There really isn't a specific displacement or rpm. A 500" engine making peak power at 8000 needs a big valve. A 632 making peak power at 5500 doesn't. Having said that, a conventional BB Chev head will run out of valve area long before it runs out of port.

 

OK then, to make it a little more specific.

Lets say a 565. 4.600" X 4.250" @ 7500 RPM. Does it want the bigger valve? (2.300" versus 2.350")

If so, which factory 24 degree CNC head would be a better choice? (A head you can buy from any major parts outlet/dealer and not have to wait months for a porting shop to complete.)

 

That puts you in the 2.4+ range for an intake valve. (port needs to be about 3.4 sq in). There are a couple shifted valve conventional heads that can run that big of a valve. I think Broidix and Edelbrock both have one but you're probably not going to find a set on the shelf anywhere already finished, waiting to be sold. (not yet, anyway ) Or, you're in SR20, Dart 20* or Dart 18* range, or spread port heads but they all seem to have much larger ports than necessary (IMO). A 2.35 valve will limit your rpm on that combination. You can sneak a 2.375 in a couple different castings with standard valve locations and still use the 1.88 ex valve. A 565 peaking at 7000 still wants a 2.37 @ 92% throat, but only needs a 3.2 sq in. port. That's usually something in the 335=345 range so find a port with a 3.2" cross section, put the biggest valve you can in it and port accordingly. CFM is not going to get the job done here. Lot of really good flowing "big" heads with 2.30 valves that will make good power, but will limit the rpm without getting really crazy with the cam.

 

Some Edelbrock Victor cnc'd race heads used a 2.30" and it should get you north of 1000hp.


Here's a "mild" 565 build.


http://www.maxracesoftwares.com/forum/viewtopic.php?f=5&t=96

 

I believe they put a 2.35" valve in the heads on this build.

http://www.superchevy.com/how-to/engines-drivetrain/1006chp-pettis-performance-598ci-big-block/

 

Darts newer 365 has a 2.350 and 1.850. I reckon would be pretty bad arse for a common cnc head

 

In my experience the bigger valve has always made more power. A 2.350 is as big as you can go with standard valve spacing without shrinking the exhaust valve. I use a 2.350 and bigger valves on a 4.50 and larger bore.

 

Good discussion.

Anyone have experience with the Dart 365 head bought bare. 2.350" X 1.850" valve size and factory CNC. It does not show much more flow on intake on Darts listed flow sheets. Same price as the Dart 355 CNC head. Pricey even on a good deal.

 

Mark, I don't really see a cubic inch limit to valve sizing but more of a bore diameter limit moreso? 4.3?? bore is much harder to get a 2.35 valve into, and 99 times out of a 100 you need to move around the dowels to accomplish this.

So as long as you're 4.4++ bore, always try and go bigger valve. Again Foxwell wants to put out thought on formulas for HIS thoughts, but even though they were a bit smaller, back 10+ years ago, BES 525 used NMCA legal at the time 2.350 valve BMF 350's (385 and 405's were not "LEGAL"). These through an UNCUT or WELDED cast single made 1180Hp and turned 94/9500 rpm. I had MANY a long talk with Tony about these as my 499 short was at least as well thought out as these, and my Pontiac "427" worked abit more. So like many have stated, back then the heads/intake was worth about 100 more, which turned out pretty close. BUT I did have 2.400 valve.

Jeff C onn here used to do some 565's with 2.35 and usually made well north of 2.1Hp per inch. PM guys like Abbottracingheads and Slick Rick on here. Those 2 played in the TPS days of conventional heads and would know pretty well what is REALLY required at that cubic inch size.

FYI I believe the highest Hp conventional head, NON SR20 with a single is Alex Hayes 588 with BMF 330's and cast SNIPER. Made 1330Hp with Slick Rick induction.

