Sbf stroker doin the dynamic compression/cam timing 2step

Ok as my stroker build progresses I find out that the online compression ratio calculator I was using was giving me wrong info. My static came out to 13.4:1 but I figured it on 5 other online crc's and it came upto 12.1:1. Better but now figuring my valve overlap my dynamic cr is only 8.6 with a cyl pressure of 168 psi. That is a little lower than I wanted. Would advancing my cam timing 4 degrees be the best thing to do here? I'm shooting for street strip... heavy on strip Thanks guys! RS59
69 351wblock
Scat 3.85 crank
Probe rods
Probe pistons
Comp hyd 305/540"
Procomp 190 alum heads
2800lb 64 falcon fx

 

i dont trust online calculators. are you using a degree wheel to set cam timing?

 

No my only options for adjustment with this timing chain is 4 0 4

 

Could help bepends on the cam just make sure you check piston to valve clearence

 

Will I give up a lot on top end? Does this basically make the engine think the cam centerline is narrower? Like 110 degrees acts more like 106? Thanks

 

It will hurt the top end some but will help the bottom end and thats the part that get you moving. After the chain streches you may only have 2 in it.

 

Advancing the cam closes the intake valves earlier, increasing low rpm cylinder pressure, and therefore, torque. It hinders cylinder filling at high rpm as the tradeoff.

 

My concern is that if left as is ( at 0 ) it will be a little light in the shorts on bottom end But 393 ci should be a torque machine anyway and I'll be running a 4 gear soooo,what are the pros and cons? If left as is the cylinder filling characteristics are less than stellar soon turn that would cause the top end to suffer also because it doesn't have a good intake charge at higher rpm either. Am I thinking this right? Am I splitting hairs?

 

JMO,,,, advancing or retarding a cam is a band-aid fix for a cam that was not correct for the app in the first place .Talk to the cam techs from the leading pro cam grinders and compare there recommendations first. then make your choice you will be happy you did.. JMO...

 

John Mullen you are absolutely correct and I'm trying to fix something now that never should have been an issue to start with. I'm at fault here. But do you think my dcr and cyl pressure is too low or am I over reacting? I know it would be more street friendly but...you know.... Thanks!

 

This prolly won't answer your question but its all about give and take and depends on your intended use. for a street app its prolly not as critical and would be ok but for a racing apps its to low. just remember if you are gona ever drive it on the street you will have to compromise somewhat and it seems less is usually more there. I have found that many of us ,me included have over built our street engines and had problems with drivability. To much comp,to much cam to much carb ect... Over the years I have stopped trying to run full race engines on the street... Check out some of the dyno simulation programs that allow you to build engines on paper and see what you get before you start buying parts. Anyway good luck with your engine build. Also go to your local library and check out a book called the Internal Combustion Engine .its a MIT engineering text book that will tell you everything there is to know about engines of any type .Best book I ever read bar none. A must read for sure...

 

I would look at ditching that cam and going to something with a 108 LSA. Pretty sure that comp grind has 4 degrees of advance ground into it, so if you install it straight up by the dots, it will be in at a 106 intake CL anyway. If you are going to play this game, degreeing the cam is MUST, you gotta know where you are at. I got a hunch with that cam in @ 106, you are going to be in trouble on cylinder pressure anyway. But yes, short answer, when calculating dynamic compression ratio, its the intake closing point that is important, from the dyn. compression ratio standpoint, the motor doesnt really care if the cam is on a 110 or 108 LSA, what counts is the intake closing point, so yes, advancing the cam will increase the dynamic compression/cranking compression.

 

Are these actual measurements or off of calculator/simulator program?

Comp cams has a pretty good site that lets you easily play with configurations and gives you a CG dyno sheet. You'll need to know quite a bit about the engine to get accurate output but its pretty good and kinda fun. I also believe there is an option to install the cam 4*+/-. Hopefully you know how to do screen captures off the computer and do a thorough comparison.

