Ever since I installed this roller cam, I've been trying to get it to idle smoothly below 1000 RPM's. But I'm afraid I may be asking too much for the setup I have, Or maybe I have some mismatched parts?

Thing is, I had a Comp XE274H cam in it before, and I had hoped to change to this roller cam because I've always heard that you can get more lift and be more street freindly with the roller profiles then a flat tappet profile, so I got this one. Except for the idle, it seems to have a ton of power in the mid to upper rpm rnge (2800-5000), but I lost a little bit of power down low. Gas milage is a joke at 10 mpg city. Here's the roller cam specs: .520/.540 lift, 236/242 duration at .050 with a LSA of 110 on a 106 CL. I know this is a bigger cam than the XE274, but am I expecting too much for it to idle at 750-800 rpm's with this cam? Here's the setup/details:

SBC 400 +.040, 3.75" crank, 5.7 rods, Dart 72cc chamber 200cc intake Iron Eagle heads, KB147 hyper. pistons (-18 cc dish, about 9.3:1 compression), PP crosswind intake (rpm air-gap ripoff). 650 DP Speed Demon carb with 1/2 spacer and 2" tall, 14" diam. filter element, MSD HEI Pro-billet dist., Edelbrock TES headers and Hooker catback with convertor. Pulls about 10"-11" vacuum at idle, timing set at 21 degrees initial (my timing tab might be off), 38 total advance. Demon is set up using a 6.5 PV, 70/81 jets, xfer slot at around .015, all 4 a/f mix screws at about 3/4 of a turn out for best vacuum. and I don't what size idle air bleeds - whatever it came with I guess.

-Since I installed this roller cam, I'm thinking that it needs to breath better at a higher rpm range so I'm considering a 750 cfm carb. Car is a weekend/toy car and not daily driven. Never timed it at a track...yet. Just trying to see if I'm expecting too much...I just know it idles lopey and sucks gas...

Opinions welcome!

BTW, the dyno #'s in my sig was with the XE274 cam...

 

I think should be able to get it to idle around 800-850RPM's with that cam. A cam that big probalby won't have a smooth idle that low but it will sound great with a nice lope and a little shake. I used to have a 242/248 .540/.560 Hyd/roller cam in my 10:1 383 and it would idle around 850RPM's. You may try locking down the timing at 36-38 degrees that will help your idle..but your starter may struggle to start it if you don't have a start timing retard.
My main concern with your combo is your compression ratio is only 9.3:1. If you bumped your compression up to around 10:1, it would match that cam better. A few other things I would consider...LT headers to help it breath better and a 750 or 850DP carb would make more power at high RPM's. I think those small changes may wake your engine up a lot.

 

With your MSD ignition, is it easy to install a starter timing retard? Or expensive?
That cam is fairly big, but not gi-normous. It's also in a 400cid, keep in mind. I might try locking out the timing, and driving it around a bit, see if the low end is better.

10mpg city with a cammed 400cid? Yea, get used to it. Drive the vibe when the wallet gets light

I agree, more compression would have given you better low end response. Unfortunately it's too late to do anything about that now. However, means you can run more timing safely.

 

Thanks for the opinions guys.

jbenge and Sonix:
Yeah, I kinda looked at the compression when I got the cam. It's basically a HR288 cam from Comp, and they said my compression was enough to handle this cam, and they advertise it for engines with around 9.5:1 compression.
-The engine was originally built at a performance shop, and the guy talked me out of going too high on compression with iron heads on a 400. He was afraid I'd have detonation issues if I went over 9.5:1. My build sheet says I have 70cc chamber heads on it, but Dart doesn't sell a 70cc head (only 72cc), and I don't see where the heads were shaved down on my reciept to 70cc. So I therefore consider it to be 9.3:1 because I have no proof the heads were ACTUALLY shaved to 70cc which would make it 9.5:1. -But I'm in the ballpark. Just thought I should explain that.

I know it's not a ginormous cam, and I can get it to idle down to 900 rpms, but it'll run rich and I can't lean it out enough to maintain that rpm at idle and not burn your eyes out. But you're right - it's lopey as h*ll and sounds pissed off. But your description is pretty acurate jbenge when you say: "A cam that big probalby won't have a smooth idle that low but it will sound great with a nice lope and a little shake." -So I may be looking for a smooth idle that I'll never have with this cam. Hmmm.

You both mention "Locking down the timing" - what does that mean?? As I said above, I'm at 21 degrees initial, and it's limited to 38 degrees total. I have a Powermaster starter that hasn't complained a bit - so far.

I never looked into it, but I don't think it would be hard to install a timing retard on the MSD distributor, if I need to.

