the infos there but most guys simply ignore the answers

[grumpyvette]

A few charts and a bit of math go a LONG WAY towards answering a few basic questions, and I'm frequently asked why a certain combination once its built does not live up to the car owners expectations.
I've constantly seen trends over the years and while I'm all too aware most of us build on a very limited budget and because that restricts access to all the components we would like to have in our builds it makes the process far longer and more difficult, yet I also see a STRONG tendency for guys to select components based more on price than part compatibility to the intended goal. in fact at times I get the distinct impression that the parts being bolted together , were almost a random selection of components with the only requirement in their selection being the physical ability too have the parts bolt together.
the fact is that a well planed selection of matched quality components will almost always perform far more effectively that the random mix of bargain priced parts many cars are built from.
a simple choice made while planing the engine, like selecting a bit less duration on a tighter LSA in a cam, or actually accurately measuring the valve train clearances and valve spring load rates can and does make a huge difference in the finished engines durability and power curve!
Id also point out that your vehicles drive train, rear gear, transmission gearing and tire diameter can have a very pronounced effect on how your engine will function
EXAMPLE one of the local guys has a son that started out in this hobby like most of us do, buy buying some ones half finished project car and a wide assortment of parts from friends cast offs and the idea that simply bolting them together , with the help of several enthusiastic but usually equally in-experienced friends,would some how result in a fast car.
YEAH! I'll freely admit I went through a sharp learning curve due to starting out on a similar manor but unlike many guys I've always had a strong tendency to step back and say to myself "WELL CRAP! THAT DIDN,T WORK WORTH A SHIT!" when I screw something up royally, but unlike many or most guys I want to know EXACTLY WHY IT DID NOT WORK!, AND WHAT I COULD DO TO MAKE THE CAR MORE DURABLE, FASTER, OR LESS EXPENSIVE OR EASIER TO WORK ON, OR WHAT TOOL CAN I USE TO DO THAT WITH A GREAT DEAL LESS EFFORT.
theres been hundreds of times where I read through some magazine article, explaining how too do some modification,and think, this guy forgot to mention you can,t do that... without doing ..#$%^&*, or that this guys SKIPPING OVER THE FACT THAT, if you did some other minor modification, the first modification would be far more efficient or more durable.

one of the local guys built a older 1968 camaro with a low compression 454 big block, engine he pulled from a donor motor home, he installed a rather aggressive roller cam in place of the original STOCK roller cam with no thought to the non-adjustable valve train, and the woefully inadequate valve spring load rates and clearances. that engine was also severely compromised, because the original 307 sbc exhaust system in the car, was designed for a small block engine that would have strangled the engines performance once the engine rpms went much past about 4000 rpm.

look at the chart below

now assume your BBC has 2.06 diameter intake valves, and displaces 454 cubic inches ,like this example did, a 454 big block chevy, thats 56.75 cubic inches per cylinder divided by 2.06 equals 27.55
looking at the chart it should be rather obvious that a much tighter LSA than the 114 LSA that was selected in this case, would have potentially enhanced the engines ability to efficiently fill the cylinders and the very restrictive exhaust was obviously used to save money but would be a very obvious and measurable problem area restricting the engines power potential.

Potential HP based on Airflow (Hot Rod, Jun '99, p74):
Airflow at 28" of water x 0.257 x number of cylinders = potential HP
or required airflow based on HP:
HP / 0.257 / cylinders = required airflow


USE THE CALCULATORS, YOULL, QUICKLY FIND THE LIMITATIONS
http://www.rbracing-rsr.com/runnertorquecalc.html
http://www.wallaceracing.com/chokepoint.php
http://www.wallaceracing.com/header_length.php

related info, that you might need
http://garage.grumpysperformance.co...heads-for-small-block-chevys.3293/#post-26213

http://garage.grumpysperformance.com/index.php?threads/what-are-these-heads.4702/#post-12742

http://garage.grumpysperformance.co...-by-step-guide-with-pictures.5378/#post-71848

http://garage.grumpysperformance.co...ther-efi-intake-manifold-info.431/#post-26322

http://garage.grumpysperformance.com/index.php?threads/porting-can-help.462/page-3#post-59145

http://garage.grumpysperformance.co...ads-tuned-intake-turbulence.12998/#post-67611

