Handling/drive-ability for optimistic engine options.
Discussion
Having read nearly this entire forum thread by thread, I know there have been discussions on characteristics of various forced induction options. I thought I remember specifically Stig chiming in on the PD supercharged aspect. But using the search function now and reading through dozens of threads I can't seem to find what I was looking for.
Nearing the time I can start an Ultima build (finally!), and am trying to get my thoughts in order so I can budget, have intelligent discussions with potential engine builders and know which might suit my needs best, etc. I've read all the threads on how much power is enough, I know I know, FI not needed, 500hp plenty crazy, etc. I believe you. But I'm only building one (!), the engineer in me wants the challenge as much as anything, etc.
I've driven a few fast cars, nothing with the power/weight ratio of a decent spec Ultima. I've had fun on autocross but no significant real track time (would probably start with lessons before daring to take out an Ultima of any spec).
On to the question... So general consensus I remember was big turbo bad for track, hard to manage hand of god coming out of corners and such. I don't question that.
Don't remember if there was much of a consensus on PD vs centrifugal. I've been investigating those options a bit, and have had varying opinions offered on which is best for a lightweight car. I would think constant torque of a PD like the whipple (factory seems to agree?) would be more predictable, even if the lower RPM torque makes burning the tires off even easier. Similar to a high compression race gas burning NA engine, right? Others have suggested that the more gentle linear build of boost and resultant build in torque with a centri blower might make it easier to control wheel spin from stop, coming out of a turn (?), etc. and build equal or better top end power.
Thoughts from the experts? Which would you prefer? My driving will probably be 90% street including short grocery trips and longer interstate romps (in US). A little fun on the tracks, and maybe the rare straight line challenge. Packaging wise the whipple looks great. Heat soak and cooling in general of course requires careful planning, but I would build for some fun track days, no real race use.
Nearing the time I can start an Ultima build (finally!), and am trying to get my thoughts in order so I can budget, have intelligent discussions with potential engine builders and know which might suit my needs best, etc. I've read all the threads on how much power is enough, I know I know, FI not needed, 500hp plenty crazy, etc. I believe you. But I'm only building one (!), the engineer in me wants the challenge as much as anything, etc.
I've driven a few fast cars, nothing with the power/weight ratio of a decent spec Ultima. I've had fun on autocross but no significant real track time (would probably start with lessons before daring to take out an Ultima of any spec).
On to the question... So general consensus I remember was big turbo bad for track, hard to manage hand of god coming out of corners and such. I don't question that.
Don't remember if there was much of a consensus on PD vs centrifugal. I've been investigating those options a bit, and have had varying opinions offered on which is best for a lightweight car. I would think constant torque of a PD like the whipple (factory seems to agree?) would be more predictable, even if the lower RPM torque makes burning the tires off even easier. Similar to a high compression race gas burning NA engine, right? Others have suggested that the more gentle linear build of boost and resultant build in torque with a centri blower might make it easier to control wheel spin from stop, coming out of a turn (?), etc. and build equal or better top end power.
Thoughts from the experts? Which would you prefer? My driving will probably be 90% street including short grocery trips and longer interstate romps (in US). A little fun on the tracks, and maybe the rare straight line challenge. Packaging wise the whipple looks great. Heat soak and cooling in general of course requires careful planning, but I would build for some fun track days, no real race use.
I've considered those routes and they are both still on the table. Whether I'll go NA as the final product depends on what my ultimate power goals are. 600 mild cam sounds great... but there's the 'building only one' and 'engineer in me' that will itch for more despite it being unnecessary. I know I'm not alone in that thinking.
But doing a NA base engine to which I add supercharging later is certainly one way yo go. Its tempting... kind of like the unfinished basement or attic space you can finish later... for time and financial reasons. But I do wonder about how much easier it would be to tackle location, installation, and routing of cooling components during the initial build... especially if it meant things like fuel tank modification and such.
I am pretty sure I want to avoid a mega-hp NA wild lopey aggressive cam option though, which is why I've been looking at FI.
