Retarding comp cam

[JimNolan]

Friends,
I'm getting ready to change head gaskets on my 410 to a thicker gasket. Thus, I have to change cams to bring my compression (DCR) back up to where I want it. I'd like to get as much cubic inch use out of it I can get on 87 octane. I've already got a cam that would work well and give me what I'm looking for but it's a comp cam ( 110/106) and to get what I need it needs to be a 110/110 cam. Can I just get a timing set with multiple degree crank gear and use the 4 degree retard keyway.
I've always used a degree wheel to insure the results of ICL but I've never really used a crank gear with multiple keyways. This 4 degree built in stuff has me talking to myself. Thanks guys.

[blykins]

Jim, if you want to increase the DCR, you advance the cam timing, not retard it.  You're trying to decrease your static compression ratio with a thicker gasket, but want the DCR to stay the same, right? 

[JimNolan]

Jim, if you want to increase the DCR, you advance the cam timing, not retard it.  You're trying to decrease your static compression ratio with a thicker gasket, but want the DCR to stay the same, right?

Yes and no. the cam I have now with a thicker head gasket would lower my Static Compression from 9.6 to 9.25. At the same time that bigger cam I have now will lower my DCR to worthless value. I've got a cam that will work but if I use it straight up the DCR value will shoot up past what I want. By retarding the cam to 110 ICL instead of 106 straight up, that will bring my DCR back down to a useable value.  The part I don't get is the built in advance of the cam. I feel like I'm changing something that wasn't meant to be changed. confused

[My427stang]

You are mixing terms here, first "straight up" isn't dot to dot, its when ICL, ECL, and LSA all are equal.  Dot to dot is just dot to dot and at best it is equal to what the cam card says.

106 is 4 degrees advanced from "straight up" which would be 110 ICL (equal to the LSA)

So, to get it to 110, you have to retard it 4, just like you originally said.

In other words, you are trying to install the advanced cam in its straight up position. So you have to "undo" the ground in 4 advance by retarding it 4 degrees

I will say this though, with all respect intended, it's a goofy way to do it.  Better to run thin head gaskets and early cam timing than to run thick gaskets and late cam timing. 

Also, I have to ask, is everything cc'd and any other clearances carefully measured?  If not, chasing DCR numbers to the specificity you are is sorta worthless

[plovett]

Jim, if you want to increase the DCR, you advance the cam timing, not retard it.  You're trying to decrease your static compression ratio with a thicker gasket, but want the DCR to stay the same, right?

Yes and no. the cam I have now with a thicker head gasket would lower my Static Compression from 9.6 to 9.25. At the same time that bigger cam I have now will lower my DCR to worthless value. I've got a cam that will work but if I use it straight up the DCR value will shoot up past what I want. By retarding the cam to 110 ICL instead of 106 straight up, that will bring my DCR back down to a useable value.  The part I don't get is the built in advance of the cam. I feel like I'm changing something that wasn't meant to be changed. confused

DCR isn't the be-all end-all.  It's just a tool.   I completely agree with MY427Stang in that a thinner gasket with a more advanced cam is likely better than a thicker gasket with late cam timing.  It'd be better to run the higher static compression, and higher DCR, in most cases. 

Can you tell us the two cam's specifications,  with your static compression ratio, current and proposed head gaskets, along with
your deck clearance?  That would make it a lot easier to sort out.

JMO,

paulie

[JimNolan]

First off, everything was cc'd and measured before assembly so I could rely on calculations. I have a Cam Research 282/288 adv, 216/225 @.050, .515/.540 lift, 110/106. .052quench which gives me 7.5 DCR and 9.58 CR and using a 750 Holley. This is all well and good for peak horsepower at 5000-5500 rpm. But, I'm not going to run my car up there again. That's over. I want gas mileage now and more horsepower and torque at lower rpm where I can possible get better gas mileage cruising at 1850 rpm (65mph) with the Tremec. I can gain about 42 lbs of torque and 20 hp at cruise with a cam that is more compatible with peak horse power coming in at 4500-4800 rpm.
What I planned on doing was using a XE256 comp cam, that's 256/268 adv, 212/219 @.050, .487/.493 lift, set on 110/110, .063 quench which would give me a 7.78 DCR and a 9.25 CR using a 570 Holley for carb. I think I need to stay within a + or - 4 degrees of a 208 @.050 Intake duration cam that I would need for a 9.25CR.

Now, some of you guy's helped me with this engine before, I'm going to hang onto everything you guy's say, it's worked before. Tell me what you'd do to get what I'm looking for. Thanks.

[plovett]

My opinion is that you should keep the tighter quench and higher static compression ratio, and then just choose the best cam you can.  I would tend toward a single pattern cam if you want low rpm drivability and mpg.  Maybe one with less aggressive ramps than the Comp XE cam you mentioned.   The XE's are reputed to be noisy and the short advertised duration is hurting you with respect to DCR.  There is a limit to how low you can go on duration without having detonation issues, but maybe you can thread the needle so to speak.

