84 4+3

If you make more power... be it horsepower or torque, you're gonna burn more fuel too. So using conservation of energy chances are you'll burn more fuel if the tpi gives you that low end grunt and extra power to 4500 you're looking for. Everything else being equal. Horsepower for horsepower on pretty much any sbc fuel delivery method you're going to use about the same amount of fuel. They're only 20-30% efficient. So whatever the KJ or btu content of the fuel you are using is, only that percentage is converted to usuable power. More power means more btus in the fuel or more available. It is a vicious cycle.

At least drive a tpi car and see if it's what you actually want. The easiest thing to do is research a hypothesis before you go on to it. If someone already did the leg work why reinvent the wheel...

arbee

One thing you could do to increase your cred. is to stop calling it a motor. It is a fkn ENGINE! Motors run on electricity.

81c3

amen!!!!

MatthewMiller

I was going to type this exact same thing. Efficiency for an internal combustion engine is actually not measured in mpg, but in Brake Specific Fuel Consumption: the units of fuel consumed per unit of power produced. There are relatively minor variations in BSFC between an L98 and LT1, but they are all in favor of the later LT1 being more efficient. There are multiple reasons for this - a lot has to with more advanced engine management - but one reason is the higher compression ratio of the LT1. Without the resonant supercharging of the TPI intake at one narrow rpm band, the CR could be raised a bit without inducing knock. All else being equal, the engine with the LT1/MR short-runner intake can use a higher CR than the same engine with a TPI intake.

Another interesting thing about BSFC is that larger-displacement engines always tend to be more efficient than smaller ones (if we hold other variables constant, such as engine management). There are thermodynamic reasons for this (combustion surface:volume), as well as mechanical reasons (friction of a slower-turning engine, etc.). But with only one very recent exception, all of the piston engines that are in the top tier of BSFC efficiency are humongous industrial units, like ship motors and generator units.* I wrote all that to say this: the most efficient way to make more power and move the powerband lower overall, while still keeping the very wide torque range of the LT1, is to build a stroker motor. It does everything the OP supposedly wants, and will be as cheap or cheaper than all these other crazy plans.

*The one exception is the last two years or so of F1 and WEC engines, which are going nuts with super-exotic ignition, chamber, and management technology to achieve astound BSFCs. Of course they are on the bleeding edge of tech, and they break a lot, but if we applied that same tech to giant industrial engines, they would improve too.

This is great advice, but the problem of course is that his car has been broken all this time - not running properly. And my bet is that if he isn't just trolling us (which is still my best bet), it's probably still not running well. All the implications are that his car like low-end power and responsiveness, which is NOT a characteristic of an LT1 that is running properly. Think about it: these cars all came with CAGS, which forced drivers to shift into 4th gear at 10-15 mph to conserve fuel. They had to be able to pull cleanly from ridiculously low rpms just to function with that "feature." Even the more cammy LT4 engines came with CAGS, as did LS1s and LS6s (maybe even the LS7s in C6 Z06s?). So all this inference that an LT1 doesn't pull hard from down low is bullshit (as the comparison dyno graphs prove, btw). It's probably based on a faulty car.

So he has no valid sample to test against a TPI car. He needs to drive a known good LT1 car first.

856SPEED

84 4+3

Very well said. I didn't feel like getting into the thermo but basically if you can run more volume and pressure the more efficient the process. Hence the bigger it is the better.

And I agree with the skip shift and all that about a proper running lt car as well. I keep forgetting that there are "issues" real or not with the car.

GREGGPENN

And, I take back what I said too.....Rocket man. This won't be a thorough reply -- because I'll be shamed and crying.

No you're not, you're trolling multiple forums BSing us about a fantasy motor you THINK you can build out of the one you have. Researching means DRIVING cars to see what they do. YOU shunned that idea multiple times.

And what would YOU think if you read Matt, myself, or any of this forum's other members complain because our Corvettes "shoot up in RPM too fast"? OMG....get a grip. You can't be serious -- which makes you a troll.

Hey guys of the Corvette Forum: I apologize for not posting as much from 2012 to last year. After building my AFR/383 stroker, I ended up being upset because it shoots up in RPMs too fast. As such, I was ashamed to post anymore.

