max HP, you have a point but, as far as I can tell, the question was as stated and indicated (as I saw it) the potential for max hp.

All things being equal, that 2.25 valve, unshrouded, will create more hp than the 2.09 valve, as the flow demand increases. Not only that but, depending on the ports design (ability to keep velocity up) it can out do the smaller valve in the lower range, too. You know that, I know you do.

In that case, then we just need to fit the biggest valve we can fit in any head, right? 

You need to think a little more about that one. 

[frnkeore]

For max attainable hp, with a good flowing port, yes.

Are you going to use 2.03 valves in your 352?

[blykins]

I’m gonna use the valve that’s appropriate for the port and throat size. 

I think I’m gonna see if a 2.450” will physically fit and then I’ll take a grinder and cut a chunk out of the cylinders.  Whatcha think?

If you’re thinking of fitting the biggest valve in your SBF head that you can fit, the 2.08” or whatever it was, you really need to take some time to rethink that.  Get away from that 60’s thinking of “I’m gonna make it as big as I can make it.”

[WConley]

Unsteady, compressible airflow is a REALLY complex thing.  Throw some atomized fuel into the mix and it's beyond crazy.

Some ports like tulip valves, some like nailhead.  The valve seat angle(s) have a huge effect on flow.  Bigger valves don't always work better, since the cylinder wall can get too close and back up the whole works. 

You would think that the wall only affects a small area, so the big valve must flow better overall?  Nope!  That small area can trip up the flow over the entire cross section. 

Despite spending a few years in wind tunnels during undergrad and grad school, I still only know enough about this to be dangerous.  I worked on afterburners for F404 jet engines (F-14 Tomcat proposal).  We found that adding restriction actually increased performance!  The restriction was carefully shaped winglets on the fuel spray bars, which added swirl to better mix the fuel.

It's a black art.  More is often less...


Edit - For the purists, we were working on an improved F404 proposal for the Tomcat.  Ultimately they passed on that and GE developed the F110 (from the improved F404) for the F-14D.  The F404 made its way into the F-18 Hornet.