And yeah, I'll take your advice about getting LT headers, and a 750 carb. I was thinking it would wake it up a little too since this cam breathes better higher in the rpm range than the previous cam did. Like I said above though, it has tons of power but I know there's more to be had.

Wish you guys were in my area.....I'd buy the brewskies!!

 

Locking out the timing - basically removing the springs in your distributor, and "locking" the timing advance all the way out. Try a search on the boards, I think F-bird'88 is the usual suspect who gives that advice, and he's described a good/easy way to do it temporarily (zip ties). That'll give you 0 spark advance with RPM, so you just set it to 36/38* and go. However starting the motor is hard with that much timing. You can probably get away with it temporarily (since you have a good starter), but long term, the starter retard module would help. But yea, you can lock out the timing and drive it around for a day. A lot of timing helps the motor at low RPM. I run 24* initial, and my combo isn't all that wild. 750RPM rock steady idle, not rich.

 

Ahhhhhh.....did a search......I've never tried that. Never heard of tie-wrapping the weights before, but thats just to test right?

I was thinking it would be too much advance and I'd detonate in the upper rpm's. I already know it would idle smoother with more initial, but trying to bring the rpm down to 800-850 might be the trick. I'll give it a shot!

I don't think the vacuum can on the MSD HEI is adjustable though. And I dont think they make bushings for the mech advance that would limit the additional advance to as little as 10-12 degrees (Like it sounds like it'll need)..

I'm sure I can figure something out though...I'll install a retard module if it needs it -

I'll try it and report back then!

 

I locked my timing down with the cam I mentioned in the previous post...it idled much better that way. I have a digital 6 box, it has a start retard function built in. If you already have an old analog msd box you can add a timing retard pretty easy. Confuzed1, I have a Promax 750DP(basically the same as proform) I just took off my engine if you are interested..pm me.

 

confuzed - I think you're confused
When you lock out your timing, you don't need to limit the mech travel, you eliminate it all together. So you lock it into full advance all the time, and set that to say 36*.
You should have a wee little half moon thingy to limit your vacuum advance travel to whatever you like, but that shouldn't need to be messed with. You're not giving yourself any more timing than you had before, you're just making sure you get it from idle to redline, without having to bring up the RPMs to get the advance.

 

Confuzed1,
The timing can be locked down very easily with an MSD HEI( I used to have one). Check out the directions if you still have them. You just have to take the distributer gear off and rotate the distributer shaft and lock it down then remove the weights ect that you don't need anymore..its very easy.

 

my 400 with 238-247 on a 109 lsa will idle at 750-800 noproblem. Vacuum is much lower, <8. But the demon I have has had lots of tuning work. Does the carb baseplate have any air holes in the butterflys? Start with about a .060" dia hole. Then work with your idle fuel restrictions.

PS, my timing is 18degrees initial.

I dont think you really need to spin that cam more than 6000 on a 400. I doubt it will make hp up there. The same basic cam is used in the ford 393 crate motor and it makes peak hp at 5600-5700 with a vic jr.

 

Yep, that's why my screen name is appropriate!

Sorry, I had other stuff to do the past couple of days, but I decided to try locking out the advance.

I wanted to get a ballpark of where all my settings are at before I change everything, and I found I was running 31 degrees advanced instead of the 21 I said earlier in the post. And the vacuum can was disconnected when I checked it. So I don't think it's a huge leap to lock it out, add 6 degees more and see if I can lean this carb out a little more and get some low end grunt back.

Just got done removing the carb, setting transfer slots to about .030, turned the a/f screws 1 1/2 turns out from seated and reinstalled it. Pulled the distributor, locked it out (It WAS in the instructions BTW), and reinstalled it. I need to re-index the distributor so my vacuum can isn't against the intake runner, so I gotta find TDC and go from there. And I plugged the vacuum advance line. Anything else I should do?

Should have it running very soon, I'll let ya know.

Oh, and jcb999,
I can get my engine to idle at 21 degrees initial, and at 800-850 rpm's, but I kill every bug on the block!! The a/f screws are only backed out 3/4 of a turn with the transfer slots at the recommended setting. I called Demon, and they want me remove all 4 a/f screws and drill the holes bigger with a .048 bit "and try that". And I'm supposed to have this nifty "idle eeze" feature so I don't have to drill holes in my plates. It doesn't do jack except make my engine stall if I open it up too much. I got the cam with a 6000 redline in mind.

 

Leave the vacuum advance line hooked up. It's hooked up to ported vacuum? With the advance locked out @36*, ported should be fine. If it doesn't work, you can go back to a regular timing curve, and use manifold vacuum advance. See if that changes anything.

