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Discussion Starter #1
Hello...as everyone knows from my previous posts, I am still very much a novice with regards to my 1973 XR-7 convertible. The engine was rebuilt back in 1998 by someone who did an okay job, but I'm not exactly sure what he did. I know the engine had its first bore at that time, and he replaced the cam with some type of custom cam. This was a 351C with a two barrel carb and it now has a four barrel. Well, I am thinking of switching out the intake manifold, from a Holley to an Edelbrock Performer RPM or RPM Air Gap and putting a Holley street avenger 670cfm carb on it. My question is whether or not this is something I should even attempt. I'm getting more and more comfortable with things (I've taken off the carb and put it back on), but just wondering if this is something I should try. I also read about cylinder heads made by Edelbrock for the 351C that got rave reviews. If I'm going to attack the manifold and carb, should I consider the new cylinder heads while I'm at it? Thanks as always for any insight. Tyson
 

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Which Holley intake is on it now?

An standard Edelbrock performer is just an aluminum copy of the factory four-barrel intake, so no real performance advantage there. According to the Edelbrock website, there is no Performer RPM for a Cleveland, just the RPM AirGap. The problem with the Air Gap is that it sits so high that air cleaner-to-hood clearance becomes an issue. Those low-profile triangular Edelbrock air cleaners should be avoided for a number of reasons better left to another post. Even an open element air cleaner should be avoided since the engine will be breathing hot underhood air. The best solution is to duct cold air to the carburetor from either below the front bumper or in front of the radiator.

You must also remember that 351Cs had two different intake and exhaust port sizes - the 2V is smaller than the 4V. BTW, 'V' back in the day was Ford's way of saying 'barrel' - it actually stands for Venturi. So...... you must first determine which cylinder heads are on the motor now. Easiest way is to look at the upper corner just outside of the valve cover - you will find either a raised 2 or 4 there. If there is no number, those are 351M/400 heads, which are essentially 2V heads... Once you know which ones you have, we can get the intake with the correct corresponding port sizing. You can get an aftermarket four-barrel intake with either port size.

The Cleveland intake is a 'dry' intake - meaning there are no water passages going through it. Simply take off the 12 bolts holding it on, and replace it (using new gaskets of course).

OK, that takes care of the intake side of the engine. Doing all of that will not do squat if you still have cast iron exhaust manifolds and a single exhaust! The exhaust manifolds don't hurt as much as you'd think, but a single exhaust will choke the exhaust flow. a dual exhaust system - even the factory 2-1/4" system - will help immensely. With your convertible, your exhaust choices are somewhat limited since 'verts use an additional crossbrace under the front seats.

Cylinder heads. The factory Cleveland heads are entirely adequate for a healthy street motor. Changing heads is quite a bit more involved than just bolting on a carb. Many other things will also need to be changed. Most aftermarket heads will use guide plates, which necessitates hardened pushrods. Also, most aftermarket heads are not for pedestal or positive-stop rocker arms like your factory ones which means you'll need new rocker arms...
 

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Discussion Starter #3
Hi Milo...thanks for all the information. I haven't had a chance to look at the cylinder heads, but I imagine they are the 2V version because I'm 99% sure that they were rebuilt and reinstalled when the engine was rebuilt in 1998. I'm not sure which intake manifold the Holley is. It is interesting...it is a single plane intake with no divider however the opening is not perfectly square. I had to use a metal plate and gasket from Edelbrock to put the Edelbrock square bore carb on, however Edelbrock assured me that even though I didn't know the exact model of the Holley intake, if it was single plane then it was made for a square bore carb. I was mainly wondering how hard it would be to change the manifold and wondered if it would make much difference with horsepower. I spoke with a Holley technician, and he spoke highly of Edelbrock intake manifolds. I want the engine to run as well as possible without getting crazy and I guess wondered what it do as far as performance boost to go with a 4V intake, the Edelbrock (or other 4V) cylinder heads. It does have duel exhaust, however it doesn't have "headers", which I've been told make a decent difference (up to 30hp or so at the rear wheels). So I guess I still have the cast iron exhaust manifolds. If you have any recommendations that would give you about the best street performance for a 351C that came from the factory as a 2V, I'd love to hear them. Thanks again, Tyson
 

