1988 Chevy K5 Blazer build - An unorthodox approach

[adam728]

Originally Posted by Big Dave

I don't think any K-Blazers were ever built in a 4x2.

You could get a 2wd Blazer up until either late 70's or early 80's.

[cRiPpLe_rOoStEr]

Originally Posted by elhigh

I find the whole idea fascinating but I think your best money would be spent making yours the best SBC 350 it can be, not trying to retcon it into an Atkinson-ish model.

The TBI isn't really sophisticated enough to handle the tune you want for Atkinson function. Like the other guy said, the sensors are wrong.

really I think the Atkinson project does have enormous potential, but starting from a TBI SBC is probably the second-hardest way to do it (first hardest being carbureted) - but skipping past the more mundane but proven techniques that might get you closer to your goal anyway.

In the 30's and 40's when EFI was nothing but a pipe-dream, Miller-cycle engines still had to rely on carburettors. And what is nowadays labelled as Atkinson is basically a Miller without the blower.

[elhigh]

Originally Posted by cRiPpLe_rOoStEr

In the 30's and 40's when EFI was nothing but a pipe-dream, Miller-cycle engines still had to rely on carburettors. And what is nowadays labelled as Atkinson is basically a Miller without the blower.

Right, but my understanding of those was that they were generally industrial engines, tuned for a constant speed and with well known projected loads. This application would be a lot harder in my opinion.

Point of fact: a true Atkinson has a funky conrod arrangement that makes the expansion stroke longer than the compression stroke. Strictly speaking, modern "Atkinson" (or as I call them, Atkinson-ish) engines fake the effects with cams. A true Atkinson wouldn't have the contraflow effect that bollixed the sensors.

[cRiPpLe_rOoStEr]

Originally Posted by elhigh

Right, but my understanding of those was that they were generally industrial engines, tuned for a constant speed and with well known projected loads. This application would be a lot harder in my opinion.

Gotta have to agree with you at some point, since a constant speed and load factor would help to get the engine tuned at its higher efficiency, but it wouldn't be unsuitable to an automotive application because the supercharger is enought to push the regurgitated admission charge back to the cylinders.

[BabyDiesel]

Been off here a few days for school and reorganization of ideas. Good news is that I passed both of my fast track courses, so I have one class between me and graduation in May

Adam728 -

Am I reading that right, a total of 50 degrees of intake valve opening?

You will severely limit lift this way, as there's simply not enough time to open and close the valve very far. I would be very surprised if even 0.10" valve lift could be accomplished in that duration. Trying to push it higher is going to be a fairly violent lift/stop/close cycle, the ramp angles and valve accelerations will simply be too much.

Because of the short duration and tiny lift you'll get very, very, very poor cylinder filling. A huge compression ratio won't matter, as there won't be much mixture in the cylinder to compress. If I remember from back-in-the-day the BMW system that utilizes valve lift and duration for throttling runs a minimum of 90-100 degrees duration and 0.05-0.06" lift on the intake valve. That's for idling.



I hate to be all negative, but you are chasing a path of 35 year old technology that didn't prove itself to be worth keeping around. You're looking to do a huge tear up in terms of machining, custom cam, changing efi systems, etc, to have something that will give less power and possibly no better mpg than a more "standard" build. You yourself admit to knowing little about engines, yet seem bent on designing one. Camshaft events are the heart of an engine. A few degrees change in overlap can make an engine idle smoothly or misfire and stall. There's a LOT going on, and I would argue (strongly) it's best to follow a more well known path, at least until a very indepth understanding is developed.


If I were to do a mpg build on my truck (92 C2500, TBI 350, 5200-5300 lbs on scale) it would consist of the following. Goals would be good usable torque for towing, and decent mileage.
Leave it a 350. No going to a 305 and the bore shrouding that goes with it, nor going 383 and the cost/slight mpg decease that comes with that.
TBI heads - they've proven to be great for fuel efficiency and torque. For a mild build they don't give up much on Vortecs until 4000 rpm or so. With hotter cams the Vortecs start out performing the TBI's at a lower rpm.
TPI efi system. LOOOOOONG runners, port injection. Known to make huge torque numbers, great fuel efficiency, then choking the engine to death under 5000 rpm. I think this system should have come on trucks.
Then there's the game of cam timing, compression ratio, and quench. I'd setup for around 0.035-0.040" quench, and figure out what it needs to get there (deck milled, heads, head gasket thickness), while also keeping an eye on final compression ratio (which is based heavily on cam choice) and deciding where material needs to come or go to get to that compression ratio while holding that quench number (head, piston dish).
Camshaft - short duration, as much lift as can be mustered, decently wide LSA. Stock cam is under 200° duration, which is great for torque, but signs off early (mid 4000's), and everyone wants to ditch them for more power. I'd rather see something still under 200°, but with more lift than the stocker. Won't get much, but a little could help.
Long tube headers with small primaries, 1-1/2 to 1-5/8" max. Single 3" from there out.

