I've been collecting parts to motivate a Model A coupe project. It's going to be a 60s street racer. The plan is for a blown 327 with six carbs. So far I have the engine, a GMC 6:71, NOS 492 angle plug camel back heads, and a NOS 6098 cam which I think is a solid lift Duntov unit. I don't know if the engine is a small or large journal or if that even matters? But I do want this thing to scream. So am I on the right path with this combo? Or is my desire to use all these old parts going to hold me back? Sent from my iPhone using The H.A.M.B. mobile app
If you want to go fast on the street then what you have so far looks great! If your going to race this car and want to go fast fast then there is better heads and cams avaliable. Looks good for a period correct build.
Watch the compression ratio...probably need dished pistons to work with those heads. The block has a fitting in the back for the PCV valve, so it's gonna be a small journal, from what I can tell.
What 6 carbs are you going to use? If you use the Holley 94 and you get a backfire, be prepared to possible replace 6 blown power valves, I would use Rochester's or Stromberg 48's (the small ones)
Squirrel, would 74 cc heads be better for the blower. They are 70-71 large chamber ones with the large valves, don't have the casting # handy. The reason I ask is I will be replacing them soon for some aftermarket heads and I will let them go cheap. They were rebuilt and good to go with little mileage on them.
If the heads are angle plug, they are "over the counter" parts - precursers to 292 Turbos. I would definitely splurge for blower pistons for the engine. They'll be pretty pricey for a 327, but not as expensive as building the engine a second time when a piston comes apart. Build it right, build it once.
Based on the angled exhaust manifolds I'd guess that's a truck motor core. I would spend some time on the phone with cam and blower makers to get their suggestions. Using that cam just because you have it might not give you the results you want. A combination of well matched components will work better and you won't be fighting to tune around the compromises.
There are multiple ways to get the static compression ratio down to about 8:0 - 1 . . . bigger chamber heads, dished pistons . . . some of both, etc.. When you say you want this this to fly - how much money and what type of parts are you going to put into it? All 327's are 2-bolt mains -- some had steel cranks (maybe all of them) -- the rods are a bit weak. So, if you really want to flog the thing and put more than about 5 - 6 lbs of boost on it - then you better consider what parts you're putting into it. If it was mine, I'd build it on a 4-bolt main 350 block - with a forged crank and a good set of rods . . . but if you already have an engine, then go for it, but limit your boost. Another issue is the SBC crank snout - you'll want to have it double keyed for the blower hub and ensure that you run a quality crank hub and have everything balanced extremely well. On oiling - I tend to run a bit bigger bearing clearances on a blown motor - so talk to your machine shop about your application BEFORE you have the crank reground. I'd shoot for .00225 on the rods and probably .0025 to .00275 on the mains. If you're running a manual transmission, then .00275 to .003 on the rear main (due to heat coming into the crank from the clutch). Make sure your heads are setup with the right springs for the cam and blower boost you're going to run . . . seems like you're running a pretty mild setup, so that should be an easy deal. Get the best performance valve job and head work possible - is key to the whole package. You'll need high quality forged pistons and good rings. I love the Akerly Childs HTD moly rings for supercharger builds . . . but there are plenty of good options out there. I'd also run a good set of roller rockers - with probably a 1.6 ratio . . . checkout 'Scorpion' . . .
It's been awhile since I ran a blower but I can tell you that it takes a lot of money to do it right. You might get by for a short time with lesser parts but you need forged pistons with dished top, a forged crankshaft and the best rods you can afford. The newer head gaskets are much better than anything you could buy in the '60s, we had to "O" ring the blocks for any hope of sealing. Your blower looks like a salvage stock unit so it will need a complete rework. When you have the crankshaft at the machine shop have them cut a second keyway and drill the snout for a bolt to secure the balancer. You will need them to keep the blower drive pulley on. The camshaft you need should have higher lift and different duration specs to take advantage of the forced induction, you can fine tune with different over/under drive pulleys. MSD makes an ignition box for blower applications that retards the spark at higher pressuers, get one. If you miss a gear and overrev the sound will live in you memory forever. Kind of a cross between a garbage disposal full of spoons and a grenade at 200 decibels.
Want it to scream - How about some numbers to that statement? "Scream" is subjective and means something different to everyone. A plain old 375 HP 327 screams pretty good too. Likely make your butt hole pucker too if you're not paying attention. 700 hp isn't enough for some folks and they want 375 more hp out of it so it screams. Brush up on your math, your 327 has less swept volume than 350. so the standard and over published treefiddy recipes won't work without a calculator tweak. Don't know the cam specs, didn't look them up but the above applies there too. As a general rule a blower will tame down a cam, so you usually want to bump the cam up, and a smaller displacement (327 vs 350) will make the cam seem more radical.
