Timing chain vrs Gear drive

so guys i thought i would educate myself with some opinions of my hotrod (experts)and i use this word loosely. My million dollar question is for my 347 rollerized engine ,what is better a double roller timing chain or a geardrive for a engine running 6800 to 7200 rpm ? cheers Outlaw Jimmy2gates

 

Have used both and really not seen much difference. The dogbone idlers are just a few more things to cause friction and having to modify the inside of the cover(very simple to grind off the extruded piece of aluminum) does not warrant the xtra bucks IMO. For a mean sound on the street, they are great, if you get the noisey one's. Performance is nill, compared to a "Good" dbl. roller set, and engine HP and rpm are not hampered by having to turn those extra gears. Not that much is lost but every little thing is calculated into finding more speed etc, on the track.

Thinking they are better than a chain is everyone's own deal, and may improve the mental attitude of the driver etc. Kind of like when you really detail your car out in the summer, they always seem to run smoother and better afterwards. If you want them go for it, it's your decision to make.

 

Very good read.

 

That's what I said, without the exact numbers, cause every engine is different on the dyno. Course I am just an old retired engine builder who does not have money or place to get dyno readings to compare figures. For the average Joe racer who has limited funds instead of bottomless pockets, the simple explanation and opinions from others, will suffice.

 

the simplist explanation is this:

Gear drives are expensive. They also eat up HP. Cover mods have to be made. Sometimes the fuel pump eccentric won't fit. They are noisy and abnoxious.

Chains: they bolt in with no mods, the pump eccentric fits just fine, use less HP to run them and they cost a LOT less. They're also quieter.

Sounds like a no brainer?! That said, if you're going to gear drive, you can probably find a cam company to grind a reverse rotation camshaft, then run a gear-to-gear setup (with no idlers) like some sprint cars use. Then you'll have the ultimate in timing accuracy, but also the ultimate expense.

If you MUST have the absolute best, get a belt drive but be prepared to fork out $1000+

 

I've never had a gear drive. Looked into it, but everyone i talked to said stick with the roller chain.

 

If it were the 1980;s I would say go for the gear drive. I installed some back in the day cause it was the in thing. Nowadays we know the double roller is really the way to go, unless of course as stated before, the belt drive is the way to go if money is not a factor.
Dan

 

Belts and chains stretch and wear out and the gear drives will last a lot longer. They do make noise and they do cost a little HP but they are overall more reliable and stronger if you are going to run big valves and a wild camshaft with high spring rates. As gears wear-in the hp loss decreases and the noise does too. Distributor timing is more accurate and that means your tuning is more consistant.
There are plusses and minuses with all the differnt cam drive methods. Get to know all of them and then make your own choice.

 

Gear drives cause alot of BAD vibrations in the motor and are hard on the crankshafts, especially at higher rpm's! Most engine builders say not to use them...

 

I have heard engine builders say that the gear drives can transmit unwanted harmonics to the valvetrain and cause spark scatter with cam-driven distributors. Probably for a strictly low rpm street engine it wouldn't matter much.

 

There are some nice belt and gear drives to choose from, but a good double roller will do the job, and for far less money.
Rollmaster timing sets with Iwis chain are as good as they get, pre stretched German chain.

 

Id personally go w/ a double roller... Very inexpensive, very easy to install.

As for the sound of a gear drive... hate them.

I dont have the $$ for a belt drive so that rules that one out.

I've seen very fast cars run regular ole double rollers and never had a problem with them. Todd and Dave are prime examples... both fast cars and I dont recall an issue w/ them ever breaking one... usually the blocks break first

 

Wrong. A quality roller chain and gears will outlive a gear drive every time.

Double wrong! See this answer for the correct information......
I have heard engine builders say that the gear drives can transmit unwanted harmonics to the valvetrain and cause spark scatter with cam-driven distributors.
This is what happens with a gear drive. The chain will stretch an infinite amount due to the spring pressure but a gear drive won't. Guess what it does? It tries to move. When it can't move it begins to eat itself all the while it is transferring harmonics through the camshaft into the valvetrain. Why do you think serious race engines use a belt drive?

 

how can so many of you hate the sound of gear drives? i think you're all crazy, they sound awesome!! but sound isnt what i build my engines for so i stick with 2x rollahs

 

I just scanned through the responses quick, but I will say that I have used both and so I comment.

I read a comment about a drive using up 15-25 HP.
I know they have more parasitic loss, but I seriously doubt it's anything like that.
Very dubious of that figure!

I used Pete Jackson for a long time in a 306 and loved it.
That said, a true roller is probably the best thing to use for every ounce of power.
My engine revved fast and high, so I can confidently say I didn't have harmonics issues. The idlers are very free moving and balanced, so I didn't see them wearing funny or binding in such a way that I felt nervous about harmonics.

I say if you want the sound, don't be scared of a gear drive, but in all truthfulness, the true roller is more practical. Make sure you get a full on roller chain though.
There are slight differences in chains that I have noticed that will make some more efficient than others IMO.

I would use a drive again, and will eventually.
They sound very sexy in a Ford engine due to the aluminum timing cover with integral water pump. It tames the gear noise to a very pretty whine/hum.
Don't listen to a Chevy and think that horrible broken chainsaw sound is what you get with a Ford. The divorced water pump and steel timing cover make them sound like pure $hit on a Chevy!

My .02
Dave