porting your heads with no experience? read this(long)


about 9 or so years ago when i was 19 years old i had been into small blocks and working on them regularly for 5 years or so. i had also ported a set of double humps for my shop teacher while in high school at 16 years old, it actually turned out well and my heads actually picked the car up .2 tenths or so in the 1/8th if im not mistaken. i was building a 383 by the time i was 19 for my 67 chevy pickup. i was a member of chevytalk during this time asking as much as i could to learn as much as possible , i had read david vizards entire series of books on small block chevys including "how to build and modify small block chevy cylinder heads" from front to back a hundred times. i broke down and bought a set of pro action 200cc heads for 800 bucks which was alot of money for a 19 year old kid. decided to port them myself, raised the port roofs, narrowed the guide boss, paid extra attention to port bias,blended short side radius and cleaned the runners up some not touching the opening of the intake ports at the gasket surface.also raised exhaust ports slightly, narrowed the guide boss and widened the port taking material away from the busy side of the port. i didnt port these heads to the max by any means. my data on stock pro action 200s with 2.05 valves was 240-245 cfm @ .600, high 170s on the exhaust at .600. i had my heads flowed and ended up with a 215cc(very close to this, cant remember exactly . head that flowed around 290 on the intake side at .600 and my exhaust ports were around 195 or so if im not mistaken. ofcouse these are just figures for .600 lift not taking into account low lift numbers but the head improved all the way across the board. the porter who tested my heads thought i had done a good job and i feel i had at that point as well. months later i still hadnt put the heads on anything and i became ancy thinking book knowledge could replace experience i went deeper into the cylinder heads this time around (before they had even been run) and did a full port job on them. had them sent off and flowed on the same bench by the same person. he told me he had good news and bad news. the good news was that my flow at .600 lift from 315 cfm , i was around 210 on the exhaust. my intake port was now 224 cc or so. the bad news is that the turbulence in the port was so severe that he said the time he wouldve had to invest in fixing them for me wouldnt have been worth it and that was assuming he would have been able to sort them out anyway. i know this is a long post but i just want to share my experience for anyone thinking they can do a full port job with out a flow bench and years of experience. had i stayed with my basic port job the first time around i wouldve had some decent heads that wouldve suited my 500hp goal with a 383. instead i had two lumps of junk. PLEASE do not attempt to go beyond your skill level as i did. do a basic port job as grumpyvette would suggest, if you want to get the most out of the heads find someone with a flow bench and good reputation. Book knowledge doesnt equal actual knowledge in some scenarios.
having 315 cfm of flow at that lift range is great, but if the quality of the flow is poor you are only hurting performance. like i said, sorry for the long post, but if someone actually reads this all and decides not to go grinding on a thousand dollar set of heads because of this cautionary tale then its worth me typing it out. good luck to everyone
your certainly far from the first guy to screw up a home porting job on cylinder heads, because theres a strong desire, in most newer guys trying the art and science of head porting to just start removing metal , from the inside port walls, in the often erroneous expectation that just increasing the ports internal size automatically will result in a head that increases the engines air flow rates and by doing so the resulting power. theres a great deal to be said for having the courage to go out and learn how to port heads, buy the tools and research whats required to do it correctly, and that learning process is almost sure to produce some less than ideal results, its part of that learning process.
Just the fact that you bought the tools and made the effort shows your in a rather limited percentage of the guys that generally if persistent usually build the fastest cars, simply because they are willing to do more than bolt parts together.the problem with that concept is that the engine will run best on a UNIFORMLY DISPERSED fuel/air mix in the combustion chamber and that almost mandates a rather consistent air flow speed thru all areas of the runner cross sectional area, in the intake manifold runners and cylinder head in the intake ports.
there's also the constant realistic potential , that you'll screw up and cut enough material out of the head casting in a critical area that the head can leak coolant
I know that the first set of big block heads I ported showed it was a marked improvement over the AS CAST from chevy out of the box condition, but looking back I know I could have done far better now simply because Ive carefully inspected dozens of professionally ported heads and eventually you can,t help but notice the better port jobs concentrate more on limiting abrupt changes in direction and guiding the air flow to the desired points behind the valve rather than just opening the port to max size.
Yes you can make significant improvements with a port and bowl clean-up , but your usually far better off spending the extra cash to buy a better brand of cylinder head like BRODIX, or AIR FLOW RESEARCH, TRICK-FLOW, ETC. than trying to get a port job on a much lower cost cylinder head to compensate for the lower out of the box flow numbers







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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
I can supply a few tips ,and bits of info for anyone willing to jump down the rabbit hole, when your looking to machine cylinder heads for different valve springs, keep in mind your machinist needs to be careful as enlarging or deepening the valve seat depth and diameter, if done too much weakens the heads and installing stronger valve spring load rates adds considerable stress, so its possible to run into problems rather easily , if machine work is too extensive, ID suggest calling the cylinder head manufacturer for info on that! along with having a discussion with your machine shop.

manufacturers can supply info , similar too but not limited too info ,like this
that DIFFERS with each head design.so don,t blindly start machining heads for larger springs with higher load rates , ask and get the CORRECT answers first!

















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