How adequate are stock heads?

[Edmond]

Will the stock Valve covers clear 1.6 Roller Rockers? Be a cheap mod for my 84.

The oil drip tabs must be snipped.

 

[Moonunit 451]

I was pondering this question today. How adequate are they? Now much power could the 1.94/1.5 valves be good for? Could they achieve 325 horsepower for the L98?

I was thinking about what to do with my heads later this year. 1.6 roller rockers are definite. What if I rebuilt them to stock spec and ported the opening from the intake manifold?

Compared to what, is what I'd like to know? What do you want to accomplish?

I have only seen reports of one, maybe two cars that will run in the lower 12's with these heads, heavily moded. Not saying it can't be acomplished, but it takes a lot of $'s from what I've seen.

I don't have the book, took my advice from folks that have done this stuff and read the book on forums like this. I don't know why people would consistantly buy heads costing 2K plus if they could go fast with modified stock heads, but I'd like to

 

[Edmond]

I wouldn't even care about drag strip passes; I just want a fearsome street machine.

I guess what I want to know is: for a street machine (stoplight to stoplight), does it make sense for me to have the heads ported and polished with bigger valves if all I want is a stoplight to stoplight vehicle?

 

[Moonunit 451]

Not sure, but what would the MAN say Still gonna be a big ticket

 

[Edmond]

Not sure, but what would the MAN say Still gonna be a big ticket

Well, that's just all in theory.:L

 

[Edmond]

I went into one of the local shops today. I saw they had an advertisement about cylinder head inspections. I asked him where was a good shop to have the heads ported and polished, didn't know they did it there. He told me that they do it there for $200 for labor, parts not included.

Is that a good price?

 

[vetteboy86]

It depends on what they will do. Are they going to increase the intake volume, and machine new valve seats for larger valves, and then bowl/pocket port them. I would spend 200 bucks to have my heads done, opposed to 1250 for a swap. I can't see why these heads wouldn't support a 350 hp engine.

This is straight out of the book: John Lingenfelter on modifying small block chevy engines.

You know that my emphasis on a wide powerband street engine calls for a cylinder head that will make torque even at lower engine speeds. This eliminates the 200 cc and larger intake port heads, especially if the engine is a daily driven 350. Based on this concept for a street engine of 350 to 383 cubes I prefer to use heads arund 170-180 cc intake ports. I use the aluminum corvette head on many combinations because the head makes excellent power in a slightly ported condition and because it is bolt on.

So that is what I went on. I find it hard to not trust this guy.

 

[bossvette]

to me the "Bible" on small block Chevys is availabe from your local GM dealer
and is called simply "Power Catalog" I should really go get a new one since my newest is the 6th edition and they were still running carbs

it is a very technical volume not a catalog like the name appears to be well worth the asking price it is geared more to the serious mechanic then the shade tree guy.

 

[ben73]

http://users.erols.com/srweiss/tablehdc.htm

 

[Hrtbeat1]

to me the "Bible" on small block Chevys is availabe from your local GM dealer
and is called simply "Power Catalog" I should really go get a new one since my newest is the 6th edition and they were still running carbs

it is a very technical volume not a catalog like the name appears to be well worth the asking price it is geared more to the serious mechanic then the shade tree guy.

That one and its companion I believe it was called "Chevy Power Secrets" I hear ya. My newest copies don't even include the Gen 2 motors ... and they are on Gen 4 .... :duh

http://users.erols.com/srweiss/tablehdc.htm

Thanks for the link mate. Some good info there. I was stoked to see my old 462 camel humps and the numbers they put up. If you look through the chart at the I/E volumes I see a pattern similar to what vetteboy86 was refering to ... good volume and good velocity.

 

[Mad-Mic]

Edmond,

lets not confuse everyone with what heads you have because there are 2 casting #'s L86 and 87 got a different less flowing head than 88-91 cars. your Dports are the same heads TPiS use on their applications. my friend Phil aka Wheelsup over on CF went 11.20's with a M6 90 vette with 4.10's, mini ram, Dport 113 heads ported and revalved by TPiS, ZZ9 cam (nearly equivelent to a Ling 219 cam but a tad beefier) and a mini ram. with the right setup and gear combo anything is possible. HP is all in the head. Don't let ANYONE fool you. When i met Phil he is the one i bought my TPiS headers from and he lives local to me so we became friends. When he told me what the car ran on a ZZ9 cam i couldn't believe it. his friend Dave that had the identical setup with the 219 cam was still very stoutly down there with him. i'm sure we all can agree that the 219 and ZZ9 cams are "Baby" cams for our cars but that is VERY impressive! did i mention this was on a stock shortblock from 1990?

on the flip side of this todays head techonology compared to late 80's GM mass produced technology that wasn't a clean casting like you get today out flows even the best of TPiS D port 113 head. with that being said alot of the money going into YOUR heads goes into cleaning that casting up. ie bowl blending and the actual port job. OUT-OF-THE-BOX from just about any aftermarket dealer out there, their heads will FLOW BETTER than your heads EVER will with no matter how much money you put in them.