But doing a NA base engine to which I add supercharging later is certainly one way yo go. Its tempting... kind of like the unfinished basement or attic space you can finish later... for time and financial reasons. But I do wonder about how much easier it would be to tackle location, installation, and routing of cooling components during the initial build... especially if it meant things like fuel tank modification and such.
I am pretty sure I want to avoid a mega-hp NA wild lopey aggressive cam option though, which is why I've been looking at FI.
Edited by rhosch on Friday 28th August 02:29
Thanks guys... you are asking a lot of the same questions I have asked and will continue to ask myself.
Answer to a big one... yes, "just 'cos".
Big part of that is the mech engineering background... the "beauty of the machine" has appeal separate from but not entirely disconnected from the driving experience.
Rambling thoughts and preferences which are somewhat an exercise in contradiction... I prefer revvy engines to big loping cams mostly based on preference of sound. But I don't mind a great throaty growl from the LS engines at all... much prefer that to a little turbo fourbanger. Reliability and durability is important, would prefer to design valvetrain to survive 8K+ rpm, and limit to 7500 or so for example. Would rather have a little boost to make HP targets (undetermined) than pushing displacement, compression, cam, and RPM to the max. Don't mind complexity as long as it isn't unnecessary or a negative in the big picture.
And while I have no intentions of putting a $100K motor in an Ultima, the cost isn't tops on my list. Dropping in a crate engine is certainly tempting for simplicity, time, and cost considerations, but I don't mind starting with the right block (OEM or aftermarket) and building an engine with quality parts, especially since I live in the heart of NASCAR and oval track country in the US and GM engine shops are literally on every corner. The price of a built engine might be same or better than an expensive crate option, like the LS9. I think my starting point, regardless of how I get to the goal, is strong block, quality internals, top end capable of surviving higher RPM if needed or especially for headroom.
Factory, thanks for the insight on the LSA vs LS9. Something I'll keep in mind even if having an engine build. Weight distribution isn't something I had considered enough I suppose.
Answer to a big one... yes, "just 'cos".
Big part of that is the mech engineering background... the "beauty of the machine" has appeal separate from but not entirely disconnected from the driving experience.Rambling thoughts and preferences which are somewhat an exercise in contradiction... I prefer revvy engines to big loping cams mostly based on preference of sound. But I don't mind a great throaty growl from the LS engines at all... much prefer that to a little turbo fourbanger. Reliability and durability is important, would prefer to design valvetrain to survive 8K+ rpm, and limit to 7500 or so for example. Would rather have a little boost to make HP targets (undetermined) than pushing displacement, compression, cam, and RPM to the max. Don't mind complexity as long as it isn't unnecessary or a negative in the big picture.
And while I have no intentions of putting a $100K motor in an Ultima, the cost isn't tops on my list. Dropping in a crate engine is certainly tempting for simplicity, time, and cost considerations, but I don't mind starting with the right block (OEM or aftermarket) and building an engine with quality parts, especially since I live in the heart of NASCAR and oval track country in the US and GM engine shops are literally on every corner. The price of a built engine might be same or better than an expensive crate option, like the LS9. I think my starting point, regardless of how I get to the goal, is strong block, quality internals, top end capable of surviving higher RPM if needed or especially for headroom.
Factory, thanks for the insight on the LSA vs LS9. Something I'll keep in mind even if having an engine build. Weight distribution isn't something I had considered enough I suppose.
Yeah I would think that would help. In fact, I've thought about the possibility of intercepting the pedal output with a selectable voltage divider or similar to create a valet mode and perhaps a "sane don't kill myself" daily driving setting as well lol.
That's a worry for a bit further down the road, but since it came up, how is the output from pedal/input to ECU configured on say LS7 style DBW which I figure is the prevailing option for modern builds? Does the pedal act as a bank of potentiometers, or is it more sophisticated?
That's a worry for a bit further down the road, but since it came up, how is the output from pedal/input to ECU configured on say LS7 style DBW which I figure is the prevailing option for modern builds? Does the pedal act as a bank of potentiometers, or is it more sophisticated?
