Lincolnman

This is a post that I did on the LS1Truck forums first, and then was told to come here.
I will simply cut/rephrase and paste the ideas and responses (from there) for the perusal and response of this forum.
Please feel free to speak up, even to say something stupid.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

THIS IS AN ENGINEERING EXERCISE, NOT A BUILD DIARY.
GEN III+ based engine.
Trying to go from idle to red line under full throttle milliseconds faster. So we are not "revving to the moon" just revving to 7,500 REALLY FAST. Think super bike throttle response, or as my father said "a motor that comes on like a die grinder". Let's assume that this is in a stand, so there is no confusion on transmission choices, weight of vehicle or gear ratios. Motor plus flywheel, only accessory drives are water pump, alternator.

Naturally Aspirated
11:1 Compression Ratio
91 octane
7,500 RPM red line
Hydraulic lifters
Aluminum (4 bolt head) block
2 valve heads

Everything else goes.

So - in order to build this there are certain things a person can do in order to achieve faster revs. Lets start out...

1. Shorten stroke - this brings the outermost swing of the crankshaft more in line with the center line of the crankshaft, therefore allowing faster revving at the expense of torque and displacement. This could even be done with the shortest stroke crank available (4.8 crank AFAIK at 83 MM) offset ground to reduce stroke and reciprocating mass simultaneously if using different rods... That or a custom billet crank.

2. Lighten/blueprint/balance reciprocating assembly - including (but not limited to) aluminum flywheel, custom flyweight pistons, aluminum or titanium rods...

3. Reduce reciprocating drag - knife edge and polish crankshaft, add windage scrapers, synthetic lower viscosity oil...

4. Increase air flow - Higher flow from intake, heads, and exhaust. How much flow (if any amount) is too much considering the red line? First things first, ITB (Individual Throttle Bodies) intake. Then, in order to increase the flow to the maximum allowed by two valves one needs the largest valves that will fit at the best angle possible. The best I have found is the LSX-DR heads 19166979 (http://www.crateenginedepot.com/stor...P2572C114.aspx) but they are a 6 bolt head. I am told the 6 bolt heads work on the 4 bolt block. I read somewhere that these will flow 430+ CFM intake side (at like .8" lift) and they claim to be good for 900+ NA HP. If they do not work as a 6 bolt head on a 4 bolt block then the next best I see are the LS6 CNC ported 88958665 (http://www.crateenginedepot.com/stor...-P852C114.aspx) though I may have missed something. They claim these are good for 500+ HP and they will flow 304 CFM at .570 lift. NOW - that being said, the former heads require a minimum 4.125" bore whereas the latter heads will fit a stock bottom end of any GEN III+. Keeping that in mind, the increased bore is a good thing in one respect because it allows not only the largest valves but it also prevents shrouding of said valves. If a person uses Darton sleeves the bore can be increased up to 4.200". This would allow maximum valve diameter and either head with minimal valve shrouding. ON THE OTHER HAND, the larger bore requires more air all other things being equal. More air means more time to fill the chamber, which may in turn mean an incomplete fill for a given time (inefficient) or more time for the increased volume. Then at what point (given a de-stroked motor) is the displacement a limiting factor on the given flow numbers. Also keep in mind that the flow numbers given are peak and an average flow will be considerable less. Additionally, the .8" lift of the DR heads is probably unrealistic to clearance. Add to this the chamber differences (50cc for the DR and 65cc for the CNC'd LS6) and we run into changing piston dish to maintain the 11:1 ratio. So the head choice is as clear as mud.

5. Valve train - Assuming that we are using the lightest weight components that we can, then to lighten anything further would be to use smaller valves, allowing weaker springs to limit mechanical losses. Would it make more sense to use the stronger springs to control the valves better? Also, where is the trade off for small, light valves and flow? Roller everything in the valve train seems like a given. Add in a double roller chain. Taking the valve train the the extreme I know that some of the piston engine fighter planes from circa WWII even hollowed the camshafts. Also, there is the possibility of "dimpled" valve on the fluted portion (forgive my lack of proper terminology) as per the "golf ball" effect which has been shown to offer some improvement in flow over standard shaped valves. Dimples and laminar vs turbulent flow.

6. Accessories - The most aggressive accessory under drive that I know of is 60% - like the ATI 916097. Take this further and put on the smallest alternator available. Is there a MECHANICAL water pump that takes less power to run than others? I have even heard of people under driving their oil pump, though I cannot find that link... Also - what about using a chain to run the accessories? In the case of a motorcycle a chain has less friction losses than a belt, but more intensive maintainence. The fact that is uses less power to transfer power (along with it being narrower and stronger) than a belt is why hogs use belts and (real) sport bikes use chains.

