Retarding comp cam

[JimNolan]

The car has a 3.50 true trac and a .64 5th gear on the tremec.
The 406 has a .030 quench with 10.7 CR and a 8.1 DCR. I had trouble with pinging going to Tupelo last month. I ended up using 93 octane down there and it still pinged some. When I got back to Warsaw I lowered the ignition timing from 17 to 14 and I'm running 89 again with no pinging. I run a Lunati 282/296, 214/224 @.050, .500/.500 lift, 114/110 LSA/ICL in it. PS, I've got a new 268H with new lifters on the shelf but it has a 218 @ .050 intake duration on it. I figured that was too much for 9.58 CR.

[plovett]

I thought you were currently running a 268H in your 410 and wanted to move the power band down?  And I thought you had the Cam Research 282/288 in hand, and were considering getting the XE256?   I'm not sure if I got that all correct.

The 268H is not very big for a mild 410 and is not too much cam for a 9.58:1 compression.

What's in your 410 now?

paulie

[plovett]

Also, those dyno programs aren't perfect either.  They'll get you in the general range, but they don't give you the exact power you are going to make.  My experience is they can be close at the power peaks, but they can be way off at other points in the power curve.  That could be particularly important in your case if you want good power at the very low end of the range.

JMO,

paulie

[rockhouse66]

I don't understand this cam stuff like you guys but I ran a 265 DEH in a 428 engine and was unhappy with it.  It didn't come on until much higher RPM rather than being a good low end torque cam like it should have been.  I later came to believe that this cam needs a fair bit of static compression to work properly, and I was running low 9s.  So I would not go that direction with your lower compression.

[JimNolan]

Rockhouse66, you got real time information. That's what I was looking for. I read all this stuff on cams, run it through a computer dyno program and all you get is a comparison between the different cams you input. That's like figuring what octane you can run. The information from a engineering firm ( or credible looking website) says 7.6-7.8 DCR is good for 87 octane, 7.8-8.0 DCR is good for 89 octane, 8.0-8.2 DCR is good for 91 octane, 8.2-8.4 DCR is good for 93 octane and anything above that you need racing fuel. We also know from experience the aluminum head and a low quench will aid in preventing knock. Now I just got through putting 1600 miles on a car with an 8.1 DCR with iron heads but a quench of .030". I use 89 octane because of the quench, I'm sure of it because depending on which gas station I got gas from my engine would ping on that trip. I get 13mpg so I used a lot of those service stations along the way.
Anyone can study information, some of it fits my calculations, some of it don't. But the reason I get on here is for real time information and the experience you guys have got. That makes two of you that don't like a 265DEH. I don't like it either now.

[My427stang]

With the added info I would say a few things

- Paulie gave you good info on the 268H, it matches what you want.  I also think its a better cam than the 265DEH. I do not understand why you are concerned with the .050 value and compression, but it's not an issue. That's a nice match with the tight quench

- You may need to tweak your distributor with the new cam, so be prepared, you are changing intake valve closing time significantly, and although you are accounting for it with the DCR calculation, it is different and may like a slightly slower curve. 

- Your 406 wasn't pinging because of too high of DCR, it was too much initial timing for that motor (or too quick of a curve)

- That 570 will be way down on peak power, and a smaller carb doesn't make more torque, so expect power loss, but if you like the way it cruises and it gets a little better mileage, go for it.  Make sure you don't lean it out too much, a lean motor is more likely to rattle.  Don't be afraid of the 750 though, when not hammering it, they can get good mileage

Last...

3.50 X .64 = 2.24 final drive.   

That is going to be very tough to be where a 410 wants to be all the time.  If you are unhappy after the change, consider changing to a 3.89 gear.  11% more mechanical advantage would be significant and would free up power everywhere while still having a 2.49:1 final drive.  It would likely even get better mileage.  I probably would have done this first

Heck I'd even consider 4.11s, but I assume your tire is pretty short, so first gear may get a little short when horsing around

[Royce]

Jim, I don't know if you have considered this, but widening the LSA to 112 or 114 will broaden out your torque curve and get you a real smooth idle which helps save gas.. The old mileage maker cams from the 70's were short duration wide LSA. You could also consider (forgive me Jay) the old Sp2p manifold. it makes more torque below 3000 rpm than any other manifold

[Royce]

I just remember somewhere in my files i have some dyno data on the Sp2P vs a regular Performer on a truck 416 that I did years ago. That had a small Isky cam in it  Something around 260.  I will see if I can find it.

