Long Runner Intakes & DCR / Increased Detonation Risk

NewbVetteGuy

NewbVetteGuy

Well-Known Member
Grumpy and Grumpites,


I appreciate all the help with my build so far; many of the variables in my build are slowly turning into constants and that's enabling me to model my build in a number of Engine simulation software packages and "make sure" before I begin purchasing things.

Here's my issue in large nutshell: I'm looking at a static CR of 10.2:1 with my Gen1 SBC 350 and aluminum heads. I'm doing a very torque-focused build with a reasonably small cam and a long-runner high flowing F.I.R.S.T. fuel injection (TPI on steroids) intake. As I model the combination in Desktop Dyno & PipeMax (an acquaintance modeled it in EA for me, too) I'm getting some slightly scary high cylinder pressure / trapped air estimates that make me think that near my torque peak RPM, I could very much be getting into a high risk of detonation.

Ask: Please review my situation and provide your appraisal of how much detonation risk I'm actually in and recommendations of how to best remediate it. I'd like recommendations that won't hurt fuel economy, ideally.

It's the stock 350, 2 piece rear mains, 4 bolt, L82 forged everything bottom end- never over bored never "refreshed" at all. 13,600 miles on it.

Bore: 4.0
Stroke: 3.48
Rod Length: 5.7"
Peak HP RPM: 5,500 (according to both Desktop Dyno and EA) -hp peak is pretty wide/flat from 5,500-6,200 in simulations
Peak Torque RPM: 4,500 according to Desktop Dyno, EA -and BadSS from the ThirdGen forums who has built some incredible FIRST intake-based engines; PipeMax is estimating a peak closer to 4,100
Static CR: 10.2:1
Pistons are 0.025" down the hole -estimated, not measured based upon other measurements from other 1979 L82 corvette engines
Felpro 0.015" gasket with 4.1" bore
5cc valve relief flat-top pistons

2.02" intake valve; 1.6" exhaust valve
Intake and Exhaust lift with 1.6ratio RRs: 0.600"
Duration @ 0.050" 227/232 (although my retrofit roller lifters have a 0.700" diameter wheel and the cam was rated for a 0.800" wheel so my actual duration @ 0.050" will be reduced by about 1 degree so closer to 226/231 effective)
Duration @ 0.006" / Advertised: 272/280
LSA: 110
ICL: 107

Exhaust: coated full length headers, 3" collectors, 3"-2 1/2" reducers, no cats, high flow mufflers; H-pipe within 20" of collectors (not yet sure about whether it's a tuned length or not; working on it...)



So if I used the internet calculator's "DCR" calculation (not dynamic but adjusted for the intake close event, anyway), I end up with a DCR of 8.256, rounded to 8.3.

Pipemax takes things a bit further and it has a calculation that can adjust that very simple, single variable (ICL event timing only) DCR calculation and adds to it valve lash (which can impact actual timing) and then helps to better estimate the amount of trapped air by adjusting for your Volumetric Efficiency at Torque Peak RPM. -Since BadSS modeled my engine with the first intake in EA, he came up with 110.5% VE @ 4,500 RPM. (The long-runner intake's tuned length is maximizing air velocity by using the reflected waves and can stuff more air into the cylinder than atmospheric pressure; if I get my exhaust properly tuned that will also help PULL the incoming air charge into the cylinder too.)

PipeMax then estimates then when adjusting for valve lash (which is essentially 0 with my hydraulic roller lifters) and volumetric efficiency, I would hit a DCR equivalent of 8.757... (obviously @ sea level but considering I live at sea level...)


This does not seem like a very safe DCR... Pipemax is pretty smart and converts this into a required octane of 95.8... (I can only regularly buy 92 octane in Washington State.)


I'm trying to figure out what I should do now...

I already plan to use a 3 row aluminum radiator and lower temp thermostat to try and keep engine temps lower. Roller lifters and roller rockers help a little bit with oil temps. I will definitely be using a Cold Air Intake and my intake does NOT have an exhaust cross over to worry about.

I'd really like solutions that don't hurt fuel economy; so running a fat AFR or pulling timing (particularly when my DCR peak is at 4,500 so pulling timing would hurt my torque throughout most of my curve) are probably my least favorite solutions.

