tips for getting lightning-quick throttle response?

by fishhead Thu Dec 04, 2014 12:23 am

Just compiling info for a hot street motor project and looking for generic tricks racers use to get hair-trigger,snappy throttle response from a Holley 850 double pumper?

by bracketchev1221 Thu Dec 04, 2014 1:18 am

First make sure it is the right size for the engine in question. Too big and it will be lazy. Without the right air velocity through the carb, it won't atomize correctly and run rich at idle and not clean up until higher rpm.

by fishhead Thu Dec 04, 2014 2:37 am

Thanks.I have a race ignition setup to help keep the plugs clean at idle/low rpm and .456 gears with 4000 stall converter to get things moving quickly.

by bracketchev1221 Thu Dec 04, 2014 5:11 am

How big of an engine are you looking to build, what intake, what cam? The ignition is not going to correct the carb. And if the car is a footbrake car instead of a transbrake car, low rpm response is crucial.

by Joe73 Thu Dec 04, 2014 7:03 am

Definitely carb and its adjustments. And fine tune the ignition timing.

by fishhead Thu Dec 04, 2014 1:04 pm

I'm researching roller cams for a 406 with a super victor intake and dart 215cc angle plug iron eagle heads.Leaning toward a solid roller but it's a challenge reading all the pro's/cons of a solid roller on the street.I'm building a toy for local cruise-ins/ car shows so I don't care about street manners.I was thinking of a transbrake but I've heard that's a no-go on the street so I'm researching that also.

by Oldschool454 Thu Dec 04, 2014 1:33 pm

fishhead wrote:I'm researching roller cams for a 406 with a super victor intake and dart 215cc angle plug iron eagle heads.Leaning toward a solid roller but it's a challenge reading all the pro's/cons of a solid roller on the street.I'm building a toy for local cruise-ins/ car shows so I don't care about street manners.I was thinking of a transbrake but I've heard that's a no-go on the street so I'm researching that also.

Ask Johnny Hunkins from popular hot rodding about a solid roller cam on the street at lower rpm use. lol! They had one in their project laguna and driving it everyday it eventually got too hot and blew out one or some of the roller lifters and sent the little roller bearings all through the engine ruining it. But...that was just that case. Who knows. If you only drive it weekends and such you may be fine. Was an interesting story though.

by fishhead Thu Dec 04, 2014 1:54 pm

Haw! Yep,that was a tragedy I would rather avoid given the fact I don't have anyone providing parts and labor expenses.Sometimes I'm tempted to sell all my race parts and settle for an old school 454 with a mid-level hydraulic flat tappet before I die of old age.

by Joe73 Thu Dec 04, 2014 2:05 pm

Just curious. Why isnt a transbrake.good for the street?

by Oldschool454 Thu Dec 04, 2014 4:05 pm

fishhead wrote:Haw! Yep,that was a tragedy I would rather avoid given the fact I don't have anyone providing parts and labor expenses.Sometimes I'm tempted to sell all my race parts and settle for an old school 454 with a mid-level hydraulic flat tappet before I die of old age.

My 454 had 3 flat tappets through the course of 1 1/2 years and every one had lobes wear down on them until after the 3rd one I got so frustrated I saved up $ for over a year just to get the kit to convert it to a hyd roller cam. I did a text book engine break in and everything. Needless to say I'm weary about going back to flat tappets on big blocks but I know there are TONS of them out there with no problems so who knows what the deal was. I had one phone tech even say it could be bad metal they were using in the cams (crane cams) because they had been bought out by some other company recently at that time. But after swapping to my hyd roller I've had ZERO issues with it the past 5 years and still running as strong as ever if not better. It's made me a real follower and believer of roller setups. But yeah nothin like an old school big block with a simple flat tappet.

by dynchel Thu Dec 04, 2014 4:44 pm

A little weight reduction helps also. Remember these cars are lead sleds..... tongue

by bracketchev1221 Thu Dec 04, 2014 8:12 pm

Transbrake on the street doesn't do anything. Put a toggle switch in line with the power button so you can't accidentally bump it and you are fine. A manual valvebody transmission DOES tend to lose the engine braking function, so be aware of that while stopping.

Now on to the other questions. An 850 will be fine on 406, its a little big but can be made to work. I ran my 850 on a 615 hp 383 and it worked. An 850 on a 406 can handle over 7000 rpm. Generally you can get away with a 30 cc on the front and 50 cc accelerator pump on an 850. Though I have run twin 30's on mine with a transbrake and a 2 step rev limiter. The only things I have ever had to do was put a lower powervalve in the front with a decent size roller cam and I like to eliminate the rear PV and bump the jets up about 8 sizes. After that, depending on if it will idle or not, you can either drill small holes in the primary or install an adjustable secondary bracket and crack the rear. Keep the initial timing as high as you can get it and it should be clean. If you still have an off idle stumble then you can mess with squirter sizes and MAYBE a pump cam.

