Hey everyone, I’ve been haunting these boards for a very long time, love this stuff! I feel I have read every 4–71 blower on a flathead article on the Internet. Anyway, I’ve got a 27T roadster, my plan was to rebuild my ‘53 flatty And make it a 293 stroker. I already have 95% of the parts. Including Edelbrock, slingshot manifold, and Edelbrock 65 cc heads. And 2-97 Stroms up top. “plan your build, build your plan” went in the toilet because I just scored a 4–71 blower in great condition. Which is now changing my direction. so my question is Can I rework my Edelbrock heads to lower compression so that I may add the blower? is this more cost-effective than say selling them and buying Navarro blower heads? Also, going to have to find a different intake manifold, can I use the risers from the slingshot on top of the blower? It will be tall as it is, might as well go for the moon! You see any problems/challenges in going this direction? Thanks in advance, Gorilla
Quick thoughts. How much boost are you planning to throw at it? Those edelbrock heads probably don’t boost compression up enough to make it an issue for “standard” amounts of boost on the street. as far as the sling shot on top I don’t see why You couldn’t as long as you’re handy with metal and can make the top plate for the blower suit that arrangement.
How much boost? You could increase the CC of the heads to lower the compression and slow the blower down to decrease the boost, both will help with final compression ratio. Are the rods and pistons up to the task?
I’m not sure what “standard” boost amounts are. Not looking to go crazy, I was thinking 6 or 7 pounds. I see that the Navarro “blower” heads are 74 (75?) cc’s. And my Edelbrock‘s are 65 Cam is a Schneider, S – 100 grind. I’m hoping with the added boost, I don’t need to go larger valves and porting. New rods, cast aluminum three ring Ross pistons. As far as reinforcing the lower end, are billet main straps enough? Again, not looking to force too much air…
I own a blown 8BA with a 471, mecr crank and I kept the CR at 8.5 with modified, Navarro blower heads. I run 8 pounds of boost and a MSD 6-BTM with a dash mount knob to adjust timing retard and a built in rev limiter. More importantly than heads though, what are you going to do to the bottom end to hold it inside the pan?
Billet steel main supports at a minimum. I’ve seen some other hot, custom set ups, braces, etc. Should be hovering right around 300 hp at the crank. Recommendations?
These, at a minimum. Not cheap but neither is a blown flathead. H&H caps. Maybe more important than CR is breathing. Are you going to relieve the block? And port it? My recommendation is buy Joe Abins book on supercharging a flathead and follow it religiously. You can make your 300 mark but it won't be cheap.
Gotcha Tim. Definitely doing the billet steel straps at a minimum. Many of the gurus said that relieving the block did not achieve the goals. originally, before I acquired the blower, I was definitely going to relieve that block when she goes in for the valve job. I was also under the impression that with forced induction, I could stay with standard size valves and ignore the porting I’m definitely not opposed to having her breathe better, just trying to get the best bang for my buck. Joes books (thumb drive) hopefully in the mailbox today when I get home!
I am not a "guru" but I built a .125 over flathead that made north of 300 on it's dyno pull with a relieved block, 1.5" and 1.6" chevy valves, and lots of porting like Joe said to do. Like I said, I am not a chef, but I can follow a recipe. You bought the cookbook, time to make a cake.
No to hijack 27Tgar's post, but Billy just for ****s and giggles could you post up a clip. with yours idling? I'd love to hear what it sounds like as I have thought about doing this with my flatty as well.
I was pretty light on the throttle blip. Still a very new engine and I was not filled with confidence yet. I also wasn't as grey as I am now. I wonder if the flathead had something to do with it? Oh, you can ask... It's a custom grind that Mike at H&H recommended for this build. I have the card but I will have to dig for it.
Agreed, steel main caps at a minimum. I found a cap and girdle set made by flatattack The girdle seems like something that is easy enough to fab up. Should I only be looking into this for more than say, 8 pounds of boost? if so, what happens to the oil pan, guessing I would need to modify that as well. Hours and hours of reading I have found it seems it’s not the best, but it’s a step above caps only. Excessive or good cheap insurance?
Billy, I would love to see that cam grind card. I have a Schneider cam S – 100, I’ve been told it would be OK with the blower but I’d like to see how it looks against yours. Thanks for all the insight!