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Sounds like you have a Holley Street Dominator single plane intake manifold. The Holley Street Dominator is an economy type single plane intake with small runners and plenum. The ports are actually smaller than a 2V's but Holley advertised it as a universal fit for both 2V's and 4V's. Holley's claimed RPM range is idle to 4800 RPM but I have heard people said it was best between 2500 and 5500 rpm. The carburator flange is not square so it could also accept spreadbore carburators. You need to find out the specs on the camshaft you have so that your combination matches. The Performer manifold runs out of steam at around 5800 rpm. The Weiand X-celerator 2V is said to pull to 6200 rpm but without knowing what your engine combo is it is too hard to give any valid recommendation. Changing an intake manifold isn't difficult and can be done easily with a gasket scraper and torque wrench. Cleveland engines can be built to run very strong and still behave well on the streat. Give us some more info about what you have and what RPM range you want to spin your Cleveland and we can help you out. All the best.
 

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Agreed - I'd try to ID what you have as best you can. Just because it was overhauled in year X, doesn't mean much. Was it replaced at some point....etc. To many unknowns. Any contact with the PO to shine some light on it..
 

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Discussion Starter #6
Hello Hawk1 and Bad69cat...I REALLY appreciate the insight. I think I have a little bit better understanding at this point. I know the engine was a 351C 2V converted to a 4V but with the stock cylinder heads, but I don't know what type of camshaft it has. I know it came from Competition Cams, and I actually have a call into the mechanic who did the work back in 1998, so I am hoping that he might remember what he put in it. I've read in a couple of places that certain cams would possibly cause the engine to run roughly at idle, which my 351C certainly doesn't...It's pretty smooth at idle. I'm looking to keep it running smooth from idle to probably the top end of the the Performer manifold which you mentioned to be between 5500 and 5800rpm. Is there a way that I could possibly ID the camshaft without having to totally tear apart the engine? Thank you again for all your insight. Tyson
 

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Not sure on the 73 exhaust setup, but.....................

My 69 vert (351W2V-4spd) had single exhaust, but was changed to dual exhaust mostly installed by me. I actually took the setup off of my 70 Std 351W2V-FMX.

On my '70, I used a dual exhaust head pipe that was originally made for a 351C with stock manifolds. It had to be modified (passenger side) to reach up to the manifold. A good muffler shop did it for me back in 1979.

I bought stock left and right extension pipes to go to the mufflers. Thes are both configured to tuck UP next to the drive shaft at the tailshaft, in the "hump", and then come back DOWN at the locations for the stock mufflers. They do fit ABOVE the convertible brace plate, although they were not originally for a convertible.

I installed 45's and ran straight Thrush mufflers out in front of the rear tires for years. Eventually I installed mild turbo mufflers, with the same in-out configuration as stock. The 45's were turned down and ran that configuration until the '70 was parked and eventually stripped for resto (still sitting).

When I got the vert, I took the dual setup (still standing in the corner of the garage in one piece) and put in on the freshly rebuilt 3512V. Had to add a hanger at the rear. Since I couldn't find tail affordable pipes, I took it to a local shop (2 yeares ago) and they made and installed them. ALL the connections are clamped - no welds.

Love the sound and it breathes well. Getting ready to swap out the stock 2V intake for a stock 4V intake and add a 4bbl for economy and power, when wanted.

Mike
 

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Tyson, If the engine is in good shape you can get a good indication as to how radical the cam is by connecting a vacuum gage to the intake and seeing how many inches of vacuum it makes at idle. The less vaccum generally means you have a more radical cam with regards to duration and lift. Check it out and let us know what you find. Do you know what kind of Holley carb you have? The best bang for you buck may involve tuning your current set up and adding a dual exhaust with headers? It all depends on what you want as increasing HP takes $, time and the ability to piece together your engine components to optimize the power you are looking to make. All the best.
 

