FrontEngineDragsters.Org Forum
Technical => Matt Shaff's Engine Shop => Topic started by: denverflatheader on February 17, 2013, 04:16:26 PM
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Hi Matt, my name’s Alan. Got a question, a few have asked me and I really don’t know the answer. I started a twin engine dragster build in 2011, powered by V8 flatheads. The engine coupler design and fabrication was done by Landers Engineering in 2012. They also splined crankshaft snout for coupler. For my question, assume both engines built identical and dyno 250hp-300 ft. lbs. torque.
For back engine connected to transmission, that’s 250hp? For front engine, connected via coupler, does that add another 250hp? Would total be 500hp and 600 torque? Will it hurt either engine’s internals or balance if they do not output identical hp and torque? Do you have suggestions on clocking both engine crankshafts, like cylinder 1-1 together or……?
Here’s close up picture of coupler and at car show under construction. Thanks for help and forum. DF
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Denver:
Can't say as I have ever been involved with "twins".
Keith [Roo-Man] can jump in here and help with this one.
The car is short and motors in the rear so it looks like not much flex in between the engines like a front engine car.
Horsepower wise it makes sense that you will get double. 8)
Lots of top gas cars from the sixties did well with "twins".
Good luck: Matt
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Matt – Yes, 1.50” top/bottom rails, a little bit stiff….... but not dead : ) The est. hp is 2.5 times higher than stock engine output. Key ingredient is camshaft and ignition for fh (one internal component, one external). One friend told me his gas dragster went 171 on blown gas, he never forgets his mph, but couldn’t remember et as well, somewhere in the mid 8s. What's important different for each of us. Thanks Matt, will see if Roo comments. DF
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Clocking. That's a very interesting question. I wonder if there would be any noticeable difference in the effect of two cylinders firing together, such that the rearmost output sees their power combined at the same time, versus staggered so that the same flange sees twice as many evenly spaced single hits??? And could there be any bad effects as far as rapid and repeated loading and unloading at the coupling in the case of staggered firing??? Such that the splines might either stay loaded in the first case, or force reversals make them beat themselves up in the other??? And was the coupling timing designed and installed with any of that in mind???
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janjon - coupler design allows almost infinite settings to clock the two engines. I’m thinking of starting with both engines on #1 tdc. I was thinking if the two engines don’t like where they’re clocked, maybe it’ll show up in the main bearings, and also in the ets…. DF
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This is an interesting question, it would be nice to try and clock them so that they try to smooth out the power stroke "pulse". In stead of a 12 cylinder Jag, you have a 16 cylinder American monster.
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Glenn - 296moon's twin 455 olds..... that's the real 16 cyl. monster! He's got lot's more cubic inches and half the wb... got to admire his thought process : ) DF
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Glenn - 296moon's twin 455 olds..... that's the real 16 cyl. monster! He's got lot's more cubic inches and half the wb... got to admire his thought process : ) DF
this one is not bad either
(http://www.buicks.net/misc/images/Ivo_Cover.jpg)
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In 1970-72 I had a dual BBC Top Gas Dragster. When the chassis was 1'st built the engines were hooker together with sprockets and HD chain. We, Parisey-Hansen team, ran it that way for the 1'st year, but when we wanted to cut the chassis to make room for a rear engine blower drive, we converted the engine couplers to the type used on rear-ends now. Couldn't see much of the coupler because most of it was inside the rear motor lower blower drive. We ran in the sixes and 225 mph on gas, with no signs of wear on the coupler, even tho we were running the current Top Fuel tires. We tried different clocking, mostly trying to even out the firing, but we found no improvement in ET's. So we just set both engines at TDC, for easier tuning. Which was confirmed by Walt Austin when we talked at a GoodGuys race in Seattle about 2006. One thing that we thought helped our combo, was the front motor was a 396 ci out of our single engine BB/GD we won class at 69' US Nationals, and the rear motor was a tall block 472 ci.
The idea was one motor made bottom end power and the small one made higher end power. We beat the "Freight Train" at the 71 US Nationals with that combo.
Have Fun with your new project !
Jon Hansen, 800-624-3803
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John do you remember Richie Shott from the east coast ? He ran top gas
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JrFuel Hayden - very useful information, certainly clears the water. "71 US Nats... Freight Train, wish I could of been near the starting line to seen that race. Thank you DF
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Thanks Jon! Good info and nice pictures.
Welcome to the Front Engine Dragsters forum. Your knowledge will be very valuable here.
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This is on my "to do list" 8)
I have heard you should clock the crankshafts 22.5° apart, so the rear crank only endures one powerstroke at a time.
i have also gathered that its not hp+hp, but more like hp+hp x 0.75.
For scientific facts, I've got nothing.
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Magnus, I agree 22.5° makes sense if only to allow the cranks to live longer. In 70-72 there were no RacePak computers like I use on our NHRA Heritage Jr Fuel now. I would have loved to have all that feedback that I get now, back then. So clocking the cranks may be a good idea on flat heads, since there is a big difference with Flat Head cranks and BBC cranks.
When ever we raced the Top Gas car we always were asked "doesn't one of the engines hold back the other" but we always thought the extra engine added to the rear engine, "cup half empty vs cup half full" stuff. Again we didn't have any crankshaft issues, just valve train, because we were always trying to run more RPM. Like when we had a match race in Minn in 72, and we ran alky and it went real fast MPH and the motors got up over 10,000 rpm, = bent valves. Ah, another learning curve !
Bill, I don't remember Richie, but then again we never ran further East than Ohio back then, since I was living in Milwaukee Wisc.
The furthest East I ever raced was EnglishTown driving Jerry Newman's Top Fuel John Buttera build RED on the way to our 73' Div 3 Top Fuel Championship. Yes, "back-in-the-day" NHRA used to race Top Fuel at Division events.
Maybe they should offer Nostalgia Top Fuel and N/FC to run Div races, that would put "butts in the seats".
Good Luck with the Flat Head project.
Jon
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I have heard you should clock the crankshafts 22.5° apart, so the rear crank only endures one powerstroke at a time.
i have also gathered that its not hp+hp, but more like hp+hp x 0.75.
For scientific facts, I've got nothing.
Maybe not scientific, but sounds pretty darn logical from an "eyeball engineering" standpoint. Which is all I have to rely on...