7. Electronic tuning - I know little to nothing about this, so inform me.

THOUGHTS or SUGGESTIONS?

P.S. - I don't need to be told that you can make more power with a 14:1 454 LSX.

Also, sorry about being so long-winded.

RESPONSES

A vacuum pump was suggested, based on the thought that if the crankcase has a vacuum, things will move faster due to the lack of air. I take issue with this logic in two parts:
1. The parasitic loss of running the pump will negate the benefit of not "pushing the crankcase air around"
2. The vacuum pulled will mean that pistons coming down into the crankcase are not pushing air out of the way, but any air pushed by one piston is also pulled to another area by another rising piston simultaneously, so it's "stirring" the air rather than compressing it Admittedly, this "stirring" action occurs too quickly and so compression and decompression will occur, but I do not think that it will be a significant change, albeit perfectly measurable.
I could be wrong on this vacuum pump thing, but I will need more solid evidence than "I saw a guy do that once and he was fast..." Later the comment was made that since the vacuum pump is usually electric "there is no parasitic loss" which is simply false because the electricity to run it isn't free power or we would all just run electric motors tied to alternators. Sound familiar? There was also mention that pulling vacuum in the crank helps the rings seal better and therefore is an improvement, but I am less certain that will help rev quicker. More power, sure - but I don't see it making things rev quicker, which was the point.

There was some question as to my motive for limiting to 11:1, to which I responded with the following -
"I consider 11:1 to be the threshold for 91 octane compression. More compression generally means more power so I figured it made sense to run all the way up to the maximum practical limit there. Also, higher compression keeps the throttle response snappy so that it doesn't "hang" at higher RPM for an undue period of time. I have also read that you can modify your IAC to help drop RPM quickly after rev up, but I don't know how that works."

I also asked about the "unstreetability" of the 60% "ASA racing" underdrive - under what circumstance would it be useful, then? At what (sustained) RPM is it useful? The response I got talked about idle (where all under drives are negative) and highway RPM as being 2K, which was deemed still too low to get any good out of the alternator or water pump.

Numerous people parroted my initial comments on keeping all moving weight to a minimum.

All contesting and arguing aside I think that it was a good place to start (especially since I was not yet a member here at the time), but now I am looking for more thoughts from new perspectives.

P.S. As far as the block goes I have been thinking Darton sleeved (4.200") or LS7 (4.125"). Any other suggestions are welcome, too.

Brief Encounter

iTrader: (6)

A "purpose Built" engine needs to be spec'd out according to what your goals are within a certain criteria, IE: displacment, power requirements, powerband, and most importantly cost.

With that said, I'll spec out a theoretical build with the following parameters.
Displacement: 382 c.i.
Bore: 3.622
Stroke: 4.125

With 382 c.i. and a red-line of 7,500 a set of heads that flow 400+ CFM with huge ports, are going to kill your throttle response. What you would be looking for would be something in the neighborhood for a 225cc intake runner. A smaller runner will give better port velocity which in turn will provide better throttle response.

Valvetrain wise, a solid roller will inherently provide better response, as well as lightweight roller rockers( not aluminum) and lighter valves as well.

I'm not a camshaft timing master, so hopefully someone will have some useful input as to what specific valve timing events would be more conducive to rapid response. I can assure you though that having the properly spec'd cam will make or break the build.

Bottom end is pretty straight forward, lighter is more often than not better. Take note the a change in reciprocating mass has a greater impact than a change in rotating mass. If you plan on staying N.A. then I would sacrifice some compression height for a little bit longer rod, it does make a difference.

Dry-sump is the only way to go lubrication wise. Less parasitic loss as well as doubling as a vacuum pump, not to mention dead nuts reliability. Cost is the only drawback.

I.T.B.'s are fine, just make sure to have the proper runner length and throttle body bore. this will have a great impact on your response.

Most importantly, the flywheel will make or break the deal. You have just spent 15,000$ to shave maybe 5-7 lbs of engine mass, why would you put a 50lb clutch assembly behind it? Best bet is a multi-plate clutch setup with an aluminum flywheel. There is no comparison with an automatic so dont even bother.

If you would like something more specific, just ask.

~Rich~

ZV8

iTrader: (2)

yea all that was mentioned was good with the biger bore smaller stroke and lighter components but what does make a huge difference is compression. If ur just worred about puting pumpgas in it then get some meth injections, its cheap, effective and would absolutely make it rev up faster as well as rev down faster. im thinking 15:1 compression ratio's with a permanent meth injection unless u have access to E85 or just building a racecar?

