383 tow motor cam question

General engine tech -- Drag Racing to Circle Track

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n2omike
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Re: 750 carb

Post by n2omike »

bigjoe1 wrote:I drove this truck many times, and the manual secondarys are the secret.. You can open the secondaries just a little, because you can feel the linkage with your foot.. It would scream up a big hill with a car on the trailor, and you never had to push the carb wide open.. I have told several other people about this, and when they tried it, they could not believe how good it works. Most people would never even thing to try it, but it really works good

JOE SHERMAN RACING
I never like the Holley Vacuum Secondary setup, as there is no direct control of it. I like manual secondaries, and that's one reason I like the Edelbrock carbs on STREET engines. I like the fact that (aside from better fuel mileage than a Holley) even though the secondaries have an 'air valve' like a Q-jet, they are indeed manually controlled. When you stick your foot in it, you KNOW the 4bbl is 'kicked in'.

Too many Vacuum Holleys quit working without you knowing it because of ripped diaphragms or leaks. They also don't usually open all the way. Plus, most of Holley's 'generic' vacuum carbs like the 1850 and 3310 that are priced comparably with the E-boks use those crappy secondary plates instead of a real metering block that the jets can be changed in. I LIKE the metering rods in a E-bok, as the ENTIRE fuel curve through all throttle positions can be tuned. They don't just use a 'power valve' that simply dumps extra fuel at a pre-determined vacuum level. The E-bok is much more precise and fuel efficient. Sure, you -might- give up possibly 10hp on the top end compared to a 'race' carb, but gain it back in what really matters on the street. Plus, I don't think any of the 'generic' 600 and 750 vacuum Holleys that are in the same price range are going to make any more power. Maybe less.

Sorry for the rambling. Thanks for all the info on truck/tow cams!
digger5
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Post by digger5 »

OK. Let me drag this up one more time. I decided to use the HT383 crate motor hydraulic roller cam largely due to price ($60 for a new one) and this is a budget build.

My question is would this cam be helped significantly by using a 1.6 ratio rocker?

The additional lift would require some work on the valve guide to lock clearance but it is not too big of a deal. I suspect these lift numbers were used by GM in order to be compatible with off the shelf vortec heads and that's why I'm asking if the additional lift would be beneficial and worth the extra effort and cost. Or maybe even a 1.6 intake and 1.5 exhaust based on Cam King's advice.

Again, this is a motor used for towing and torque is the biggest concern (with fuel mileage being secondary rather than horsepower).

The cam specs are 196/206 @.050 and 431/451 with a 1.5 rocker 109 LSA.
Heads are stock vortec
Lift Intake Exhaust
0.100 66 57
0.200 129 101
0.300 186 136
0.400 219 149
0.450 225 150
0.500 216 155

Thanks for all the help.
RogerF
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Post by RogerF »

If you already have them, use them. The .030" additional intake lift will help slightly. I wouldn't buy another set though if I already had a set of 1.5's.

Post up your opinions of the combination when you finish.
Rog
bigjoe1
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tow cam

Post by bigjoe1 »

The 1.6 ratio will usually help 7 to 10 HP, at MAX RPM-- down low ( 3000) you will LOOSE HP with the higher ratio--- NOT GOOD

JOE SHERMAN RACING
rmcomprandy

Post by rmcomprandy »

After trying several camshafts in different tow type vehicles, I personally have settled on a specific grind ELGIN cam which is available in many makes of engine.
Because it seems to be a "generic" piece it is probably also available from other sources.
Single pattern - 208°/208°@.050" - .280"/.280" lobe lift - 111° lobe seperation; (depending upon the engine make) 103° to 106° intake centerline.
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