Cam Change

[tdangle]

I'm considering changing out the cam in my new GM SP350/357 crate motor. I'm not really liking the idle and would like to smooth it out. I've narrowed it down to the cam in the Ramjet 350/HT383 crate engines #14097395. Really would like not to loose too much if any at all for normal driving.

[The Rocknrod]

Is the SP350/357 radical cam like? or what?

[truckster]

Originally Posted by tdangle

I'm considering changing out the cam in my new GM SP350/357 crate motor. I'm not really liking the idle and would like to smooth it out. I've narrowed it down to the cam in the Ramjet 350/HT383 crate engines #14097395. Really would like not to loose too much if any at all for normal driving.

I think you'll like the HT383 cam. Lots of torque and pretty smooth idle.

[PGSigns]

Its not a big cam in that motor. What intake, carb, convertor and timing are you running?
Jimmy

[tdangle]

The cam currently in the motor is 215/223 at .050 with .473/.473 lift (1.5 rockers) and 108 LSA. This makes it not idle quite so smooth. It has lots of power especially from 2K up. I'm running 10 initial with 22 advance, ported vac advance and a Holley 670 carb. All of this was setup by Westech on a chassis dyno. Running a 2004R with stock torque converter. The idle is not real bad but vacuum is about 11 inches in drive 14 in neutral and you can actually see the vacuum bounce around with the bumpy idle. Would really like a smoother idle. Didn't know this was the case when I bought the motor.

[AussieinNC]

Originally Posted by tdangle

The cam currently in the motor is 215/223 at .050 with .473/.473 lift (1.5 rockers) and 108 LSA. This makes it not idle quite so smooth. It has lots of power especially from 2K up. I'm running 10 initial with 22 advance, ported vac advance and a Holley 670 carb. All of this was setup by Westech on a chassis dyno. Running a 2004R with stock torque converter. The idle is not real bad but vacuum is about 11 inches in drive 14 in neutral and you can actually see the vacuum bounce around with the bumpy idle. Would really like a smoother idle. Didn't know this was the case when I bought the motor.

Before you do any major work, find a full vacuum source for that dissy and block off the ported vacuum....reset timing and idle...start at 12 at idle, with 34 all up by 3000......then decide if you need a cam change.

[tdangle]

Originally Posted by AussieinNC

Before you do any major work, find a full vacuum source for that dissy and block off the ported vacuum....reset timing and idle...start at 12 at idle, with 34 all up by 3000......then decide if you need a cam change.

That is the way I had it set up. throttle response wasn't great and even rougher idle. I paid good money for the dyno tune by one of the best per my research. He said not to run full vacuum, ported only. Per GM and most of what I have read, with Vortec heads you don't want to exceed 32 total. GM actually says to block off the vac for the dist completely.

This is straight from the paperwork that came with my motor:

Set spark timing at 32o before top dead center (BTDC) at 4000 RPM with the vacuum advance line to the distributor disconnected and plugged. This setting will produce 32o of total advance at wide open throttle (WOT). The HEI vacuum advance canister should remain disconnected. This engine is designed to operate using only the internal centrifugal advance to achieve the correct timing curve.

[burnin oil]

Whats the base timing at idle? That is not a big cam at all and should have no vacuum issues. I have 250 duration cam in my truck and still have vacuum brakes that work. It sounds like you need a recurve of the distributer. I would hook the vac gauge back up and twist it to you get a good vac reading then limit the advance to the 32 degrees you want overall. Once the curve is set you can play with the vac advance if you like. I dont have it hooked up on my truck and milage is horrible. 7.5mpg on a good tank! I am willing to bet that it will run better with vacuum advance when the curve is set up correctly and gain a little mpg as well. I would not listen to GM here unless it is a track only vehicle. They are not always correct.

[cadillac_al]

I can't imagine running a street engine without vacuum advance. I guess the "experts" know best.

[tdangle]

Originally Posted by burnin oil

Whats the base timing at idle? That is not a big cam at all and should have no vacuum issues. I have 250 duration cam in my truck and still have vacuum brakes that work. It sounds like you need a recurve of the distributer. I would hook the vac gauge back up and twist it to you get a good vac reading then limit the advance to the 32 degrees you want overall. Once the curve is set you can play with the vac advance if you like. I dont have it hooked up on my truck and milage is horrible. 7.5mpg on a good tank! I am willing to bet that it will run better with vacuum advance when the curve is set up correctly and gain a little mpg as well. I would not listen to GM here unless it is a track only vehicle. They are not always correct.

I agree, it doesn't seem like a big cam. It has a LSA of 108 (LCA of 107 and 109), so even thou it's not a long duration cam it has more overlap than you would realize making it seem like a bigger cam as far as the idle goes. I've learned way more about cams than I care to know at this point. I'm going to raise the initial and work on limiting total advance to see it that makes it better.

[burnin oil]

You are correct about lobe separation but it is not a huge affect. My cam idles like crap and is a tuning nightmare but was designed for circle track. Its in the 250s for duration on a 106 separation angle solid cam. Idle is below 1000 rpm and will still run the factory power brake system on my 72 k20. I have no choke and first start at a low idle speed is the only time I have an issue. I typed this out to illustrate that you should not be having vac issues like you say. I have done everything possible to make the system not work. You are on the right track now. Good luck.

[The Rocknrod]

Well I'm keeping my eyes peeled on this thread cause that engine is my engine of choice for my 64. Keep us posted please.

[burnin oil]

One thing I forgot that may be at fault here. Reset your valve lash to double check you don't have a valve not seated all the way. An overly tight valve will cause the vacuum gauge to bounce and low vacuum.