You like good head your car likes good head for opitimal performance too! :L

just some food for thought. most machine shops if you tell them you have X amount of money they will do X amount of work. It really depends what you are eventually doing with the car down the road.

 

[Edmond]

My car likes good heads, it's plural!:L:L:L

I think I'll just keep the stock valve sizes and rebuild the stock heads. I'm not looking for a drag strip car, I just want a fearsome street machine with a lot of torque.

 

[grumpyvette]

just some info

http://www.chevyhiperformance.com/techarticles/41598/

http://www.kendrick-auto.com/head_flow_figures.htm

http://www.malcams.com/legacy/misc/headflow.htm

http://www.dw1977.cz28.com/photo2.html

http://www.geocities.com/z28esser/headcomp.html

http://home.earthlink.net/~hennad/results.html


while theres no direct linear relationship between port flow and hp there is a relationship.
the ballpark formula is
.257 x port flow x 8 = potential hp

EXAMPLE
if your intake port flows 250cfm
.257 x 250 x 8 = yealds APPROXIMATELY a 514hp figure before your heads become the limiting factor
this ballpark formula is based on average results FROM WELL TUNED HOT ROD TYPE ENGINEs USEING DYNO FLYWHEEL RESULTS
NOT true race only engines or street engines
also keep in mind that the results youll get will differ and to get those numbers it requires the engine to operate in its best rpm range with a cam and compression levels that match and all other components must also match
if your heads flow 279 cfm at .700 lift but your intake only flows 240cfm and your cam has a max lift of .550 your not going to get the max potential HP results
for the ballpark formula to work you must have a tuned exhaust, a cam that matches the compression ratio and all other parts must flow at least close to as well as the heads at the max figures
also keep in mind that the ports cross sectional area should keep the airflow in those ports in approximately the 200fps-300fps ranges
airflow speeds that very greatly from that 200fps-300fps will not tend to give best results, thats why huge ports that flow exceptionally well don,t work well on smaller displacement engines
port lenth also has a large effect on the rpm range that the ports can effectively pack the cylinders at due to harmonics in the collum of air
PORT SIZE FLOW AND THE RELATION TO CAM DURATION, and your displacement and the tuned rpm that your headers operate best in for scavageing the cylinders also comes into play here!


FIRST, This will not be anything more that a brief glimpse into a subject that takes years to understand and I’m sure there are a few people on the site that can give more exact info! This is meant to apply to the 350-383 sbc engines most of us are useing
My purpose is merely to give an idea as to the relationship between the factors and yes IM ignoring several minor factors to make things easier to understand
But lets look a a few concepts
(1) There are 720 degrees in a 4 cycle engines repetitive cycle of which between about 200degrees to about 250 degrees actually allow air to pass into the cylinder, (the valves open far enough to flow meaningful air flow) and the piston has a maximum ability to draw air into that cylinder based mostly on the engines displacement and the inertia of column of air in both the intake port and the suction (or negative pressure the PROPERLY designed headers provide) this produced a max air flow thru the ports, the greater the volume of fuel/air mix effectively burn per power stroke the greater the engines potential torque production, the faster you spin an engine the greater the NUMBER OF POWER STROKES PER MINUTE, and up to the point where the cylinder filling effectiveness starts falling off due to not enough time available to fill that cylinder the torque increases, above that rpm or peak torque it’s a race between more power stokes and lower power per stroke
(2) look at this diagram
(3)