Then it's all up to good dyno tuning. MBT sweeps, running as much closed loop as possible (or even OL lean), etc. Keep the truck down low, geared tall, and don't expect it to get Honda-like numbers. You should end up with something that has more power than stock (mostly torque), and improves mpg a fair amount.

I appreciate the brute honesty! Seriously, I was getting frustrated trying to figure out how to make this junk work. I've been going back through and designing this motor from the ground up, planning on building a motor similar to what you have listed.

- 350 block, bored .030 over (355)

- ported and polished 193 TBI heads. Polish the combustion chamber and increase the cc's to 66-67 for all. This will reduce the chances of one cylinder being knock prone. Also, exhaust will be ported and polished. Z28 springs, screw in studs, 1.5 rockers int./1.5 or 1.6 rocker exht.

- Flat top pistons with 4 valve reliefs, +6cc tops

- Stock crank and stock rods

- 0.039 squish/quench

- 08-525-8 Comp Cams Tri-Power Extreme roller cam, 116* LSA, 194/206 @ 0.050" duration, .470/.464 lift, 800-5000 powerband

http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=1550&sb=2"]http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=1550&sb=2

- Static Compression Ratio of 10.04

- Dynamic Compression Ratio of 8.25

- Possibly TPI EFI Found some sets around here for less than $500. If not, TBI EFI.

- 1.5" primary headers, ceramic coated, with 2.5" collectors into 2.5" duals. Y those together into a 2.5-3" single out the back with a good flowing muffler.

I'm thinking that I will take this project slowly and take my time with this build so that it will be the best possible when the motor is bolted in.

As far as exhaust piping is concerned, would a single 2.5" or single 3" be better? Pros & Cons??

[BabyDiesel]

Elhigh -

I find the whole idea fascinating but I think your best money would be spent making yours the best SBC 350 it can be, not trying to retcon it into an Atkinson-ish model.

The TBI isn't really sophisticated enough to handle the tune you want for Atkinson function. Like the other guy said, the sensors are wrong.

Your truck is an aero disaster. I think there are likely a lot of things you can do, things that aren't too gross to look at, that will clean it up a lot. You're already doing nearly 15mpg and for a vehicle that size with that engine, that's pretty good. Tune your mill to its very best, and leave it alone.

I remember reading about Hot VWs "Mileage Motor" project - virtually none of which will make a hill of beans' difference to your project - but they found a lot of mileage after giving their test vehicle a chassis tune: setting up bearings correctly, alignment, fixing brake drag, etc.

You don't have to give your truck a heart and brain transplant in order to make it perform well, I think. I suspect you're just going for the biggest, sexiest project that has the greatest possible potential - really I think the Atkinson project does have enormous potential, but starting from a TBI SBC is probably the second-hardest way to do it (first hardest being carbureted) - but skipping past the more mundane but proven techniques that might get you closer to your goal anyway.

I'm taking your wisdom and using it! You are right, TBI isn't well suited for an Atkinson motor.

"You're truck is an aero disaster." made me LOL. I have thoughts of a partial grill block, undertray, and a bigger air dam. MAYBE an AeroCap as BigDave mentioned.

I think a chassis tune would be beneficial to my truck. Setting up bearings correctly, alignment, fixing brake drag, could all add up to 5%. A 5% increase from 15 is 15.75 mpg. An increase none the less!

I was going for awesome and sexy... it seemed viable and not too too complicated. I still have plans for a Atkinson/Miller cycle LS1

[BabyDiesel]

BigDave -

Think about what you are trying to do.

The OEMs have engineering resources you cannot even imagine. You can bet the farm they've taken a long hard look at this and rejected it unless it uses a direct injection engine and/or hybrid drive. You run into control issues and a loss of torque that makes the vehicle a burden to drive. The OEMs rejected it for good reasons.

Another very doable and proven effective strategy (maybe long term for you) is to ditch the automatic and get a stick. That's a slam-dunk 2 MPG improvement. there are all sorts of kits available to convert these vehicles to a NP4500 five-speed manual. The manual enables you to run a lower ration final drive. Yukon makes a 3.23 R&P set for GM 12 bolts front and rear. That's a 14% reduction in engine RPM at a given road speed If you need more torque, push the pedal and yank the stick and Viola! There it is.

A NP4500 and 3.23 gears. We're talking a 4 MPG improvement and a big improvement in reliability. You keep your 4x4 for off-road driving, and don't have to do any body work.

Not cheap, but entirely doable and you can expect a 33% increase in gas mileage.

Every time i park my F350, I feel like the Captain of the USS Nimitz trying to bring her alongside without any tugs. A short but still roomy vehicle like yours might be the answer.

I don't think any K-Blazers were ever built in a 4x2. There were some 4x2 Broncos but those are as rare as honest politicians. 3" front and 6" slam kits are available for F150s so should work on a Bronco.

4x2, moderate slam, manual transmission, a Cummins QSB (4.5 liter four-banger), 3.08 gears, and some aero cleanup. You'd have a easy to park but roomy vehicle that would scare 30 MPG.

