When does the bore of a 5.3 liter vortec start to hurt headflow?
05-15-2006, 07:16 AM
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When does the bore of a 5.3 liter vortec start to hurt headflow? Basically, becuase the 5.3 liter vortecs have that 3.78" (AFAIK) bore instead of 3.9 like the LS1, I was wondering when it would actually impede headflow and the ability to make power.
I tried searching and havent really seen a thing about it... If I ever play with one Id have it in a RX7, so its not like Id need displacement for torque.
Also, Im not even really considering doing it now, but I am curious if the head design of the LSx heads can support good flow with that bore without needing some serious work done to the chambers, valves, etc. Well, that and I like to soak up knowledge when Im bored, so here I am
That said, Ive seen 290+ cfm from ARCA heads on Ford's
old 2.3 which has the same bore, albeit at .7" lift @ the valve - all I'm saying is 'small' bores and 2 valves dont necessarily mean a motor cant breathe.
I tried searching and havent really seen a thing about it... If I ever play with one Id have it in a RX7, so its not like Id need displacement for torque.
Also, Im not even really considering doing it now, but I am curious if the head design of the LSx heads can support good flow with that bore without needing some serious work done to the chambers, valves, etc. Well, that and I like to soak up knowledge when Im bored, so here I am
That said, Ive seen 290+ cfm from ARCA heads on Ford's
old 2.3 which has the same bore, albeit at .7" lift @ the valve - all I'm saying is 'small' bores and 2 valves dont necessarily mean a motor cant breathe. 
05-15-2006, 05:46 PM
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Richard@WCCH posted about some edelbrock castings on a 5.3L bore diameter in the performance trucks forum. I'd search for that post. It has some good info as I recall.
05-16-2006, 10:49 AM
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http://www.performancetrucks.net/for...d.php?t=364632
Ported numbers are pretty damn good! Unported was also more than Id expect.
Stock is more than sufficient for some serious fun with a turbo, especially if you lower a comprsesion and get a high pressure ratio turbo (two holsets anyone?) and even unported could make some good power N/A.
Damn... Go GM
Ported numbers are pretty damn good! Unported was also more than Id expect.
Stock is more than sufficient for some serious fun with a turbo, especially if you lower a comprsesion and get a high pressure ratio turbo (two holsets anyone?) and even unported could make some good power N/A.
Damn... Go GM
05-18-2006, 12:31 AM
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I doubt you will ever have to worry about this.
Furthermore, it isn't just bore that you need to take into consideration, but also stroke, as it is displacement that matters. The problem would arise if a single cylinder can pull in for example 1/2 cubic foot of air in an intake stroke, but the cylinder head is capable of flowing more than that amount of air. Thus you run into the same situation like having a huge intake manifold with short runners and a huge throttle body, but crappy heads and a small cam. The components are simply not matched to each other.
In nearly every internal combustion engine, the head is the inherent flaw. Not only do you have space restraints, but the air has to turn often times 90* to get in, then turn again at 90* to get out. Furthermore, it has to go around the valve stem. Then it has to go into the smaller than port-sized valve opening, then negotiate the valve itself. Exhaust is even worse, the air has to go around a flat valve that doesn't have a smooth angle to direct it, then collapse into the opening, around the vale stem, turn 90*, then exit. Now this is exagerrated of course, but the cylinder head is flawed.
Yamaha used to use Reed valves, which were essentially flaps that opened and closed via a shaft that ran on the side. Sort of like a throttle body, except it rotated about one side so when it was open, it did not restrict airflow at all. I believe these were only used on 2-strokes though..
Now the valves also add a positive aspect in performance, and that is swirl and the fuel/air mixture. The valves, as bad as they are for airflow, do help in terms of mixing the fuel more evenly. Plus the swirling helps velocity. I'm not sure which has higher potential, reed or typical, but it'd be interesting to know.
What this all is getting at is that no matter how much your heads flow, how Godly they may be, I doubt they will ever overcome your assumed 100% VE airflow with just 2 valves to work with (Basically how much air the engine can bring in at 100% VE). But then we get into acoustically tuning your intakes, etc, and it becomes grey.
Furthermore, it isn't just bore that you need to take into consideration, but also stroke, as it is displacement that matters. The problem would arise if a single cylinder can pull in for example 1/2 cubic foot of air in an intake stroke, but the cylinder head is capable of flowing more than that amount of air. Thus you run into the same situation like having a huge intake manifold with short runners and a huge throttle body, but crappy heads and a small cam. The components are simply not matched to each other.
In nearly every internal combustion engine, the head is the inherent flaw. Not only do you have space restraints, but the air has to turn often times 90* to get in, then turn again at 90* to get out. Furthermore, it has to go around the valve stem. Then it has to go into the smaller than port-sized valve opening, then negotiate the valve itself. Exhaust is even worse, the air has to go around a flat valve that doesn't have a smooth angle to direct it, then collapse into the opening, around the vale stem, turn 90*, then exit. Now this is exagerrated of course, but the cylinder head is flawed.
Yamaha used to use Reed valves, which were essentially flaps that opened and closed via a shaft that ran on the side. Sort of like a throttle body, except it rotated about one side so when it was open, it did not restrict airflow at all. I believe these were only used on 2-strokes though..
Now the valves also add a positive aspect in performance, and that is swirl and the fuel/air mixture. The valves, as bad as they are for airflow, do help in terms of mixing the fuel more evenly. Plus the swirling helps velocity. I'm not sure which has higher potential, reed or typical, but it'd be interesting to know.
What this all is getting at is that no matter how much your heads flow, how Godly they may be, I doubt they will ever overcome your assumed 100% VE airflow with just 2 valves to work with (Basically how much air the engine can bring in at 100% VE). But then we get into acoustically tuning your intakes, etc, and it becomes grey.
