so the more and more i read most of the thirdgen.com threads and others out there that are dealing with high(er) performance motors, it occured to me that i am wanting to build my engine for a truck. most of you street guys are looking for higher revving 5k+ engines, while i doubt in my application i would ever see much time above 4k tops.

so i am wondering, what characteristics affect the engines power, and where that power is found mostly. im looking for more torque obviously, and down low, so do i want big ports or smaller ports? AFR heads or ported stock heads? Basically id like to learn which variables are going to affect how the engine fits my bill, so i can put the power in the right spot. I wouldnt mind an engine that can spin 6k if it has the grunt down lower too, but as of right now about all i know is that TPI is the best torque producing injection system due to its long runners, while the LT1 is more suited for higher revving applications due to short runners. so questions like "is the LT1 system going to inhibit my ability to produce more torque down low, or is it a superios system that i can adjust to give me what i need?" need answering.


sorry that was a long post, maybe didnt make too much sense, but im still trying to get a feel for all of these variables of the engine, as it is obviously so much more complex than the CI and peak horsepower.

 

Here are a few rules of thumb for you.

Horsepower is found in the higher RPM range, it is the "pull" you feel when you have your foot (and the gas pedal) to the floor. Horsepower is defined as the the amount of work that an engine does.

Torque is found in the lower RPM range, it is the "shove you in your seat when you mash the gas pedal" feeling. Torque is just the "oomph" a motor has, it does nothing for making a car go fast. I.E. Diesel motors.

You want torque, low RPM torque, but you already know that. Heres how to get it.

These are all relative to a standard, a "baseline" if you will.

Long runners=torque. A good example is TPI.
Short runners=horsepower. A good example is LT1.

Long cam duration, low lobe lift=torque.
Short duration, high lobe lift=horsepower.

Long stroke=torque. A good example is the 383 stroker.
3.75" stoke, very torquey with a low redline.
Short stroke=horsepower. A good example is the 302. 3.00"
3.00" stoke, great high end HP.

Big stall converter=torque
Manual transmissions=horespower

Engine timing advanced=horsepower
Engine timing retarded=torque

Cam timing advanced=torque
Cam timing retarded=horsepower

**Note: With timing, this is all relative to a base timing number and we are just talking a few degrees either way.

These are just a few rules of thumb, this does not apply to everything, everywhere. So basically, the best combo for torque is a 383 TPI with lots of duration, stock engine timing, cam retarded 2 degrees, with an automatic and a big stall converter.

Now thats tree stump pulling torque!

 

Fisherbody gave you some good rules of thumb to go by. Here is some more theoretical information to expand upon that. First off I'll give you a shocker, there is no horsepower, it's just torque multiplied by a constant at a certain RPM. That will help you make more sense of the rest of this. An engine flows air as a system. Max torque is reached when the system is flowing air at its highest velocity without restriction. So a "restricted system" (ie TPI, 1-5/8" headers, low lift cam, smaller head ports) is going to reach that spot very quickly in the RPM range. Increasing the flow will bring this torque curve further up into the RPM range. A higher flowing motor (ie LT1, 1-3/4" headers, high lift cam, large port heads) will flow alot of air and thus not meet restriction until high RPMS where the cylinders require that amount of air. What you want to do is basically choose the RPM range which you want the most air velocity. Keep that in mind when choosing parts.

With that being said you can pretty much follow what fisherbody said. Run TPI if you do nothing else. ****, even stock TPI pumps out low RPM torque like an LS1. Hope this helped some.

 

definitely both very helpful, thanks guys. that is exactly the kind of stuff i was looking for. i guess continuing on that, i have a lead on a complete LT1 for a pretty good price. are the short runners too much of a hinderance on torque, or can that be compensated for elsewhere?

thanks

 

Power is found, and made, in the heads and cam. The rest are compliments to them, of course assuming the heads match the cam. Putting 200cc+ intake ports on a mild cam is foolish. Inversely, putting a monster cam in with factory heads isnt the best idea either.