Too pricey for a college student but within the reach of an average working person.

With my aero package right (it need work right now), diesel engine, 4x2, manual transmission, 3.08 my F350 routinely gets 27 MPG in the summer without even having to bother with aggressive hypermiling. That's not an instantanous ScanGauge reading but a three tank full (1,500 mile) average in real-world mixed driving. And all that in a 7,800 lb vehicle. A 4x2 Bronco or Blazer would come in at roughly 5,000 lb. A 37% weight reduction would have to buy you some MPG improvement even in flat terrain. 30 MPG looks attainable.

Imagine. A roomy, comfortable vehicle with all the virtues of a SUV but getting (stock) Honda Fit range mileage.

You bring up an excellent point. GM surely knew what Crower was doing less than 10 years before and rejected it for good reasons.

The manual may not be long-term. I have to rebuild my 700r4 and it will take over $800. For less money, I can buy a used NV3500 will most of the components Do you think the NV3500 will handle the K5? I'm also on the lookout for higher gears/ high geared axles. To be honest, I was planning on putting in 4.56 R&P. Why so deep? Because @ 50 mph (my usual cruising speed) with 32" tires and in 5th gear, I'd be turning ~1750 rpm. This is on the lowside of the efficiency rpms for a 350. @ 65 mph, my rpms would be 2272. Which is not super bad for my aero and weight.

Could 3.23 gears cause lugging? @ 50 mph in 5th with a 32" tire, the rpms are 1238. Remember that lean burn cruise is planned and that can change everything.

BTW, a future project of mine is a 1985 C10 2wd with 3.08 in the rear I would like to keep it a 350 gas because it was my granddaddy's pickup (deceased now). I have played with the idea of a LS1 with the Atkinson cycle and a 5-6 speed manual and a suspension slam. At 1/2 your size (3500-3800 pounds) and better aero, it will be the gas truck to top 30 mpg just have to get there first! A man can dream, right?

[BabyDiesel]

Found this sweet gem of a deal last night

http:// http://raleigh.craigslist.or...896240943.html

I will be going tomorrow and inspecting his setup. If it checks out, the K5 is going TPI! And I'll be selling my TBI setup!

[wmjinman]

Dunno how hard core you want to get about MPG, but my experience is that running at LOW rpms gives better mpg even if below the "efficiency peak rpm". But instead of getting lower gears and bigger tires, you can just get SMALLER tires. Again this would be a hard-core mpg play, not a "bad-ass looking truck" play, but smaller tires would also lower it and reduce aerodynamic drag.

Speaking of aero drag, depending on how much driving you'll do at highway speed, that is what will yield your biggest results (assuming the new engine runs well). And by "running well", I mean stock re-build - nothing fancy or exotic. You mentioned a bigger air dam. YES. take it down to the same height above the ground as the lowest hanging stuff under the car. Grille block: again YES. I got 2 mpg just from that. Block off as much as you can & not overheat. You might be surprised and be able to block almost all of it! Looking at your side mirrors.... again, for hard-core mpg and "screw the looks", how about getting some really small car mirrors on there? Then finally, build some sort of lightweight Kamm-back or boattail.

I know you are all into your engine mod ideas, but my experience is that as long as the engine doesn't run like crap and waste lots of gas because of that, the bigger gains will be from aero and hypermiling techniques. Of course, do the lightweight synthetic oil and remove all unneeded parasites running off the fan belt (and the fan itself, probably - replace with an electric one). And same thing with lightweight synthetic gear lube in the differentials, too. - and keep the tires aired-up to max sidewall or above.

Simple things like that will, I'm guessing, add up to more mpg improvement than the most exotic specially engineered high-efficiency engine would.

I'm reminded of MetroMPG's story (I think) about a 1st generation Honda Insight hybrid he got. Thing is - the battery pack was shot & he didn't want to buy a new one, so just disconnected all the hybrid-related stuff and got like 100 mpg out of it as a conventional gas car!!! See, it wasn't the exotic engine (hybrid system) that made the 1st generation Insight so great (although it helped - some), but instead, it was overall shape, size, and design of the car itself. I'll bet you could transplant just about any similar sized, modern efficiency gas engine into a 1st generation Insight and still get stunning mpg with it just because of the CAR, not the engine. So I say if mpg is your main goal, don't put so much effort into the engine, but instead, somewhere it'll REALLY help - like a boattail, air dam, grille block, etc, etc...

[oil pan 4]

Originally Posted by dirtydave

Wouldn't a V6 swap get what you are looking for* without all the hard work?

*still a K5 V8 20mpg is bad ass.

GM made V6 blazers in the 80s. They were gutless and got almost the same fuel mileage at their V8 counter parts.
Only time they gave any benefit was unloaded on flat ground, where you wouldn't miss the power it should have and where the V6 is all you really needed.

Now if you had a turbodiesel 6.5L V8 and if it only got 20mpg then you would some kind of problem with the engine, or a fuel leak or 2 some where.