[FElony]

I'm with the idea that 5th is drastically undergeared. I saw this problem in my forum years back. Can you drive some without using 5th at all? Check mileage after a bit and I think you'll see it's better without. If so, the change to 4.11's will lower off-the-line stress, too.

Mileage and 410/428's don't really go together.

[ScotiaFE]

I'm with the idea that 5th is drastically undergeared. I saw this problem in my forum years back. Can you drive some without using 5th at all? Check mileage after a bit and I think you'll see it's better without. If so, the change to 4.11's will lower off-the-line stress, too.

Mileage and 410/428's don't really go together.

I second the gearing thing. Lugging them down to try and save gas causes "piston rattle".
It's going to get 12 to 14 no matter what you do. So keep the rpm up in the power zone.
And stop trying to cheap out on gas.
You guys down south don't even know what expensive gas is.

[57 lima bean]

Howdy Jim.......Hope things work out for ya.

[JimNolan]

Well, time's up. I'm going to go with the 268H cam and keep the rest of the motor the same. I'll gain 8% in HP and Torque at 2000 rpm and only loose 5% HP on top end ( if you can believe the computer dyno). It may not be accurate but it does give you the same comparative reading on different cams. DCR on this cam installed 110/106 is 7.9. Thanks guys. Now I've got a bigger problem with the True-Trac differential.

[plovett]

I think the 268H is a good choice.  And I also agree that more rear gear might help.  I don't know what your tire size is, but with a 3.50 gear and a .68 overdrive the rpms are going to be awfully low for most carburetors to deal with.

If you have 27" tall tires, at 70 mph you would be turning about 2073 rpm.  That's not easy for most carbs to deal with.   I'm not an EFI guy by any means, but very low rpm fuel metering is where EFI really excels, in my opinion.

A carburetor has to have a certain velocity/volume of air passing by the boosters to make them meter fuel well.  That means more rpm.  Annular boosters can help that situation, but not nearly as much as EFI.  So if you get your cruise rpm up a few hundred rpm, it might work better with a carb.  With 27" tall tires at 70 mph with 4.11 rear gears and a .68 overdrive you'd be turning about 2435 rpm.  That's likely pretty close to the sweet spot for a good carbureted engine. 

JMO,

paulie

[JimNolan]

Paulie,
   At 70 mph I'm turning 1950 rpm. My 5th gear is .64.
The last truck motor I had was a 74 DTE 105 390. In this same car with same rear end and transmission. All I did was buy a new set of timing chain gears to get the retard out of the cam and I got 20 mpg with it on trips. My 1/8 mile times were the same as the 410 I have now (same tires). It went through the quarter in 15.2 sec. That's not bad for a 250-270 horse engine. I did put a 570cfm 4V carb on it and used the stock heads and stock exhaust manifolds. Making this 410 achieve what the old 390 did is impossible though. Too much engine, stroke , heads, exhaust and intake. I think this 268H cam that gives me another 8% hp and torque at 2000 rpm might let me better enjoy a trip as well as enable me to keep beating my buddies Bullitt Mustang.

[plovett]

Well, you're mixing together so many variables, different cars, engines, cams, carbs, etc., it's no wonder you can't make heads or tails of it.  Okay, so your current overdrive gear is 0.64.  Got it. 

I still think carbs like to (or are only able to) cruise efficiently at higher rpms than a good EFI setup.  A smaller carb relative to the engine size will help this.  That is because a smaller carb will have a higher velocity past the boosters for a given rpm.  But then you pay a price in the mid-range and top end.  Like I said, I'm not an EFI guy, but I acknowledge the benefits.   

Bottom line is, getting your cruise rpm up a few hundred rpm will likely help both mpg and performance.

JMO,

paulie