Pathetic? You? Your car? I don't see it.

GREGGPENN

Plus.....And I'm being really, really serious about this now. I took a 5-yr driving school so I could learn NOT to let my car lung forward at stop lights!

ddahlgren

Did you take the near impossible driving 303 not rolling backwards at a stop sign or the advanced refueling your car one? The next one I have enrolled in is 'your oil goes in here'.

GREGGPENN

I would be interested to know how the bulk of LTx cars had better "engine management" than L98s? Sequential injection (ODBII) is the next level of improvement in my personal learning.

I question your conclusion. Don't SC/Turbo engine exceed cylinder pressure/filling compared to NA versions? I'm wondering how the method used to raise air pressure in a long-tube intake differs from SC/Turbo applications? IOW...what makes you think "TPIs" can't be made to resist detonation...just like they tried with higher-compression, reverse-cooled LTx cars? Brian pointed out (earlier in this thread) only half-a-point difference AND the L98 wasn't reverse-cooled. I understand where you're thinking lies but I question your ability to make that conclusion. If L98's were reverse-cooled, it sounds likely they could handle the same compression.

Obviously, the ability to handle compression includes other factors as well (which I considered in my L98 build).

I agree with the stroker suggestion EXCEPT that I think Phoenix sits may ALSO (in addition to other suggestions) be a product of the "Millenial" generation. As such, he's hopelessly torn between caring for the environment and wanting power. Months ago, I wrote a conclusion in (possibly) his first thread suggesting he do some sole-search to decide what he really wants...cause I don't think he's willing to accept that. At the very least, he's unable to accept more power MEANS more fuel burned. It takes x-amount of power to pull our 3.5k lb cars to "speed". It will take more to accelerate that "work" faster. But hey...he doesn't WANT the car to accelerate too fast. He wants it to PULL in lower rpms so he can shift and stay low longer.

I'm not sure your "large engine theory" above concludes that he will use less fuel by having a larger engine? Again, I understand what you are saying but we've been the OWNERS of before/after stroker conversion and KNOW we don't use less fuel. We build specifically for the happy pedal. This poor sap doesn't realize more power is impossible to IGNORE if you have it. More importantly, if you actually DON'T care, don't build for it!!!

Obviously, I agree he needs to determine how functional his LTx car is...but I can also relate to wanting more "pull" in 6th from ANY LTx or L98 that's working correctly. But, it's geared super low FOR A REASON. And, many people may not be aware that 6th gear isn't designed for hard-pulling. There was an article on this years ago.

The reason for my two posts above...and SEVERAL non-forum-related "pep-talks" is to see if he's smart enough to gain some personal insight, communicate better, and avoid statements that put the proverbial "kick-me" sign on his back.

The more I read, the more I doubt his ability to do that. More importantly, the more I doubt his ability to finance, follow-through with, accurately communicate, and overcome the (reasonable) desire to NOT build in his personal efforts to save the planet. If we stop responding, he'll be forced to settle-down and read. Maybe (over time) he'll get a chance to drive other L98/LTx cars. For now, his intensity and stupid comments are their own obstacle to knowledge.

MatthewMiller

SFI at some point (not sure if that was there in the first LTs), faster computers with more bit rates for data processing (I'm guessing), etc. By 94-95, the almost-OBD2 PCMs were more sophisticated yet, and would also do a better job of telling drivers like Penix when something was wrong with the car. The 96 real-OBD2 PCMs really implemented the latter to the max in C4s. In general, though, things have steadily progressed toward finer and faster adjustments of fuel and spark, with the ability to process much more information much faster. I'm guessing that sensor design and performance has improved over the years, too.

We've been down this road before, and maybe just have to agree to disagree. The half-point between the final L98 and the first LT1 is only part of the story. You don't know what ignition tables were being run stock, so maybe they have more aggressive advance on the LT1 as well, which also (to a point) increases power and efficiency. You also don't know if GM just chose to run the last L98s closer the edge of detonation, possibly to eek out a bit more mpg for CAFE ratings. It would get better mileage under light-load cruising to improve the numbers, but then the knock sensors would pull more timing when being run at WOT near torque peak. Or maybe the NOx level was tightened and they chose to run the LT1 at a lower-than-optimum CR just to reduce NOx at the expense of the other two gases they test for. Who knows?