If by chance you have chosen the entirely wrong cam, pick a new one and be done with the headache and ulcers in an afternoon. And don't play with hard parts without a degree wheel.

 

Took a quick look at thier website, you are right, that cam is ground straight up.
Are you running outside air, or underhood? Whats the trans and rear gear? Piston/head clearance @ tdc? Dome or flat-top?
If you want to go farther with this, I would suggest we go to PM's, most of the HAMB thinks this stuff is voodoo.

 

Put it in with the intake at 106, 4 degrees advanced. Degree it and check V-P. Then you will have a baseline and can back the cam up if it detonates.

jm2c

 

I dont post here much, but have a lot of experience with street strokers and a ton of experience with the SCR/DCR calculator I use in strokers and standard displacement street builds, so I trust it.

Assuming you are running a 60cc chamber, Probe 3cc pistons, zero deck with a .039 gasket, you'll be at 12.13:1 compression, and DCR is 8.37 with the cam at 108 ICL. That'll work, but you are killing compression with the cam, more than most, so you'll probably have to watch your ignition curve

If you have 4cc pistons and are deeper in the hole, that's a bit better, in that case, at .010 in the hole and 4cc you are at 11.67:1 and then I would run the cam at 106 ICL for 8.24 DCR, small movements in intake centerline wont kill top end but sure will make it happier part throttle.

The bottom line is you need to know exactly what parts you have and we can go from there. FWIW I run 10.7 / 8.33 in my 489 inch FE, and have so carbed and then later EFI since 2006. It'll run on pretty much anything I put in the tank in town, although I will put 91 or 93 if I am running it hard.

Circle back with head gasket compressed thickness, rod length, chamber size, which piston you have (part number), as well as the entire cam card info and I'll run them again

As far as advancing or retarding the cam indicating "the wrong cam" it's just not so, its another tuning tool and working cam timing to your advantage is a smart thing to do

 

RS59, Keep in mind that all of us giving you advice have different opinions as to what is best for your engine. We all can contribute info as we see it but in the end what will work for you best will take much trial and error. as 427stang says moving the cam +/= .is a good tuning tool ...but only after you get the correct cam for your intended purpose. If you are moving it to correct your dcr then it is the wrong cam. Cam technology today is so much better than back in the day when you only had so much to work with that you had to move things around to make it work. but nowadays you can get anything you want in a cam profile. .....READ THE BOOK FROM M.I.T. there is so much info there.it will help you much better than sifting through all our opinions including mine. they cover things like fuel burn speed vrs piston speed, fuel btu rating, specific gravity of fuels, comp ratio, bore /stroke ratio, cam timing, rod lengths air, velocity, valve size, runner size, and on and on.....all real world tested technology, you will be amazed ...

 

X2, total bs. I'll respond to your pm tomorrow, today is going to be hectic.

 

I hope you will keep posting hear as we all want to see where you go with this. Just curios to hear what falcongeorge has to contribute. I'm all ears and always ready to learn something new... You started it hear so finish it hear don't hide it in your PM... Curious minds want to know.....

 

Any updates? A list of part numbers would send us off and running

 

WOW...well my427stang, I guess we scared them off!!!!!... They must be to smart for us or ???????????

 

I'm still here and haven't heard any more thru pm. That cam is in fact ground straight up I have installed it 4 degrees advanced. I misplaced my scratch paper. I'll post what this computes to......

 

Ok here is the lowdown on everything...

Bore 4.030
Stroke 3.85
Gasket thickness .042
Deck -.001 (based on stack measurements vs block deck .001 out of bore)
Piston volume -4.0cc valve relief.
Combustion chamber 60cc
This gives me 12.08:1 static compression

Rod length 5.956
Intake closes 78degrees abdc ( with cam advanced 4degrees )
Alt 586'
This computes to :
chamber volume 72.63cc
Effective stroke 2.81"
Dynamic comp. 8.97:1
Cranking pressure 184.26 psi

Comp cam part # 35-331-4
Lift .540 .540
Dur @ .050 253 253
Lobe lift .339
Ls 110
Valve timing @.006 intake opens 43 btdc closes 82 abdc
Exh opens 82 bbdc closes 43 atdc
I checked PVC with a Kraft cheese slice ( hamb ingenuity learned here) no interference This is in a gutted 64 falcon with a t10 and a 9" equa loc 3:55 for in town and 4:11 for strip I'm guessing around 2800 lb. straight tube axle 8" slicks ...oh yeah , it has a dent in left door and I have a scar above my left eye. Have I forgot anything?.

