Cylinder Heads 101

[BJR Racing]

I'm going to attempt to help people out that don't have much knowledge about cylinder heads so they don't make mistakes. Some of this info will be helpful to some, and more helpful to others. I'm going to be dealing with intake ports only for now as you only need 70% exhaust to be efficent so its easy calculations later.


cyl. head valve size port ccs airflow .100 .200 .300 .400 .500 .600
4027163 stk 1.78 120 54 104 155 182 188
3769973 gm,bb,bc 1.78 126 72 137 183 213 201
915 stk 1.88 150 85 130 177 189 190
915 bb,bc 1.88 154 65 143 180 203 212
Commando stk 2.02 190 80 115 177 219 251 290
Commando ported 2.02 196 87 142 209 250 303 316
915 ported 1.88 168 96 185 229 248 283 285
587 ported 2.02 170 94 177 223 251 287 287
302 HP ported 1.78 136 89 164 216 232 231 231
302HP gm,bb, 1.88 130 83 141 204 218 213 213
915 bc 1.88 150 85 168 201 213 216 216
915 bb,bc 1.88 153 90 181 219 228 226 226
915 bb,bc nail head 1.88 155 85 166 210 228 228 226
915 gm,bb,bc 1.88 159 91 177 219 231 232 232
587 gm,bb,bc 2.02 167 92 178 228 247 248 248
273 powerpac 1.78 134 86 138 199 223 228 225
ported

These are just some of the few heads with different modifications that most people would have, other than the commandos.

bb= bowl blend
bc= back cut
gm= gasket matched

If you will notice that the smaller valves flow very similar to the bigger counterparts that this would tell you that the valve is too big for the port, and as the air flow drops so does the velocity. Also you will notice that as the port volume increases the air flow doesn't in low lifts on some heads, which tells you that some heads are better with modification than others.
The main thing to do is to keep the velocity up and use the smallest valve that you can get away with.
Use 318 heads on 318s as the valves won't be shrouded in the cylinder as it opens. Keep in mind that the bore on a 318 is only 3.91 stock and this is the reason that the factory use a smaller valve on the engine and to keep efficiency up. Now as for the 360 and the 340s the bore is bigger and will accept a larger valve, this is why they put 1.88s in the 360 heads from the factory as the bore is 4.00 and 2.02s on the HP 340s as the bore is 4.04 stock.
Now as for testing a 318 with the 360 heads and a 1.88 valve the engine lost HP and torque, not just because of the compression but because of the port volume being too big for the little engine, and the velocity being down. Cylinder bore size creates suction, smaller bores pull less than bigger bores, this is partially why they made the ports larger for bigger engines. Thus the old saying bigger is better in the case of Cubic Inches. This is why port volumes are much bigger on big cubic inch big blocks, as the bores are in the 4.50-4.65 range. Also keep in mind that the stroke comes into play here also, so when bigger strokes are put in and the rods get shorter, thus the piston speed increases greatly. When this happens the pull is less due to the piston speed so the port volume has to be increased greatly to supply the engine at high rpms.
Example: Big block Chevys have big ports and big valves, short rods and longer strokes, compaired to the 440 dodge with a small port and valve and a longer rod and shorter stroke. Yet they run very similar. Partially because the rod angle isn't as bad as the Chevys and the rod to crank position is better on the Dodge thus the increased torque.
So in general, the idea is to keep the valve and port as small as possiable and achieve your goals. This will give you the best performance per the engine used.
Our test engine:
318 .030
KB 167s
mopar .528/284 cam
lightened rods- stock with 80 grms. removed
bob weight 1937grms.
ported 302 HP heads with 1.78/1.50 valves
block square decked so the piston is .020 out
heads ccd at 50 ccs with .040 cut off deck and intake sides
ported intake M-1 manifold
750 cfm alky carb flowed to 1030 cfms
corteco .055 gasket to achieve .035 quench
compression ratio 12.52:1
201psi cylinder pressure
heads ccd at 136 port volume
heads efficiency intake 67.8%
exhaust 65.2%
heads flow 231 @ .500 intake
180 @ .500 exhaust
hedders 1 5/8 dynomax open exhaust
corrected elevation:
29.98
75 degrees
56 dew point
3253 ft above
Atlanta, Ga. in October

3000 3500 4000 4500 5000 5500 6000 6500 7000
Brk TQ. 333 404 453 471 471 462 449 431 383
Brk HP 190 269 345 403 448 484 513 533 511

Average Tq. 419
Average HP 417

vol. eff. 84.4 97.4 108.4 115.3 117.7 116.5 113.7 108.8 102.3
int. vel. 217 254 290 326 362 398 435 471 507
exh. vel. 183 213 244 274 305 335 366 396 427


This is just something to keep your minds busy, if you have spare time.