What we do know - and this is incontrovertible - is that if all else is equal, the more air/fuel we pack into the cylinder, the higher the cylinder pressure will be, and therefore we will either have to reduce CR or spark advance. We also know that the torque curve is a good approximation of cylinder pressures. It's easy to imagine that you can run a higher CR (or spark advance) if the cylinder pressure is relatively flat across the rpm range at WOT, as opposed to having to deal with very peaky cylinder pressures at one rpm and lower pressures at other rpms. If you compare the L98 and LT1 torque curves, it's easy to see that the LT1 has much less peaky cylinder pressures, and is therefore easier to run at a higher CR. The bottom line is this: the theory is obvious, but I don't have the real-world data to back this up. However, I am very good friends with a nationally renowned race engine builder (a Chevy small-block specialist, in fact) who does.

Yeah, that's true. I thought about adding that, but didn't want to complicate things even more. So yeah, the stroker is only more efficient if you accelerate at the same rate as before. As you note, most of us tend to use the extra power we just built, ergo we see less fuel economy. Human nature and all that...

Phoenix'97

Perhaps the LT1 in the Caprice/Impala/Fleetwood used that cam as well. The B-bodies had two motor options, the 4.3L L99 or the 5.7L LT1. The B-bodies needed a camshaft with more torque production and that would work with 87 octane fuel. According to the B-Body forums, this camshaft makes 10 or 15 horsepower less than the F-body and Corvette camshaft but it makes a mere 5 pounds more torque and sooner than the other camshaft for the sports cars.

I am not sure how this camshaft would work with the TPI. A different opinion claims that it will result in power reduction across the torque curve. So, if this camshaft is a poor choice, would the ZZ4 be a better choice or perhaps even the Crane 227 cam! Instead of spending this money to get nearly the same power out of my LT1 with a TPI intake, why not put in a better camshaft? This is what I am struggling with right now.

GREGGPENN

I looked and see you have a 96 which means you have SFI which was the first year in use (along with ODBII) from what I know. I'm assuming the 97 served as the topic of this discussion uses both too. I'm not sure I wouldn't attribute better BSFC to compression and SFI only...both of which seem to ignore that pre-96 cars don't have much advantage over L98s...in terms of engine management (that I feel significant anyway). I gotta say it seems unrelated to the OP too....though who knows what comes next!


The only thing "we all know" is that longtube TPIs peak earlier in rpms. If reversion is raised to the point it's not able to improve cylinder-filling...like longtubes, I don't see that more timing (to offset whatever) makes the short-runnered LTx intake "magic". I see both as experiments in the extreme which were BOTH abandoned. More so that LSx cars decided to actually utilize the "boosted" cylinder pressures of longer (mid-length) tubes.

If I decide to post a thread on the reasons I built with longer tubes (though moderately shortened from stock), I would post the pros/cons of that decision. People don't always want to build for idle-to-redline rips and don't always drive every shift like that. If you actually record where your average, daily shift...and average rpm fall, you'd see why some make a case for leveraging maximum cylinder-filling via longer TPI or even LS intakes. Because there are reasons for building that way, it might be worth opening a discussion on it.

But, it wouldn't be for our visitor because he's hopeless. There are some points (like the ones above) that seem to warrant detailing. I would suggest than another post (made by in August) could use some counterpoint regarding the issue of intake flow vs reversion harmonics. There are other aspects I'd throw in...but not in this thread.

Unless/until I posted more of the reasons, my view may not seem particularly valid. So, it's kind of pointless to carry out a full-blown debate in a thread targeted to an LTx conversion...and what camshaft to use. It's because I also worked with a good builder...and modeling software...that I learned a couple of things most people don't know about longtubes. Doesn't really matter though...since it's rare that people care to build for anything short of tenths in the quarter.

Most importantly, I do enjoy the exchange of ideas with the KNOWLEDGEABLE people of this forum (including yourself). I'm not trying to be combative. No one knows everything -- which is why forums become a good place to share!

