The combination was a drag race only 406 cubic inch SBC. It featured all of the goodies that you would expect to find in a drag racing engine: 14:1 compression ratio, custom grind solid roller camshaft, AFR 210cc heads, Edelbrock Super Victor intake, and 950 cfm Holley carb. Nitrous was fed into the engine via a cross-bar plate under the carb.
The owner was complaining about a lack of top end power. He felt as though the combination was running out of steam before the finish line stripe. Given that this combination primarily runs the 1/8th mile, this was a real issue. If the owner ever decided to go to a 1/4 mile track the situation would only have gotten worse. Our performance objective was to increase top end horsepower and extend the usable rpm range while retaining the current short block (namely pistons) components.
We went to work with our pencil and paper to develop a plan before we started to change parts. Using cylinder head sizing techniques found in the link below, we felt that the AFR 210cc heads were holding the engine back at RPM. If we were to increase power at higher rpm levels, we would have to address the MCSA through the cylinder heads. A limiting factor regarding cylinder head selection on this combination was the stock valve pocket location(s) in the pistons. Originally the pistons were selected to match the AFR 210cc heads (stock valve arrangement). The owner did not want to go through the expense of changing the pistons to a 60/40 pocket arrangement, but was open to the possibility of changing the heads if a better suited head was available that would fit the current pistons. After much research, and many phone calls to the various manufacturers that we work with at SRS, a pair of as cast Dart Pro 1 230cc heads were decided upon. This would open up the MCSA from a measured 2.19 sqin in the AFR heads to a measured 2.48 sqin in the Dart heads. We also called Bullet Racing Cams and ordered another custom camshaft that would better suit our target rpm and nitrous usage. The original camshaft was 258/269 duration @ .050 and had .688/.672 lift on a 110 LSA. The new cam spec'd by Bullet was 275/290 @ .050 with .683/.683 lift and a 112 LSA. Our plan was to eventually spray 350 hp worth of nitrous through the cross-bar plate and Bullet ensured us that this camshaft would allow us to do that more efficiently. Custom length pushrods from Manton and a set of shaft mount rocker arms from T&D Machine finished off the new top end. We were ready to run the refreshed combination on the SRS dyno and see if our planning was going to bare fruit.
Once all the work was complete, we loaded the combination onto the SRS chassis dyno and went to work to objectively quantify and dial in our work. Initial naturally aspirated testing showed that we were making similar peak power numbers when compared to the original combination, but we were now carrying NA power out all the way past 6,800 rpm. Previously, NA power was starting to fall off by 6,000 rpm. So far so good, but the good news doesn't end there. Bullet stated that this new camshaft would really start to shine once the nitrous was applied, and boy were they right. We loaded two #59 nitrous jets into the cross-bar plate. These are the required jet sizes for a "225" hp shot. Power jumped up by 220 horsepower and carried out past 7100 rpm. Previously, with two #65 nitrous jets (a 250 shot), we made 72 less peak power versus the new combination, and power was starting to fall of rapidly by 6,700 rpm. An interesting note, at 6,700 rpm the new combination was up 90 horsepower (with a smaller nitrous jet) over the old combination. That's a win!
Don't leave your engine combination to chance. At Simpson Racing Solutions we are passionate about helping our customers achieve their performance goals. We have many dyno proven combination on file and know what works. If you are planning a new build or want to breathe new life into an existing build, we have the experience to help! Contact us today 236.422.1180
406 SBC, Super Victor Intake, Holley 950 carb, cross-bar nitrous plate.
Testing the new 406 combination on our Superflow Autodyn 30 chassis dyno.