Okay guys I have some questions. I have my 5.3 and I'm thinking of making it into a 383 stroker but want to use used none junk parts to do it on a budget. So to make sure my thoughts are correct you bore it to 3.905, use a 6.125 rod, amd then 4" stroker crank correct? Also I'm wanting to use a set of 241 heads ported and polished as I can get them for $100. And I can find a set of 243 heads locally. I know they are not the best heads but they better than the 862 heads correct? I'm not trying to cheap out but I'm not trying to spend more than I need to. What can I expect from this set up? Is there a better stock head combo? I will be getting a custom grind cam built around the motor build. Is there something I am missing here? What should I be looking for in combustion chamber volume? Stuff like that.

 

Ported 241's flow about the same as stock 243's. Get the 243's.

 

Heads are more important to HP than displacement.
staying cheap on heads in a blind quest for displacement is a great way to be embarrassed by an average heads/cam car that cost less to build.

Ideally we can have great heads and more displacement but if on a budget, money is better spent on the heads/cam/intake/valvetrain .

 

Even those 862 heads will probably do as good as the 241's

 

Problem is I can't find a set of 243 heads locally. Also the whole bottom end isn't going to be done at the same time. When I find a set of pistons the plan is to bore install wait until I find the rest of the parts and finish. I'm not looking to build the highest horsepower motor with the best of everything right away. I'm not looking to beat everyone or anything like that, just looking for a starting place. But even with the 243 heads how would these stack up with the 383 stroker?

 

Also I have a victor jr intake and will be running carb setup.

 

Yeah, that's about it. The pistons will be specific for the stroke though, so you'll be looking for something with a compression height of about 1.1xx"

Yeah, the 862's have smaller valves which isn't really good for power. The 241's may not be much better if they're ported by Ray Charles either though. The stock 243's would be great and would have more potential later on.

The 243 heads are about as good as you can get with OEM heads. None of the rectangle port heads (L92 or LS7) will fit the 3.905" bore, but IMO, the 243's are plenty capable. Some LS2 Corvette guys have made 500whp with stock 243 heads and having them on a 383 will make it easier since you can run a bigger cam without worrying about PTV and without having to actually turn the RPM a 346 would have to.

A 64cc chamber, like a stock 243/799 head, would get you over 11:1. You can use a Compression Ratio Calculator to play around with the numbers a bit to get it where you want it though.

 

KCS thank you that was exactly what I was looking for. And I completely forgot about those pistons being stroke specific I'm glad you brought that up.

 

Send the 862s out to be ported - TEA or AI can do it for about $1k... Or send to Tony Mamo and let him work.

The other option is to move to a PRC 5.3L Ported head for about 1250 without valve springs or something like the TFS 220s worked by Brian Tooley for about $2k.

What's your budget? Any of the heads I mentioned can easily hit 480rwhp or more with a 383.

Also, I would recommend you buy a 383 rotating assembly kit from TSP or Thompson. You can get one for about $2k that includes the bearings and balancing. That would be your cheapest and best bet.

 

Great post....and right on point.

I see this situation quite a bit play out on these boards and even with the guys that call me inquiring about some help to go faster. They shoot their checkbook on additional cubic inches and then go cheap on the heads thinking it wont matter as much. Its completely counter productive. Larger cubes only guarantee more torque but unless you improve their breathing capabilities (the heads representing the size of an engines lungs), they run out of breath quickly and the power curve rolls over quickly. They need more air to be efficient and larger engines place an even larger demand on the cylinder head that can effectively get the job done.

And by far, a 346 with a great set of heads would outrun a 383 with a so so set of heads because airflow.....and namely how much you can ingest and exhale, is what really determines peak power. The shortblock just addresses the size of the pump and the shape of the power and torque curve but ultimately power is made with a deep breathing set of heads. In fact the most time in any professional racing engine development is spent on the heads for that exact reason.....a killer set of heads is the foundation of any combination you may stroll across that makes above average power. They are the foundation of every serious engine build.

Big torque wont accelerate your vehicle....horsepower is all that matters when discussing acceleration.....torque matters in steady state situations like pulling a heavy load at the same MPH. Power is the God of acceleration (dynamic state situations).....its the reason any speed calculator you might use only requires weight and power for its main inputs to spit out an ET and potential trap speed. The more elaborate programs may look for frontal area and such but torque is never in the picture because its a useless figure when discussing an object getting from point A to point B and how quickly it can get there.