As air enters an engine it normally travels thru both an intake system and the cylinder heads intake port to eventually pass into the cylinder thru the valve. The valves in a normal small block corvette engine are between 1.94 and 2.08 in diameter, that’s between 2.9sq inches and 3.4 sq inches of area, but because the valves require a seat that at a minimum are about 85%-90% of that flow area we find that the intake port even with out any valve has a max flow of not more than about 90% of the flow thru a port of valve size. Or in this case 2.46 sq inches-2.9 sq inches of port area, Since you gain little if any flow having a port that’s substantially larger than the valves AT NORMAL ATMOSPHERIC pressures and since you can’t substantially increase the valve sizes for several mechanical reasons you must improve efficiency, this is done in two major ways, you can match the intake port length and cross sectional area to the engines most efficient rpm range on the intake side, to build a positive pressure behind the intake valve as it opens and match the exhaust length and diameter on the exhaust side to provide a negative pressure to help draw in more volume this will require the cam timing match that same rpm range of course. By experimentation its been found that air flow port speeds in the 200-320 cubic feet per minute range are about the best for a chevy V-8 now lets say you have a 383. 383/8=47.875 cubic inches per cylinder, the rpm range most used is 1500rpm-6000rpm so that’s where are cam and port size must match, you can do the math , (47.875 x ½ engine rpms = cubic inches, divided by your cams effective flow duration, (use 210-235) as a default for a stock cam) x 720 degrees/1728 (the number of cubic inches in a cubic foot) to get the theoretical max port flow required (I will save you the trouble its 250cfm-275cfm at max rpms and about 2.4-2.9 sq inches of port cross section, depending on where you want the torque peak, or use this handy calculator,

Intake Runner Area = Cylinder Volume X Peak Torque RPM 88200
Or this helpful site
http://www.newcovenant.com/speedcrafter/calculators/intake.htm
Either way you’ll find that you’ll want a port size in the 2.4sq –2.9 sq inch area
Now use this calculator to figure ideal port length, REMEMBER youll need to add the 6” in the cylinder head to the intake runner length to get the total length and you can,t exceed the engines REDLINE RPM which with hydrolic lifters seldom is higher than 6400rpm

http://www.bgsoflex.com/intakeln.html


Ever wonder why your engines torque curve gets higher with the engines rpm level until about 4000rpm-5500rpm(DEPENDING ON YOUR COMBO) but fades above that rpm level?
well it depends on several factors, first as long as the cylinders can fill completely you get a good fuel/air burn so you get a good cylinder pressure curve against the piston each time the cylinder fires, THE ENGINES TORQUE CURVE INCREASES WITH THE NUMBER OF EFFECTIVE POWER STROKES PER SECOND, at very low speeds there’s not enough air velocity to mix the fuel correctly or produce a effective ram tuning effect but as the rpms increase the cylinders fill very efficiently until the rpms reach a point where the cylinders just don’t have the time necessary to flow
enough air through the valves to fill the cylinders , remember a 5000rpm the intake valve out of 720 degs. in each cycle opens for about 250degs of effective flow even with a hot roller cam, now that’s only about 35% of the time and there’s 41.6 intake strokes per second , that’s only 1/60th of a second for air to flow into the cylinder
Its your engines ability to fill the cylinders that increases your power and the more efficiently you do that the higher the rpm level you can accomplish that at the more power your engine makes, remember the formula for hp is (torque x rpm/ 5252=hp) so moving the torque curve higher in the rpm range increases hp but at some point the time available to fill the cylinders becomes so short that efficiency begins to drop off rapidly, the peak of efficiency is reached normally in the 4500rpm-5500rpm range, and as rpms increase its a race between more power strokes per minute trying to raise the power and the increasingly less effective percentage of cylinder filling dropping the power.
Volumetric Efficiency
The volumetric efficiency of a 4-stroke engine is the relationship between the quantity of intake air and the piston displacement. In other words, volumetric efficiency is the ratio between the charge that actually enters the cylinder and the amount that could enter under ideal conditions. Piston displacement is used since it is difficult to measure the amount of charge that would enter the cylinder under ideal conditions. An engine would have 100% volumetric efficiency if, at atmospheric pressure and normal temperature, an amount of air exactly equal to piston displacement could be drawn into the cylinder. This is not possible, except by supercharging, because the passages through which the air must flow offer a resistance, the force pushing the air into the cylinder is only atmospheric, and the air absorbs heat during the process. so, volumetric efficiency is determined by measuring (with an orifice or venturi type meter) the amount of air taken in by the engine, converting the amount to volume, and comparing this volume to the piston displacement.
this increases until the torque peak then falls as the rpms increase. Here is a rough guide to match duration to port flow at different rpm level

if you’ve been following along you’ll find that you’ll need intake ports about 2.3-2.9” sq inches in cross section, and between 12” and 21 “ long (DEPENDS ON WHERE THE ENGINE IS DESIGNED TO MAKE MAX HP) and cam timing in the 215@.050 to -240@.050 lift range, as the rpms or displacement increase either the port flow or the cams duration must increase or the engines cylinder fill efficiency rpm will drop!
Now this is important, as the port flow efficiency goes up though the use of longer and larger intake ports the cam duration could remain the same or even be lower and you get more efficient cylinder filling as the rpms increase, that’s why high efficiency port designs like on the LS1 can use lower duration cams to flow similar total air flow thru the ports than the lower efficiency ports like the old fuelie heads could but at some point all ports reach max flow and an increase in the time the valves remain open at higher rpms increases the cylinder fill efficiency and that increases the engines ability to make torque at that rpm range, you must account for the average RPM range and ENGINE DISPLACEMENT in your comparisons

 

[vettered91]

Wooow! :eek

¡Thanks Grumpyvette!