Magic919 said:
You'd leave the pedal gear alone and just map the response in the ECU these days. Valet mode would swap maps when you flick the switch.
Oh, well that's interesting. I had read enough to know generally a TAC with lookup tables sets output trottle body position based on pedal sensors, and knew some manufacturers use multiple maps/tables for various conditions (didn't know if GM did or not)... but I didn't know that could be user selectable.That would be pretty cool. Any chance you know how many maps you can create, and how easy it is to swap maps from the user perspective in cockpit? A true valet mode with minimal power (like 10%) would be very useful. Something that keeps power sane, like under 500hp, for normal driving might be useful. I also wonder how the interaction of throttle and boost with a supercharger might work... if you had a map that kept the bypass open (say on a whipple), but had useable power, couple of hundred horses maybe, for everyday driving, it might provide a way to run pump gas daily and race gas for more enthusiastic sprints without swapping pulleys?
Max_Torque said:
All modern EMSs are "Torque based". That is they use engine torque as there primary arbitor. As such the accelerator pedal is simply used as a driver demand, and it's position is used to set a target torque at that moment in time.
OK, well that is interesting too. How does the EMS monitor engine torque? Is that a lookup table too of sorts, a "should be" value for combination of RPM, throttle, timing, fuel, etc.? Or does it monitor engine load more directly? Makes me think my original PD vs centrifugal charger question becomes relegated to the back seat, with throttle mapping really being the pertinent issue. I mean, if the EMS sets conditions to achieve a torque target for a given pedal position, does it really matter if that torque is generated vs PD or centri? And if your mapping requests say linear torque for linear pedal travel, can the EMS make that happen (within bounds of what the engine can output of course) for either type of charger?If so, the a PD/whipple may have more low end torque, but wouldn't "force" you to use it depending on how you had your pedal mapped. Well, of course the right foot is always the ultimate torque control, but what I mean is it wouldn't necessarily be more twitchy or prone to melting tires from the line or out of a corner than a centri unless that is how throttle was mapped. Might be nice to have that low torque, for overtakes in 5th for example, knowing it wouldn't make it any harder to put down the power.
Interesting... I'm glad the discussion wandered in this direction. More to read about!
Storer said:
I would spend the money on some track time and instructor fees. Better value and more fun.
That's going to be the first thing on my to do list once car is finished. Have to start first though![quote]Throttle travel is long and very progressive with the DBW LS setup. To get things really out of shape with warm, sticky tyres you do need to be driving at very silly speeds on public roads. Major throttle openings in first gear will spin up the wheels and at higher revs in second too. But the Ultima is like most race cars in that you feed in the power on exiting a corner finally nailing it once straight.
I fail to see why you would want traction control on track (where you can be a bit of a hooligan) and for the reasons above I fail to see why you want the complication and 'nannying' on the road.
chuntington101 said:
A waste gate seems the best solution. Used a lot in race cars that are superchargered to give the desired torque the drive wants and chassis can handle.
From my understanding, although sometimes done by street guys, venting/bypassing while under boost creates excess heat and drag and is generally discouraged by Whipple. Right?Max_Torque said:
If you have a positive displacement supercharger, ie one that does not use internal compression...
Yeah, so that rules out the Whipple I suppose. From what I can gather, aside from cost, this may be one of the biggest disadvantages of a Whipple - the difficulty in controlling boost levels short of pulley swaps.BTW, and OT...
How does the PM system on PH work??? I've received a couple of email from forum members sending me a PM regarding this thread (thanks, great info!), to which I responded via email.
Don't know if the email response was sent or received, so thought I'd send a response PM through PH just in case. I can't find the damned thing anywhere! And I realized I can't even figure out how to send a new PM to someone should I want or need to.
Looked at the website feedback portion and didn't see a how to for idiots like me. Help!?
How does the PM system on PH work??? I've received a couple of email from forum members sending me a PM regarding this thread (thanks, great info!), to which I responded via email.
Don't know if the email response was sent or received, so thought I'd send a response PM through PH just in case. I can't find the damned thing anywhere! And I realized I can't even figure out how to send a new PM to someone should I want or need to.