Now your $3500 budget BARE!!!! There are a ton of heads out there and most will work very good by the time you fill them and tailor them YOUR combo. I don't think there is a "best" but HH have been well received and so has the Profilier Snipers. BUT I'm sur you would by much better off with a good USED set from guys moving up to the SR20 stuff.

 

I never should have sold that top end combo. Thing was nasty good. I mean we've already destroyed its power numbers with my new sr23 headed combo and billet intake but yeah that thing was worked out

1338@8100

 

Here is a partial plan for a 565 BBC for a "what if" combo. Not a max effort, just good power for a faster bracket race door car.

Dart 4.600" bore short deck. Billet main caps.

Dart 24 degree CNC 365 bare heads. OR ??

Manley Severe Duty stainless valves.

Pac or PSI springs double. 275#@2.050" installed height.

Wiseco Quick 16 48.7 CC dome pistons. .043"/.043"/3 MM rings. gas ported. Off the shelf.

Total Seal AP series ring set.

Molnar 4.250" 8 counterweight 4340 crank.

Molnar 6.385" H beam rods. ARP 2000 bolts.

Custom solid roller camshaft. .800"/.800", 288*/292* @ .050", 110 LSA. Or??

Rollmaster Gold timing set.

3/8" X .135" pushrods.

Comp Cams Ultra Pro Magnum steel stud rocker arms, 1.7 ratio.

Jomar stud girdle.

Edelbrock Super Victor intake. Ported.

1250 Dominator carb.

A bolt together bracket race combo with just the normal good machine shop procedures, one can get together in a month or two after getting all the pats in one pile. No waiting 6 months to get trick heads.

 

Raised cam block?

 

Something that makes you go hmmm..

Just had an engine builder build a 632 for a mud racer. We used my iron Dart head. 363cc, 2.350 valve. The engine had some lift, like .880ish..

Had a Edelbrock 632 manifold. Peaked at 7300. Made 1140hp.

 

That's impressive. Lot of work for those classes that require iron heads.

 

We'll be doing a serious effort (not max effort) conventional head 565 this winter. I don't think a 2.35 valve is going to cut it. Not sure what we'll do for heads at this point. Customer doesn't want a lot of maintenance so will be limited to making peak below 7500. Should be a fun build.

 

Two other things to consider Mark.
1) .903 lifters
2) 7/16 pushrods

 

If more than .800" lift I agree on .903". Trying to plan a decent bolt together agenda. You don't really find Dart blocks stocked anywhere with .903" lifters. Dart wants a month to do it and recommends bushed lifters for oil control with the thru holes getting bigger with bore increase. 7/16" pushrods are easy on exhaust, not so easy on intake with wide ports and no offset lifter. Not enough room on AFR CNC heads either without getting thin on intake port material. Short deck blocks used to fit some GM stock engine bays with off the shelf headers. Raised cam blocks are more money to the combo too.

 

We order and run Dart blocks with .903's and no bushings. Never had an issue. The passenger side lifter galley needs to be plugged at the back, in front of the distributor hole, especially with hyd. rollers. I would upgrade to a .903 long before .800". Pretty much any solid roller will benefit. AFR's and 7/16 push rids...never had a problem there either. Some guys just put heads on a mill and move the entire pushrod hole over but if you do it by hand and only remove material where the pushrod is hitting, you won't break through the port. You're not going to throw something like this together in 8 wks. If you don't have the time to do it right, you might as well just buy a complete "shelf" engine somewhere.

 

Then off-set lifters and rockers. Anything to help / improve BBC valvetrain geometry is a plus.

Raised cam block = shorter pushrods = less deflection.

 

Thanks Alex. I figured as much. Haven't really followed Ultra since Butch stepped out, or NA 10.5 since Mike put it on the back burner also. So rules are where they are. BUT I am glad to see some of the rule makers seeing some of the conventional head are getting close to the spread port stuff.

Congrads on the record and good luck

 

As for pushrods, I'm not even sure they make them in 7/16's but I would have to believe so since I have them in 1/2", but wouldn't a double taper pushrod help this clearance issue?

