How to Build a Bulletproof 7.50 Blown
By Brendan Murry
Reprinted by permission of nostalgiafunnycars.com
Brendan Murry won the 1998 Good Guys race using the motor described in this article.
Photo thanks to Brendan Murry.
Reprinted by permission of nostalgiafunnycars.com
Brendan Murry at Performance Motorsports has provided this information. Anybody, who uses any part of this information or just reads it should go and visit his web site. If you want to buy parts and pieces for a motor of this type, consider buying from him. This kind of information to this detail is very hard if not impossible to find let alone share. His web site is
www.racecarparts.com for those who can't wait. I would recommend waiting and reading this article through a couple of times before deciding on a racing direction. --
There are many ways to skin a cat; this is how we do it at Performance Motorsports:
Start with a tall deck Chevrolet 4 bolt-main truck block. This block has the following advantages:
|Truck block has thicker cylinder walls|
|Almost always comes with a steel crankshaft|
|Block is fairly inexpensive|
The first two items come in handy for this project.
Block Machine work:
Deck the block and bore it to .030 over size to make sure the bores are straight. Finish hone it to a smooth finish with 320 grit and plateau brush the bores this makes for a very even, clean bore.
Next o-ring the block and install the o-ring wire.
Wash everything with plenty of hot water and soap. When thoroughly dry, install Milodon main studs, and oil restrictors. We use the Donovan gear drive front cover (RCD makes a very fine piece too, very similar in design in all billet aluminum.
The crankshaft is sent to the crankshaft shop, to be turned .010/.010 under sized on the main and rod journals. We usually run our motors on the loose side, .004 rod and main clearance.
This is a good time to cut the crankshaft for two keyways on the snout to better hold the blower pulley. While it is at the crankshaft shop be sure to have it checked for straightness.
Have all the oil holes chamfered and the crankshaft polished.
Installing the Crankshaft:
We install the crankshaft seal (the gray one) and use our special mixture of 50 weight Kendall and assembly lube on the bearing surfaces of the CHILDS and ALBERT bearings. Carefully lay the crankshaft in place after installing the crankshaft gear.
You can check the clearance with plastic gauge, this should be done dry before final assembly (plastic gauge is an easy way to check clearances and very easy to use even at the track).
Torque the mains to 110 Lbs. and back off 3 times, this will pre-stress the hardware.
Next, install the camshaft and the camshaft thrust plate.
Install one ARIAS 11.1 piston and rings combo and a .500 long Brooks aluminum rod in #1 cylinder. (Long rods makes less stress on the cylinder wall ------less stress =longer life).
We will find TDC and install a RCD crank hub, mark top dead center and proceed to degree the camshaft.
We usually run 2-4 degrees advance with a 701/320/114 Howard's cam and Crower roller lifters.
701/320/114 Cam means:
701 = Valve lift
320 = duration
114 = lobe centers
Connecting Rods & Pistons:
Install the other 7 piston-rod combos with the ring end clearance set. The rule is looser is better than tighter. We add .005 to whatever the manufacturer recommends.
Torque the rod bolts to 75# loosen and re-torque three separate times, this will help in the long run. Check the rod clearance for .030-050 side clearance.
Button up the cam cover and the fuel pump drive extension.
Install the TITAN sportsman oil pump and shaft and install the MILODON 8 quart dragster style oil pan. We run KENDALL 50-weight oil and with the TITAN sportsman oil pump we run with 85 lbs. of oil pressure.
Cylinder Heads & Valve Train:
Install Milodon head studs hand tight in the block. As for cylinder heads, there are many ways to go. I prefer the Chevrolet iron 990 casting. We do a little port matching and bowl blending with our Standard Abrasives porting kit.
We use the iron heads because:
|We are shooting for 1000-1200 horsepower|
|They are readily available|
|They flow well|
|The iron is especially durable and holds heat well|
They run $200-$450.00 and since you don't run water sometimes finding a crack can be a bargaining tool.
We install Milodon stainless exhaust valves and intake valves and add .002 to your valve guide clearance. Install K-Motion kr1000 valve springs and titanium retainers and keepers set. Use 235-lb. spring pressure @1.950- and a good 3-angle valve job.
We bolt on the heads and torque to 80 lb. with a SCE .060 head gaskets. 060 gives you a softer hit and something to tune with at altitude where you can change this to .043 gaskets for more compression.
We install Crower push rods and rockers. Norris stainless rockers are very durable, but are a little heavy. Next, install your favorite brand of stud girdle. Mine is the Moroso's I've had since 83'. We use the B&B valve covers or the Billet Fabrication valve covers. I install the quick release breather 1" tube to a puke tank.
Blower & Fuel system:
For an intake manifold I prefer the Littlefield tall deck manifold and a 6-71 Littlefield alcohol Teflon lined blower turning 25% over drive. We use an Enderle bug catcher and the Nitro barrel valve at .009 (69 % Leak on the barrel valve).
An Enderle 110 pump and a high speed set at 65 lbs. with an 85 jet. Use a 140 -170 main jet and 52 jet for the injectors.
We use the Mallory Super Mag III with Mallory wires and NGK #9 spark plugs.
This combo is a proven setup, not real fancy with trick of the week gizmos, but a reliable setup with which we have won six world championships. You can update or change this recipe to suit your tastes, but it should give you a baseline with a minimum of headaches.
Your Online Supermarket of Race Car Parts
1520 Minnesota Avenue
San Jose, CA 95125
Jim's Notes: So there it is, your own combination to build a blown Big Block Chevy without having to sell your first born child. Yes you can go with a Merlin block. Yes you can go with a Rodeck. Yes you can add your favorite aluminum heads BUT the sole purpose of this article was to share the knowledge that is simply not available...
I think you owe it to Brendan at least to check out his goodies for sale. I personally have been associated with people who have bought parts and pieces from Brendan and everything was exactly as advertised....
I personally will buy there when the time comes. Oh yeah, no I don't get anything from this and Brendan supplied this article without any thought of a return. He did it for the same reason I do it and that is to help people race safely....
One last thought...The picture above was the 1998 Goodguys winner circle using this very combination.