Looked at the website feedback portion and didn't see a how to for idiots like me. Help!?
Corsair613 said:
So long as I own it, the only other people who'll ever drive my GTR are the two friends who regularly assisted me during the build (both experienced race drivers) and, maybe, my wife (carefully around the neighborhood only).
OK, you caught me. Probably have the wife, brother, cousin, etc. and especially (GASP!!) children in mind more than anything else. Not sure if I would ever let any of them drive the car, but I wouldn't summarily rule it out either and a low power option might come in handy if not overly complex to implement.Steve_D said:
To send a PM click on the person you wish to contact which will take you to their profile. In the top right corner of the profile page click on 'Email me'.
It will send a mail but you don't see the email address. You will only start to see the address after you have entered into a back and forth via mail.
Steve
Thanks, finally! Would have never found that.It will send a mail but you don't see the email address. You will only start to see the address after you have entered into a back and forth via mail.
Steve
Thanks Stig... saw the option from AS. Factory "approved" and kinks worked out is certainly appealing. The only reason I'd consider reinventing the wheel is because in this part of the US it is so common that labor and support is relatively cheap, and I'd likely save quite a bit of cash for a similar result. Haven't ruled that out. May settle on NA but aside from cost and complexity (only, ha!), a bit of boost seems an easier (or at least more durable) way to get there than NA tuned to the nines.
Could I tease more comments out of you about your previous GTRs and whether you felt it was hard to control traction vs your experience with turbo setups?
Could I tease more comments out of you about your previous GTRs and whether you felt it was hard to control traction vs your experience with turbo setups?
Definitely would plan for the long haul. I've thought about the "upgrade path" engine option. I suppose it could be build "FI ready" but that would mean lower compression and different cam profile far from optimal for a NA engine. I wonder how much base power might be made? 400 hp or so perhaps, which would probably be fine and scare me just as well. Would require likely repurchase of some stuff later mainly associated with pulleys, accessory mounting, and main belt, would have to pay for tuning twice, maybe some duplicated cost in engine control electronics... not the most efficient. But my biggest concern is cooling. Not sure I could or would want to properly fit intercooler and supporting pump, etc., without the charger in place, and wouldn't it be a lot harder to do on the back end?
Still an appealing option. I'm just trying to think through how it all could play out so that I don't get more of a headache later by trying to avoid one up front!
Would require likely repurchase of some stuff later mainly associated with pulleys, accessory mounting, and main belt, would have to pay for tuning twice, maybe some duplicated cost in engine control electronics... not the most efficient. But my biggest concern is cooling. Not sure I could or would want to properly fit intercooler and supporting pump, etc., without the charger in place, and wouldn't it be a lot harder to do on the back end?Still an appealing option. I'm just trying to think through how it all could play out so that I don't get more of a headache later by trying to avoid one up front!
Definitely where I live heat will be an issue. Not having an Ultima yet it's a bit hard to conceptualize what options there are for increased cooling capacity. I've read lots of the old threads on the subject, seems the factory have incorporated most of the common upgrades into the new standard config for the Evo.
Perhaps the biggest potential upgrade would be removing the dual fuel tanks, relocating to a single race bladder (behind seat seems the only option, but there are other benefits of a single fuel tank anyway), and leaving side pods clear for cooling (oil, charger, secondary rad, etc.). I guess that would nix the luggage spaces completely? On first thought I wouldn't want to lose that, but on second I doubt I'd ever convince the wife to take a trip in the Ultima long enough to require them. lol, it would be me in one car, her (way) behind in another!
Perhaps the biggest potential upgrade would be removing the dual fuel tanks, relocating to a single race bladder (behind seat seems the only option, but there are other benefits of a single fuel tank anyway), and leaving side pods clear for cooling (oil, charger, secondary rad, etc.). I guess that would nix the luggage spaces completely? On first thought I wouldn't want to lose that, but on second I doubt I'd ever convince the wife to take a trip in the Ultima long enough to require them. lol, it would be me in one car, her (way) behind in another!
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