Actual track results - diff vs. spool

Anyone have actual track results going from a good functional differential to a spool without any other changes ?

Same ratio, tires, etc.

I didn't see any change

I went from a 742 cased 8 3/4 with an Auburn cone sure-grip and 3.55 gear to a Dana 60 with spool and 3.54 gear. Car ran identical to the hundredth despite 50 lbs. weight gain.

Very typical for a 8.75 to Dana swap.

I saw no difference. Back when my car ran 11.40s w/ an 8.75 rear and a stock suregrip. Broke the suregrip, so I upgraded to 35 spline axles and a spool. Ran the same as it always did, although it was easier to drive...wandered less through 1st gear due to the equal distribution of power to each tire.

Thanks for the replies received.
That answers my 8-3/4” question.

Now - going from a standard Dana limited slip to a spool.

Best I can remember the weight difference was around 40+ pounds.

Been bench racing and using the Wallace Calculators on the engine side of things.
Now trying to figure out how much if any one would expect to lower their e.t. by

1) Going from 11” drum brakes to drag race weight disc brakes
2) Merge collectors vs. standard
3) Eliminating the water pump drive ( going to electric drive drive )
4) Eliminating the mech fuel pump
5) 904 vs 727 with 2.45 low gear. ( heard .10 e.t. reduction )
6) production windage tray to scrapper ( heard 18-20 hp)
7) 70’s era stock eliminator cheater cam to current designs allowed with higher spring rates, etc.
8) Diamond piston versus old cast piston used in item 7

If anyone has real world testing results I would appreciate your responses.
If no actual track testing then actual dyno test results would be helpful too where applicable
Vehicle is old stock eliminator 69-1/2 car.

What do you expect the merge collectors to gain?

I'm not sure the water pump is that big a deal, especially if the electric deal you have can't control the coolant temp.

Nothing to be gained by losing the mechanical fuel pump if it was keeping up.

I run a tray and a scraper. RPM and oil control are big factors in how much improvement you can find with stuff like that.

Changed to a spool in my dana back when the Barracuda was running mid 11's . Didn't notice any change from the change.

Based on some feedback so far all the stock eliminator cars using merge collectors are wasting their time. Same with all the guys that went from simple belt driven water pumps to electric, dropping the mechanical pump, spool, etc.

Last time I ran an engine on the dyno just going from no collector extension to a longer one picked up 18 lbs. ft.

Sounds like all these “improvements” only lighten up one’s wallet.

Thanks for the comments so far.

went from a diff to a spool.....did not break the spool that was the change I saw

When I bought my car about 30 years ago,it came with the spool that is still in the car.I did remove the 5:13 and go 4:10

This is most likely a case of “the whole is more than the sum of the parts”. “High performance” is usually not a piece by piece equation.

When we do testing we don’t make 9 changes and hope for an improvement.

Oh well, onward and upward.

I asked about the collectors because I think there is way more to it than just the merge collector. Calvin Elston has written on this a bunch.

It's more of a thought process that actually starts with the intake tract and works its way to the collector. It's all about making the intake more efficient by using a smaller exhaust valve and working your way out. The smaller exhaust allows for a bigger intake. Then you have to engineer your way back out, including cam timing, to the header pipe (which he says should be the exact size and shape of the port) then out to the collector.



It's as much an art as it is a science when you are working with the exhaust side of the engine.

That’s not what I was suggesting at all. It is more than plausible in my opinion however that you could measure each of these modifications in a vacuum by themselves and see no improvement with any single one of them. But when the right ones are hooked together; bam...... a full tenth.

My favorite was a buddy telling me my K&N airfilter was a huge restriction.

Ran 11.41 with it, next run ran 11.41 without...

My buddy Mike tried merge collectors on his Slant stocker. He said they made little difference on the dyno, but picked up .02 in the 60'.

Every car i have raced went from stock waterpump and fan setup to electric water pump and fan at some point in its transformation
Every car picked up right around a full tenth. It isnt myth. My brother few years did exactly the same, in fact we made the swaps the same week on both cars we had at the time. He in fact still has that one. We bith went personal bests after the swaps with those cars

Just 3 years ago my 318 equipped 71 Duster( not grandmas 318) ran a best of 11.79. Raced the car several years.
One outing at track took off all the stock belts, pushed the car to the line and went 11.66 with it. Had power steering too. Also unhooked that
I know for a fact because i have done it on multiple cars/ combo’s that electric water pumps and fans pick up ET a good bit over stock. Zero doubt about it.

Merge collector testing can be a day of dyno testing on their own. A lot of stock eliminator guys run them, but they'd be custom. The generic ones from Dynatech etc etc have mixed results from what I've seen.
They are one thing I am going to play around with on a factory headed 360 I have. With any luck we will dyno before Christmas, after I get home from PRI.