Start to view torque as "low RPM horsepower" and once you realize that the larger HP numbers are found in the higher RPM portion of the curve, its easy to understand how a large motor with alot of torque can lose to a smaller motor with alot of horsepower.....at the end of the day horsepower is all that matter and assuming the same vehicle weight, the car with the most average power wins.

-Tony

 

Okay lets back up guys, I know the difference between horsepower and torque. I do know flow is essential park of horsepower. My idea is that this is a low buck build I have less than $1000 in everything on this motor set up currently. So my idea is to build the cheapest motor with the most power I can, whether it's new or used parts it doesn't matter to me. I'm not doing it to be cheap, i'm doing it to see what can be done with the least amount of money. I know money is key to power, but I guess it'd be easier to view this as an expirment and learning expirence for me. If I wanted to build a killer motor I'd start with a new block and new everything from there. I'm not trying to cause chaos here, I'm just looking for a ways or ideas on how to make a decent motor on mainly stock or used parts.

 

No chaos at all....it just bring good topics of discussion and alot of what I type I type thinking it can potentially help alot of people reading it and I like to be thorough and make things easier to understand.

That said if your looking to experiment and make a reasonable amount of power for low money, spending money on displacement at the expense of a good set of heads is moving you further from your goal and that was the main point of my discussion.

You are better off with a junkyard stock cube engine (or use your current stock engine if its in good/OK shape) and invest in more airflow, better heads, etc., not more displacement because at the end of the day the airflow is what is going to help you generate the bigger numbers (HP), not the increase in engine size (TQ).

Its OK (and fun) to have both btw but if you can only choose one, go with HP every time.

-Tony

 

Tony talking about this topic of head flow, say the 862 versus 241 versus 243. Now the 243 is the best flowing head because why? Is it due to the fact that it has larger valves and smaller combustion chamber? Are the 241 heads worse than the 243 because they have the same size valves but larger combustion chamber? And if this is correct does that mean 862 heads would flow as well as 243 heads if it have larger valves installed?

 

No that's not the right way to think about this. The intake port is designed differently as is the combustion chamber itself. The 243 flows more air because it is designed differently compared to the 241 or 862. The 241 and 862 actually use the same port with different chamber designs and valve sizes due to the engines/bores they were designed for. While it's true the 243 and 241 use the same size valves, the 243 flows more air for about a 20HP bump with a very marginal bump in compression. The 862 would bump compression up more but won't flow as much due to the smaller valves, but I'll get back to that.

If you applied the same CNC port program and added larger valves and a 5-axis valve job to the 241 and 862... taking them both to say 218cc ports with 2.02" 1.575" valves and milled them both to have 61cc chambers... they'd be the same head.

The 243 would use an entirely different port program and valve job than the 241/862.

Larger valves can add more flow at the cost of velocity. Just like opening up the intake or exhaust runners can achieve more flow at the cost of velocity. The 243 has about the same velocity of the 241 but with more flow due to an intake runner that's approximately 10cc bigger. It just moves more air.

 

So can the intake runner be opened up to increase flow on the 241?

 

Another question I have real quick, can a motor have too much head flow for say a small displacement motor?

 

No such thing as too much flow....only too large a port for certain application(s).

Point is if you select the size of the head properly for the application in question, you want as much flow as you can get in that properly sized port.....in fact the higher flowing port is likely accomplishing that thru a better designed sum of all its parts and has increased velocity in addition to the added flow.....a win win and a situation that's almost guaranteed to make big numbers if your cam and rest of the package is even close.

One of the reasons I'm excited about my new MMS 220 head is that it's a small to medium sized runner that flows as good as the current crop of (higher quality) medium to larger sized runner heads, not to mention does so with a smaller valve giving you a very high discharge coefficient (aka in English its a small port that flows alot of air and is very efficient....LOL). It has airspeed and significant peak flow (which determines peak power capabilities) and due to that fact it will widen and fatten the overall power and torque curve.

Good stuff....

-Tony

 

So what is the actual downside of having too large of a port on a motor?

 

What Tony said. Too large and for the same CFM the air is moving slower losing that ramming effect. It's kind of like exhaust. You need to balance "flow" without sacrificing too much speed of that flow.