[LS short box]

I'm LS engine guy and the LS cam guys would say a LSA of 108 is going to give you choppier idle. I would all suggestions above to see if it will make it livable as is. If not look at a cam with similar duration and lift but maybe 110-112 LSA.

[tdangle]

To be clear, the idle is not real bad, just have gotten use to modern cars where you don't even feel the engine idle. Never stalls, just a little bumpy.

I have already readjusted all the valves 1/4 turn from 0 lash per the documents. Yesterday I pulled all the plugs check them and reset the gap to a specified .040. They actually looked pretty good with a few thousand mile now. Light brown on on side of the porcelain insulator. Adjusted the timing to 12 BTDC and adjusted the idle and idle mixture a bit. Also made sure I had no vacuum leaks at the carb base and hoses. Very little change. I have about 15 inches at idle in park which is about 800 rpm. In drive 625 rpm and 10-11 inches of vacuum. If you have a manual trans or maybe a looser torque converter it might be a bit bitter. Still looking at all options.

[LS short box]

It would be interesting to see what would a looser? converter would do. I run a 3000 stall converter in my 68 LS C10. It's somewhat tight and some what expensive converter (about $450-500) that drives like a stocker until you lean on it. I like Yank and Circle billet converters. There are others out there that just as good. A stock 200R converter has a stall speed of maybe 1800 rpm?

[tdangle]

Originally Posted by LS short box

It would be interesting to see what would a looser? converter would do. I run a 3000 stall converter in my 68 LS C10. It's somewhat tight and some what expensive converter (about $450-500) that drives like a stocker until you lean on it. I like Yank and Circle billet converters. There are others out there that just as good. A stock 200R converter has a stall speed of maybe 1800 rpm?

About 1800 is what I was thinking, being a lockup type a higher stall wouldn't affect cruise on the hwy. I did see that GM Performance package that includes my motor and an auto trans calls for a 2400 stall per their catalog. Does a higher stall have the same amount of creep at same idle speed as a lower stall? I do know I drop around 200 rpm from park to drive. Never really noticed the drop with the stock motor.

[burnin oil]

I higher stall should have more slip thus less creep. A big part of this is torque at low rpm. The more torque the quicker the convertor will work. This means a 3k stall may come in at 2600 on one motor or 3200 on another. I am a stick guy but that is my understanding.

For fun run your motor up to about 18 or 20 degrees of timing and see if there is any more vacuum to be had. I. Eleven that you are about maxed out and will only find 1 or 2 more inches of vacuum. If you are lucky. A 112 or 114 grind will probably net about the same gain. Honestly as small as that can is you need to see the valve timing and compare the valve overlap and intensity of the lobe. This will tell you if a cam change will really do anything for you. A valve barely off its seat will have less lump than one that flies open a few degrees later since the valve is further off its seat. Dont forget that getting that wide separation angle will make a longer power curve but less power overall and probably weaker off of a turn. LS cam timing is nothing like a factory sbc. They did some crazy things with lift, lobe angles and duration that would have blown cam grinders minds just a couple years before they hit the market. They really optimized the better flowing heads of the LS for a production motor. They also make their low end grunt a little higher up the rpm band.

[LS short box]

Yeah the cam I have in my 68 LS swap is 220I/226E with 590 lift and LSA 114. Has a bit of a chop at idle. With the 3000 stall converter it has a bit of creep at idle. Runs the power brakes just fine.
I think it would be worth the time to call Yank or Circle and see what they recommend. If you haven't driven something with a good stall converter I think you be impressed how the converter allows the engine to rev a bit more to get more into the power band of the engine. They create a bit more heat so run a good trans cooler. And as said above with lock up it won't slip going down the highway.

[tdangle]

a higher stall converter may be something to look into. Actually easier to change the tq than the cam, at least for me.

I do have an update, bumped the timing up 2 to 12, and messed with the idle mixture screws. Thought I had it at best lean idle, then put it in drive and wow it was really bad idle. I had it at 625 in drive. Started turning the idle screws out to richen the mixture and it smoothed out quit a bit. In park you can hardly hear a lope. In drive it is still not real smooth but not bad and a consistent lope now not what it was before. It also brought the idle speed up and I had to lower it a bit. Going to drive it a bit and see. Defiantly better throttle response. Now I know what the guy that did the dyne run was tasing about. He mentioned it like it a bit richer than normal. I'm probably now have the idle mixture screws close to what he had them adjusted to. If I remember he had them out about 4 turns out, I have them at 3 1/2 now. Wishing now I had forgone the deluxe model and bought my own intake, distributor and a Holley Sniper EFI unit.

[burnin oil]

Now for fun hook up the vac advance and see if that helps the idle in gear. Just make sure its on manifold vacuum. It may need a advance limiter being that the heads don't need as much overall timing.

[geezer#99]

Originally Posted by burnin oil

Now for fun hook up the vac advance and see if that helps the idle in gear. Just make sure its on manifold vacuum. It may need a advance limiter being that the heads don't need as much overall timing.

Here’s info on an advance limiter.

http://www.crankshaftcoalition.com/w...EI_distributor

[LS short box]

Back in the day I was a line tech a Chev dealer ship. We were taught to use a vacuum gauge to adjust the idle mixture screws. Back the screws out and then turn one until the vacuum drops and then turn it out 1/4 turn or so. Then do the same thing with the other screw. Go back and forth to achieve the best vacuum. You can do do the same thing by ear. Just turn in the screws until it stumbles a bit, then back them out a bit going back and forth a needed.

[The Rocknrod]

I wonder if the PCV has anything to do with it? Maybe this would help? - http://67-72chevytrucks.com/vboard/s...d.php?t=787630