383 Due Diligence

[chadmacb]

My motor went bad a little while back and I finally have the funds to build a 383. I am trying to plan this out properly so I dont get to the end of the project kicking myself for not doing something differently.

At this stage I am looking for some recommendations for good books on rebuilding small block chevy's. There seem to be hundreds out there, but I would imagine some would be better than others. I am not trying to build a screamer, I just want a ton of torque and reliability.

I am all ears at this point.

 

[mr_blasto]

Been a while since I have been on here, and I didn't realize I have two accounts. Anywho, I am the OP, so any PM's or whatever can be directed to me.

 

[Mikey von]

i don't know crap, but here is a bump to get it back to the top.

 

[mr_blasto]

Haha, thanks for the bump. I have not ordered any books yet for lack of direction, but here are a few rudimentary things I have found out while doing a little research. Most things tend to be a trade-off between top end and bottom end. Hopefully this will get the ball rolling for others to contribute too. Feel free to correct me or expound on what I am saying.

As you get closer to a more square (1:1) bore to stroke ratio the motor will produce more bottom end torque. A 383 typically has a stroke of 3.750 and bore of 4.030-4.060, whereas the HT383 from gmpp has a bore of 4.000 and a stroke of 3.800 which should help it produce just a little more low end grunt.

The rods typically used are 5.7" or 6.0" rods. The length of the rod determines how the piston moves. A longer rod will give you more low end power, but a shorter rod will give you more top end.

When comparing the runner volume of heads, assuming the runners are of equal length, the lower volume runners will give you more bottom end while sacrificing top end (equal length but lower volume indicates a smaller cross-section). The vortec heads everyone is so fond of have an intake runner volume of 170cc, which is part of the reason why they produce some solid torque numbers.

IIRC when you are going for low-end torque, flow numbers for heads are not quite as important as port velocity. Hopefully someone can confirm or deny. I will update and/or edit this as I find out more.

Anyone got some guiding principles for choosing cams, intakes, or carbs especially as it relates to maximizing low end torque? I am a total and complete novice without any experience... so learn me something.

 

[camok5]

You seem to be on the right track. The only good sugestion I can give you because I just got done building my 383 is to keep it somewhat simple for your first build. Meaning dont go off the deep end and end up with something that doesnt work for what you want to do with the engine. If I were going to do it again I probably would just match an engine that you know works good like the ht383. Also you mention carb in your post so I assume F.I. is out which will also help decide how to build it. It might help to give us a little back ground info on what the engine is going into and what type of driving you plan on doing plus your budget.

 

[Hogback Fabrication]

As you get closer to a more square (1:1) bore to stroke ratio the motor will produce more bottom end torque. A 383 typically has a stroke of 3.750 and bore of 4.030-4.060, whereas the HT383 from gmpp has a bore of 4.000 and a stroke of 3.800 which should help it produce just a little more low end grunt.

Generally, longer stroke motors tend towards bottom end torque and tend to be slower revving and harder on parts (not always the case, I'm sure your 383 will rev much quicker than a stock 350). Shorter stroke will rev quicker and easier (race car motors often have short strokes).

The rods typically used are 5.7" or 6.0" rods. The length of the rod determines how the piston moves. A longer rod will give you more low end power, but a shorter rod will give you more top end.

It all has to do with the rod ratio. For a 383, the 6.0" rod will make between 1-2% more power throughout the powerband and will last 1-2% longer. This is because the longer rod keeps the rings from digging into the cylinder walls as bad as shorter rods. The downside to 6.0" rods (other than cost) is that the piston has to be shorter which can cause piston slap issues.

5.7" rods work fine and are a perfect compromise IMO (stock 400 use even shorter rods than this)

When comparing the runner volume of heads, assuming the runners are of equal length, the lower volume runners will give you more bottom end while sacrificing top end (equal length but lower volume indicates a smaller cross-section). The vortec heads everyone is so fond of have an intake runner volume of 170cc, which is part of the reason why they produce some solid torque numbers.

Pretty much. Smaller intake runner volume = better low end torque while hurting top end.

IIRC when you are going for low-end torque, flow numbers for heads are not quite as important as port velocity. Hopefully someone can confirm or deny. I will update and/or edit this as I find out more.

Flow numbers are important at any RPM. Your engine won't make optimum power (or torque) unless you get as much fuel and air into the cylinder as possible. The cam, intake, intake runners on the heads, etc. determine where the peak torque will be made.

When looking at heads make sure to compare the flow numbers at all lift heights.

Anyone got some guiding principles for choosing cams, intakes, or carbs especially as it relates to maximizing low end torque? I am a total and complete novice without any experience... so learn me something.

In a truck you will want a dual plane manifold. The carb determines whether this will be a street truck or not. The cam also depends on what you are looking for.

There ya go.

