REELAV8R

I rebuilt the stock L-48 engine last year in my '77.

It started out as a top end to bump up the power but soon I discovered that my CR goals were not going to be able to be met with the stock 17 cc dish pistons.

I already had a 2400 stall converter, a B&M Th-350 with a shift kit installed, and 1 7/8" (only size they come in) hooker headers with side pipes and STS baffles.
I had done all the typical tuning, re-curving the distributor, overhauling the carb via Cliff Ruggles' book and installed aluminum radiator with electric fans. Car ran great, but still not enough power.

That's how I got started on the top end. So after finding that the CR could not get high enough to compensate for the loss of cylinder pressure due to my altitude I swiched gears and did a complete over haul of the engine.
The only stock components retained were the Q-jet, the block and the oil pump.
Block was not decked and the cylinders were ball honed by me since they were still at 4.00" and had no measurable taper. Block was boiled and cleaned and new freeze plugs and oil plugs installed.
Components as follows;
Scat steel cast crank (better windage than stock)
Crank scraper
scat con rods
KB 12cc D-dish pistons (measured 11.7cc's)
Felpro .015 steel shim gasket for a .040" squish
Dart SHP heads shaved down to 61cc's and lightly ported.
Lunati retro roller cam 270/270 219/219 @.050 .549 lift with 1.6 RR rockers 108 LSA
Performer 2101 egr deleted intake, also ported and textured with oil splash shield installed
Howards roller lifters
Dual roller timing chain
Final CR 9.9:1

At my altitude of 4000 feet on a cool day that makes equivelent CR about 9.0:1

In retrospect I should have gone to around 10.7:1 or so. This would have allowed me a better cam without loosing too much bottom end. As it is I don't think I would add any more duration to the cam with the current CR.
It's great on coolish days (up to about 80* or so) but on hot days you really feel that loss of cylinder pressure due to DA.

On the dyno it topped out 263 HP and 288 torque. I used 89 octane for the run with no detonation. Temps was 87* humidity 60%. Dyno should adjust for that but was a bit muggy around here for engine power.
I have some tuning to do as you can see by the AFR line. It's way too rich up till around 4000 rpm then falls in pretty much at 12.4:1 to 12.5:1.
Just making an adjustment to the secondary air flap gained me 6 HP on consecutive runs. That's all the tuning I could get without paying the hourly rate or dyno tune rate.

If I assume 15% loss from gross hp to net hp and then an additional 18% loss through the drive train this gives me a gross HP rating of 377 hp at the crank. These figure like jb78l-82 has pointed out seem to be fairly accurate for an estimate of gross crank power.
It's not as good as I would like, but it met my initial goal of 350 hp at the crank and a little more.
I might be able to get another 10 hp at the wheels if I invest in an AFR gauge and do some tuning.
I unhooked the shift down cable so we could do the pull from 2000 rpm. The converter stalls at 2600 rpm now, so that is the initial jump in the graph. Then the AFR goes rich and it's slow to acclerate until about 3200 rpm or so. This is with a 3.08 rear and the Th-350 combo so it is ratio challenged to put it optimistically.

gkull

one way to look at it is: you are producing more hp than the bragged about 70 Lt1. :thumbs

Lars could tell you how to correct the afr

augiedoggy

I'm sure you are already aware of this but I bet you could free up some power with a better intake if you could figure out a way to cram it under the hood...

http://www.carcraft.com/techarticles...s/viewall.html

Your advice was very helpful to me when I was building mine and my setup is similiar to yours except I have a bit higher compression with smaller cc flat tops, 64cc dart iron heads and different dual pattern lunati 262/268 cam...

I plan to get mine on the dyno (local speedshop advertises $100. to do so) and my goal is to have over 350hp at the crank as well.
Progress has been slow for me but it moved for the first time under its own power yesterday to clean up the garage floor.

REELAV8R

Sounds like a good way to look at it.

Would be glad to hear what he has to say to correct it.

I thought about it overnight and think I have a plan. I adjusted the airflap to almost no tension while there and that gave me the 6 hp increase and leaned the AFR from 10.1 to about 10.7 in the richest area on the curve. So since no more adjustment is available on the air flap I figure I'll start with hanger height and see what that does.
Probably what I'll end up doing is getting different secondary needles with a fatter taper on them.
I'm not sure if the leveling off of the AFR above 4000 rpm represents that the air flap is full open and metering with the tips of the needles or if it just represents a balance between the air flap partially open and still metering on the taper on the needles.
My guess is it represents a balance with air flap partially open. So I'll likely need to play with air flap tension again to get it right.
In either case I may need an AFR gauge to really nail it down.