 

OK, (.7854) x 4.03 x 4.03 x 3.85 x 16.387 = 804.75 cc's in the cylinder
60 cc's in the chamber
Although the OP didn't bless us with the gasket bore, I suspect that he has used the Ford Racing M-6051-A302 that measures 0.042 x 4.100" bore.
Since the piston pops up out of the bore by 0.001", let's call the gasket thickness 0.041" and call the motor zero deck.
(.7854) x 4.100 x 4.100 x 0.041" x 16.387 = 8.87 cc's in the gasket.
This leaves us with a 0.041 squish. (Nice!)
0 cc's in the piston deck height.
4 cc's in the piston crown.
804.75 + 60 + 8.87 + 4 = 877.62 cc's
Deduct 804.75 from 877.62 and find 72.87 cc's.
Divide 72.87 into 877.62 and find 12.043639:1 Static Compression Ratio.

The OP says he is running this cam....
http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=874&sb=0
The timing numbers @0.050" tappet lift are as follows....
IO (16.5) BTDC
IC (56.5) ABDC
EO (56.5) BBDC
EC (16.5) ATDC
Overlap is 33 degrees
IC is 110
EC is 110
LSA is 110

Different calculators will spit out different numbers for DCR. Now, no matter whose effective compression pressure ratio calculator (Dynamic Compression Ratio Calculator) you use, the key to finding valid numbers is to use the same calc on each and every build over a period of time. That's what I have done. I've used the KB calc for decades now and have a pretty good idea of what to expect when building to the number on their calc. Anywhere between 8.0:1 and 8.5:1 will be a good street motor that will behave well on pump gas with iron heads, so long as a tight squish (0.035" to 0.045") is built into the motor when the combo is being planned. 8.5:1 to 8.75:1 can be run on premium pump gas with iron heads (suggested max 9.5:1 static compression ratio) and a tight squish if the chambers are de-burred and the spark plug ground straps are cleaned up so that there is no thin material (dingleberries) on them to glow red hot and pre-ignite the mixture.
Over 8.75:1 dynamic compression ratio, in my experience, will require aluminum heads and a max of 10.5:1 static compression ratio on the street with premium pump fuel.
Entering these values into the KB calc results in this DCR.....
Compression ratio 12.040
Stroke 3.850
Rod length 5.956
Intake closing point + 15 degrees 71.500
The result is 9.094:1 Dynamic Compression Ratio with the cam installed straight up on the numbers (intake closes 56.5).
http://www.kb-silvolite.com/calc.php?action=comp2

I've also been playing around with a software dyno from Comp for a couple of years now and have compared my results to hard core dyno pulls with a couple of engine builders on another site. I've consistently been within 2% of their numbers.

Now, lots of fellows will say that the DD results are bogus, because they ran the same combo and made a hundred hp less. You have to understand two things about a DD result. The software is designed to give you results based on 100% spot-on tuning and is dependent on you giving the software the correct cylinder head flow. Most of the amateur engine builders will not achieve 100% tuning and most cylinder head manufacturers will fudge their numbers a little in order to help them sell cylinder heads. In other words, if I find a head mfg who has based their SBC head flow on a 4.200" pipe, I will downsize the flow they publish by 5% or 10% just to try to be real with the results. I mean, come on, how many of you have ever seen a small block Chevy with a 4.200" bore? Also, you don't know if they used a single angle valve job or a 3 angle valve job or a 478 angle valve job. You also cannot be certain that the mfg used 28" of water or not, as a depression figure. You have no idea what the relative humidity or the air temp was the day that they flowed the heads. You don't know the dimension from the valve face to the table and you don't know whether the valves were parallel on the stems or undercut. That's the biggest problem with DD results.

