Effect on Stroker - New Cam?

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jimmyray

jimmyray

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CURRENT Motor details:
408 cast crank stroker
9.6:1 compression
93 Octane gas
mild port/polish on Edelbrock RPM heads, closed chamber,
Weiand Stealth ported and gasket matched (heads too)
Carter TQ 850, initial tune by Demon Sizzler, tuned further with AEM A/F gage
Comp roller .544/.541 236/242 110 centerline
FBO ignition, ditributor curved to 16 inital, 34 total @ 2900 rpm
Hooker comp 1 5/8" headers (dented bottoms on driver side, naturally) 3" collector
3" pipes into/out of welded 3" mufflers into a-body tips
TKO 600 5 speed tranny
3.73 TrueTrac in a narrowed Dana
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I am planning to put in the following cam:



NEW CAM
Comp roller Intake/Exhaust .522/.521 224/236 114 Centerline


I know it's less cam, by design from my perspective. Tired of the rough idle and hoping for better performance, if that's possible


The previous cam delivers a best MPG of 17.5 (5 speed), and the best ET is 12.003 @ 111.46 mph.
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Thoughts on new performance, mpg, etc.?


Will I regret this move?

Thoughts on new performance - mpg, et, speed, etc?



 
jimmyray said:
Tired of the rough idle.
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I think you have a very nice package as is. I can see a almost stock idle with the cam your looking to put in, but the 236*@.050 cut on a 110 you have now should be really mild with a 4" stroke. I'm not one to tell anyone how to spend their money, but I just can't see any real advantage to the 224*, other then making it as mild as possible.
 
What is rough about the idle? Engine shaking? The new cam will definitely be much tamer at idle with more vacuum.
 
You can try running a before and after through Comp Cams Camquest software that is available on their site. It will give you an idea of the impact of HP and torque you can expect. You can then estimate the change in your ET's.
 
What do you mean by rough idle? What rpm does it idle at? That cam on a 110 lsa should be mild mannered. I had a 390 stroker small valve rhs heads with a cam
516/516
237/241 @.050
109 lsa installed at 105 icl
it would idle smooth at 750 rpm. If its idling rough try more initial timing mine liked 22 and 35 total. Car weighed 3600 with 3.73 ran 11.70's at 115.
 
JimmyRay obviously finds the current cam a little too hairy. I can see that. The duration is a little too much for a real tame engine. I see this all the time where a customer thinks they want that bad *** sound and idle but find out that it really makes the car a pain in the *** to live with when you are driving it a lot. The cam you are considering on a 114 CL will knock the crappy manners right out of a 400+ cube mill. Just make sure your dynamic compression doesn't get out of hand. Otherwise you will love the new personality of your engine. J.Rob
 
It'll lower the cylinder pressure on the 114, so you'll be fine for the DC #s, the idle quality will greatly improve, But there is a drawback, You will loose overall perf. & it won't pull nearly as good.

I will say this, that cam your running is not much IMO to be considered too much to tame, I ran an XE284H with 240/246 dur. @50 in a 370 sbm with stock 915 heads, It had a nice crisp cammy sound but nothing crazy, Now i ran a square bore style carb (750dp), the larger primaries help calm down the signal at idle & cams will seem less aggressive, some may think this isn't true but trust me it is, Try installing a 750dp or even a 950hp & you'll see what i mean. IMO, i think you'll be disappointed in the loss of perf. changing out cams.
 
I have the same cam, in a 416, 10.5 comp, air gap, 850 quick fuel, it took a while to tune it ...it likes a lot of initial advance, I am running 24* initial with an addition 10* mechanical. the carb tune is also quite important...After tuning it will pull down to idle in high gear and pull away cleanly...
 
Great advice, all! The car runs good, but has a fairly choppy idle, and with the 5 speed tends to lug and buck at everything under about 1800 rpm in gear.

It will idle at 850, but it is rough, and likes 1000 better. at 850, pulls about 10 inches vacuum.

Before I change the cam, I will play with the timing and put more initial in to see how it behaves. May forgo the cam altogether.
 
Try 20-24 initial as long as it starts ok when hot. See if that tames some of the raspiness.

16 isn't enough to get a clean idle with your set up. It's a safe point, just not optimal. Simple, twist the distributor CCW a bit, if it picks up RPM, it wants the timing at idle.
 
Well, I got my old copy of DYNO 2003 out, and ran the numbers, and also pulled the Dynamic compression numbers off of the Keith Black website. Static compression is at 9.6. Max HP went down, but avg HP, Max Torque and Avg Torque all went up! Thoughts?
 

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I think those dyno sims are extremely light compared to reality.

4" arms with those cams should be pushing high 4's for TQ, like over 480 at peak.
 
Comp Cams CamQuest software yielded the below numbers forthe current cam, but did not have the other cam in it's library, and you apparently can't set up a custom cam. Numbers about 40-50 higher. But the other numbers translate to my track experience better.
 

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Are you tuning it for max MPH or shooting for an A/F number?

If the latter, abort that and go for max MPH.
 