I have never seen so much usefull info in just a few lines, I'm reading right now one of David Vizard books (How to Build Max Performance Chevy Small Block) because I'm building a 389 from my LT1 engine all by my self and I've been reading everything I can about the subject. It's incredible how much performance you can get from a pair of heads with the proper job, there are many things like if you get a 30° seated valve instead the 45° conventional will give you a 23% more through flow passage at .050" can give you real advantages with low $ expenses!!!

Enough to start learnig more about it if you ask me!

 

[grumpyvette]

there seems to be a HUGE mis-understanding about port size and how it potentially effects your engines torque range,
port size should be thought of more as a restriction to reaching necessary flow than a benefit to making a significant torque curve PROVIDED your matching the total engine component list to the intended rpm range and expected hp peaks the engine will be expected to produce and run at!
its not port size but the ports cross sectional area and length matched to the other components like the engines displacement,compression, cam timing and bore/stroke ratio PLUS the exhaust systems designed scavage effiecincy range at any give RPM level has a major effect on results, the size of the ports in your cylinder heads are one of the least> THATS RIGHT I SAID THE LEAST important of the factors that determine where in the rpm range your engine builds its best power, while its true that smaller port cross sectional areas due cause the airflow speeds to increase,its also very true that the runner length and cross sectional area of the intake used, the compression ratio and the cam timing and the design of the header primary tubes are at least two to three times as important simply because they control the airflow thru the cylinder to a much greater extent, and the engines stroke and total displacement are extremely important, changing JUST the displacement and cam timeing has a HUGE EFFECT on WHEN and HOW the airflow in the ports gets its vacuum signal and how the port responds to that change in pressure.
you can build a torque monster engine with large ports in the cylinder heads, quiet easily if the other factors are carefully matched

notice that the 180cc AFR heads which are known for torque production have basically the SAME cross sectional area as the TRICKFLOW 195 cc heads and that the differance between the AFR 180cc haeds and the 210cc heads is only approximatly a 6% increase in size so the true air flow thru a 210cc head will be only approximately 6% slower on the same engine.........swap to a 383 from a 350 which is approximately 8% larger and you quickly see where the smaller heads can become more of a restriction than a benefit to the combo!

know I know from experiance building engines for years that a rought guide to matching hp to the intended engine port flow requirements can be guessed at fairly closely useing these formulas below, play with them then measure the port cross sectional area in your engine at its narrow point, and don,t forget the cam lift your restricted too and the valves curtain areas in the combustion chambers

"Fortunately for our purposes, these complex calculations can be broken down into a very simple formula that is useful for us as speed crafters.
Intake Runner Area = Cylinder Volume X Peak Torque RPM 88200
This formula takes into account the best theoretical speed that air can move down the runners, to give the best volumetric efficiency. Peak Torque occurs in an engine at the RPM where the engine is enjoying its highest volumetric efficiency. "





below youll find some things to read/play with

http://www.n2performance.com/lectures/airflow.pdf

http://www.rbracing-rsr.com/runnertorquecalc.html

heres a chart FROM THE BOOK,HOW TO BUILD BIG-INCH CHEVY SMALL BLOCKS with some comon 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


http://www.rbracing-rsr.com/runnertorquecalc.html


play with the calculator,, notice the vortec heads 1.66 are would peak the torque at about 3100rpm on a 383, while a dart 215 cc with its 2.14 port only moves it up to about 3950 rpm AND THATS ASSUMING the larger port head has a matching larger intake runner the whole way to the carb venturies, if you stuck the same intake and other mathing components on BOTH cylinder heads the differance in rpm ranges would be more likely to be in the 300rpm range

 

[vettered91]

Well... Thanks again for sharing with us these usefull info, the more I read about it the more I think engine building it's a sience-skill that takes years to dominate, but the road to get there is very entertaining.

Here some links to interesting articles:

http://www.mercurycapri.com/technical/engine/intake/pt.html

http://www.geocities.com/MotorCity/Track/6992/vizard.html

http://www.babcox.com/editorial/ar/eb90252.htm

 

[Larry's Yellow Rdstr]

Grumpyvette,

You took the words right out of my mouth!