Racing Fuel Systems

I took on this conversion with the owners understanding there might be problems I had little to no experience with. Early 70’s 750dp’s with side hung pri bowls front & rear for inline application. All other original parts used/modified/replaced(140bf N&S, pump diaphrams, Nitrophyl floats) for E85. After 2-3 tuning corrections, too much rear pump shot and too small on IAB, performance out paced the gas setup in the 60, 330 and 660. Only moved 3-4 thousands from afternoon heat to night air where gas setup was gaining 5-7 numbers. Good manners everywhere except one, start, idle, burnout, launch, 60, 330, 660, lifting and dropping back to clean idle. Gains some heat on the run 10-12 degrees, 175-180 when turning on return road, then another 20-30 degrees back to trailer. Just as bad as the gas carbs were. I suspect he is returning with just enough throttle to cruise back using t- slots only. On the dominators I do I restrict the t-slots in the 72-78 range and have little or no heat gain on the return. On these 750’s the t-slot feed was left stock assuming they would work as is since other mods were minor. The owner is very satisfied and not complaining but I want to fix the excessive heating because it will cause problems in a round robin situation. I have no problem with drilling tapping and increasing the size of the t-slot feed. Is this the right way to go or am I overlooking something else?

ghs

what size is the idle feed restriction, and idle air bleed? how much timing at idle?

IFR 42 and IAB started at 59 but too rich and went to 66 with trim at 1 3/4 out. Timing locked at 36, tried 34 but went back to 36. Even with the 59 IAB it built heat on return road but idle was fat and didn't want to keep idling.

Well I got the 2 750s back from the owner and checked the TS hole for size again at between 115 and 120. That should be plenty if not too much so went another route. Cracked secondary's 1/2 turn to barely expose the TS in the rear (front idle only). Closed primaries 1 full turn to where the TS is barely exposed square. Maybe this will put more vacuum on the slot to richen it some. But I expect idle issues now but will see this weekend. At least they can be put back to square one if this doesn't work. May have to drill holes in primary bleeds to get them closed enough. Just need to cut back on engine heating on return road otherwise performance is better than gas and very consistent.

If you closed the blades to reduce the amount of T slot showing below the blades, then there is more of the T slot ABOVE the blades to let more air in & lean the mixture.

My hope was that it would idle with the TS only showing about .020 so that when he was at part throttle it would pull harder on the slot with less deflection on the blades. Didn't work anyway as idle wasn't stable and I had him reverse the changes. Had him double check the front floats and raise fuel level to the bottom of the check hole if needed. Mains may not be starting soon enough and on a lean hole on return road. Other than checking the float level I had him change the jets from 92 to 94. That should only be about a .003 change and we can see if temperature changes any down track. May help some if it is lower but easy to change back if it's the wrong way to go. Tried to get him to put my LM2 on but he is afraid the headers are too thin to weld on. I may start sneaking back down on the IAB's til it starts acting up on idle as I just jumped from 59 to 66. They may need smaller than 25 on MAB and smaller on emulsion than 18 and 22 so there are still things to do in small steps. Thanks for the comments.

After going back over my notes on original specs of these 750's I may have went too lean on IFR for E85 and have the IFR/IAB balance off. The reason for this thought Is because the original IFR for gas was a 39 which seems large for a 750. Maybe I should be up around 43-44 on the IFR and this should richen the TS. Any comments? Or am I still barking up the wrong tree?