Anyway, I'll put this combo into the software and see what happens. It's not actually a DD, it's a CompCams DynoSim 4.2

There isn't much info out there for flow on the heads, so I'll use what's published on the Stan Weiss website as recorded by Muscle Mustangs and Fast Fords magazine. I have no idea what parameters the magazine guys used to determine flow, but we'll use their figures on this pull.....
0.100"...59...47
0.200"..116...85
0.300"..167..126
0.400"..213..157
0.500"..241..171
0.600"..251..176
0.700"..258..180
If anyone has flow figures that differ from these, I will be glad to change 'em up and do another pull.....

393 Windsor Ford with ProComp 190 aluminum heads.....
This pull was made with an 850 carb on an RPM intake manifold and large tube headers running through mufflers......

RPM....HP....TQ
2000....144....379
2500....187....393
3000....238....417
3500....305....458
4000....372....488
4500....434....507
5000....481....506
5500....511....488
6000....515....450
6500....503....406
7000....440....330

Peak volumetric efficiency 99.6% @5000 & 5500 rpm's
Peak BMEP 194.6 lbs @4500 rpm's

Nice motor. I couldn't find any more power by advancing or retarding the cam. Motor is down 6 hp and 3 ft/lbs using a 750 carb. Single plane intake is down throughout the range, until 6000, where it makes the same hp as the RPM. Single plane is a disaster for torque, down throughout the range of rpm's and down 18 ft/lbs @4500. I don't care how you slice it, the RPM is the most efficient intake manifold there is when using a 4-bbl carb and making power from idle to 6500.

Large diameter, stepped tube race headers make 530 hp @5500 & 6000 / 526 ft-lbs @4500 & 5000 with 100.6% volumetric efficiency @5500 and 202.0 lbs BMEP @4500. The hp and torque curves with the stepped headers are real pretty to look at, like smooth bell curves. Interesting to note the double peaks for both hp and torque. I've never seen that before on a software pull. Real nice motor.

 

Are you serious? Who gives a damn what most of the HAMB thinks? Anyone who can't at least try to understand this stuff is a mental deficient anyway and should be paid no attention to.

 

In my experience, these threads attract a lot of drama and chest thumping. OP, I've had a pretty busy week with work, didnt even get home from work till 9.30 last night. Sorry, I was too busy trying to earn a living to answer your pm in a timely fashion.

 

Falcon George no problem I understand the joy of being a working stiff.
Fridaynite man that's really thorough. Thanks so much, the numbers I came up with we're a little different. I may have figured something wrong? Or the difference in different calculators. I have installed this cam advanced 4 degrees How much will that change things according to your calculations? Thanks guys. Rs59

 

OK, same motor, but with the cam advanced 4 degrees and installed on these 0.050" numbers .....
IO (20.5) BTDC
IC (52.5) ABDC
EO (60.5) BBDC
EC (12.5) ATDC
IC is 106
EC is 114
LSA is 110
Overlap is 33 degrees

RPM....HP....TQ
2000....149....392
2500....191....402
3000....246....430
3500....313....470
4000....379....497
4500....436....509
5000....481....505
5500....502....480
6000....506....443
6500....474....383
7000....412....309

Max volumetric efficiency 102.3% @5000 rpm's
Max BMEP 195.5 lbs @4500 rpm's

 

I don't know what converter you're using, but I would think at least a 3500 stall unit. So, you have to throw out all the hp and torque numbers below 3500 because they will not apply when the motor zips right past them on the way to 3500 where power is beginning to be applied to the tires.

So, in my opinion, it makes no sense to give away power at the top and put it at the bottom where it will be wasted as the motor goes right past those lesser rpm's. Am I making any sense?

 

He's running a t10.