Lincolnman

Displacement does not matter, although I was thinking in the direction of smaller stroke, larger bore. The bore is the goal, and since overall displacement is not destroking saves weight, lowers stresses, all that jive...

Forget power requirements - I am not shooting for a solid number here. I am simply building something that will respond to the throttle a certain way, the HP will follow (insofar as to be quite in excess of necessity).

Power band or curve goes with power - anything that an LS based engine build produces will be greatly in excess of necessity, so peaky and high (closer to 7,500 red line) is fine, if the engine is able to run at all it will make enough (or too much) power at all points.

Cost is not a concern - I can modify plans as I go to adjust that later. Right now my concern is the theoretical penultimate design. I should say that there are things that could cost more but without benefit (E.G. billet engine block) and so let's not get into that sort of thought. ITBs are expensive by most people's estimation, but they also really work. 382 CI is definitely overkill. Now, mind you - I am a believer that nothing succeeds like excess but the 4+ inch stroke just seems silly.

As for the smaller runner volume, do you have any good links on that? That is exactly the information that I was looking for - now I just want to understand why that does or does not work. Here's a starting link for anyone reading this that is also on the learning curve as I (always) am. I need something that explains why so I can determine when is too much. Too often I see people espousing their own theory as fact based on their lack of experience to the contrary. Just because you haven't done it doesn't mean it won't work. To put this more plainly, if someone has only ever built high performance engines with small bore and long stroke, and two valve cam in block - they may believe that is the "proper" way to build a really strong engine. F1 would disagree.

You mentioned solid lifters "inherently" offering better throttle response. I believe this is true and could be measured, but how much difference does it make? I am not ruling out the possibility of solid lifters entirely, but I am reluctant. There is a guy here that claims to have gotten .4 and 4 MPH for his 1/4 mile, but that seems too much to me. If it really works that well, it is completely worth it and everyone who is even halfway serious ought to be going solid, so it seems sketchy that it would be that "hands down" better. Also, while you are reading that, read the signature for Blue44deuce - and laugh at how that seems a little like what I am doing. For what it's worth I am not trying to poo-poo any input offered to me, I am just asking why it's so and to what extent.

Why not aluminum roller rockers? Do they fail from the repeated stress, like aluminum rods, do they flex and walk, or what?

As per your argument for long rods, I agree with that in theory on making more power, but I fail to see how it could help with throttle response, in fact it seems counter intuitive. After all, a longer rod weighs more. Keep in mind I am only looking at RPM acceleration here, not power production.

According to what you have said dry sump is a win-win. I like the sound of that. For anyone following this and wondering about a primer on dry sump oiling, go here.
I fail to see why a dry sump has less parasitic loss, though. Could you explain that to me? With more pumps and processes it seems like it would be the other way around, although again it would make more power, it seems the throttle response would be poorer because there is more going on.


I like the idea of increasing the compression, but meth is not an option. I need something I can get all the time, anywhere. Now, water injection (to cool intake air and therefore decrease the likely hood of detonation) would be possible or something like it, but nothing "exotic". Also, no ethanol - that's more a personal vendetta than anything but I don't want to get off topic and on a soap box here.

THANKS FOR THE RESPONSES SO FAR, GUYS - KEEP 'EM COMING!

ZV8

iTrader: (2)

oh just do a 50/50 mix, so all you gota buy is windshield washer fluid and ur good to go. a gallon of that depending on how u drive will last a few fill ups before u need more.

blackmagicturbo

iTrader: (2)

Big bore, short stroke ,ring tension ,dry sump, knife edge or slayer crank, light weight 15;1 pistons ,solid roller ,titanium springs, lightest valvetrain possible, 10pd total weight clutch, think indy car,,.. might shut off tho from low rotating mass ?

Lincolnman

LOLWUT?

Big bore - 4.200" in an LS based engine - CHECK
Short stroke - 4.8 crank, possibly offset ground or custom billet - CHECK
Ring tension - You lost me there.
Dry sump - CHECK
Knife edge or slayer crank - Slayer? Is that a brand? - otherwise CHECK
Light weight pistons - CHECK
15:1 - that's not 11:1, that's not 11:1 at all!
Solid roller - Reluctantly - CHECK
Titanium springs - They can make springs out of Ti?
Lightest valvetrain - figured on it - CHECK
10LB clutch - got a suggested one?
Why do you think that it might shut off from low rotating mass? Perhaps because there is little to no "flywheel effect"?

Otherwise I like where your head is at - mostly.