Volume (CCs) of Head Gasket
CCs of Head Gasket = Bore x Bore x 12.87 x Thickness of Head Gasket
COMMON SBC INTAKE PORTS
felpro # 1204=Port Size: 1.23" x 1.99"=2.448 sq inches

felpro # 1205=Port Size: 1.28" x 2.09"=2.67 sq inches

felpro # 1206=Port Size: 1.34" x 2.21"=2.96 sq inches

felpro # 1207=Port Size: 1.38" x 2.28"=3.146 sq inches

felpro # 1209=Port Size: 1.38" x 2.38"=3.28 sq inches

felpro # 1255 VORTEC=Port Size: 1.08" x 2.16"-2.33 sq inches

felpro # 1263=Port Size: 1.31" x 2.02"=2.65 sq inches

felpro # 1266=Port Size: 1.34" x 2.21"=2.96 sq inches

felpro # 1284 LT1=Port Size: 1.25 x 2.04''=2.55 sq inches

felpro # 1289 FASTBURN=Port Size: 1.30" x 2.31" 3.00 sq inches
http://users.erols.com/srweiss/calccsa.htm

Your RPM computed from your Cross Sectional Area of 1.95
(the smaller AFR HEADS)
and Bore of 4.03 and Stroke of 3.75 is 5,569.12 .

Your RPM computed from your Cross Sectional Area of 2.05
(the Larger AFR HEADS)
and Bore of 4.03 and Stroke of 3.75 is 5,854.72 .
you,ll barely notice the about 300 rpm shift in the power band on the lower part of rpm range but appreciate it much more on the upper edge of that power curve


heres a chart FROM THE BOOK,HOW TO BUILD BIG-INCH CHEVY SMALL BLOCKS with some common cross sectional port sizes
(measured at the smallest part of the ports)
...........................sq inches........port cc
edelbrock performer rpm ....1.43.............170
vortec......................1.66.............170
tfs195......................1.93.............195
afr 180.....................1.93.............180
afr 195.....................1.98.............195
afr 210.....................2.05.............210
dart pro 200................2.06.............200
dart pro 215................2.14.............215
brodix track 1 .............2.30.............221
dart pro 1 230..............2.40.............230
edelbrock 23 high port .....2.53.............238
edelbrock 18 deg............2.71.............266
tfs 18 deg..................2.80.............250

USE THE CALCULATORS
http://www.rbracing-rsr.com/runnertorquecalc.html
http://www.wallaceracing.com/chokepoint.php
http://www.wallaceracing.com/header_length.php
http://www.superchevy.com/how-to/en...-0902-chevy-engine-port-variations-measuring/
http://www.hotrod.com/articles/choosing-the-right-camshaft/
http://garage.grumpysperformance.com/index.php?threads/bits-of-383-info.38/

Last edited: 1 minute ago


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[philly]

hey grump you must have double clicked the submit button, as this thread appeared twice, but to comment further on the lobe centerline chart, since that seems to be the foundation of everyones argument, that chart is for engines between 9.5:1 and 11.5:1 compression ratio (static) and as you shift away from those points, every ratio 1:1 more that you go, the LCA must be adjusted two degrees. so an 11.5:1 motor with 23 cid / inch valve calls for a 106 LCA but a 15.5:1 motor is 4 ratios higher (8 degrees) and would require a 114 LCA given the same 23 cid/inch valve dimension...

the line on the chart is made for street motors in the 9.5-11.5 range, and vizard cautions to always err tighter given the option, because one degree too wide can cost 10-15 hp on an otherwise 500hp motor

thats only part of the equation tho... possibly the most important and usually oversized spec on a cam always seems to be overlap. people tend to get crazy with the overlap when whats needed really isnt all that much. however amount of overlap in relation to the lca seems to balance out... theres a chart ive got somewhere maybe in a book that goes into loose detail about what kind of overlap you should shoot for.

once overlap is chosen and lca is picked from the chart, the duration is already computed into the spec. iv you have X lca with Y overlap the duration will be 2X+.5Y every time. its a function of those other parameters so it cant be something its not.

as for lift most street motors with good heads and a proper cam will make power with ATLEASt .28 of the intake valve diameter and still have manners and street use longevity. that is to say a 2" valve should have atleast .560" lift after accounting for lash to make the power you should be making with it

 

[philly]

david reher of reher morrison on cfm...

http://rehermorrison.com/tech-talk-70-a ... /#more-389

“The pursuit of a big cfm number has ruined countless cylinder heads.”

“What’s it flow?”

Whenever a conversation about cylinder heads begins with that question, I cringe. I know where this discussion is going, and it’s not good. When a racer wants to distill the performance of a highly developed cylinder head down to a single number, I know I’m dealing with someone who is fixated on the flow bench.

I can speak from hard-earned experience, because there was a time when the flow bench was the center of my universe. When my partners Buddy Morrison and Lee Shepherd constructed our first flow bench in the ’70s, it was a revelation – or so we believed. We were addicted to airflow, and like three flow bench junkies, we convinced ourselves that big flow numbers translated to quicker elapsed times. But that was more than 30 years ago, and since then I’ve learned to avoid the pitfalls of flow bench testing.