The final setup regarding the 383 TPI for ultimate torque that fisherbody laid out is a prime example of something that looks good on paper, but in reality, isn't so good. A factory TPI chokes a 350 by 5000 RPM. If placed on a 383, the choking point would be even lower. Keep that in mind. Also, the thing about transmissions stated by fisherbody isn't entirely correct. generally, the factor of converter versus manual has very little to do with power output of the engine. A larger stall converter is typically associated with a higher horsepwer engine as the camshafts powerband is raised. The torquier cams are complient with the factory stall or lower stall speeds. Big stall converters are for the engines who have more aggressive cam grinds, cam grinds designed to give more top end power. However, keeping in mind the job of the torque converter, stall speed COULD be relativly high versus the size of the cam, its all up to the user.

Also, the cam itself is a key determing factor of how the engine will perform. As stated, high lift and low duration will make a top end monster while a lower duration and lower lift will make for a torque beast. There is also lobe seperation angle. generally, a tighter LSA makes for a more peakier torque curve while a larger lobe seperation makes for a more broadened torque curve. Closely tied into that is the valve overlap. Increasing/decreasing overlap has the same overall effect, for the most part, as lobe seperation.

The runner length of the LT1 intake should not post too much of a hinderance on the engines ability to produce low end torque, so i would not worry too much over that. Related to runner size/length is the size of the intake ports. The larger the intake ports, the more they are geared for higher RPM engines. No need to put 220cc intake runners on a factory LT1. For your case, ported LT1 heads would probably be sufficient. But i guess that depends really on how involved you want to get with the engine.

 

By all means go with the cheapest motor to find, be it L98 or LT1. However I'm just going to jump in and say that this is exactly the application TPI is best suited for. It will make more torque out of the box in the 2,000-4,000 RPM range you are looking for. The LT1 does NOT LACK low RPM torque at all, but you will have to modify it to get TPI torque at that RPM. Actually, try searching (not necessarily on thirdgen.org) for dyno sheets of a stock L98 and an LT1 motor. You'll see what the power band looks like instead of us just telling you. What are you using this torque for? It either motor doesn't give you enough a heads/cam combo or forced induction will probably solve all your problems. Either motor is only running at like 30% of its potential for its displacement so there is plenty that can be done.

side note - Actually, the 383 TPI setup suggested is ideal for this application, yes it will meet restriction sooner but let's not forget thats what he actually wants in this case. But yes, Stekman is right that everything flows as a system and the best results will be obtained when the parts are matched to each other.

 

If I were in the position where I didn't have any parts yet, the first thing I would do is formulate a complete and pretty detailed plan, start to finish.

It sounds like you already know what RPM range you want the engine to operate, so you're already started. An engine's output is limited to how many units of air and fuel it can use to produce power, so an engine of a given size has a finite power potential. It is up to the supporting parts like heads, intake, exhaust, cam timing, etc. to make the most of this potential in the desired RPM range. If you are after maximum average power over an idle to 4000 RPM range you have made a key decision in the direction of your build. Sounds like its between a 350 & 383 in terms of size. For either size motor I would look at cylinder heads with flow characteristics that would be best suited to max average power over the idle-4k range, probably something with great low/mid lift flow and high intake velocity (highest flow for a given runner size) with the engine's size in mind and chambers that result in compression ratio that the cam calls for. A cam with duration chosen with idle-4k range in mind that will compliment the cylinder head flow characteristics, headers with primary sizes that compliment the idle-4k range for the engine's size (along with the rest of the exhaust sized for minimum restriction). I see you are from California, you may be quite limited in your intake selection--which may not be of severe consequence since the two intake types with emissions provisions--LTR or SR--may be your best bet for the task at hand. The above would be my starting point. It was the easy part, the difficult part now begins, and consists of determining:

What heads will best accomplish the goal?