I'm thinking that maybe I should polish the combustion chambers, pay attention to my spark plug temperature and I'm wondering what else... (Basically I need to gain 3.8 octane worth of detonation resistance somewhere...)

I was also thinking of retarding the cam by a few degrees and buying an adjustable timing chain and 2 piece cover- the cam has 3 degrees of advance built-in; I'd honestly prefer to just put the cam straight up either all the time or in summer when it gets hot rather than to pull timing.

I'm 90% certain my Holley EFI supports knock sensors so of course I could and should buy a filtered knock sensor and set it up to pull timing when necessary but I'd really like to put myself in a good situation to avoid having to have engine timing pulled.

Does anyone think going with a big baffled oil pan and a large oil filter with an oil filter heat sink on it would help get me a few more degrees and help with detonation risk? (Loved reading that thread here.)

I'm just not quite sure what it's going to take to get 3.8 octane points worth of detonation resistance.... -Should I just ask the CAM grinder to add another 5 degrees of duration to the intake and exhaust to bleed off more pressure?

Is 110.5% VE just a ridiculious number to even start with for an old SBC 350 with a FIRST intake? (If it is, then I'm probably worrying about nothing.)



Thanks for helping me think this through; I externally process information so even writing this out helps me to think through my options.

Adam
 
why not just install the cam retarded 3-4 degrees from split overlap that way it retards the valve seat timing about 7 degrees from the listed ADVANCED timing figures, raises/moves your whole torque curve about 350 rpm higher and significantly reduces the potential of detonation, without adding duration that reduces low speed torque or makes the brake booster and manifold vacuum, or idle characteristics less street-able?
I've almost always suggested cams be installed at split over-lap or strait up vs 4 degrees advanced
yes try that in your calcs.
two other factor's you might consider is,
polishing the combustion camber and un-shrouding the valves,
and getting the quench distance to fall in the .040-.044 range.
those mods will make the combustion process more efficient!
both actions tend to reduce "HOT SPOTS" in the combustion chamber and you obviously have the option of thermal coating on pistons and combustion chambers to limit heat transfer and octane booster added to the fuel.
but simply tuning the car to get the fuel/air ratio to run closer to about 12.6:1-13:1 after 3500-rpm and when under load goes a long way toward reducing the engines tendency to detonate.

Cylinderspressure.png


Stoich.gif

volumetric.gif


well I'll assume you previously read the links on engine building,and quench, and you have at least tried to build a well balanced combo with reasonable quench,and tried to match the cam duration and lsa to the engines compression and intended power range, and you selected a fairly well matched cam timing and reasonable compression, but at this point in the tuning ,your still having indications your getting into detonation.
keep in mind that keeping reasonably consistent and as low as practicable , combustion chamber temps are a huge factor in avoiding detonation issues, having an auxiliary oil cooler and a trans fluid cooler with a powered fan, and the proper fuel/air ratio and ignition advance curve along with matching your cars engine dynamic compression ratio to the available fuel octane can go a long way toward avoiding detonation issu
Octane_Requirement.gif

http://garage.grumpysperformance.com/index.php?threads/lca-or-lsa.11523/#post-53150

http://garage.grumpysperformance.co...hanics-of-adv-ret-a-camshaft.4532/#post-12045

http://garage.grumpysperformance.co...ng-cam-and-shifting-the-lca.10553/#post-44949

http://garage.grumpysperformance.com/index.php?threads/degreeing-in-a-cam-correctly.3097/#post-8240

http://garage.grumpysperformance.com/index.php?threads/cam-gear-and-timing-marks-etc.724/#post-1021

http://garage.grumpysperformance.com/index.php?threads/cam-degreeing.9010/#post-32126
 
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That is one hell of an intake if it can achieve 110.5% VE.
I cannot post all kinds of links to back up my thoughts, but here goes:
You are going to be using fuel injection, which is supposed have more precise control of
your A/F ratio vs a carb. That should translate into you being able to run a higher DCR.
You already mentioned all the ways of keeping your temperatures down, so do those anyway.
As far as knock sensors go, my recent research me has convinced that knock sensors might not
be "hearing" detonation at all, and if they really are, then damage might already be done.
Make your own listening device to hear knock out of one of those cheap listening devices - the
one you add a length of wire to the microphone and attach the mic to a battery clip.
I'll try to find a link.
 