I'm not sure how idle-eeze works, so I can't comment on that...

 

I was going to try without vaccum advance at first, then try it hooked up to see whether it pings or not. When you say "Ported", you mean "Timed" as in above the throttle plates?

jbenge - As I recall, you ran a hyd roller cam one step lumpier (292??) than the one I have. Did you have these issues? What did you do with timing yours?

 

yes, timed = ported.

he said he locked his timing out for that cam...

 

Yea I had some of those issues and Sonix is right I locked down my timing. I didn't use the vacuum advance either. With the vacuum advance hooked up it never ran consistantly..had surging issues. It ran better without it, something you may want to try.
I also had to do a lot of carb tuning. I had to drill my throttle blades, install larger squirters, and change accelerator pump cams before I was totally happy. Even after doing all that it was still a little rich at idle but not too bad. I got my old Promax 750DP tuned very well eventually but it took some trial and error. I ended up buying a Prosystems carb after that...money well spent. All I had to do was bolt it on and adjust the idle mixture screws and idle speed. It has custom metering blocks, squirters ect. set up for your combination. You may want to give Patrick at Prosystems a call if you are in the market for a new carb and want something you can bolt right on and not have to do a lot of tuning.

 

Well, I gave it a try. I set the timing at 36 advanced, centrifugal locked out. I started the car and adjusted the 4 corner mixture screws for best vacuum (I had my gage hooked up). Initially, I managed to get it pretty steady at 14-15" vacuum idling still a bit high at 1000 rpms. Still smoked a tiny bit, but looked promising for a change. I then shut down a bit on both the secondary and primary transfer slots a tiny bit to try and get the idle down to around 800-850.

Problem is, after I made the adjustment down to 800 rpms, vacuum degraded to about 12", and it started puking gray fuel rich smoke again. Tried to hook up the vacuum advance to ported vacuum, and I can hear it sputter in the upper rpm range with it hooked up. Tried stepping back and setting it up to idle somewhat clean at 1000 rpm's again, but it refuses to do it again...grrrrr.....

I think advancing the timing overall helped, but it still wants to smoke and run rich for some reason which has me at wit's end. I've spent literally HOURS upon HOURS trying to get it to idle lower than 1000-1100 rpms and tweaking on this carb in hopes that I can lean it out at idle and racking my brains out. Sounds like a good idea you have jbenge, about getting a new carb set up from Prosystems, but I'm afraid I'll pay big $$ and end up no better off than I am now....I've sunk ALOT of $$ into this thing already.

I was thinking - I still have a CAT installed - is it possible the CAT is building up raw fuel in it and causing it to smoke after it warms up even though I'm actually running lean?? Reason I ask is because it seems to smoke at it's worse after it's fully warmed up.

 

You might want to change your idle feed restrictors or idle air bleeds. That should clean up your idle.

 

Idle feed restrictors may be an option for you but I could never make myself do that, I never liked the idea of a piece of wire in the metering block. Another option is to drill holes in the throttle blades. You may still want to look at Pro-Systems you could probably get something for around $600-$700. They have great tech support and customer service..they actually allowed me to try a couple of different sizes of carbs.
One more idea...what spark plugs are you using? If you are running a very cold plug it will tend to foul easier than a hotter plug.

 

Red,
I think the idle feed restrictors are drilled into the metering block, and I;ve done searches and heard of sticking wires in the holes. Like jbenge said, I'd rather not do that.
The idle air bleeds might be a possibility but I don't know if thier removable or not. I need to find out.

jbenge - I'm using NGK #UR-4 plugs. I'm probably going to get some new plugs again. Gettin tired of changing them....it's a PITA. I might need a pros advice on this, like the place you mentioned. I'm stumped so far.

 

if this is a demon all metering body restriction holes are threaded and replaceable. The airbleeds might not be threaded if it is a speed demon. Comp sells pre sized idle fuel restrictions and also air-bleeds. No drilling or wire needed. If they said you need a idle restriction of .048 they are on drugs. Try about .034-.036
Start here and work from there (select the carb you have on the dropdown). Specification Charts
I really cant promote the LM1 wideband from innovatemotorsports enough. Its really worth the money - LM-1 Wideband O2 Digital Air/ Fuel Ratio Meter | Lambda Sensor Controller

I would also be prepared to toss the cat. You will never get near 14.7 to 1 airfuel ratio and for that reason, a cat will not live long. You will have too much raw fuel in it and it will burn it self down.