What cam will best suit the heads in pursuit of the goal?

What compression is required to suit the cam?

What intake will compliment the above parts best?

What will you need to do to the rest of the drivetrain to best use the power?

What compromises will you need to make in the above plan to meet a budget, emissions, avoid working on a SR ( example: the characteristics of a superram would probably best suit the engine I'm assembling, but I'll probably go with a different intake because it looks like a biiig headache), etc. and what other changes will be prudent to make the best of these compromise(s).

You are basically looking to make the most efficient use of the cubes you have to work with in your operating range. The engine is a system, and can only work as good as the worst bottleneck allows it to. Also, if you approach it as such you may be surprised that you don't necessarilly need the biggest shiniest parts depending on your goal; a 'too big' part can hurt just as bad as a 'too small' part.

Lastly, I am a novice; take the above for what its worth. I am currently in the process of correcting some mistakes I made in my first build; some of which I would not have made had I done the above. This board has a few members whose experience and knowledge is apparent in their posts, I'd listen to them. Information from the experienced is the best; they have already done the research for you.

Good luck.


**edit**

Sorry, in all that I forgot to add this: If you are upgrading from an L05, I would venture to say an LT1 undoubtedly has more potential even under 4000 RPM. It probably is not the best choice of intakes for this range, but the rest of the engine is more suitable to the pursuit of power--heads should be more than adequate with a basic bowl port. If the engine will nevereverever be expected to produce power over 4000RPM, then in this instance only it might be worth considering stepping down to an LTR (aftermarket baseplate and runners not factory). I personally still wouldn’t do it because I don’t even like working on an LTR induction; I personally would gladly take a very small hit on torque (and this small hit is debateable) to gain the beautiful simplicity of the LT1.

 

wow thanks guys, thats a lot of good stuff. from what i have read, i agree that TPI 383 is the ideal combinations, but being in CA i cannot use a TPI system since its older than 94, which i was really bummed about. LT1 seemed to be the next best thing, and i have found that complete motor for a pretty good price. t

i would say the main goal is good idle-4000 power with a pretty flat curve as stated above, but if i sacrifice a little low end and end up with more top end, that is fine. Tentatively, if i get this engine i would like to make a 383 of it, just kinda go bigger to begin with. My idea was LT1, stroked to 383, probably stock LT1 heads with a good port job (dad used to race alot and knows a killer porting guy who does tons and tons of race heads), brand new full exhaust, headers, and a good custom tune (can one self tune an LT1 with close to as much simplicity as a TBI?).

thanks again guys, if all else fails, it will be a TBI 383, aftermarket alum heads (debating model), porting, headers, custom tune. i will definitely do the tuning myself if possible, pretty computer literate and my dad is plenty engine literate.

 

What do you mean? I live in IL so I have never heard of this?

And by the way, Iroc n roll was right when he originally was talking about the relationship between torque and horsepower. The actual formula is:

Torque=(Horsepower x 5252)/RPM

 

CA laws as i understand them say that for a car to be registered, passed in SMOG etc, then a few things have to pass.

first of all, no matter the engine, the vehicle must pass the sniffer with whatever the stock levels were for the vehicle if that makes sense.

second, you may not swap in any older engine, only same year or newer than the vehicle. TPI never came in a vehicle in 94, so therefore it is out as it would not pass the visual.


these are the laws as i read them and as told to me by a few members on this board, could always been wrong though.

 

Last month or so we were exchanging some info, I can't remember exactly what was said and I couldn't find the thread either. But it sounds like you've been doing your homework, and thats a good thing.
The 383 LT1 would be a good bet for you, so would a 350 LT1.
The thing about it is, as a Cali resident, your hands are tied. I'm sure you're aware of that by now tho.
The good news is, although your choices are limited, they're limited to some of the best options that there are to be found.
The legal routes that are open to you are:
Leave it stock
Edelbrock MPFI
LT1
Plus you could add a stroker kit to any of those.