I'd Scrap the heads in favor of New Aluminum heads that are going to have good seats in them and do better with today's shit fuel as well as hold up to higher compression without detonation. If you are worried about them looking older you can paint them to match the block.
Cool you are trying to get a 327 to scream. I put a 327 in my 1967 chevy II. It is cool to hear the scream. dish pistons will help. Make sure you stud the heads. extra pressure in combustion chamber will want to lift the heads off the block. Than you can play with the drive pulleys. under drive or over drive the blower to keep engine last. If you want to go faster than the 327 will let you, you're going to have to go to more cubic inches and more cubic dollars$$$$. But let us know how in runs. GOOD LUCK.
Why stop at 350? Get a dart block and go 400+ cubes lol... easy to spend other people's money isn't it! Sent from my SM-G920V using The H.A.M.B. mobile app
Thanks for all the great advice. I know this is going to cost a boatload of money, but this is going to be a finished car and that's why I'm still in the parts collecting phase, and I'm going to have to sell a couple cars just to get the project rolling. If I'm building a car to replicate a certain era, then that's what I want to stick with. My model A roadster would be a lot more reliable with a 350, T5, and a 9" but it has a flathead, '39 three speed and a banjo rear end because I wanted an immediate postwar look. So I want the 327 with camel back heads because I'm shooting for a mid 60s look with this car. I'm figuring on at least $3K for the blower and almost that much for six new Strombergs, and that's IF the blower is usable? I'm planning on running the M-21 Muncie that's on the floor next to the blower and that's going to need some upgrades as well. I guess I'm wondering if I'll be disappointed if I go with the stock components like the heads? I was definitely planning on a forged rotating assembly, but is it unrealistic to think I can squeeze 500 HP out of a blown 327 with camel backs? I can take or leave the cam, but I want to keep the heads. So far I have new ASC '32 rails, a 9" housing cut to size for a deuce chassis. Wilson Welding brakes for all four corners, most of a polished Super Bell front end, a Walker '32 radiator, Pete & Jakes ladder bars and a rear spring. Oh, and probably the nicest Model A coupe body you've ever seen. I've been hanging onto it for seven years now patiently collecting pieces. Plans include a 4" chop, black paint, chrome firewall, chrome reverse wheels and black walls, probably some kind of cheater slicks. Sent from my iPhone using The H.A.M.B. mobile app
We've built blown street 327's using forged 350 pistons. The difference in wrist pin height between a 327 & a 350 will give you a compression ratio that works, & the pistons are reasonable.
Any really hot blown 327 back then would have had some serious work done to it. Porting those heads... stroked crank etc. If I was building a blower motor I'd be inclined to make sure it lasted with a roller cam setup Sent from my SM-G920V using The H.A.M.B. mobile app
Hi I have a small bearing 327 that was built in the early 60's with a 471 BDS blower, flat top forged pistons. It has small rods, steel crank, with small valves. I put it in a 68 Camaro in the 90's and it ran 12.2 seconds 125 mph in the 1/4 mile. then I put it in a RED in the 2000's and it went 10.2 seconds 135mph. Never blew up Now it is in my 1930 ford coupe that I am in the process of building. What I want to say is that this engine is all a basic stock engine with a blower and is all you need in a model A It will scream and can scare the pants off of you. Put it together and use the blower, limit the boost and RPM. You will need the thin bearing back plate for dist. clearance. Regards Dave
OP, in the 60s everyone would be using those heads because that is what existed. Stick with your plan to use period pieces. Don't go crazy on the boost until everything is dialed in and you're confident with things. Good luck; you are on a really good path.
you really don't need to go crazy on parts for this thing, if you are just wanting a nice performing blown 327 for driving around. Seems to me that cams don't really change their rpm range with the addition of a blower, and rods only need to be strong enough to handle the rpm they are spun up to. Keep the rpm reasonable, with a moderate cam, and the rest of it will live and work ok. seems that some guys when they think "blower motor" they assume that after you make as much HP as possible with the normal hot rodding tricks, then you add the blower. I approach it differently...I start with the blower in mind, and build the engine to work around it. Moderate compression, moderate rpm, build torque, drive it, have fun
X2^^^, the best advice in this thread. I've said it many times, decide what you expect out of the car and then design the total package around that.
While I love the Strombergs for being simple in design and pretty good on preformance for street use I would 2 AFB,s. I have been told when using a blower to richen the mixture and not set the timing so fast.
Hi If you use any carb's that have a vacume power valve set up, make sure that you reference all of them to, under the blower and NOT under the carb's or you will lean out your motor when you take your foot out of it under boost. Just one of may things to think of in a blower motor. Blower motors like lots of initial timing and take some out at the top end under boost. Regards Dave
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