throttle stop cam for sbc

sg5985 · 01-24-2010, 05:01 PM

Hi,
The shop that did my converter last year told me that my cam wasn't a very good throttle stop cam which got me thinking, what are the characteristics of a good throttle stop cam for a sbc? I run a 3.750 stroke 408 in a 2140 lb roadster, currently on alcohol but going back to gas. My cam is 718/667, dur @.050 is 263/267, lobe centres 106, intake centre line 100.0.
Any input or suggestions on a proven combination would be very welcome.

Thanks,
Rob

Adger Smith · 01-25-2010, 12:35 AM

Way too little duration @ 50.
That puppy is a stump puller. Does it knock the tires off coming back from the stop? May not because of a loose converter.
If that 400 has any compression, at all, put something like a 274 or 276 In / 280-284 ex @ 50 in it. Elevate the Tq curve. You have at least a 5200-5500 converter in it? That cam probably makes peak Tq in the upper 4,000 RPM range and goes over when you take it up high. Take it out to 108 or 110 separation, but installed @ 106-107. That will elevate the curve and make it longer and smoooooother.
I would say gas is better. The 400's I have worked with need BIG heads to run gas and even BIGGER heads to run alky.
.02 for free.

Tom Goldman · 01-25-2010, 12:15 PM

Adger's right about that cam being a stump puller. ....However,it would probably work ok IF you are shifting on time ,and running the stop in high gear at a low [ under 3000] rpm. .....It will have the torque to pull thru the lower rpm .........If you want to run the stop in lo gear , change the cam as Adger said. ........2 cents more. [and you'll probably get a lot more] ......Tom

sg5985 · 01-25-2010, 07:46 PM

Thanks for the responses.
It did knock the tires off in 1st gear coming off the stop so I shift on time and come off the stop in 2nd. I'm on the stop at 4800 rpm and the RPM is pretty steady. The car doesn't charge well off the stop and my mph is down about 9 mph from a full pass.
I need to change my combination to what will hopefully be a better throttle stop set up. My compression is almost 14/1 but I'm looking at heads that flow over 300, better intake manifold (super victor 2925 maybe?) for better power coming off the stop, and the right cam. I'm concerned about going too big in intake port size because it may hurt throttle response off the stop so that limits the flow potential of the heads. Input or suggestions would be welcome.
RM has a cam that they use in their 412 super series engine that's close to the specs you're talking about; .675/.653, 272/284 @ .050, LC107. 1.6 rockers would give me .720/.696 lift.
This is a great forum for a rookie like me that needs all the help he can get.

Rob

Adger Smith · 01-26-2010, 12:13 AM

With that stroke and cu in you don't need to worry about having too big a head. I don't know of any std 23 deg head that will be too much for your application. The intake is a good choice. I have used them before.
It's nice to hear you know your current combination well enough to know that you need changes.
Good luck.

01-24-2010, 05:01 PM	#1
sg5985 Junior Member Join Date: Jan 2010 Posts: 16 Likes: 0 Liked 0 Times in 0 Posts	throttle stop cam for sbc Hi, The shop that did my converter last year told me that my cam wasn't a very good throttle stop cam which got me thinking, what are the characteristics of a good throttle stop cam for a sbc? I run a 3.750 stroke 408 in a 2140 lb roadster, currently on alcohol but going back to gas. My cam is 718/667, dur @.050 is 263/267, lobe centres 106, intake centre line 100.0. Any input or suggestions on a proven combination would be very welcome. Thanks, Rob

01-25-2010, 12:35 AM	#2
Adger Smith VIP Member Join Date: Dec 2001 Location: Texarkana Ark/TX Posts: 2,360 Likes: 445 Liked 686 Times in 267 Posts	Re: throttle stop cam for sbc Way too little duration @ 50. That puppy is a stump puller. Does it knock the tires off coming back from the stop? May not because of a loose converter. If that 400 has any compression, at all, put something like a 274 or 276 In / 280-284 ex @ 50 in it. Elevate the Tq curve. You have at least a 5200-5500 converter in it? That cam probably makes peak Tq in the upper 4,000 RPM range and goes over when you take it up high. Take it out to 108 or 110 separation, but installed @ 106-107. That will elevate the curve and make it longer and smoooooother. I would say gas is better. The 400's I have worked with need BIG heads to run gas and even BIGGER heads to run alky. .02 for free. __________________ Adger Smith (Former SS) Last edited by Adger Smith; 01-25-2010 at 12:36 AM. Reason: sp

01-25-2010, 12:15 PM	#3
Tom Goldman VIP Member Join Date: Jan 2003 Location: Allentown,PA Posts: 2,438 Likes: 785 Liked 703 Times in 206 Posts	Re: throttle stop cam for sbc Adger's right about that cam being a stump puller. ....However,it would probably work ok IF you are shifting on time ,and running the stop in high gear at a low [ under 3000] rpm. .....It will have the torque to pull thru the lower rpm .........If you want to run the stop in lo gear , change the cam as Adger said. ........2 cents more. [and you'll probably get a lot more] ......Tom __________________ Tom Goldman 1500 SG , 1506 STK

01-25-2010, 07:46 PM	#4
sg5985 Junior Member Join Date: Jan 2010 Posts: 16 Likes: 0 Liked 0 Times in 0 Posts	Re: throttle stop cam for sbc Thanks for the responses. It did knock the tires off in 1st gear coming off the stop so I shift on time and come off the stop in 2nd. I'm on the stop at 4800 rpm and the RPM is pretty steady. The car doesn't charge well off the stop and my mph is down about 9 mph from a full pass. I need to change my combination to what will hopefully be a better throttle stop set up. My compression is almost 14/1 but I'm looking at heads that flow over 300, better intake manifold (super victor 2925 maybe?) for better power coming off the stop, and the right cam. I'm concerned about going too big in intake port size because it may hurt throttle response off the stop so that limits the flow potential of the heads. Input or suggestions would be welcome. RM has a cam that they use in their 412 super series engine that's close to the specs you're talking about; .675/.653, 272/284 @ .050, LC107. 1.6 rockers would give me .720/.696 lift. This is a great forum for a rookie like me that needs all the help he can get. Rob

01-26-2010, 12:13 AM	#5
Adger Smith VIP Member Join Date: Dec 2001 Location: Texarkana Ark/TX Posts: 2,360 Likes: 445 Liked 686 Times in 267 Posts	Re: throttle stop cam for sbc With that stroke and cu in you don't need to worry about having too big a head. I don't know of any std 23 deg head that will be too much for your application. The intake is a good choice. I have used them before. It's nice to hear you know your current combination well enough to know that you need changes. Good luck. __________________ Adger Smith (Former SS)