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Discussion Starter #9
Hi Hawk1....fair enough. Here's where I show my ignorance...where on the intake would I connect this too? The carb has two lines connecting to it - would it be one of those two? Thanks again for your help. Tyson
 

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< I am still very much a novice with regards to my 1973 XR-7 convertible. My question is whether or not this is something I should even attempt. I'm getting more and more comfortable with things (I've taken off the carb and put it back on), but just wondering if this is something I should try. >
Regardless if you change out your manifold, learning to work on your Cougar and diving into more challenging mods or repairs can be very rewarding. Here are some useful tips to start off with:

1) Invest in the factory shop manual so that you have the proper assembly sequence instructions, torque values, etc.
2) Use your digital camera to take pictures of EVERYTHING before you disassemble. Take pictures as you go. Trust me, you won't remember exactly how things go back together a few days or a week later.
3) "Bag and tag" all your small parts, bolts, clips, clamps, etc. using small Ziplock bags and or masking tape and a Sharpie. Draw a rough sketch of the parts bolt pattern on a piece of cardboard and push the bolts through the carboard in their proper location. For example, the bolt pattern for the waterpump on a 302 has many different sizes and lengths. When you're trying to put all the bolts back in quickly, before your gasket sealent starts to dry, it helps to grab the correct bolt and install them without having to figure out which one goes where.
4) Number or mark all your wiring connectors and hoses with a piece of masking tape and a Sharpie so you can connect them in their proper place.
5) Loosely install all your bolts first before you start the torque down sequence. This will allow the part to float a little bit so you can get all the bolts in. And, always run your bolts or nuts down a few threads by hand before you put a wrench on them to prevent cross threading.
6) Make sure you have ALL the bolts out BEFORE you try to pry a part off with some sort of wedge or screwdriver. Check and double check.
7) Thoroughly clean all gasket surfaces before installing new gaskets. I use a spray on gasket remover (which disolves paper) and a razor blade. I use rubbing alcohol to clean the surfaces afterwards.

Organization and remembering how it all goes back together is really the biggest hurdle. Once you consistantly do that, it's not that difficult.
 

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Hi Tyson, Connect the vacuum gage to the nipple directly on the intake manifold. My guess is that you have between 17 and 21 inches of vacuum at idle. Let us know what you find. All the best,
 

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Just my 2 cents worth sea foam jcode just said, tinkering and fixing it yourself can be VERY rewarding. Don't be afraid to try it. There are plenty of knowledgeable folks on here that are more than willing to help. Believe me, they have been more than patient with my questions. I just put a new cam and intake on my '68 ant it runs great. Get to know what you got and do research. Working on older cars is not really that hard when you really get down to it and the more you know about your car, the more you will grow to love it. Good luck and enjoy! You can do it!
 

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An standard Edelbrock performer is just an aluminum copy of the factory four-barrel intake, so no real performance advantage there.
That's not true at all. The 4V factory intake has much larger runners than the F351-4V aka Performer. The Edelbrock intake easily outperforms the factory intake is probably one of the best performing intakes for a 4V "street" engine.
I published actual dyno comparisons of multiple intakes way before Dan the Pantera man started the well-known Cleveland intake dyno comparison. He has a far larger collection of data now but the results point to more performance with the Edelbrock as well.
 

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I don't have a Performer on hand, but I do have a very old F351-4V and it has the same port size as a factory iron 4V intake. It was a sometime later that Edelbrock made the Performer 4V runners a bit smaller. Not as small as a 2V port, but a tad smaller than the factory 4V port. I think that they were trying to get rid of some of the drivability 'sogginess' caused by the too-big factory 4V port for the moderate displacement of the motor.
 

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Discussion Starter #15
I got some updated information. I spoke to the guy who rebuilt the motor back in 1998, and he believes the cam that he put in the engine is a 268 versus the stock one which was 240-something. Does that sound right? He also said that the pistons he put in would raise the compression to around 9.5 to 1. Does that sound right? He kind of explained different piston types to me and said that the ones in the convertible were flat top but with some "eyebrows" in them? I just read that for an engine with cast iron heads 9.5 to 1 is about the max compression (maybe 10 to 1 if you wanna push it). Anyhow, if anyone has any feedback on whether or not the 268 camshaft (I guess that stands for degrees that the valves open?) I'd love to hear it. Thanks again, tyson
 

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http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=841&sb=0 This is the link to the specs for this cam. It runs to about 5500 rpm and is definitely more stout than the stock 2 barrel cam. The compression sounds about right for that cam, heads and pistons. I run 10.6 to 1 with the stock quench chamber 4V heads but my cam is more aggressive which lowers the dynamic compression. Did you find out what kind of carburator you have? Your might want to focus on exhaust and gears. All the best.
 
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