I think you are on the right track with the new cam. Strokers like a wider LSA. While it is true a wider LSA will not make more peak power and torque, it will make more on the bottom side and the torque curve will be flatter, which is desirable for a street engine. Also an added benefit will be better street manners and a higher vacuum signal. Just because a lot of people latch onto those tight LSAs doesn't mean they work in every situation. Why do you think the factories used wider LSAs? For all of the reasons I just described above. Plus, they knew cars with a rough idle would be a hard sell in most cases. Plug the build into any dyno sim....as you did and you will see low HP and torque go up compared to a tight LSA. Lastly, people saying "wider LSA will lower cylinder pressure" are incorrect to use that blanket statement. Especially in your case. Cams with the same specs other wise, that would be true. Because as you spread the LSA apart, you are opening the intake valve later and later. This causes the cylinder to begin building pressure later in the compression stroke and equals less cranking pressure. However, in your case, you are doing two things. Reducing duration @.050 AND going to a wider LSA. Those two things will counter act each other somewhat and in your case you might just end up with the same cranking pressure you have now. Less duration @.050 usually means closing the intake valve sooner so that may well offset the wider LSA. Remember too, cranking pressure ain't the end all be all. What the engine does on the other end of the spectrum and in between is important too. People get too caught up in cranking pressure thinking the higher pressure will make more power. That's not true across the board by a long shot. Many more things play into it besides cranking pressure. I would make the cam change. I believe for what you are doing it is a step in the right direction.
 
RustyRatRod said:
\While it is true a wider LSA will not make more peak power and torque, it will make more on the bottom side and the torque curve will be flatter, which is desirable for a street engine.
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I agree. Looking at the numbers from the Desktop DYNO 3000 and the curves below, the torque curve is higher and lasts longer. I was afraid the compromise lower cam would really hurt performance, but I am starting think it will be a wash on ET, and may actually pick up a little time. My best ET was when I shifted at 6800, but I prefer keeping it below 6500, or even 6000. I am convince it will be much better on the street. I will get a good set of rpm/vacuum numbers before and after for comparison, and eventually some ET/MPH 1/4 milers as well.
 

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I'd tune a little more first, before the cam swap. But in the end, that may be what makes you the happiest with the car.

I downgraded a few cars that the new buyers insisted on a milder idle. One in particular had a decent sized solid FT & good flowing heads. It definitely made the idle smoother and the torque curve flatter, but it was weaker across the board...significantly. Fortunately you have such a torque friendly engine, that on the street, it probably will still be a stout driver.

I'm not a fan, but I'm shocked the Rhodes lifters haven't appeared in this thread as a alternative...:D.
 
OldmanRick said:
I'd tune a little more first, before the cam swap. But in the end, that may be what makes you the happiest with the car.
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I am sure the proposed cam swap will lose top end power, but I wonder if the flatter curve will offset it, for a more driveable but similar overall performance.

I've read a lot of threads,and many go for very large cams, sometimes into the 260 @ 0.050 range for a street engine. Having never ridden in one with that size of cam, can't help but wonder at it's manners on the street. Maybe mine just needs more tuning, but that engine sure moves around a lot, although the car has a nice rhythm to it at idle...

Switching to a manual transmission really revealed the lugging nature of the cam. And, it barely pulls below 2500 rpm. going uphill in 5th at 60 mph requires a downshift when it dips below 2000, as it just loses mph.

Love the sound at idle, tired of the drive-ability, and inability to break into the 11's for the tradeoff.
 
But how much were or are you up in the power band where the power "might" be lost? And who's to say it will lose power? You don't know till you try it. Less than 10* duration on both sides. How much do you really think it'll "lose"?
 
I'm really surprised to hear it lugs so much with your current cam. I have a 408 with a cam of very similar size and it's ground on a 108 center, although it is a solid flat tappet and I am running an automatic but it's smooth as silk from 900 up. I don't doubt the smaller cam your looking at will add some bottom end torque and idle better but I think it'll loose a good amount of HP up high too. It may be close in the 1/4 mile performance but before I went through the work of a cam swap I'd do what the others suggested in putting in more initial timing and maybe even trying a square bore carb with a 4 corner idle system. Your last post describing how it won't even pull a hill below 2500 rpm really makes me think it's a tuning issue. Mine pulls like a freight train everywhere.
 
Jimmyray, it's good to hear your real world experience with that combo. I have to admit, i'm a little surprised that it's not more street friendly, but sometimes the actual results are different then what they look like they should be on paper.....


Rob, my main concern was the cylinder heads. If they indeed flow in the 280 range, I was afraid the milder cam would lose more then it was worth.....monetarily. The case I spoke of in the other post was a 3.48 stroke engine...any guesses what that was...lol. It still had a 4.10 gear & 3600 stall, but I was shocked at how different it felt going from a 530"/250* solid to a 480"/230* hyd. It did still have a single plane on it though which didn't help. I don't know how much was lost, but the converter actually stalled a few hundred r's less, and it was nosing over in the 5500 range vs the previous 6700.
 
It sounds to me that the Rhoads lifters would solve your want for low end torque without changing cams. May lose a little on top end but wouldn't lose as much as that other cam. If you've got that much head flow then you need 236/242 cam to make it work. I've got a 408 w hughes 236/242 @ 112 lsa roller cam and stock roller lifters. The heads flow about 270 and it made over 500hp. The idle is little lopey but smooths out w a bit more rpm. I run 18* initial and 34* total. But the low end torque is fantastic, it's like a BB. Good luck in your decision.
 
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