How about this Howards cam?  263/263, 209/209, .490"/.490", 111 LSA.  If you installed it with an ICL of 110 the DCR is around 7.86.   I think this on the small end of what you can do with 9.58:1 compression.

http://www.summitracing.com/parts/hrs-250021-11/overview/make/ford

Or the Crane 266 Energizer?  266/266, 210/210, .516"/.516", 110 LSA.  I think Crane measures advertised duration at 0.004" as opposed to the more usual 0.006", so the advertised figure might be a couple of degrees higher if measured as other cam manufacturers do.  It's also not much different than the cam you have now (High Energy 268?)  in advertised duration, but has less duration @ 0.050", so maybe not much to gain there.

http://www.summitracing.com/parts/crn-13404/overview/make/ford

The Lunati Hi-260 is 260/260, 210/210, .508"/.508", 110 LSA. 

http://www.summitracing.com/parts/lun-10330205/overview/make/ford

The Comp High Energy 260 is 260/260, 212/212/, .484.484", 110 LSA

http://www.summitracing.com/parts/cca-33-222-3/overview/make/ford

Go any bigger than those and I don't think you'll see an appreciable difference from your current 268H cam.   A decent rule of thumb is every 2 degrees of cam duration @0.050" will change the rpm peaks by 100 rpm.   Maybe that will help you decide.

JMO,

paulie

[JimNolan]

I'll run them through the computer. But, the 265DEH gives me a lot of hp and torque at 2000 rpm. It's an 8.0 DCR though.

[My427stang]

Jim, what are you running for heads?

I like the idea of tight quench better, but that .063 quench / 256 cam combo will run ok, I sure don't expect it will be that strong unless you have a serious set of heads, but it'll likely work OK

You may be gaining some torque using a calculator, but don't forget that overlap allows torque once you get off idle due to scavenging of the chamber pulling more into the cylinder.  That 256 cam has very little overlap and probably wont perform as well as the dyno programs say it will. Although I do think it'll be a nice cruiser and get good gas mileage

Once you respond with which heads and what has been done with them, I will give you my 2 cents.  I do think with 410 cid though, you need to have an efficient set of heads and intake to fill the cylinder well with a small cam




 

[JimNolan]

Ross, Please do. This is the 410 engine you helped me build. It's got the Edelbrock RPM heads and Edelbrock intake with the 750 on it. Yes, give me your 2 cents. Thanks

[My427stang]

Jim, a couple of things

I can't get to your numbers, but I can stay under 8:1 dynamic with the 256 on 110 ICL with the .052 quench.  To make a very mellow cruiser I think that would work, although I don't think you need to go as small as 570 cfm, it'll likely do OK for a Sunday drive through the hills car.

If I could figure out were our numbers differ, I may be able to see why you want to do both the head gasket and the cam.

BTW, if you are serious about top gear torque at low RPM, a change to a Performer from the RPM might be wise, but then you'll lose even more at the peaks

Have you ever though about just regearing what you have to get 5th more usable?  In my case, going from 3.70s to 4.11s gained mileage and allowed nicer cruising, as well as in town being much happier,  I forget which TKO and rear you have, but maybe match the gearing to the use rather than detune the motor

FWIW, the reason I am coming at it at a different direction than you is that to really do a "truck" motor like you are trying to do, the heads and intake are not really perfect and you may be spending more than you need to to make a happy cruiser

[turbohunter]

BTW, if you are serious about top gear torque at low RPM, a change to a Performer from the RPM might be wise,

LOL Ross you know I'm smiling.
Seriously, I am learning so much from these posts.
Thank you Jim for your posts and the rest of you guys for the great insight on this and others.

[JimNolan]

Ross, what do you think about a 265DEH cam. That'll give me about 13 more horsepower and 33 ft. lbs torque at 2000 rpm. It takes away about 25 horsepower at 5000 rpm but I don't want to go there anymore anyway. The only bad thing is if I put it at 110/106 I'll have a 8.0 DCR. I don't mind that as long as it don't get to 8.1. My 406 has 8.1 and it teeters on 89/91/93 octane depending on where you get it. And on a trip that sucks. I think 8.0 DCR would be secure with 89 octane. What do you think, leave the motor as is and change the cam. Also the 265DEH intake duration at .050 is 211, which would be right on for 9.58 CR.

[My427stang]

BTW, if you are serious about top gear torque at low RPM, a change to a Performer from the RPM might be wise,

LOL Ross you know I'm smiling.
Seriously, I am learning so much from these posts.
Thank you Jim for your posts and the rest of you guys for the great insight on this and others.

His may...yours no no way

[My427stang]

OK, so first, whats the difference between your 406 and this 410?  Quench, heads, piston design, intake, ignition, carb, gearing etc.

The reason I ask is that like Paulie said earlier, DCR is just a tool, I run 8.35 on the Mustang and 8.2 in the truck and neither has fuel issues, matter of fact the Mustang is easier on fuel choices than the truck

So 8.0 vs 8.1 really is not significant, something else is contributing.

So for the use of the car though, I think the 265DEH on 106 would be OK, I'd probably run a 268H Comp though (for no good reason LOL) to peak around 4800-ish and I'd leave the quench tight. I'd look at the timing curve and mixture if it pings at that point.  Typically the DEH cams are not very well loved for power, but it'd probably do fine for your needs.

Is your car a .64 OD and a 3.70?