those DCR friendly please help...hotrod 427 and others please advise

mike 1985 · 10-28-2003, 01:59 PM

i am not able to down load this so what cam woul be recommended to keep me 93 premium friendly ? Looking for hyd and max rpm of 6000
350
10-1 CR
dart iron eagles 64cc -180 cc runner
weiand stealth dual plane
holley 750 vac secondary
700 r-4
2500 stall 3.07 gear 26" tall tires

3440 with driver.

looking for a healthy sbc that can be driven with detonation.

gkull · 10-28-2003, 02:50 PM

You have to figure out the actual compression ratio. Or inform us of some specific dimensions. If some one tell's me that they have 10:1 compression. I don't believe it out of a .030 overbore 350 with flat tops and 64 cc heads. Even in a non decked engine and 4 valve relief forged pistons. your closer to 10.5 with standard .038 compressed gaskets.

All these figures are very import to get actual DCR with a certian cam type.

Just with the parts you have I would recommend the Crane power max 272. with headers and free flowing exhaust it will be a fun machine.:)

mike 1985 · 10-28-2003, 03:10 PM

the motor is std bore with the stock 1985 vette forged pistons that have one long valve relief going across the entire top of the piston. The stock rating with the 76cc heads was 9-1 with a thin steel shim head gasket and now i have 64cc heads. that's how i came to a 10-1 compression ratio.

i have 1-3/4 " hooker long tubes with 2.5" dual ex.

Lt1er · 10-28-2003, 05:59 PM

http://www.csgnetwork.com/compcalc.html

Check this site out. With a 4 inch bore and 3.48 stroke 4.060 head gasket .038 compressed pistons are -6 cc dish with a large valve cut. Un decked .025 piston down in the hole. You only get 9.6 compression.

Just change to a steel shim .015 head gasket and it's up to 10.16 That makes a big difference.

I have never had good luck taking an older bottom end motor and throwing hotter cam and heads on it. It's like putting Viagra in a 80 year old. It runs like hell for a little while and then the ticker just gives out.:)

Your better off to freshen the bottom end also!

mike 1985 · 10-29-2003, 09:20 AM

thank you

427Hotrod · 10-29-2003, 09:05 PM

Hi Mike....

GKull is being honest with you. The calculators are actually easier to use if you already know a specific cam you're interested in and have all the specs. Then you can plug in all the #'s and come up with what the DCR actually is.

You start out with info about basic engine....stroke..rod length etc, then plug in all your cam actual opening/closing events. It takes those calcualtions and arrives at an actual piston position when the intake valve closes. It uses that as "real stroke" so to speak. Assuming compression doesn't really begin until valve is completely closed. ( I don't know if I totally agree with that). Then it has you "build" the rest of motor to get "static" compression ratio, for example 10.0 or whatever.It uses measured deck height, gasket thickness, bore, stroke, piston cc's, chamber cc etc to determine it. THEN you can plug in the "real" stroke from the previous calculations and get the DCR.

It's actually pretty easy to use. Any reason you can't download it? Maybe we can send it to you? The only reason I say that, it you can literally spend hours playing with it and arrive at many different combos to get same results. It's best to pick a particular cam that fits your needs and then approach it as "how do I tailor the motor" to work with it. I spent a long time working with it using cam catalogs and lobe spec sheets to work mine out.

You could "reverse engineer" the formulas but it's not as easy. I'm not trying to cop out on you, I just don't want to give you a cam that will meet the DCR yet still run crappy in your car.

DCR is a very valuable concept to building a strong engine, but you have to understand the whole concept and what the numbers tell you.

For example, I can put a little tiny cam in it with 9.0 compression and make 8.5 DCR. Or I can put in a larger cam with 11.0 compression and make 8.5 DCR. Which do you think will be faster? There is another Forum member here who gained over 20hp on the dyno by retarding his cam a good bit. That made DCR go LOWER...yet it made more power and ran even easier on pump gas.

You really need to get your hands on it and play and not get too hooked in the actual number.

I've got lots of thoughts on this stuff and we could run this for hours!

Let me know if I can help you. Give me some specific cams you are looking at with actual intake opening and closing events (advertised duration NOT .050) and LSA and I can run them for you and give you a few ideas. All depends on how you want to drive it.

FWIW..I ran a couple of deals through it to give you an idea. Assuming lots of stuff just as GKULL said... I ended up with 10.148 static compression ratio. If you use something like a plain 'ole Comp 268 high energy with 268/268 on 110 LSA installed at 106 I/C, you get 8.39 DCR. Pretty high but doable with good tuning. Something like a 272/272 on 112 LSA installed at 108 I/C gets you 8.15 DCR. A 280/284 on 112 LSA installed at 110 gets you 7.76. That same cam ground with a 108 LSA instead and installed at 106 I/C all of a sudden has 8.02 DCR. As you advance cam DCR goes up. So a larger cam ground on a tighter LSA and/or advanced will up DCR as compared to a wider LSA. A smaller cam with a wide LSA can have similar DCR as the larger cam. It will be smoother...but will be someone fun to jump on a the red light and blow them into the weeds!

In that last example, if you had the rest of the combo set to use it it would be great. Wouldn't idle as well, or be as smooth but would sure sound tough. It would run on pump gas fine and pull like crazy. Just have to decide how you really want it to act...what gears, converter etc you want to run..it all makes the combo. If you want a pure stump puller, one of the smaller cams might be better.

Hope this gives you a little direction...