 

i had a similar cam and combo and my motor would never idle properly and when it did I would puke out fuel as well at idle. For some reason my buddies kept saying over and over it was the carb and I wouldn't believe them. They let me borrow a 850 race demon, a 750 proform and a different 750 holley double pumper. I was trying to tune a 850 double pumper on my camaro at the time. No matter what I tried it didn't matter, I had several opinions and tried several different things. Just bolting on the other holley had the same issues, then I tried the demon and it was slightly better, then tried the 750 proform race series carb and it started in under a second and ran at 800 rpm instantly...no pumping of the pedal or anything needed. Comp told me not to expect under a 1000 rpm idle and now in gear with this carb I can run it at 700 rpm at idle with a lopey sound. The whole car shakes up and down probably an inch at idle and it runs amazing right out of the box. I also locked my timing out at 32 degrees for this particular head/cam combo. Try a buddies carb and see what happens, I know it saved me months of headaches as I already spent 5 weeks screwing around with mine.

 

Thanks for the help from everyone so far.....I appreciate it!

jcb999 - I'd love to buy a wideband O2, but I'd end up spending 350 plus, and still have to experiment with air bleeds, restrictors etc....
I have no doubt you know how to tune with a wideband O2, but I have too much time invested in this thing already - time to give the pros a shot at it.

Sorry if I wasn't clear, but Demon told me to remove my 4 corner mix screws and drill out the passages bigger with a #48 wire drill bit, which I did. Not sure what that was supposed to accomplish because it didn't seem to do anything. And you talked me into it...I'm taking the CAT off, since I think I'm loading it up with fuel anyway and probably killing it. I have a section of 3" pipe I'll replace it with.

xpndbl3: Glad to hear I'm not the only one having this pig rich problem. Unfortunately, I don't have any buds with carbs I could try on my engine (wanna loan me yours? lol)
I've been blaming this carbeurator of mine since day one, because the engine kicks *ss off-idle and WOT.

jbenge: I've started looking into Prosystems. I filled out the online info on my setup and sent it to them for a price quote, then I'll call them and bombard them when questions. I'm looking to either get this one rebuilt/upgraded or a different carb altogether. If they can assure me they'll work with me until this is fixed, I may be thier next customer.

 

Well, looks likw I'm going with the Pro-systems carb. I'll post up how it goes. Should arrive in a week. I really hope this does the trick.

 

Wow!! That was quick!!

It arrived today, and I just ordered it 4 days ago! Wet flow tested to a true 780 cfm, custom metering blocks, etc.

Had plans to try it today, I and then remembered the Demons fuel inlet fittings are a different size from Holley's..... So I now have a 6AN AND 8AN fuel inlet manifolds that only fit Demon. Looks like I'll either have to buy some type of adaptors or ANOTHER manifold..

I can tell this place has shipped a few carbs before. Packaging was excellent.

 

Glad to hear you got your carb. I was impressed with the packaging too when I got mine. I think you will be impressed with how your car runs with the new carb, it shouldn't require a lot of tuning. And if you have any issues just call Patrick, I emailed and talked to him several times while tuning mine. He was always very quick to respond to my questions. He recommends a higher fuel pressure, slightly higher float levels and the amount of the transistion slot exposed isn't as critical on these carbs as a stock Holley DP. Once I followed his advice my car ran perfectly.

 

Hey all,

I figured I'd give an update on how the new carb went. The car runs even better at WOT, and about the same at part cruise. The lack of a choke or even a provision to add one is an inconvenience - esp in WI....but I knew that before I bought it, and it's not a daily driver anyway. But it don't wanna play when it's cold, but will finally idle on it's own after a few minutes - that's with an outside temp of 40 or less. I think it may start easier when it warms up a little around here (hopefully).

I also noticed right away that the 4 corner idle screws make a much bigger difference in idle quality and vacuum than I had with the Demon carb.

Now for the bad part. I can't get it to stop smoking at idle still. I've come to the conclusion that the grayish smoke at idle has to be oil, not fuel. Out of frustration, I took my car around to have a few other guys with various experience with cars take a look at it, and that's what they thought - oil. I also let them look at a set of plugs with less than 1K I changed out. They look pretty dry and black with plenty of carbon buildup. I then pulled a plug I installed right before I drove the car to them (less than 50 miles on it) - and it already was showing signs of carbon deposits.

I've taken compression tests (wet and dry) , and leakdown tests on this engine before, and all seemed OK to me. I've changed intake gaskets numerous times - no change. About the only thing I have not checked everything on is the heads. I have looked at the valve seals (teflon) - and they still look new. I have NOT however, checked the valve guides. If it turns out they are OK, then ANOTHER complete engine teardown will be needed to find out where it's coming from I guess.