I have done a lot of work with merge collectors and I can tell you they do work, BUT (there is always a but) if you think you can buy a merge collector off of eBay and pick up a bunch you are going to be disappointed. On my engine I built a set of headers and after seeing the results ordered a new camshaft, made more power with less exhaust duration and the exact same intake lobe. Didn’t go far enough.

So as to not to hijack this tread anymore, let’s just say if you see any carbon in the intake track you can made some power with a merge collector but you’re going to have to let go of some old wives tales (yes, I know that is sexist).

Joe

I see your point now, thanks for clarifying. And yes, I agree with you now.

Don
Which fans were you running?

As pointed out already the stock fans and belts draw about a tenth on small blocks - and back in the 70’s it was common on a few cars to purposely misalign the alternator so in a burnout you would blow the belt off, effectively running down the track without the belt.

Usually done on class racers or when running a tight race against a similar class car in the eliminator.

Back then the rules said everything had to be stock and hooked up. Rules didn’t say they had to stay hooked up - another “read between the lines” interpretation.

Electric fan= Derale..... nice unit......Moroso billet water pump

Stock was stock production fan setup and waterpump

Thanks.

I have the MP viscous fan kit on my Dart and am curious if there was enough gain to justify the cost to change over. My deal is street/strip so if I changed it would have to work on the street too.

I changed too much at once to do a back to back on the stock water pump vs electric. But the quick cool down between rounds is priceless, I can be ready for another run in minutes. I have also had no problems on the street.

the issue with making changes you have to do a-b-a testing and do at the same track on the same day. merge collectors and step headers might require a cam change also, so much is related to each other you cant say joe gained a tenth so I should, this is especially true in stock eliminator type cars its the whole package not just one part

Few companies make them any more, but I have had some decent results with the 4-2-1 type collectors, they pick up the low end torque. I built my current headers and used a set of Hedmans on it and they are about 1/2 tenth quicker. compared to a standard 4 into 1 style collector.

I have done water pump and fan at the same time, never one or the other at same time.

My notes below

1) Going from 11” drum brakes to drag race weight disc brakes
My experience was going from ten inch drum brakes to four wheel disks, I saved forty pounds but did not pick up any ET or MPH that I could tell. However it sure stops a lot better and I would do it again. Dual calipers on the back are very much like having a transbrake.

2) Merge collectors vs. standard
I have them on a 2 hp per CI small block but no AB tests.

3) Eliminating the water pump drive ( going to electric drive drive )
There is a good episode on "Engine Masters" where they tested this, big gain if I remember plus the ability to cool faster between runs and mentioned by Bad340Fish. Meziere would be my choice if for no other reason their great support.

5) 904 vs 727 with 2.45 low gear. ( heard .10 e.t. reduction )
The low gear may or may not help you but the 904 is worth at least a tenth.

8) Diamond piston versus old cast piston used in item 7.
In my opinion anything you can do to raise the compression, use thinner rings and have lighter recpicating weight will help. Even at the same horsepower things that will help the engine accelerate faster will help on the track. (My opinion).

You did not mention it but in my experience, documented on the dyno, vacuum pumps make horsepower in engine with gas ported pistons, thin rings and low tension oil rings. Your mileage may vary.

Good luck and let us know your experiences.

Bill Lamb

Getting rid of the stock clutch fan, but keeping the belt driven water pump dropped my ET a tenth on a high 11 sec combo.

Going to an electric water pump over a belt driven pump (electric fan already installed) dropped the ET another tenth on a mid 10 sec combo.
These tests were all done w/ 440 engines in my cuda.

Do it, leave it off for quicker warm ups, cools stupid fast between rounds or after you park on the street and the et gains are real as others eluded to me included picked up a couple tenths going to elec. fan and pump.....

Trans man, you will probably not pick up enough ET to be measured at the track by swapping from a posi unit to a spool as long as your tires are within 1/4 to 3/8 inch of each other on the circumference
I didn't see any gains at the track by swapping to a spool on my old M.W stocker with the 8 3/4 third member, the spool was a "lightweight" racing spool also
The special lightweight racing 30 spline spools are heavier than the same brand and model of the 35 spline spools are also, maybe do both changes at the same time to get better, stronger axles also

I remember an article by Cecil Yother (maker of leak down testers, torque plates etc.) saying a limited slip differential was quicker than a spool in his high 10 second 70 cuda.

I don't recall many other details from that article except that it was flat top piston, iron head 440, auto trans. I'm not even sure what tire size, but I think it was leaf spring equipped ....I wish I could find the article.