 

[BlazerBud]

I just acquired a 383. It has a cracked block, but all internals have less than 3 hours use. The previous owner let it freeze. It has a ground 400 small block crank. Are you getting a custom 383 crank or building from stock GM parts? Originally, the 383 was a Frankenstein motor made from GM parts, nowadays, it is almost always after market guts only. A really knowledgeable guy I work with told me instead of building the 383, just get a big block, no substitute for cubic inches.

 

[mr_blasto]

You seem to be on the right track. The only good sugestion I can give you because I just got done building my 383 is to keep it somewhat simple for your first build. Meaning dont go off the deep end and end up with something that doesnt work for what you want to do with the engine. If I were going to do it again I probably would just match an engine that you know works good like the ht383. Also you mention carb in your post so I assume F.I. is out which will also help decide how to build it. It might help to give us a little back ground info on what the engine is going into and what type of driving you plan on doing plus your budget.

This post is meant more to gather information regarding resources (like books) for motor building concepts. I wasn't able to get recommendations for resources so it is more a way to keep all my findings in one place. At this point I am just trying to wrap my head around the different considerations and comprimises to consider when conceptualizing the ideal motor

I apologize if it came across as a what should I build thread, or help me build my first motor--hell I might not even be the one building it. I appreciate your advice, and keeping it simple is defintely a good suggestion. FI is not out of the question at this point, it just adds another degree of complication. I am in the planning stages, and I would like to come up with a good plan to then be critiqued. I just need to understand what parts I'm going to use and why.

 

[misterfnygy]

Well based on my experience- I bought this book

http://store.summitracing.com/partdetail.asp?autofilter=1&part=SAD%2DSA26&N=700+4294924480+400217+4294923452+4294906764+115&autoview=sku

and built my first motor with the knowledge that I gained. A few hiccups from rookie mistakes but the motor ended up running great.
As for parts- I think it is hard to beat all of the research that the big companies have put into their parts. Companies like Edelbrock spend tons of money on R&D to produce an affordable part that will work every time. So I say buy the matched Cam, intake and maybe even heads from someone like that to take the guesswork out of things. On another note- unless you are building an all out race type motor most of the high end parts are not needed.
I am building a 383 right now- .30 over 2 bolt block, updated camel hump heads (manley valves, double springs, stock rockers), 9.5:1 (used) cast pistons, reground cast crank, factory rods with new bolts, edelbrock performer RPM cam and intake, double roller, etc. etc. I bought the guts, block and heads from someone, added a few needed parts and will have a good runner for about $1400 total.
I say take your time, if you have it, and scrounge for some parts to build it yourself. Of course- you dont get a warranty this way- but you will know how to fix it if it breaks!!

 

[blazinzuk]

Just remember don't spend all this money on a motor and them put a old crappy carb on it, or a stock HEI ignition, both of those need dealt with too. If I were you I would look for a book that had some builds in it, I beleive there are books specific to building stroker chevy motors.

Remember the more efficiant the motor, things like a crankscraper, baffled oil pan, well designed exhaust, roller whatever you have the money for, etc etc will make the motor that much better

 

[mr_blasto]

Generally, longer stroke motors tend towards bottom end torque and tend to be slower revving and harder on parts (not always the case, I'm sure your 383 will rev much quicker than a stock 350). Shorter stroke will rev quicker and easier (race car motors often have short strokes).

http://en.wikipedia.org/wiki/Stroke_ratio says what you said with a little more depth if anyone cares

It all has to do with the rod ratio. For a 383, the 6.0" rod will make between 1-2% more power throughout the powerband and will last 1-2% longer. This is because the longer rod keeps the rings from digging into the cylinder walls as bad as shorter rods. The downside to 6.0" rods (other than cost) is that the piston has to be shorter which can cause piston slap issues.

5.7" rods work fine and are a perfect compromise IMO (stock 400 use even shorter rods than this)

There is a lot more to rod ratio than side loads on the cylinder wall. I found this thread helpful: http://www.hotrodders.com/forum/stroke-rod-ratio-32680.html

Flow numbers are important at any RPM. Your engine won't make optimum power (or torque) unless you get as much fuel and air into the cylinder as possible. The cam, intake, intake runners on the heads, etc. determine where the peak torque will be made.

When looking at heads make sure to compare the flow numbers at all lift heights.

I agree that your motor won't make optimum torque unless you get as much fuel and air into the cylinders as possible, but my point is there is more to it than flow. You can have heads with huge intake runners and ports that produce great top-end power, but suck for low end. The velocity seems to be the focal point for low end power: http://www.carcraft.com/techarticles/116_head_flow_explained/index.html


Thanks for the good input. It certainly made me dig a bit deeper than I had initially, which is always helpful.

 

[jonrpick]

Subscribed... I do a lot of reading that I hope will help me choose parts for the best TRUCK motor I can build. It's a different kind of performance build. Sounds like you're on a similar path.

It's interesting to note that all the design features you're considering (engine that favors stroke over bore, mild cam, small runners) also make for an efficient engine that generally gets better fuel economy than "racing" engines.