The flat spot on the curve after 2600 and before 3500 rpm I can feel with my butt dyno. So I can start with that anyhow.

Maybe. I"m not sure that is the restriction or the cam is. I'm going to concentrate on widening the torque curve and bringing it up faster with some tuning.
CFM on a 350 at 100% VE is only 526. The 2101 should be able to flow that easily I would think.
Probably biggest crutch to my low end torque is the heads ccing out to nearly 200 cc's instead of the 180 they are supposed to be. Likely I'm loosing some velocity in the intake tract. In addition the 1 7/8" primaries are less than ideal and make for a late torque peak, but they are there to stay.

Glad to help if I can. Anxious to see how it dyno's out.

jnb5101

Flat spot could be the secondary air valve. Check the spring tension and the choke pull-off. Nice numbers.

augiedoggy

The thing is, while when looking at it on paper 526 cfm is plenty but in real life it has been proven time and time again that the formula does not hold true.
even on my 355 setup when I change from the 625cc carter carb to a 750cfm carb desktop dyno picks up between 5 to 10 additional hp and tq. And I have read countless accounts where someone bolts on a 670+ carb and picks up additional power.
the performer 2101 performs on par with stock from everything I have read its just lighter.. higher rise intakes do have advantages besides flow like better velocity from a less obstructive path. thats one of the reasons carb spacers can make a difference.

MotorHead

That should be a fun engine to drive, congrats, reminds me of my warmed over L48 waaayy back. It had a tad more power and torque and it was fun to drive with a 2.87 first gear and 3.08 rear end.

Is that SAE corrected for your altitude, temp, humidity etc or raw uncorrected data ?

I have been seeing many chassis dyno printouts lately that don't say what the correction factor is or whether or not it is corrected or uncorrected data.

My dyno runs show a printout for uncorrected and SAE corrected. My uncorrected dyno pull was 480RWP and an end result of 465RWHP SAE corrected.

REELAV8R

Those are supposed to be corrected values. I don't know what correction filter/factor is being used. It does say filter mode "FIR" and filter value "6" if those means something.
It's a Mustang dyno.
Has no CFM data available either.
Best run was with the lid on the air box.
Removed it for one run and lost 3 hp.

toddalin

With those heads and that cam, your engine is not breathing somewhere. Aren't you running headers? You should be making peak power ~5,500-5,800.

Are you sure that your carb is opening all of the way?

cardo0

Ya know REEL'r, dyno numbers for automatic cars are terribly low. Had my camaro z28 dyno tuned with a new GM advertised 350hp/400ft-lb cam and dyno said its nearly 150hp less than that. the operator said dont look for big hp numbers with an auto - just use it as a reference for modifications and tuning changes. and that was on a load bearing Mustang dyno. I know my camaro is faster with that new cam but the dyno says its 100hp less than the stock cam w/o headers.

But thats the only dyno i tried so maybe better numbers with autos can be had elsewhere. Then again i had someone else say the same thing with his auto trans LS powered C2 - his dyno numbers where very low for a 11sec car.

Ive come to believe the only real hp calculator is the dragstrip and timeslip.

augiedoggy

Ive read the th350 drivetrain with usually chew up about 18-22% and the th400 is closer to 25% of the engines power...

REELAV8R

What makes you think that? I believe this cam is what is controlling the peak power point.
Take a look at comp cams roller cam of similar duration and build. It makes 342 HP @ 5100 RPM.
http://www.compcams.com/information/...0HR-10_001.asp

The flat tappet equivelent makes 348 HP @ 5300 RPM.
http://www.compcams.com/information/...62H-10_001.asp

So this combo seems to be doing about what it should. I have less equivalent CR and fewer CI's than either of the comp cam engines.

REELAV8R

I tend to agree. This is pretty much a bench mark for this engine. Tweeks or improvements can be made and then measured with a comparison dyno. That's the real value of a dyno I believe.
But it can also serve to compare to other similar builds to see if your engine is making the mark or if there is a serious mismatch of components. Like this one it can be seen what effect large primaries have on peak torque rpm on a 350. For the 406 I hope to build they will work much better.
I had a goal in mind and I think I made that, plus a little extra. So I'm happy with this one. A little tuning and it will be spot on.

toddalin

Because you combo is more aggressive than mine and I make more power with a peak at just over 5,500 RPM.

This is with the 327/350 hp hydraulic cam.

Are you telling me that with almost as much duration and much more lift (with 1.6 roller rockers and with custom heads no less), your engine should be doing that much less than than this? And I think I'm loosing power due to valve float.