Here's a followup for things I've discovered for the heating issue. After taking a close look at his cooling system I don't think it is sufficient and has some mistakes. His radiator (496) is larger than mine. Mine on a 582 (sirocco pro-stock with double sealed fans) that actually cools too much. His fan and water pump are not switched separately. The fan is not shrouded. There is no coolant expansion room built into the system. So every pass it pukes into and fills the puke can. On questioning him on differences in problems he is experiencing between gas and E85 I found out it is harder to warm up the engine than it was on gas. It still builds heat on return road but not as bad as gas was. So that makes me think the idle/t-slot circuit is not too lean. He is addressing the coolant system. ——Another issue we had was Fuel spiking after burnout and lifting at the other end loading the system by flooding. The fuel wasn’t coming from the bowl vents so we determined bowls were filling up and flooding/enriching through the rear down leg booster system. That caused us to start lowering the rear float levels until the problem went away. The car still ran better than on gas with ets only changing 1-3 thousands over an evening of racing and not building hardly any heat down track. When the weather turned cooler he started picking up a slight misfire on top end. On inspecting the carbs the front float levels were fine but the rear were on the bottom. There was so little float drop I don’t know how it ran as good as it did. I had warned him I had no experience with side hung floats on E85 and wasn’t sure they would work. The floats were changed to black nitrophyl and I used 140 bottom feed seats. There is a warning on using these on the wrong floats. So, from the rounded shape of the float and smaller surface area exposed there may not enough bouyancy for E85, just a guess on my part, and using bottom feed seats on these floats may have aggravated the problem from pressure exerted on the float arm. We are in the process of changing to an old Victor Ram 2R intake that will mount the carbs sideways (same as I use on my 582 with 1050’s). Going to center hung dominator bowls. I am successfully using these bowls with 140 bottom feed seats with no known issues on a Holley t-ram 2X1050 5 teen 588 car now. I’ll just write off the side hung bowls as a learning experience on E85. And, I hope I have drawn the right conclusions on the side hung bowls.

“After 2-3 tuning corrections, too much rear pump shot and too small on IAB, performance out paced the gas setup in the 60, 330 and 660.”

I thought I would explain this sentence better from my starting post for any interested how I determined too much pump shot from the secondary pumps. We were Friday night testing on the track watching burnout, launch and down track performance plus reading ET slip. The first pass was a 6.10 which was close to his gas times of 6.08-09. Kind of disappointing. Changing float levels and IAB and trim screws. Second pass I think was a 6.11 or 12. This was back before the season ended (still hot) and going from memory (what little I still have) but some things stuck from the dramatic change in performance. Still lazy off the line. On the original conversion I had replaced the rear 30cc pumps with 50cc thinking I would not have enough pump shot going to E85. So for the third pass I changed the rear pump cams back to the 30cc cams from the yellow 4500 cams. I did not change the pumps, only the cams and adjusted the pump arm. I went this route as a simple, quick and easy change to make so as to not lose too much time. Well this was an eye opener. The 496 was crisper and up on the converter hard when the tree started down. Launch was hard, tires slipped some but still a harder launch as Friday night gets a lot of street tires on the track. ET on this pass was a dead 5.900. Daytime temps were still in mid 80’s. Down 2 whole numbers. Owner was happy (me too) so we called it a night. Next day, points race day, on a prepped track the car ran low 5.80’s and I think he dialed 5.81 or 2 turning 6500. He made a few rounds before a red eye got him (against me no less! maybe I intimidated him a little too as I had taken over the points lead and 3 times his age to boot). In cooler weather he ran high 5.70’s but picked up a skip on top end. His performance on gas in hot weather had never been this good he said. I’m reluctant to attribute the performance gain solely to E85. I suspect his gas carburetor setup wasn’t as optimized as it could have been and I think he may have had a detonation problem from using 110 gas. I think 114 at least is what he should have been using based on what he described his engine as being. His main reason for going E85, like mine 10 years ago, was to decrease fuel costs but still be able to run a high compression engine. E85 last year ranged 1.89 to around 2.69. Now it is 3.09 but still as an alternate fuel for a high compression engine I have no complaints. So, here we are today switching from an old Edelbrock TR2X with inline carb mounting to a Victor Ram 2R and 4150 top using adapters to turn the carbs side ways to clear the 4500 dominator bowls (fuel line options) I’ve added. The 2R has some age on it for sure but they still make good power for a bracket racer who wants moderately fast but consistent performance. My 582 Camaro with the Victor 2R and 2 dominators on E85 at 2800# runs mid 5.20’s in cool weather and 5.30’s in hot keeping RPM below 6800.

George

Problem solved. Complete overhaul of the cooling system solved heating issues which I originally thought was caused by the carbs. First race of the season here he put it in the winners spot. Also it was the first win ever in his dad's old car for him. Slowest pass was a 5.91 and fastest in final round 5.885 breakout win dialed 5.89.