CamaroZ28_LS1

iTrader: (5)

7,500 rpm stall converter should flash to 7,000 rpms and make the rpm's jump instantly if using an auto.

^ Just felt like being counter productive lol. And it would be a tight tight converter so there is barely any slippage.

01ssreda4

iTrader: (96)

No reason to really comment on whether I like this idea or not bc its irrelevant. However, if this motor ever got built, what would it go in?

Lincolnman

I was telling people to imagine it in a stand at first and then (since people can't do that) a super light endurance cart. No electronics beyond ignition, etcetera, no weight issues, no rear end ratio choices.

Regardless, this exact motor will never be built (by me, anyway) but a version of it will. Some of the items will not be done because they are not applicable to my use, I was just chasing the extreme end of theory to find the limits.
I tend to work that way - run all the way to the limit then back off slightly.
In case anyone is wondering what my actual application would be, it is a 1989.5 Mazda Miata.

Leafy

Remember mass flow rate has to do with air density, velocity, and flow area. But as flow area goes up, velocity goes down thanks to Bernoulli. A certain displacement engine at a certain rpm is going to be able to pull in a certain amount of air per unit time. Now density is for the most part fixed in that equation so the only real variables are velocity and area and they're both related. Too small of area and you choke flow and your velocity doesnt go up any more, too big of an area and the air slows down too much and then you dont flow enough either. Theres some more stuff in there two that would finish solving it but frankly I dont completely understand it and I'm not going to attempt to look like I do.

Compliance. You can have the greatest cam in the world but when your aluminum rockers flex it all goes to ****. Just like in suspension, compliance will kill any hard work you put into a valve train. And in depending on how close to the razor edge they were designed they could fail from repeated loading, but so could steel ones and again that depends on all kinds of factors; design stress concentrators, machining flaws (also stress concentrators), charlie sheen, etc.

This is an interesting thread and I certainly want to here more of what comes of it. Whats funny is that the first think that came into my head for this one was, well retarded globs of power will make the rev's climb faster. And my second thought was, "damn, naturally aspirated."

Wnts2Go10O

iTrader: (12)

the components themselves will have a lot to go with it because of weight. with ci being irrelevant to this discussion, which crank design is the best balance between strength and weight? the crank/flywheel weight will have a lot to do (at least i think so) with the speed at which the engine revs.

in terms of head and intake flow, if youre limiting it to 7500rpm THEN it becomes an engine size issue. to gnarly of a setup on a smaller engine and you dont get a bulk of the power until maybe 1500 rpm before your limit.

for the intake, again, with the limited rpm, you will be sort of limited in order to get the power wanted/needed before the 7500rpm limit. ive seen that after a certain point, TB's will only increase throttle response and not much more. so, an intake setup with runners that will work well within your limits and the biggest tb(s) that can be feasibly used will help with getting that super bike throttle response.

ZMX

1. Flatplane crank.
2. Smallest stroke possible.

ie - sportbike.

A.R. Shale Targa

iTrader: (2)

Neat thread just wanted to spit-ball here...............
4.200 boreX 3.25 stroke=360 cid.....6.615" rods for 1"comp.height pistons
Light tension oil rings....Total Seal gapless single compression ring (approx.
60% of an engines rotating friction is piston rings)
Dry sump oiling (keeps crank cleaner and diminishes crankcase pressure which
flutters the rings and unseats them allowing compression to escape south)
C5R heads w/intake port floor epoxied to make volume about 215 cc
Piston tops and comb. chambers thermal coated to reflect heat
Pressurized oilers @ the piston undersides (cools the piston...reflects heat
back into chamber which allows more ign. timing b4 detonation..more TQ)
Agressive hyd.roller cam w/mid 240 deg duration @ .050
Carbon composite pushrods...stock LS rockers trunion upgraded, all Ti
valves,springs,retainers...even crank and rods if money is no object....
Tri-Y headers with merge collectors
Sheetmetal intake...tunnel ram like shape...single TB
Lightweight clutch/flywheel
Spec. important***cam timing events need to be positioned to maximize DCR
higher cyl. pressure kicks the slugs harder

94transbird

Aluminum has no real point to where you say its will not break under this load like steel has. Eventually it will break and give under the same load after repeated use. Its just a property of aluminum.

Lincolnman

I had kind of forgotten about this thread (winter snow and all) and it was pleasing to see that there were some newer responses that I had not read yet.
I just wanted to say than you to everyone who contributed, and I will let you all know if I ever get anywhere near this build.
As of current, I just found a lot more cancer in my number one project car, so "extra" funds will be short for some time.