Yellow Bullet Forums banner

101 - 120 of 137 Posts

·
Registered
Joined
·
7,928 Posts
How close to the valve job is OK to mill? Why can you go closer on a SBC than a BBC, or am I mistaken about that?
If you want to take the time and spend the money, you can cut the heads for new intake valve seat inserts then angle mill the head then install the new seat inserts then do your valve job, that way you can cut off as much as possible and still be able to put the top angle on the valve job.

Angle milling and rolling the head over was done to get compression and more than likely hurt port flow. That's the reason RM welded up the intake side of the head deck surface before they angle milled their BBC alum. heads while developing them.

It's as simple as that the small cuin sbc gained more from the compression increase than did the big cuin BBC's than the decrease in port flow hurt them. And add the cost of milling the intake manifold and anything else needed to match the head angle and it makes no sense to angle mill a BBC head for the little gains you may get when you can buy much better standard angle or lower angle heads and manifolds these days.
 

·
Registered
Joined
·
23,503 Posts
If you want to take the time and spend the money, you can cut the heads for new intake valve seat inserts then angle mill the head then install the new seat inserts then do your valve job, that way you can cut off as much as possible and still be able to put the top angle on the valve job.

Angle milling and rolling the head over was done to get compression and more than likely hurt port flow. That's the reason RM welded up the intake side of the head deck surface before they angle milled their BBC alum. heads while developing them.

It's as simple as that the small cuin sbc gained more from the compression increase than did the big cuin BBC's than the decrease in port flow hurt them. And add the cost of milling the intake manifold and anything else needed to match the head angle and it makes no sense to angle mill a BBC head for the little gains you may get when you can buy much better standard angle or lower angle heads and manifolds these days.
I know very little about the BBC, but on the SBC, with say, the 292 head, or the equivalent, when you angle mill the head, and lower the valve angle, even slightly, and raise the roof, and even fill in the floor, you end up with a fairly small intake port, but you see big gains in flow numbers from .300 up. So, angle milling the SBC 23 degree not only helps compression, but if filled, and ported properly, increases flow. If you don’t raise the roof, it can actually hurt flow.
 

·
Registered
Joined
·
1,296 Posts
I believe that most shelf pistons for sbc will accept at least a .125 angle mill. I cannot remember the last SBC that I built without that much of a cut.
 

·
Registered
Joined
·
23,503 Posts
I believe that most shelf pistons for sbc will accept at least a .125 angle mill. I cannot remember the last SBC that I built without that much of a cut.
Yes, most pistons with the 23 degree valve angle cut will clear most moderate cams, only because most shelf pistons have plenty of clearance. When I’d order a custom piston, I’d always tell them the finished valve angle, but you are correct, .125 normally ain’t a deal breaker on most builds.
 

·
Registered
Joined
·
7,830 Posts
Discussion Starter #107
I thought of another question I wanted to ask the other day, but I forgot it before I could post it. It'll come back to me eventually...
 

·
Registered
Joined
·
2,391 Posts
so Randy , did you play around with Rod ratio's
 

·
Registered
Joined
·
23,503 Posts
so Randy , did you play around with Rod ratio's
Yes, but I had no clue really what I was doing with them. I just listened to guys that had experimented on ratios. And I tried running longer rods in all the 23 degree stuff, from 5.75 to 5.85 to 6 inch to 6.125. I really can’t say one worked better then the other, but for some reason in an automatic, single 4 deals, a short rod seemed to be a tad quicker. We ran some 5.485, to 5.550 length stuff in the 2 speed cars we put engines in. Now, on the Dart Buick stuff, a 5.7 or shorter worked great. I know all about the dwell time of rod lengths, but someone else can explain it better. Like I’ve stated several times, I just tried shit to see for myself.
 

·
Registered
Joined
·
7,928 Posts
This is from a 362 cuin SBC, 11.5 CR 1.94/1.50 valve/280/295/.720 cam.



