The Jalopy Journal
Discussion in 'The Hokey Ass Message Board' started by STREETREBEL, Jul 14, 2013.
Is the Offenhauser 4x2 SBC intake a good streetable setup?
There seems to be a lot of guys here that have used that combination. HRP
Yes, with a 327 or 350 run four Stromberg 97s with straight (non-progressive) throttle linkage. Be sure to run a fuel pressure regulator set for 3.5 PSI and you are good to go. If you have a 383, four 97s will feed it to around 5,500 RPMs if you build it for low and mid-range torque. If you need a bit more airflow, consider Stromberg 48s.These are identical to 97s except that they have larger main venturii and are jetted with #48 jets rather than #44 or #45 jets. 97s flow around 155 - 160 cfm each and 48s flow around 170 cfm each.
Also...... With the Offy and Edelbrock crossram intakes (the X1 types, not the later low profile Z-28 types with removable tops)...... You need to drill/tap the plenums on either side and run a balance tube of at least 1/2" diameter tubing connecting them with this style intake. You can do this at the rear if you don't want it to be seen. But if you can do it at both ends of the plenums that is best.
Note...... If you are running one of the low profile Offy 4 X 2 intakes rather than the crossram type, you do not need to do this, as they are cast with front and rear balance ports connecting the right and left side plenums.
If you want to improve off idle and part throttle performance on the street, you can decrease plenum volumes using hardwood plenum stuffers secured with screws drilled through the bottom of the plenums (seal these holes with gasoline resistant RTV before screwing them down). This is not for the faint of heart, but the end results are worth the effort if done right. You want these placed in the center between carb pads (there will still be enough open space in the center of the plenums for the front and rear carb of each plenum to 'communicate').
And if you have the hood room and want better performance and mileage, have some 1-1/2" to 2" thick 2-hole carb spacers machined from aluminum which have provisions to run engine coolant through them. Drill/tap them for 1/2" IPS threads and use barb fittings. Plumb these with 1/2" heater hose from front to rear in series, connecting to the manifold water jacket in front and to the heater core at the firewall. This helps atomize the air / fuel mix, but doesn't allow the carbs to become so hot that today's more volatile fuels boil in the fuel bowls on hot summer days.
Leave the choke blades in the 97s and lock them open (helps direct airflow). Never run without air cleaners and use large filter elements that don't choke inflow. Try to keep at least 1-1/2" or more vertical space between top of carbs and undersides of air cleaner lids (more if you have hood room).
Hope this helps,
^ best response ever?
I had one with 4 Rochesters. Rogue used it on his RPU that was in R&C many years ago. The carbs set above the ports on a smallblock so response is very good.
i have been running a X1 for 30 years with out a balance tube
yes keep the fuel pressure down. I run 2.5 and have better reaction
I understand. I have run them without the balance tube as well. You can get a good tune on them that way.
Tried the balance tube and it smoothed things out quite a bit on the street, so I add one at front and rear now.
These were Edelbrock X1s with both center carb mounts blocked off with a blanking plate and I ran only the 4 end carbs on straight (non-progressive) linkage. Also converted an XC8 and the nearly identical Offy crossram to run same carb setup by welding 3-bolt carb mounting pads to the plenum tops at each end and blanking off the center (4bbl) openings. The large blanking plates looked funky, but the larger holes allowed me to experiment with hardwood plenum stuffers.
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