Unfortunately many racers coming into the sport haven’t been taught the lessons that Buddy, Lee and I learned the hard way. Cylinder head manufacturers, porting shops, and engine builders constantly advertise flow numbers – and I confess that I’m sometimes guilty as well. In this environment, it’s understandable that some racers think it’s all about maximum airflow. They shop for the biggest cfm number at the lowest price, like finding a screaming bargain on a 52-inch TV at WalMart.

The strategy to win the “Biggest CFM Contest” is simple: Grind the largest port that will physically fit in the head, use the biggest valves that will fit the combustion chambers, and test it on the biggest fixture you can find. That head might win the prize for airflow, but it won’t win on the dyno or on the race track.

The factors that determine the performance of a cylinder head are complex. A head that is ported without considering air speed, the size of the engine, the rpm range, the location of the valves, and a dozen other parameters isn’t going to be the best head, regardless of its peak airflow. And yet I see racers who are seduced by big cfm numbers bolt a pair of 10,000 rpm cylinder heads on a 7,000 rpm short block and then wonder why the engine won’t run.

The most critical area in a competition cylinder head is the valve seat, and the order of importance works its way out from there. There are many questions that are much more important than airflow: How far are the valve heads off the cylinder wall? What’s the ratio of valve size to bore diameter? What’s the ratio of the airflow to the size of the valve? What’s the size of the port, what’s its taper, how high is the short-side radius? The answers to these aren’t as simple as comparing a flow number, but they are what really make a difference in an engine.

Airflow is simply one measurement among many that influence engine performance. With the availability of affordable flow benches and computer simulation programs, it’s easy to fall into the airflow trap. A builder works on a cylinder head, sees some bigger cfm numbers, and keeps working for more flow. But if he doesn’t stop and test the engine on a dyno and on the drag strip, it’s very likely he’s gone down a blind alley. What the manometer on a flow bench sees at a steady 28 inches of depression is not at all what the engine sees in the real world. The pursuit of a big cfm rating has ruined countless cylinder heads in terms of what will actually run on an engine.

I put more faith in dyno pulls and time slips than I do in flow benches. I’ll cite an example from back in the day when Buddy, Lee and I were winning Pro Stock championships. Lee came up with an idea for a tuliped exhaust valve. He filled in the back of the valve with Bondo, and tested the new design on our flow bench. It was killer. We instantly saw a tremendous improvement in airflow with a small exhaust port, a nice tight radius below the seat, and much more stable flow. So we had some titanium tulip exhaust valves made and tested them on the dyno – and the engine didn’t run well at all. We had great airflow on the bench, but the engine didn’t care.

We were working late one night, and Buddy decided to yank the heads off the block and have Lee open up the exhaust throats. Well, Lee kept grinding and Buddy kept taking the heads on and off, and eventually we picked up 30 horsepower that night. We were porting from the dyno and not from the flow bench. When Lee finally flow tested the heads the next day, they were down 30 or 40 cfm, but that’s not what that engine saw.

The final test of a cylinder head is on the track. Frank Iaconio was our chief Pro Stock rival, and he was a smart racer. Frankie used to change valves at the track — he’d make a run, come back to the pits and switch from valves with a 30-degree back angle to a 20-degree back angle. We did similar tests on the dyno, but he did it at the track. I was impressed.

I’m not dismissing flow benches. In fact, we use them daily at Reher-Morrison Racing Engines. But a flow bench is a tool, and it’s really not much different than a micrometer. A micrometer can measure the diameter of a piston, but you have to run the engine to learn the correct piston clearance. Knowing the sizes of the piston and cylinder bore doesn’t tell you if the piston is going to gall or collapse a skirt until you run it. And knowing the airflow of a cylinder head doesn’t tell you whether it will make good power on a given engine until you race it.

Experience is the most important tool in cylinder head development. A person with extensive dyno and track experience has been through it all before, and knows how to avoid the flow bench fallacies.

 

[philly]

also of note is the emergence of very high quality beehive springs that are made by many companies for a variety of applications... do you realize that because of the small windings at the top of a beehive spring, a tool steel retainer for one is barely (a gram or two) heavier than a titanium retainer for a traditional spring for the same application? that saves money and weight in your valve train... all food for thought. goodnight.

 

[87vette81big]

The Info is buried deep on Grumpys site Phil...
Testing airflow at 28 inches of water depression is BS crap .
Needs to be tested at least 100 inches water depression.
Actuall running engine sees 200-300 inches water depression.

Also need to measure cylinder port velocity air speeds.
Its never ever fucken published. My guess is because its shit numbers.
Big airflow numbers sells new aluminium heads.

 

[87vette81big]

Cleaning my Poncho Babies next week at work Phil.
Ultra Sonic Clean them.
"614" 1970 Ram Air IV / 4's .

 

[philly]

nice! good to hear... glad 455 project is moving along.