related info

http://garage.grumpysperformance.co...temps-detonation-resistance.12842/#post-66481

http://garage.grumpysperformance.co...mble-and-swirl-quench-squish.4081/#post-35069

http://www.pcengines.com.au/calculators/Calculate dynamic Comp Ratio.htm

http://garage.grumpysperformance.co...olishing-combustion-chambers.2630/#post-50238

http://garage.grumpysperformance.com/index.php?threads/oil-stained-intake-runners.14209/

http://garage.grumpysperformance.com/index.php?threads/engine-compression-vs-knock.9252/#post-33366

http://garage.grumpysperformance.co...n-chamber-tips-and-questions.4715/#post-12810

http://garage.grumpysperformance.co...oling-and-tuning-consistency.4701/#post-12741

http://garage.grumpysperformance.co...-ratios-detonation-preignition.671/#post-1635

http://garage.grumpysperformance.co...temps-detonation-resistance.12842/#post-66481

http://garage.grumpysperformance.com/index.php?threads/cooler-denser-air.8961/#post-54496

http://garage.grumpysperformance.co...nock-sensor-and-related-info.3515/#post-51569

http://garage.grumpysperformance.com/index.php?threads/octane-boosters.613/#post-46230

http://garage.grumpysperformance.co...octane-for-compression-ratio.2718/#post-35581
 
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Are you running a 58x wheel how precise can you get with the holley you can spray the intake valve to cool it there is allot ways to tune that detonation out.
 
Thanks again, everyone.

My plan is to change basically nothing except to get a good widely adjustable timing chain, polish the combustion chambers, and focus on getting my intake temps as low as possible.

I just read a quote from David Vizard on SpeedTalk that says that every 8 degrees of intake temperature reduction equate to a roughly 1 octane number higher level of detonation resistance.

I'll make sure to insulate the intake and have a cold air intake setup from day 1 and then I can just retard the timing a little bit to delay the intake close event and therefore actual cylinder pressures. (I'll be stealing from Peter (torque) to pay Paul (HP), but honestly, this thing is going to have more torque than my tires will be able to deal with anyway.)



Adam
 
Grumpy said:
why not just install the cam retarded 3-4 degrees from split overlap that way it retards the valve seat timing about 7 degrees from the listed ADVANCED timing figures, raises/moves your whole torque curve about 350 rpm higher and significantly reduces the potential of detonation, without adding duration that reduces low speed torque or makes the brake booster and manifold vacuum, or idle characteristics less street-able?
Click to expand...
I agree my cam had to be retarded 4 to bring in a better DCR.
 
http://garage.grumpysperformance.co...ng-cam-and-shifting-the-lca.10553/#post-44949

http://garage.grumpysperformance.co...et-it-to-last-cam-install-info.90/#post-57942
KEEP IN MIND MANY CAMS ARE FACTORY SET UP TO BE 4 DEGREES ADVANCED if INSTALLED DOT-TO-DOT

ADVANCING.
Begins Intake Event Sooner........................
Open Intake Valve Sooner..........................
Builds More Low-End Torque.......................
Decrease Piston-Intake Valve Clearance....
Increase Piston-Exhaust Valve Clearance...

RETARDING
Delays Intake Event Closes Intake
Keeps Intake Valve Open Later
Builds More High-End Power
Increase Piston-Intake Valve Clearance
Decrease Piston-Exhaust Valve Clearance
camtimebush.png

lobe_diagram_lg.jpg
 
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Grumpy said:
why not just install the cam retarded 3-4 degrees from split overlap that way it retards the valve seat timing about 7 degrees from the listed ADVANCED timing figures, raises/moves your whole torque curve about 350 rpm higher and significantly reduces the potential of detonation, without adding duration that reduces low speed torque....
Click to expand...

Just so we're on the same page and neither myself nor future readers of this thread get confused; retarding the cam 3-4 degrees also reduces low speed torque (torque at all speeds), right? -If you're closing the intake later, you're trapping less air in the cylinder and therefore reducing cylinder pressure/ torque, right?