JIM

[Modified by 427Hotrod, 7:32 PM 10/29/2003]

[Modified by 427Hotrod, 7:36 PM 10/29/2003]

neverendingproject · 10-30-2003, 10:11 AM

:lurk:

very interesting... i have a question though. how does forced induction affect DCR ? can it be calculated?

mike 1985 · 10-30-2003, 11:46 AM

i bought a new pair of iron eagle bare heads that are 72cc.
using the compression chart i'll end up with 9.3-1 with a .015 head gasket. I'm thinking this gasket will help my quench too. I plan to run the crane 272 cam.

what will the dcr be with this set up ?

gkull · 10-30-2003, 11:54 AM

You have mail - I'm sending you a DCR program. to use the program you have to go out to the cam manufactures web site and copy down the cam card event numbers for each cam. Then just plug it in. I went to that C/R site listed above and it's close, but doesn't use all the figure like piston to top ring gap........

427Hotrod · 10-30-2003, 12:24 PM

I'm not exactly sure of the Crane 272 specs, but I think it's on a 112 LSA. If so a 272/272 on 112 LSA installed at 108 ( 4 degrees advanced) gets you 7.49 on your motor with 9.3 compression ratio.

Depending on how smooth you want it, you might look for a tighter LSA on the order of 108-110 with a cam that size with only 9.3 compression.

On the blown motor DCR, it would take a better math guy than me to figure it out. I know the formulas for figuring boost and "effective" compression ratio, but even they are shots in the dark exactly for this reason. We all know big cams bleed off pressure and they really affect blower motors harder because of the positive boost as compared to just tuning with atmosheric pressure. In fact as I think about it, "real effective" DCR would change with boost level which would be affected by exhaust restriction, cam, rpm etc. Pretty esoteric stuff.

I still say you shouldn't get too wrapped up in this DCR calcualtion stuff. It will help you figure out what will run on pump gas hopefully and help you figure out how far you can push it and still get by. But it still doesn't select the best cam for your application. As I said above...you can arrive at the same number with many diferent combinations that will all run different. Don't build to the number. Build what will run right and then use the calculator to verify that it should run on the gas you select. It's a very useful tool..just use it for what it was intended for.

Just as with boost, my motor does very well efficiency wise at high RPM. If I built it to match what the DCR calculator said would run on pump gas...once it hit high rpm and started really filling the cylinders it would beat itself to death. Sure I could add more compression for my cam (it would need to be 12.5 static!) and it would cruise around fine, but not take full power. I just know that from experience!

JIM

mike 1985 · 10-30-2003, 12:27 PM

thanks alot guys for your help

mike 1985 · 10-30-2003, 12:56 PM

for some reason the project1.exe says it's missing something ?

here are the cam specs from the crane web site

Application Series & Grind Number
Good idle, daily usage w/plate nitrous system, 2600-3000 cruise RPM, 8.75 to 10.5 compression ratio advised.(50 state legal, pre-computer, C.A.R.B. E.O. D-225-18) Basic RPM 2000-5500 PowerMax
H-272-2
replacing:
HMV-272-2

Cam Specifications

Degrees Duration @ .050 Int./Exh. Degrees Advertised Duration Int./Exh. Degree Lobe Separation Open/Close @.050" Cam Lift Int./Exh. Lash Hot Int./Exh. Gross Lift Int./Exh.
216-228 272-284 112 1 35-51 ( 3) .000 .000 .454-.480 107 ICL

with 9.3-1

[Modified by mike 1985, 4:59 PM 10/30/2003]

[Modified by mike 1985, 5:00 PM 10/30/2003]

427Hotrod · 10-30-2003, 02:26 PM

About 7.49 with 272/284 and a 112 LSA installed at 108 I/C.

JIM

mike 1985 · 10-30-2003, 02:30 PM

thank you very,very much.

427Hotrod · 10-30-2003, 05:42 PM

Did you already have the 64cc heads? If so why give them up for the 72's?

Looking at your combination, I think you could use a tighter LSA to wake it up out of the hole with the 3.07's since you have a carb.

I just talked to a buddy of mine that is putting a sweet little Crower roundy rounder cam in his 327. It's 268/274 adv and 238/244*@.050 on a 107 LSA installed at 103 I/C. There is a measurement called "hydraulic intensity" that gives you a rough idea of how aggressive the lobe is. It is the difference between advertised duration and .050 duration. The closer they are together the 'faster" the lobes are. In a case like his, there is only 30* difference. His cam will have much better DCR than something like the 272/284 with 216/228 @.050 numbers. Those are 56*/56* apart. MUCH slower lobes. He has smaller lobes that move the valve very quickly. This actually allows for much better airflow because the valve gets open quicker. Same concept that a roller cam uses. After initially being a little slower, the roller really flys getting the valves open.

So his will have relatively short duration numbers to work well on the street, yet it opens the valves very fast and gets great airflow. The only downside is that it won't be a 100,000 mile cam,but it will last a long time.

Before anyone settles on the most advertised cams out there, you need to do some homework and digging in the catalogs. Often the perfect cam is listed somewhere you don't expect. I've suggested certain 4x4 cams to some Forum memebrs that they loved after they used them. Not necessarily what I would have used for me..but listening to what they really wanted and what parts they had we made a choice. There are some great marine cams too that work great on the street and the roundy pounder deals offer LOTS of choices. Don't limit yourself. The EXACT cam you need is out there.

JIM

[Modified by 427Hotrod, 3:49 PM 10/30/2003]

mike 1985 · 10-31-2003, 09:11 AM

i really needed the angle plug heads for spark plug clearance and i ported a small repairable hole in one EX port, so they are soon to be on e-bay ( starting at $1 if anyone is looking). This was my opportunity to buy a set of angle plug 72cc shambers, bare for a little over 400.

i agree and have looked pretty heavily at some of those marine and 4X4 cams.

Do you think that roundy cam would have enough vacume to run the brakes ?

Since were talking about buying the perfect cam, has anyone used the company recommended in David Vizards book to get the right cam the first time ? It's says it the most acurate cam machine out.

thanks
Mike