362.661 Cubic Inches @ 7200 RPM with 104.00 % Volumetric Efficiency PerCent

Required Intake Flow between 252.2 CFM and 266.6 CFM at 28 Inches
Required Exhaust Flow between 172.9 CFM and 195.0 CFM at 28 Inches

600 RPM/Sec Dyno Test Lowest Low Average Best
Peak HorsePower 533.9 555.9 566.8 577.8
Peak Torque Lbs-Ft 431.6 449.3 458.2 467.1

HorsePower per CID 1.472 1.533 1.563 1.593
Torque per Cubic Inch 1.190 1.239 1.263 1.288

BMEP in psi 179.5 186.8 190.5 194.2
Carb CFM at 1.5 in Hg. 786 874 918 963

Target EGT= 1301 degrees F at end of 4 second 600 RPM/Sec Dyno accel. test
Octane (R+M)/2 Method = 102.3 to 104.1 Octane required range
Air Standard Efficiency = 62.84764 % for 11.459:1 Compression Ratio

Peak HorsePower calculated from Cylinder Head Flow CFM only
600 RPM/Sec Dyno Test Lowest Average Best Potential
Head Flow Peak HP = 504.5 575.1 645.7
 

·
Registered
Joined
·
7,830 Posts
Discussion Starter #113
so Randy , did you play around with Rod ratio's
Speaking of rods, what did you use for pins? It seems the current trend is smaller OD with thicker walls, but I don't know how far back that trend goes. Also, some people like bronze bushings, and others run steel on steel with practically zero clearance, but not a press fit.
 

·
Registered
Joined
·
1,584 Posts
Speaking of rods, what did you use for pins? It seems the current trend is smaller OD with thicker walls, but I don't know how far back that trend goes. Also, some people like bronze bushings, and others run steel on steel with practically zero clearance, but not a press fit.
I run .875 pins in my engines 2 1/4 inch length.080 wall tool steel rods are bronze bushed. Pistons are real light. About 340 grams. The engine is a high rpm NA combo SBC. Good reliability
 

·
Registered
Joined
·
23,503 Posts
Speaking of rods, what did you use for pins? It seems the current trend is smaller OD with thicker walls, but I don't know how far back that trend goes. Also, some people like bronze bushings, and others run steel on steel with practically zero clearance, but not a press fit.
I always ran super light pins in my early engines, and still do in my engines in the 500 to 550 hp range. I’ve ran them as lite as 67 grams, and didn’t see a problem. But, I do understand the reasons behind heavier wall stuff they run today in like Pro Stock. And most Comp Eliminator classes. The cylinder pressure in those engines coupled with extreme rpm, dictates the needs they see. And I always ran lightened pistons in the baby engines. As lite as under 400 grams. But I also understand the reasoning behind heavier pistons to keep the pistons from oil canning. Which unseats the rings, as too lite of wrist pins will do the same.

But, remember something, what’s always good for the goose. Does not make it good for the gander. Too many variables in engines today to just state that one thing works 100%, and the other doesn’t.
 

·
Long Live The King
Joined
·
95,598 Posts
Best engine build ever? Let me think. It’s one of 3 I’d say

Engine 2. Maybe the 289” Brodix spec head that put out 592 hp with the heads unported, Stock Block, and a cast hurricane intake, one 750, clutching every gear, and running 6.29 109 and change in the 1/8th mile, at 10.5 #’s per cid, and setting the local track record at the time.

Engi.
2.04 hp per cubic inch with a single 4 ?

Nice

How much compression?
 

·
Registered
Joined
·
23,503 Posts
2.04 hp per cubic inch with a single 4 ?

Nice

How much compression?
Ya know, it’s been 11 years, but if I remember right, we angle milled the heads only .125, and maybe ended up with 10.8 to one. It was hard to get compression with those heads and small cubes, because we ran a 2.08 valves in the standard location, and the head starts out as 67 cc chambers. And I used a set of pistons I had laying around that were for the bow tie heads. Now, I built a 285” for the next year that had around 11 to one, but I had the pistons custom made to the chamber. Sold that engine after track didn’t open for a song.
 

·
Registered
Joined
·
2,391 Posts
Fascinating, thank you Randy for the insight
 

·
Registered
Joined
·
7,830 Posts
Discussion Starter #119
How thick (or thin) were the head decks after you milled them? I looked at my 990 big block heads and I don't think the decks would have enough rigidity left if I had 0.125 angle milled off them.
 

·
Registered
Joined
·
23,503 Posts
How thick (or thin) were the head decks after you milled them? I looked at my 990 big block heads and I don't think the decks would have enough rigidity left if I had 0.125 angle milled off them.
Ya know, I don’t know exactly. But if my memory serves me, the 461x heads, and those in that era, .125 was a bunch. I know I had a pair of 292’s that I think were milled .175, and I remember the whole exhaust side seemed paper thin. And we ran a 2.04 valve in them. There was a bit more meat in the bow ties, and we milled most of them .175, and they claim you can mill the vortec bow tie heads like .275. Some head guys may have a more in-depth answer to that.
 
101 - 120 of 137 Posts
Top