The LT1 is the option that sounds like the most fun. A stock LT1 with some headers would meet your needs almost perfectly, and it would get good fuel economy.
It sounds like you're hesitant about it though.
My suggestion is to find a car with an LT1 engine in it to test drive. If you don't know anyone who has one, go to a used car lot and drive one. I'm sure that after that you won't have any questions about whether or not it would work for you.


A TPI would be a nice choice too, but that isn't an option for you, as you mentioned already.
I'm going to take the TPI out of my car and put it into my truck so I can put an LT1 in my car. But if I could afford 2 LT1s I'd have one of those for my truck too.

 

LT1
Stroked to a 383
Slightly larger cam
ported heads (preferably the LT1 alum. ones)
program the ECM accordingly, if needed
add some headers and choice exhaust

That would be a bad@$$ combo for your truck. That would also easily carry you over your goal while staying emissions legal.

 

California laws suck. Here in Illinois the laws are a lot more lenient. The sniffer standards are very lax, and there is no visual unless you fail twice. Cars are grouped into huge groups and the specific vehicle make and engine size are irrevelant. All passenger cars betweem 86-95 have the same exhaust gas standard no matter what make, model, or engine size. So basically you could put a carbed big block in your 94 Lexus ES400, weld up a couple of cats and pass the sniffer if you play your cards right. Cars 96-up don't even get the sniffer test. They just plug into your OBD II port and if there are no codes, you pass.

 

Yeah... but in Illinois, the surf sucks
I was born there.
I'll agree the smog laws here are ridiculous.
It's hard to figure out sometimes whether or not it's actually about keeping the air clean, or whether the lawmakers just want to keep people buying new cars. Cars last a long time here and I'm sure that there'd be a lot more beaters on the road if they weren't forced into the scrapyards cause they won't pass smog.
Personally, I like carbs. And the sanitary engine compartment that goes along with them.

 

LT1
Stroked to a 383
Slightly larger cam
ported heads (preferably the LT1 alum. ones)
program the ECM accordingly, if needed
add some headers and choice exhaust

lets assume i could pick up this LT1 i found for around oh i dunno, $750. to go over everything to make sure it is sound, and then do the above mods, what kind of additional cash am i looking at? my dads friend will most likely do the porting, and id like to go after the programming myself if possible. this is a 95 so it should be ODB I right?

also, with a good tune what kind of numbers could be expected, roughly? thanks

 

If it were me, the thing I'd do is transplant a stock LT1 in there right before your next scheduled smog check. That way you can be sure that if all the stock equipment is in working order, it'll pass.
Then do the mods.
It might sound like a pain at first, doing it that way. But it will be less of a pain than going into the smog station with a 383 that's cammed with headers and headwork, and having a bunch of unknown variables to check through, when you don't really even have any prom burning experience under your belt.
That's a position that I personally wouldn't want to find myself in. You'd be at the mercy of the smog ref and whoever you choose to help you burn a chip for the thing.

Know what I mean??

That would be nail biting - tear your hair out - nervous breakdown - frightening... to me

With the modded motor described above, you could pass smog with some tuning, and have a truck that would have mind blowing power. But I'd be a bit concerned about biting off more than I could chew, if I were doing all those mods at once.
Especially if I had an appointment with the smog ref coming up.

 

well im clear on SMOG for two years i believe, well about a year now i guess, so id have time to work out the bugs, hehe


aside from building the actual motor, does anyone know the cost of the swap into a truck. IE motor mounts, getting the wiring together, the fuel pump, etc.

 

Here's one link I saved, this site contains other links as well.
Much of the stuff for TPI swaps would apply to LT1 also.
Check the Engine Swap board too.

http://bbs.off-road.com/ubbthreads/s...rue#Post568517

Good Luck... Hope you stick with it