BJR Racing

[BJR Racing]

Sorry for the flow #s being the way that they are I had them graphed right to start with.

BJR Racing

[Mrmopartech]

Bobby,this is a great piece of tech info for all of us,you are the man,Mrmopartech

[ValiantMike]

Thanks, thats some really good insight. Mike

[7demon2]

BJR Racing, this is very interesting indeed! this type of dynoed information is going to save us alot of time and wasted money. just wondering do you have any other combos dynoed like this? maybe for a 340 or 360? thanks for the great insight on this

[BJR Racing]

Yes, I have 360 .030 with and without aluminum heads, 400s with all different cams and heads, 450s with aluminum heads and iron heads. The 360s with W-5s, 400s with Max Wedge irons, 450 with Stage 6 MW and std late production Stage 6s.



BJR Racing

[D-mailman]

BJR, Excellent post. Two thumbs up. Terry.

[OldVart]

Thanks for taking the time to post that very detailed information. It's because of people like you, who take the time from their busy schedules for efforts like this, that this is such a great board.

[moper]

I agree with all of the theory BJR, but numbers need to be taken with a grain of salt. I would caution the use of exact figures in any dyno room, or flowbench. Thoose are simply tools. I can make almost any number I need appear on a flow bench, that doesnt make it accurate. This is not an attack on you, just an observation. Your results depend on your equipment, your location, and your methods. The only way to get accurate readings on more than one head, is to have the same guy, in the same place, on the same bench, do them back to back, recalibrating after every head. I dont take any numbers as exacts..You can only use them as an indicator orf a trend, nothing more. Dynos can be way off too, again depending on the situation. Also, using an alcohol engine as an example is at least in my opinion a little deceptive too..lol. Impressive, but deceptive to a new guy. Just some more random thoughts from me anyway....

[BJR Racing]

I want to say thanks to Rumblefish for he started me thinking about doing this artical a few weeks ago. Also thanks to all who have posted! As a machinist and Race engine builder this kind of came natural for me, I didn't want to get to technical but show the results of what can be achieved with little to nothing and some elbow grease.
I have a list of over 1000 sets of flowed heads, Mopar, Chevy, Ford, some NASCAR and some Drag. Everything from B-1 TSs and Fred Brewers, to W-2 Indys and Mopars, to Chevys, Canfields, Edelbrocks, Pro Action, Fords Motorsports, C-302s, C302Bs, Roush Racing,C-460s,Edelbrocks and so on. I have charted them all!
If anyone is interested in a 360 or big block dyno sheet IM me and I'll send you the specs or I could post them here for everyone, or a seprate post altogether.



BJR Racing

[BJR Racing]

Originally Posted by moper

I agree with all of the theory BJR, but numbers need to be taken with a grain of salt. I would caution the use of exact figures in any dyno room, or flowbench. Thoose are simply tools. I can make almost any number I need appear on a flow bench, that doesnt make it accurate. This is not an attack on you, just an observation. Your results depend on your equipment, your location, and your methods. The only way to get accurate readings on more than one head, is to have the same guy, in the same place, on the same bench, do them back to back, recalibrating after every head. I dont take any numbers as exacts..You can only use them as an indicator orf a trend, nothing more. Dynos can be way off too, again depending on the situation. Also, using an alcohol engine as an example is at least in my opinion a little deceptive too..lol. Impressive, but deceptive to a new guy. Just some more random thoughts from me anyway....