The issue with solid roller vs hydraulic is that the solid generally requires spring pressures in the 200-220 on the seat and 600 open. This tends to make it hard to keep them oiled at low rpm because you don't get the oil splash. But a lifter with pin oiling helps alleviate this. Another thing that I feel helps is a rev kit. It is a set of springs that goes between the head and the lifters. This keeps the bearing needles always loaded and rolling instead of skipping.

by pila Thu Dec 04, 2014 10:22 pm

Do you plan on using 5.7 inch rods ? The 5.565 on the 400s didn't seem as strong to me as the 5.7 inch. I used the 5.7 and pistons to match. Of course the hi performance folks don't make the good rods in the 5.565 inch length that I know of....(?)
And the 5.7 will have slightly less of a rod angle also...

by mc71454 Fri Dec 05, 2014 12:42 pm

I have a great trick for the timing curve..

fill in later, gotta run to a meeting

by fishhead Sat Dec 06, 2014 12:23 am

Thanks much guys,I have a nice new set of Scat I-beam 6" 4340 rods with 7/16" bolts for this build if it ever gets off the ground.All this info is a huge help.

by pila Sat Dec 06, 2014 6:36 pm

4340 is strong stuff ! Sounds like you have all the ideas you need for a strong engine !

by bracketchev1221 Sat Dec 06, 2014 7:24 pm

Are the Scat rods the Pro Stock or Pro Comp series with the polished sides.?

by fishhead Sat Dec 06, 2014 10:30 pm

They're the Pro Comps with the polished beams and capscrew rod bolts.They're really nice for the price.The bad news is i gotta dig up more dough for a Scat forged internally balanced crank,not sure I want to gamble on a oem or cast steel.

by pila Sun Dec 07, 2014 12:38 am

The steel cranks were replaced a long time ago in the stock engines, likely because nodular cranks were lower cost to produce for stock engines. There was a nodular foundry here some years ago. It was only here for 23 years, and they tore it down. Just another GM plant among 5 or 6 that bit the dust here.

by fishhead Sun Dec 07, 2014 1:01 am

Ouch...Sure do miss the good old days when jobs were plentiful at the automotive plants.I traced my VIN on my two G3's and the Laguna was born at the Doraville,Georgia plant and the 73 malibu is from the Texas plant,I guess they decided to stay close to home.

by bracketchev1221 Sun Dec 07, 2014 9:03 am

I had the pro comp rods with a je/srp piston in my nova. I would agree if it was me, for a build in the 400-500 range I would go with a scat cast crank. But for anything over that I would use a forged crank. I used an eagle in my nova because it was a little cheaper. There is nothing wrong with either. I have an eagle in the chevelle.

by fishhead Sun Dec 07, 2014 12:49 pm

I agree the Eagles are good enough and the prices are merciful on the average hot-rodders wallet.(I fall in the PB&J for supper category).My 850 dp was built by Biggs and was tuned for an IMCA Modified engine so calibration is going to be interesting for sure.On the bright side it was never installed and is fresh as a daisy.

by bracketchev1221 Sun Dec 07, 2014 2:07 pm

The engine in the chevelle was dynoed in January at 910 hp on an eagle crank. I would expect the carb to have good drivability figuring its set for driving out of the corners. It may only need a notched rear float and rear jet extensions. Possibly a new front float but you would have to check. Sometimes they put angled floats for circle track with the lateral g forces in the corners.

by fishhead Sun Dec 07, 2014 3:45 pm

Definitely an audible whistle here on your dyno numbers and a humble appreciation for sharing your knowledge of carb tuning.The carb has #78 jets and a 3.5 power valve in the primaries and #86 jets with no power valve in the secondaries.I'm thinking the same as you about the oval corner acceleration/stall converter peak torque crossover.My switch-pitch converter should stall between 3800-4000 so I'm predicting it will hit right in the sweet spot of the torque peak if I can choose the correct cam for my combo.This build project is constantly evolving as I learn more about all the small details that go into obtaining "optimum volumetric efficiency".

by bracketchev1221 Sun Dec 07, 2014 9:25 pm

3.5 pv should be perfect for a large duration cam. I used a 3.5 in my 850 and put one in another in my friends pro systems carb to clean up an off idle
stumble.

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