 

All good stuff on the combo.

Back to original question. 24 degree factory CNC heads with 2.350" intake valve size. Which is a better?

Any one with experience with the Dart CNC 365 head?

Also noticed the Dart spec sheets for the 355 and 365 differ in intake valve length. 355 calls for +.250" extra length and 365 calls for +.350". Wonder why?

 

I would look at Snipers? You have a bare $3500.00 budget and Speier has some tunes up 500 CFM Sniper 375 XL for $3800.00. I know it's not "factory" but that seems like a pretty interesting option!!!!

 

I think the sniper xl heads are bigger 400+ cc heads from what I saw when checking them out.

 

Yup.

 

What's Wrong with the AFR 377 or 385 heads..... I know people will say they're to BIG for a 540-565
but they have a big Bowl area which chews up a lot of cc.... I have them on my 532, it makes a shit ton of power
1100 to be exact, cam has .850 lift, I run it to 8400, has a shit ton of bottom end.... it has went 1.058 in sixty foot @ 2275 lbs.... 7.40 @ 183.86 mph....

2.350 valve and I have clearance them for 1/2" pushrods on the intake and exhaust, didn't break through
anywhere.
AFR 357 would take a 2.350 valve no problem...... I like there castings, and would put them right up there with Dart, Brodix, profiler...ETC....

I am also putting a set of AFR 385's on a 565 right now.... that one has .937 lifters, 55 mm camshaft and .920/.880 lift......hoping for upper 1100's hp wise, Maybe 1200's if my ducks are in a row...LOL

 

RCM, I've never got the "heads are too big" thing? I will agree that's some heads can be too big for certain applications, but I don't believe a head can be too big.

Now with this being a street car with some track times, I would be asking more of what he wants, KILLER ET's or better street driving to decide on heads? There have been plenty of motors UNDER 500 inches that work very well at the track with heads bigger than the AFR 357/377's, but you have to turn them some RPM's. And on a traction-limited street car, this I think helps ease it off the line, then RPM and wheel speed gets the car moving!

 

There should be a , between the 375 and XL. There 2 different heads. It's not listed as 375XL on Chad's site. If you go there to look, there listed separately, 375 and XL.

Just mentioned it as the XL are listed at $3,800.00, $300 more than his $3,500.00 budget.

 

Gotcha. I just bought a used set of sniper x 375s that were done by reher morrison- Milled into front of heads. They have a the factory cnc port and a little work by RM. Angle milled to 23 degrees and a little hand blending.
Gonna try and get them flowed. Not sure if anybody on here had one of those sets on a bench?. RM just lists the flow #s for the factory 24 degree cnc heads I believe.

 

Have you checked with Darin Morgan at RM, My Profiler street heads are 449 CFM@.800 with 2.350 valves?

 

No I havnt called them. These are 2.350 valves also. They are gonna go on a street/ Strip 582 build. A little overkill probably but got them for a pretty good price with the t&d shaft rockers.

 

Thanks Scott. Yes im having the heads dis assembled right off and cleaned and freshen up valve job- Check and set springs etc. Just hope thats all they need. The intake side was corrected I was told for the manifold but well see as it goes along. You all are right I probably should call RM for some info. Kinda feel like im not doing the heads justice using them for a pump gas build and want to keep net valve lift under .800 and it seems like these heads like a lot of lift. I dont want to keep hi jacking this thread- Sorry.

 

Need some tech help. Ha ing a 632 12.5:1 built. Goal is 1100 + then adding 350 of NOS. Going into heavy pro street 74 c10. Used for car cruises but want to run low 9. Builder says dart pro1 cnc 365. What does everyone think? Tunnel ram motor so prob need to spin 7 to 7500 for manifold to work properly. Im afraid thats not enough head. Rather spend more now than ha e to buy a different set. Help appreciated.