331 CI, pump-friendly 9.5:1 CR
K&N 14"x4" air filter, Corvette drop base and lid
Holley 600 dp, choke horn milled and blended, Primary - 69, Secondary – 74, Squirters - 21
1/2" Aluminum open spacer port matched to manifold, exterior polished
Edelbrock Performer RPM intake manifold, port matched, exterior polished with all extraneous castings and lettering removed
Homemade lifter valley splash shield to keep hot oil off manifold bottom
Manifold heat riser crossover blocked
Camel hump 1.94/1.50 heads hogged out to 2.02/1.60, pocket ported, port matched, pump-friendly hardened seats, 3-angle valve job
Cylinder bores clearanced to unshroud the valves
Comp Cams 1.52:1 roller-tip rockers
Crane Cam Vintage Muscle 327/350 hp cam, 222 degrees @ 0.05, 0.447" lift (with 1.50 rockers)
Doug Thorley headers, dechromed and ceramic-coated
2.5" mandral-bent exhaust (including tips), 2" cross-over just before rear axle
DynoMax stainless Ultra Flow mufflers
Millerspeed 1-1/2” Gilmer under drive belt drive system
Mallory Hyfire IV CD ignition box triggered off Accel points
Mallory high voltage chrome coil
Mallory spiral-wound coil wire
Mallory solid copper plug wires, ends soldered to wires
Champion plugs
37 degrees total ignition advance
Carter high volume fuel pump
Melling high volume oil pump
Open breathers
Polished aluminum high flow water pump
160-degree thermostat
Flex fan with polished aluminum spacer
Polished aluminum one-wire 100 amp alternator
Header Power Bracket
Keisler TKO600 5-Speed
Hurst shifter
3.70:1 positraction with Big Block yokes
225/60/15 Firestone Firehawk SZ50s on 7”-wide Western 30-spoke Turbine Wheels

bluedawg

Motor head did a engine and chasis dyno both on his 406" and he was loosing 21% through a manual gear box. I've been lead to believe that rwhp through an automatic was any were from 27% to 35% from gross to rwhp depending on transmission accessories and drive train components with the 700r4 and the turbo 400 being the biggest consumers of paristic horse power.

REELAV8R

Looks like a good performer.
I'm not sure we can or should compare numbers here due to the numerous differences the least of which is the dyno used.

So yes, I still believe it is making what it should. I would prefer to not get caught up in dyno number comparisons for significantly different platforms.

For me the dyno is a tuning tool, and a measuring stick for that engine in that car with that dyno. And like I said it lets me know how the various components are playing together and if I was able to meet my build goals.
This information will then be used for the next engine I build and any changes that I may want to make for different results.
Or I can use the info to further refine this engine.

augiedoggy

The thing is every dyno is different... a person could take the car car and drive it across a state getting results from various dynos and they would all be different... in some areas its been shown that the dynos have been "tuned" to give optimistic results... Lets face it if your shop is in a competitive area and your dyno becomes well known to give lower performance numbers than other nearby shops its going to affect your business especially if your doing the work to the car... and most shops want happy satisfied customers... the guy that just paid you 3 grand to hop up his engine with new heads and a shiny intake wants to see more than a 50hp gain over stock so many "fluff" things to give them what they want to see... bragging rights are great when you can follow it up with "the dyno showed"
IMO Dynos work great for comparison but only if the comparisons are all done on the same dyno with the same correction values.
I read an article where someone drove had a car dynoed at numerous placed in California and got drastically different results.

ddawson

Agree all dyno's are different and should be uses as a tuning tool.

Comparing what looks like a Mustang dyno to a Dynojet dyno are going to show different results.

bluedawg

Imo bragging rights should come from road race, auto cross or strip results or for some folks fuel economy. Its that not every vehicle is optimized to make use of the power for the intended use, you could have a thousand rear wheel horse power and turn tens with a crapy 60' and smoke out to the 660', in reality a 600 horse car might produce the same et, so even though the thousand horse car makes more power it's showin no more power than the 600 horse car according to et. I guess what I'm getting at is if you can't make use of it then it's just to one up the guy at the bar or on the forum.

toddalin

I think that most here are missing the point. It is not about how much horsepower is being made or its losses through the components. And it's not about who made the dyno or what software is being applied to it.

The point is that I BELIEVE that your combination should be making more RPM than you are seeing on the chart. And if you can make more RPM, you will make more power as a result.

If the tranny takes x hp to turn, yes you loose that percentage torque and its accompanying hp, but the engine should still turn to well over 5,500 rpm before falling on its face. I don't care who's dyno you run it on.

Maybe the carb doesn't open all the way, or maybe your exhaust is restricted, or maybe your air cleaner lid is too close, or..., but something seems to be choking it off.