|11-14-2012 02:56 PM|
|gmtony55||Thanks guys. I will definitely check back and report my progress. My son is wanting me too rebuild so he can learn as well so this will be a great project for us. Thanks again to all that posted on this thread as You have helped me a great deal.|
|11-14-2012 11:51 AM|
This brings me to the next concept which is as an engine grows in displacement the need to feed the bigger breathing cylinders has the effect of bringing the power peaks of what are high RPM parts when used in a smaller sized engine downward in the RPM band and smoothing such effects as seen with aggressive cams. This is to a large extent effects that are related to mixture velocity.
For example, if you take an intake manifold, cylinder heads, and camshaft that would be suitable for a high performance 350 that let's say has a 400 horsepower peak at 6000 RPM with a semi-rough idle. These same parts on a 400 inch engine will generate 400 horses at say 5600 RPM and will idle smoother. They very likely will not make much more peak power from the 400 inch engine because they simply can't supply any more mixture. A classic test of this was done by David Vizard many decades ago where he use the 300 horse 327 cam on a 350. The 350 peaked out at 305 horses. Now there is a compresison ratio difference in the engines he tested the 327 having a ratio of about 11 to 1 where the 350 being built for unleaded fuel has a ratio around 9 which if corrected might have made a 320- 330 some horse engine out of the 350, but it still is an excellent example of the limiting effects on cam timing and what would be the related components of the heads and intake system as they relate to feeding a larger engine.
For some top notch reading that summerizes a lot of these concepts I'd recommend two of Davd Vizard's many books, these rather bring the detail subjects of his other books into a summary form that makes a lot of the connections between the various components to help you understand the integrated whole how the parts and concepts work together. Go here as many of David's books are out of print so you need to hunt for them. <<< David Vizard: books by David Vizard @ BookFinder.com >>>
My starting recommendations are "How to Build Horsepower Volume 1" and How to Build Horsepower: Carburetors and Intake Manifolds, Volume 2". These books really tie the complex engine internal subjects together. When you're ready for nitty-gritty by subject you will see that is covered as well. Some of this stuff you have to read several times to get the concepts and at that some concepts such as how compression, camshaft timing and power output relate are much more subtle than reading most any book makes clear. There is always on any subject an assumption that the reader brings some knowledge with them that isn't well defined by the book. We can help with this so don't be afraid to ask questions.
|11-13-2012 07:38 PM|
|11-13-2012 07:21 PM|
|gmtony55||good..That will save me money for sure..thanks i appreciate the advice.|
|11-13-2012 07:14 PM|
|11-13-2012 07:11 PM|
|11-09-2012 12:01 AM|
sbc 400 heads
If you are running short on money I would get rid of the big cam and replace it with something like this. Summit Racing Street & Strip® Cam Kits SUM-K00042 - SummitRacing.com. If you choose to mildly port the heads follow cobalt327 advice. Just swap your intake and carburetor to the 400 motor. Then install it in your El Camino and have some fun driving it.
|11-08-2012 10:17 PM|
|gmtony55||Ok thank you very much!!!|
|11-08-2012 09:48 PM|
Click on image for an article w/some porting info:
|11-08-2012 09:41 PM|
thanks cobalt..extremely good info. I will need an adapter because it had a holley on it before.
I been reading up on porting heads, It doesnt look hard to do at all just time consuming work. but I recarpet boats on the side so I am used to that..Do you think I should bother with that? porting that is.
|11-08-2012 09:28 PM|
If you DO use an adapter, use something like Edelbrock p/n 2693. Summit sells a similar one for a lot less although it might not move the carb back 5/16" like the Edelbrock adapter does. What you want to avoid is the 4-hole jobs (like Proform p/n 66253).
The Q-jet carb will almost surely be the 750 cfm casting, not the 800 cfm casting, although in practice there's very little real-world difference in the performance between the two. The 800 cfm casting does have a slightly larger primary bore and venturi, but compared to most any other similar size carb the primaries are still smaller- which equates to good throttle response and potentially better mileage.
BTW, it's a little known fact that the V6 4.3L GM trucks in the later years (up until '86) used a non computer controlled Q-jet w/the 800 cfm casting. I have one right here from a '86 4.3L V6 Sierra! Good place to source a Q-jet.
|11-08-2012 09:27 PM|
my head casting number is 3973493
|11-08-2012 09:20 PM|
|gmtony55||Techinspector..this is very helpful and I apprieciate your time. the cam figures I must admit is over my head but I do get the keep it close to stock. I will definitely get the book you recommended. thanks again|
|11-08-2012 09:18 PM|
|gmtony55||this is very helpful and I apprieciate your time. the cam figures I must admit is over my head but I do get the keep it close to stock. I will definitely get the book you recommended. thanks again|
|11-08-2012 06:40 PM|
|idontdrivericeieatit||I never seen the casting numbers on the heads some are better than others do u have casting numbers|
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