MatthewMiller

A quick search makes it look like SFI came about in 94. That makes sense because that was the year they switched to the OBD2-style computer, even though it didn't run the full OBD2 suite until 1996. I can and do switch between my 945 PCM and my 96 PCM without any changes to the way the car runs.

bjankuski

I am going to post these series of dyno runs from my 1986 vette, that were done 15 years ago and I am going to list the modifications that were done to get these readings. I am listing this to show Phoenix that you do not have to give up top end HP to get more low end power with the correct combination of parts. (I also assume other may find this interesting) In all situations the long block is the same except for the first run where I list the car as stock.

Long block in all runs is:
-355 SBC
-10.25 compression
-ZZ-9 cam perfect street cam seems almost stock (specs below except add 1.6 rockers to the lift number shown)
-1-3/4 TPIS headers
-195 cc trick flow heads
-1.6 rockers
-Tune by me, optimized on the dyno
-Pump gas




Stock 1986 auto vette




Engine listed above with single exhaust and large tube TPI set-up on it. Ignore the torque spike that is what happens when the converter flashes on the dyno.




Same exact combo expect superam added in place of large tube runner set-up. Notice no low end torque loss, and big gains above 3500 RPM




Same combo except the addition of dual 3" exhaust. Amazing gains.




All this is trying to show that if you want to add a TPI style intake to your LT1 you can do what you want but after you try the TPI you can the add the superam runners and plenum and you will pick-up power everywhere.

Do not run a stock low lift cam in if you are looking for torque from idle to 4500 RPM it will not work as shown above. The stock TPI was a complete stone compared to the rest of the combinations. I would leave your LT1 intake but to each his own.

GREGGPENN

The original points (a couple posts back) were about the "engine management systems (on your end) and the difference between FI vs tube pressure (on my end).

My question wasn't actually answered...which is fine. I'm not sure anyone would know what answer. Until I post the thread (I suggested), it might be hard to follow where I'm going with it.

As for "engine management systems" being a significant difference between the power/mpg of L98s and LTx cars, I look at the overall mpg difference. Then, I through out higher compression "which everyone knows is worthwhile" and try to quantify what's left to be attributed to "engine management systems".

For the point of this discussion I didn't get the connection to what the OP was asking. But, I view the discussion about cams and intakes...though we clearly would like to see him choose gears/stroking before that.


Brian,
I've seen many dynos over the years though I don't "study" them. Most, if not all, omit rpms below approx 2500 rpms. As such, I've never seen evidence to compare the lower torque of a LTx vs L98 engine. The ONLY thing I've read is an explanation of theory -- moving long vs short columns of air....and the "resistance" encountered in a "fluttering-back-forth-pump" system. I apologize if my attempt to capture (with my own made-up adjectives) doesn't convey my point -- in summary.

Your dyno doesn't provide that comparison either but is informative. As an somewhat partial observer, I wonder if it was really started at idle (which seems unheard of) and why it appears to take 500rpms for a transmission shift? (I assume it's not a "bog" considering your skill at tuning).

Finally, I'm not sure if you've addressed what Phoenix is thinking/wanting because he wants MORE power from idle to mid-rpms. You know...idle to 3k rpms...and maybe a bit more above that. I've read most/all of his threads here. Until he goes off the rails with RIDICULOUS criteria, I think I get what he's after.

The electric motor conversion is actually good due to the instantaneous torque they provide. I actually thought Tom's reverse NOS application showed clever thought...because that's where he wants torque. I my case, I would have avoided the former due to the overwhelming conversion considerations AND the loss of "bubba-la-bubba-la". We like engines for their SOUND. I would have skipped NOS because of the logistics of keeping a bottle in the (already) small hatch. And, the ongoing cost...though I would LOVE NOS!!!!

I probably said it months ago (when he first started posting) but there is an inherent limitation to the torque any NA engine can output in lower rpms. You'd have to re-engineer (out) the losses that keep combustion 1000ft/lb force from diminishing to less than 200ft/lbs once it gets to the wheels during take-off. Things like fuels or FI may be the way to improve over "gasoline losses" without redesigning an engine.