Adam
 
retarding the existing cam lets say 4 degrees shifts the entire torque curve about 200 rpm higher in the rpm band,
so for example if the cam, runs best between
( 1900-rpm through 5400-rpm) that shift to retard it 4 more degrees would likely result in, (2100-rpm-5600-rpm)
so yes in effect it has a slight effect on the engine power curve, no question there,
but the change is much less noticable than it would be if you added enough more duration too the cam,
you select to run, too reach the identical valve close point while maintaining the same LSA (lobe seperation angle) and LCA (lobe center angle)
your engines power band will change with
displacement
,compression ratio,
the cams LSA .LCA,
and factors like runner length
runner,cross sectional area,
header primairy length and diameter,
collector length and diameter,
back pressure,
altitude, outside air temperature, and a dozen more factors,
indexing the cam is one of the most effective and least likely to cause driveability issues

0607phr_11_z+camshaft_basics+lobe_centerline_angle_determination_chart.jpg

Duration_v_RPM-Range_wIntakeManifold01.jpg

craneq2.gif
 
NewbVetteGuy said:
Just so we're on the same page and neither myself nor future readers of this thread get confused; retarding the cam 3-4 degrees also reduces low speed torque (torque at all speeds), right? - If you're closing the intake later, you're trapping less air in the cylinder and therefore reducing cylinder pressure/ torque, right?
Click to expand...

Grumpy said:
retarding the existing cam lets say 4 degrees shifts the entire torque curve about 200 rpm higher in the rpm band,
so for example if the cam, runs best between ( 1900-rpm through 5400-rpm) that shift to retard it 4 more degrees would likely result in, (2100-rpm-5600-rpm)
Click to expand...

Retarding shifts the torque curve higher, but it does not necessarily lower your total torque. So if you had a low rpm detonation problem, then retarding the cam timing would lower your cylinder pressure by closing the intake valve slightly later. You would have a little less low-end torque, but you would gain more high rpm power.
Did I explain this correctly?
 
yes you seem to have that idea down correctly, keep in mind its one of several factors working together, things like getting the quench correct, polishing and un-shrouding the combustion chamber, getting the ignition advance curve and fuel/air ratio correctly matched and taking the time to polish the piston, dome, removing sharp edges from valve clearance notches , and polishing and very slightly rounding sharp edges on the valves, use of the correct spark plug heat range, removing exposed threads in the combustion chamber after you test by inserting a correct spark plug, certainly helps reduce any potential hot spots.
pencilbal.jpg


chart3e1.jpg


addcurves.jpg

if your experiencing detonation issues that are cured by swapping to higher octane rated fuel, and you would prefer to use the lower octane , less expensive fuel, you should adjust your cars ignition advance combination , so that its advance curve has either less initial timing, or delaying the mechanical advance vs. rpm with some stiffer springs, or a combination of both might reduce the pinging under load at 2500-3500 rpm where its most commonly seen,. Does this detonation or pinging, only occur at WOT? If not, limiting the vacuum advance with a stop, or using an adjustable vacuum advance unit and raising the amount of vacuum required vs. the amount of vacuum advance might be warranted also and installing a lower temp rated t-stat and adjusting the engine fuel/air ratio a bit richer may also help..

http://garage.grumpysperformance.com/index.php?threads/octane-boosters.613/#post-41341

http://garage.grumpysperformance.co...temps-detonation-resistance.12842/#post-66481

http://garage.grumpysperformance.co...ow-to-reduce-its-likely-hood.9816/#post-37278

http://garage.grumpysperformance.co...-into-gen1-chevy-small-block.4484/#post-11858

http://garage.grumpysperformance.co...e-required-octane-for-compression-ratio.2718/
 
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Another way to reduce detonation is having a more accurate control over spark a crank trigger will give far more accurate timing. Msd makes a real nice box setup now also.
 
Strictly Attitude said:
Another way to reduce detonation is having a more accurate control over spark a crank trigger will give far more accurate timing. Msd makes a real nice box setup now also.
Click to expand...
Thanks for that. As I'm already going with port fuel injection and a Holley EFI system, I was already planning to go with a crank trigger because I figured I might as well get the extra control + fuel economy bump of going to multiport. (And I figured I might be able to play with tweaking the injector timing in the back cylinders that get a little bit starved for air so that I can keep the AFR in each cylinder in the right range.)
 
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