Question for you motor guys

H

HardScrabble

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I was reading a coupleof articles this past week where Robert Yates was talking about an engine he built for the endurance races at Daytona based off of Ford's latest generation of 4.6 liter V8's. Not a lot of technical info just general stuff. He is basically trying to convince NASCAR to move to these engines.

He made a remark which caught my eye though. In talking about the 4 valve per cylinder arrangement of these newer engines he made a comment that now the engine builders in NASCAR are lifting a single valve one inch.

I have not been involved in engine development for about 25 years or so, so my knowledge is outdated at bes. But, back in those days the mention of one inch of lift in a small block which was to last for a minimum of 500 miles and reach 9000+ RPM for much of that distance would have gotten you a visit from the men in white coats. Truth be told even talking 9000 RPM for that distance at any valve lift might have had the same result.

Anyways, the question is was Robert was just seriously rounding up valve lift, or is this a realistic representation?
 
HS,

I haven't built an engine with a "flat tappet" cam since 1984. But I do know those folks uses these "one race wonders" that have lobes that look kinda like rolle lobes yet have a flat tappet, or follower.

There has been a lot of work these recent years with rocker arm ratios in the 2:1 range...BUT you know what, I don't believe the ports in those M-6049-C3Ls could ever support a full inch of lift. Never....now take a set of SC-1s and I'd say .950.

In reality, I couldn't see the port working beyond .800 on a C3L head.

The 4v heads provide really drastic flow curves. They basically double at every lift point...nutty!!!, but true!!! Plus the chambers burn just like a high turbulence wedge. You can basically run a lot of lift with very little spring (valve are real light because they are small) and moderate duration. Strong bottom, mid and top end and good valve train life!!!! Who wouldn't want that?
 
unless he has something up his sleves, because existing parts just simply are not capable. I will belive it when I see it.

With that high of rocker ratio, the increased leverage will contribute to faster valve guide wear won't it? I can see that being a problem at 9000. I always thought that the increased lift may also necessitate a stiffer set of valve springs, rather than lighter, or run springs with more clearance before bind.
 
Originally posted by NateDogg@Feb 25 2003, 07:33 PM
unless he has something up his sleves, because existing parts just simply are not capable. I will belive it when I see it.

With that high of rocker ratio, the increased leverage will contribute to faster valve guide wear won't it? I can see that being a problem at 9000. I always thought that the increased lift may also necessitate a stiffer set of valve springs, rather than lighter, or run springs with more clearance before bind.
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Nate,

The soft spring is for a 4v application. You are right that a high lift 2v app will need a lot of spring.

Keep in mind though that the high ratio rockers used in cup are matched up against profiles that are designed to work with those ratios. I still say no cup head will gain by lifts over .800.

The 4v apps can use much less lift with mch lighter valves and much lighter springs.
 
Thanks!!

Sounds as if Robert was just rounding up. Back in the day, we always considered that once we got very far into the .700 with lift we were beginning to stretch the envelope. And springs were the big issue, We broke enough valve train stuff without pushing that any further.

As to the newer 4v configurations, the little bit I've read and from what I see here the flows are very different and look very advantageous to the 2v. Toss the push rods out and it sounds both efficient, powerful and durable. Aside from the initial costs from both a material and R&D standpoint, the lsot term costs might be less than they are now for the NASCAR folks.

Which leads to a another question. If as at present NASCAR resists fuel injection, how well would a carb feed a pair of 4v heads?
 
Originally posted by HardScrabble@Feb 26 2003, 07:12 AM
Which leads to a another question. If as at present NASCAR resists fuel injection, how well would a carb feed a pair of 4v heads?
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Just fine HS. A carb could care less about what valve arrangement is downstream.
 
Originally posted by HardScrabble@Feb 26 2003, 07:12 AM
Sounds as if Robert was just rounding up. Back in the day, we always considered that once we got very far into the .700 with lift we were beginning to stretch the envelope. And springs were the big issue, We broke enough valve train stuff without pushing that any further.
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HS, sounds like you were using the old K-motion H1000s. Very good spring for the time and I even used them up until '97, but things have changed. There are new alloy$ but they work a lot better and are a lot more predictable and consisntent.
 
To be honest I don't know which spring exactly, next time I talk to Red (our engine builder at the time) I will ask him. We found out soon enough that we were better off both from a performance and a financial standpoint obtaining the engines outside. We were just two or three guys trying to race and hold down full time jobs in the process. Got most of them from Prototype Racing and a couple from Ernie Elliott's shop. Red would still freshen 'em up when necessary.

Was not sure how a carb would react to more radical flows of 4v heads. The very little I know about such dynamics won't let me interpret the effect of the flow curves I have seen on some of these designs. I only know they are much steeper and aggressive than those I remember from the older heads.

Since NASCAR seems intent on not allowing fuel injection, at least it is conceivable they could go to the new heads and keep the carbs.

Thanks again for the info and patience.
 
The beautiful thig about a carb is, it's too dumb to know ay better. Just get the jets and air bleeds to match the air flow and you're ok.

For the longest time EFI wasn't even a consideration in Pro Stock, simply because the air/fuel demand could not be matched by EFI.

You're welcome HS.
 
Realize, of course, EFI is still not legal in Pro Stock.
 
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