Moper, I'm the only one that flows heads at my shop and I do all the porting. So the methods are the same and the bench operator is the same and have spent days back to back to back flowing heads. As you say you can get and achieve most any #s on a flow bench or dyno and this doesn't mean that its accurate, I agree. But I've cross check my work on my bench with the bench at Barnett Performance, Zeeker Performance, Engine Systems and others and the #s are +/- 5 cfms, so I would say that they are fairly accurate.
Also the dyno #s that I come up with here are usually seen at the track also in the ET slip, so I have to say that this must be accurate also.
I've been building and flowing and dynoing engines for 20+ years so I have a good data base to fall back on, and trust my figures are accurate.



BJR Racing

[7demon2]

BJR Racing this is great info you have. it is awesome to have someone with this type of experience and willing to share it. as far as other combos and pm'ing everybody back, maybe you could share some streetable (say 10 to 1) combos for the slant6 ,318,340,360,383,426,440 and post them to the tech archive for everybody to have a guide line as to what to expect. this would be great to have for review. just a thought.........

[JoeDust451]

Would be nice to see some BB #s, 452s, 906s, 915s

[Mrmopartech]

MR.Moper,what would it take to convience you of head flow numbers,or to stop you from thinking that the numbers are fixed!If it was some one just starting out,I agree with you 100%,but when some one has been doing this for some 20 years and with some big names,you have to sit back and say,I have to listen to him and learn.Its not so much the reading you get,but the change you get from doing a little grinding here or there as compared to what you had before.Here we have a man who has spent the time to help all of us and can be contacted on the phone just about 24/7 to talk too and help any one here at no cost to the person ,only to help the person get better for cheaper and have better knownledge.To many people just take things at face value,and have no clue whats happening.We now have a bobby telling us the ins and outs of the art of head porting and how to get the best bang for the least amount of bucks and also for the ones that have big bucks and big cubes and want big numbers.I personally want to thank you for the 2-4 hours we spend on the phone 2-3 times a week on my dime and the trashing we do to solve problems for each of our cars and others.Bobby, I raise a nother glass a beer to you,Mrmopartech

[BJR Racing]

Originally Posted by 7demon2

BJR Racing this is great info you have. it is awesome to have someone with this type of experience and willing to share it. as far as other combos and pm'ing everybody back, maybe you could share some streetable (say 10 to 1) combos for the slant6 ,318,340,360,383,426,440 and post them to the tech archive for everybody to have a guide line as to what to expect. this would be great to have for review. just a thought.........

Can do but will take time so be patient as I'm very busy. I only get nights and weekends when not building racing parts and then it bleeds over then. I will get back to you though, do you want a fax, PM, or e-mail?


BJR Racing

[BJR Racing]

Originally Posted by JoeDust451

Would be nice to see some BB #s, 452s, 906s, 915s

Joe, Have talked to you on the phone, #s aren't anything have them all, watch your e-mail.


BJR Racing

[BJR Racing]

I personally want to thank you for the 2-4 hours we spend on the phone 2-3 times a week on my dime and the trashing we do to solve problems for each of our cars and others.Bobby, I raise a nother glass a beer to you,Mrmopartech [/QUOTE]



I'LL Drink to that! Cheers MY FRIEND!

[ta3834bbl]

Great info. I would be really interested in the 516 big block heads as compared to the other stock heads. I have a 383 with .570" roller cam and the heads are basically stock with 1.74 exh valves put in place of the smaller 1.60's. I was going to try some porting on them but have other things to do this year, (like build a new car, .lol)

Anyway, thanks for all the info.

[7demon2]

Originally Posted by BJR Racing

Can do but will take time so be patient as I'm very busy. I only get nights and weekends when not building racing parts and then it bleeds over then. I will get back to you though, do you want a fax, PM, or e-mail?


BJR Racing

the post will be fine. i am not doing an engine now. i just got through a rebuild on my 402, and am kinda tapped. i would like to see some streetable combos though as for reference if nothing else. i think it would be great for the tech archives! keep up the great work that you do

[64ragtop]

I realize that unskilled hogging out passages can result in worse performance, not to mention the possibility of digging into water passages, etc. The info on shrouding valves using oversize valves on relatively smaller bores was new, but easy to grasp. What I'm wondering is how much difference would a gentle smoothing/polishing of the ports, and matching the ports in the head and manifold or header to the gasket make? That is to ask is such gentle work worth the time and effort for a street motor just looking for a bit of improvement, but not worried about giant numbers???