I considered the girdle before going CNC mains. My engine builder made the final call. I am still looking for the dyno sheet, it has the cam card attached and a final receipt that I should scribble through.
When building a supercharged flathead for the street there's going to be a variation of opinion's on how to go about doing it. Its easy to get 300 crank HP out of a GMC supercharged flathead with a boost level that's under 10 pounds. Here's my opinion and experience on how to do a couple of thing's. First the stock Ford flathead front and center main bearing caps are plenty strong once they are supported using the basic steel main bearing support strap that's 1/2 thick by 1 inch wide - the rear main bearing cap is strong enough to not need any further support. Use ARP studs washers and nuts for the main bearing caps. Porting is a plus and so is a relief that's at least .080 deep. Valves can be 1.5 for intake and exhaust or 1.6 for the intakes. A word of caution about opening up the stock Ford valve seat intake or exhaust inserts to 1.6 or larger. When we work on a block that's over 70 years old those original valve seat inserts are no longer round this simply means they are not holding into the block as they did when first installed. Running a blower will add additional heat to the seat area when one decides to use this great power adder heck we know we are going to use the boost so give some thought to those old valve seats. I will tell you the blown Ford flathead engine's I run hard don't have valve seat inserts but they make well over 300 HP at the tires. Another important area is ignition timing. For a blower application its best to not go over 24 degrees all in I find an initial timing of 12 degrees works well with the remaining 12 coming in at 2500 RPM. I don't use a boost retard any time we retard a flathead we risk adding additional heat to the engine's cooling system. We all should know the flathead is already trying to superheat the coolant by the design of the exhaust p***ages being submerged in the coolant. When we add boost we risk adding additional heat. Anything you can do to reduce heat is important and anything you can do to get that coolant out of the block faster so it gets to the radiator is extremely important. Well that pretty much sums up what I wanted to put out there for anyone interested. Ronnieroadster
Adding boost to an "asthma patient" will indeed force more air into its lungs, and that will allow it to burn more fuel and produce more power. I think you mentioned 6-7PSI boost, close to 50% increase over atmospheric, so let's just pull a number out of the a** and ***ume you can get 40% increase in power from that alone, after deducting the power it takes to drive the blower. With a restrictive engine that blower will be working against that restriction, some of the boost won't reach the cylinders, and you'll basically be wasting power on driving a blower harder but not get the air to move where you want it. The harder you drive a blower, the more heat it adds to the air, undesirable at any time but even more so on a blown flathead. They have enough heat issues from factory, they have a horrible size and shape of the combustion chamber that won't make life easy for the fuel unless the octane rating is very high, and being blown just makes all heat related downsides more significant. If you do something to help the engine breathe, i.e. porting, bigger valves, cam choice, whatever it needs, you can get the same flow into and out of the engine with far less boost, waste less power on driving the blower just to turn it into heat OR keep giving the same amount of power to the blower and make more power. You'll be pulling the engine apart to make other modifications so it can handle the boost, you'd be best off also doing a few other modifications to make it breathe better while its in pieces. Might not need to go as far as for a N/A engine, just some more basic work to help it along, but I think not doing it when you have a perfect opportunity could be a mistake. To be clear, I have no personal experience with these engines in particular, but when building engines it's generally a good idea to make sure all parts of the plan will be working together towards the same goal. Adding boost but keeping other "restrictions" is generally not a great recipe.
Thanks 37! I will attach the numbers on my cam grind. After seeing that HNH grind, I’m hoping I’m OK with the overlap and such. I felt I was dialed in when it was going to be an N/A stroker. Ronnie and G-son thank you. I had originally planned on porting, and some relieving, some people who told me it wasn’t necessary definitely did not think about the fact that you’ll have to use more energy to blower for same results. 10–4 on the ignition timing I do not intend to build a grenade with the pin half out, but we all know what happens when we get a taste! This is my first blower on any motor, I’m taking in all the information I can. How important is Plenum size when using carburetors on top of the 4-71, am I overthinking this, should I just slap them on a plate? I already have the new Stromberg 97’s(162cfm) hoping I do not need to swap for the big 97’s. Just to reiterate, this will not be a dedicated track car, nor will it be a trailer queen. Not looking for cross country reliability I want to put my foot down and I want to have fun. I also do not want to rebuild it every winter, can I achieve such balance?
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