Firecat tuneup, part II

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Rolf Ward
5 years ago
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1 Firecat tuneup, part II The first Firecat we dyno d was the one for the AmSnow Shootout at 131+ HP, and too many Firecat owners howled in disbelief (should have been 140??). We tested some tuneup mods on another bone stock F7 a few weeks ago which made HP out of the box. After that bewildering, non-conclusive test session we were advised by the sled owner s dealer that since we had removed and left the hood off during the test session, the ECU may go into some sort of limp-home mode which surely could have skewed our results which were: 1) modifying the airbox with D&D Bullseye filters reduced airbox restriction from 5 wp to 1 wp, not a lot but added some airflow without increasing fuel flow, a moderate double winner. 2) Vforce3 reed cages didn t add any CFM; power was seemingly identical on this sled (remember we tested the stock reeds with hood on, pulled the hood to facilitate reed change and left the hood off until the last few dyno runs). 3) The D&D single pipe was much lighter, peaked at 100 or so revs lower than stock, but made nearly identical HP with a bit more torque. 4) At 9:00 PM we reinstalled the hood, the dyno air temp had dropped to 25 degrees F, fuel flow dropped to below 110 lb/ft and two or three HP appeared from nowhere??? After we heard about the possibility of the hood-off limp-home deal I knew we had to redo this test to obtain meaningful information. Bill DiFranco of nearby Lewiston, NY offered his stocker for a repeat test which we did on 2/27/03. I met Bill on hardcoresledder.com (an Arctic Cat owners website), which looks like an excellent venue for exchanging good and not-so-good info on Cat sleds. Making sure the hood stayed on for all tests, Bill s sled gave us similar results to our previous F7, baselining at HP bone stock at an amazingly fat.80+ LB/HPHR BSFC. Instead of D&D Bullseyes, Bill then added Thunder Products lowboy square filtered breathers. The lowboy breathers with stock inlet horn flowed as much air, and made identical HP to the stock box with D&D Bullseyes. This combo was also identical to the stock airbox with a large diameter (no venturi) SpeedWerx air inlet horn. 248 CFM is the number. The stock air inlet horn is quieter; but adds 5 wp (water pressure-- each of which is about.04 psi negative, not much but they all add up) restriction which was nearly eliminated with the add-on breathers (which could draw in warmer underhood air arguably offsetting some of the pressure drop benefit). The slight increase in airflow combined with the fixed EFI fuel flow maybe added 1 HP. For our money, those extra low-buck air inlets are the good deal. One HP for $40? No problem. Next Bill installed Vforce3 reed cages. With the hood back on, airflow meter in place, we were back to about 248 CFM, but power was averaging maybe another HP higher than the stock reeds (those who have read our early info on this site understand that HP increase with reed changes does not always come with airflow increase). The thing that was bugging us most was the fuel flow..80+ lb/hpr and richer than 10-1 A/F ratio is guaranteed misfire with carbureted sleds, but the EFI is making such rich

2 mixtures doable. The DynoTech BSFC guide (assuming coolant temp is controlled) has historically been:.70+ = pump gas safe for miles at WOT,.60 = OK for short blasts on pump gas,.50+ is drag spec on 100+ octane. Simplistic, but you can get the idea. All of a sudden we have a new category--.80 = 85 octane safe for 100 miles at WOT!! Nothing wrong with that since the F7 delivers 800 and 900 class performance with the richest top end WOT fuel mixture ever seen on a stocker on our dyno. Safe even for those Canadian madmen that simply must pin the throttle on the many frozen lakes and turnpike-like groomed trails, from full tank to empty, after filling up with gas left over from last fishing season at the frozen Marinas. But what if we are reasonable performance riders, and are willing to spend an extra 30 cents per gallon for High test pump gas, and/or are willing to limit our time at full throttle to reasonable periods? How much HP is there available for us if the F7 s EFI fuel flow map was reconfigured for those of us who understand this situation, have IQ s higher than 60, and will not whine when we goof? How about 5-10 more HP? Here are the unbelievable numbers. Unebelievable in that this is a low-revving, quiet unassuming 87 octane-safe twin that can make power equal to open Mod Stock engines of just a few years ago. Note that we have reduced fuel ONLY at 7200 and higher where the stock fuel flow is clean running but very rich. It is impossible to lean out midrange part and full throttle since it is so lean and crisp there. So fuel can be pulled from EGV opening and beyond. I can t reveal how we managed this because it will only inspire experimentation that will surely have disastrous results if you don t have a fully instrumented dyno to test with. We may try to come up with a consumer-friendly means to achieve this. After Greedy Bill saw the 142 HP (each run was 12 seconds at WOT on 87 octane, easily enough time for his favorite ¼ mile blast), now he s dreaming of 150 on 92+ octane. As I indicated in an early post on Hardcoresledder.com, I used to roll my eyes when people whispered about those late season grass-drag dominating F7 s cranking out 150+HP. Now I believe it. Bill has plans to achieve that, on our notoriously stingy but accurate dyno. We will keep you posted on his progress. And if we (or anyone else) come up with a reliable means to drop the top end fuel flow, DynoTech members will be the first to know.

3 test 03F711 stock F7, w/ mod airbox & reeds, stock fuel flow...engspd... STPTrq..STPPwr.AirTmp... BSFC.Fuel B.Air 2.. A/F.. RPM..Clb-ft.. CHp.. degf.lb/hph...lb/hr...scfm.. Ratio test 03F717, stock F7, modified airbox & reeds, reduced high RPM fuel flow...engspd...stptrq.. STPPwr.AirTmp... BSFC...Fuel B...Air 2...A/F..RPM.. Clb-ft.. CHp..degF.lb/hph..lb/hr...scfm.. Ratio file:///a /03F7finalexcell.htm (1 of 4) [2/28/2003 5:45:54 PM]

4 test 03F718, stock F7 with mod airbox & reeds, reduced high RPM fuel flow...engspd..stptrq..stppwr.airtmp... BSFC. Fuel B.Air 2.. A/F.. RPM..CFtLb. CHp.. degf. lb/hph... lb/hr...scfm...ratio test 03F719, stock F7 with mod airbox & reeds, reduced high RPM fuel flow...engspd..stptrq.. STPPwr.AirTmp... BSFC. Fuel B...Air 2...A/F..RPM..Clb-ft.. CHp...degF. lb/hph... lb/hr...scfm.ratio file:///a /03F7finalexcell.htm (2 of 4) [2/28/2003 5:45:54 PM]

5 test 03F720, stock F7 with mod airbox & reeds, reduced high RPM fuel flow...engspd..stptrq.. STPPwr.AirTmp... BSFC.Fuel B...Air 2.A/F..RPM. Clb-ft.. CHp..degF. lb/hph... lb/hr...scfm...ratio test 03F716, stock F7 with mod airbox & reeds, severely reduced high RPM fuel flow....engspd...stptrq...stppwr.airtmp... BSFC...Fuel B.Air 2.. A/F..RPM.. Clb-ft.. CHp..degF.lb/hph...lb/hr.scfm...Ratio file:///a /03F7finalexcell.htm (3 of 4) [2/28/2003 5:45:54 PM]

6 file:///a /03F7finalexcell.htm (4 of 4) [2/28/2003 5:45:54 PM]

ARCTIC CAT 04 F7 EFI FIRECAT UPDATE:

ARCTIC CAT 04 F7 EFI FIRECAT UPDATE: Bill DiFranco (AKA looneytune on the internet who previously provided his 03 F7 for evaluation for DynoTechResearch) swapped his sled for an 04. Then he came to the