If he's like me, the proof that longtubes are significantly worse (from idle to 2k rpms hasn't really be provided. From my POV, that's why he should back-to-back drive L98 vs LT1. He probably won't notice a difference IMO. From other comparisons (e.g., TPI Shootout), there's a clear advantage IF you want to build a 5k rpm setup....or CONCEED that you'll likely let off or RARELY use 5-6k rpms. Or, more importantly, want 3-5k rpms to be better because THAT'S where you most often DRIVE.

I get the thinking. I built because of that. And, for several other reasons not included in this post. My guess is the OP won't readily accept dynos/explanations that don't address this philosophy. To a certain extent, you can't debate the issue UNLESS you understand opposing POV. And, unless you accept that a longtube/midtube TPI can make 10% more power in midrange rpms....and that it accomplishes this through more efficient cylinder-filling.

My point is the point-counterpoint debate can't lead to a "correct" conclusion -- for the goals of the OP since that's how he thinks he will drive the car. When you have a stick vs an auto, you may very well have a different mentality of the desire to rev to redline (or not), how many gears to downshift (1 vs 2), or how often you'll run to redline in one gear, shift to the next, run it to redline, and so-on. I don't know about some of the guys in this forum, but I can tell 90% built it like it's a race car. That isn't always the case. Saying it SHOULD be built like a race car doesn't really win huge points in the point/counterpoint discussion of how the driver thinks he'll use the machine.

Maybe I'm reading Phoenix wrong. My statements above aren't necessarily designed to support HIS quest/argument. I say what I'm saying because the counterpoint often seems narrower than it should be. I "shut-down" in the case of this guy because TOO OFTEN he makes it a waste of time via endless, ridiculous suggestions that avoid common sense. Hence, the justified perception of troll.

Tom400CFI

This is the unfortunate truth. No one makes pulls from idle, so that data is very hard to come by. I do ALL my pulls from idle. I want the entire curve.

bjankuski

With an auto it is hard to make pulls below 2500 rpm because the trans tries to downshift when you go to wot and the stAll of the torque converter will always bring the rpm up to around 500 rpm higher than the stAll. You can disconnct the kickdown but you risk burning up the trans. You can also lock the converter but that risks burning up the clutch in the converter.

Tom400CFI

That is very true.

GREGGPENN

I assume it's because dyno pulls are mostly for bragging rights beyond any exercise in tuning. Plus whether auto or manual transmission, revving well into the 2k rpm range is necessary for a powerful launch. This kind of goes back to my statement about engines "only" being able to push a small portion of combustion leverage -- to the wheels.

Even for myself, this realization helps clarify why higher rpms become the desire for most builders. It take MOMENTUM...and longterm "work" to pull a 2-ton vehicle at impressive rates of acceleration. From a launch, you have pumping losses (for which you rev to overcome), traction losses that can't be solved without choosing drag radials over street tires. That kinda leaves speeds where the car has momentum for the average street car to be "built". To me, this is a good a counterpoint for building torque that I can post.

I will conclude this point/counterpoint commercial by saying building for torque only makes sense (to me) if you have a stick. By design, automatics downshift where they want/should -- to hit the UPPER rpms where best power is generated. (Plus, autos don't provide as much control over gear selection/rpms). I would even add, in C4 Corvette world, sticks have better gear strength than automatics. If I decide to post a (lengthy) thread about the reasons long/mid tubes might be considered, the first point I'd made is to avoid LONG tubes if you have an automatic. Right off the bat, it would eliminate 90% of TPI owners from even reading that thread....And, probably all of LTx owners. That's why I'm not sure I'll even do it.

My personal motivation would be to hear debate between intakes for the next few years of my stroker's life. Like the goofball here, I'm not prone to sitting at a stoplight, launching to beat teenboy, ripping through 1st, 2nd, etc... in some sort of street race. (I did that once and it became stupid due to the other kid's idiocy). Now, I just like to rip it for a second or too....just to remind myself why I own the car. The ONLY other reason to focus on a build is what it will do at highway ramp/passing speeds. On a stick, that means building for 3rd gear IMO. And, I don't think L98s OR LTx cars are very impressive in 3rd -- in their stock form. Again, an auto is different.