The previous motor we had in our car was 9.3:1, 0.500" solid cam, Torquer SR heads, single 4-barrel, run on 93 pump gas. We got a good deal on an ignition system, 7AL-2 box, Pro Power coil, switchable RPM selector, and MSD Crank Trigger, and distributor. The distributor had the advance mechanism removed, and we ran the timing locked out at 32-36*. Now we're putting together another motor, 9.5-10.5:1, 0.645" solid roller cam, AFR 210 heads, tunnel ram w/ 2-450's, also on pump gas. We're going to use the same ignition system. My question is, should we utilize some kind of advance mechanism, or continue to run the timing locked out?

 

Use an advance mechinism. Timing is not static right? If you want to make the most power incorporate an advance system into it.

 

on a lot of race only engines the timing will be locked. only way to know what's best for your combination is to try it both ways. i'll guess you'll end up locking it around 36*

 

Yep. lock that puppy down. Back in the day of Prestolite ignition systems (they were the only one around) We used a GM distributor with accell XX points. The dizz was set at between 36-40degrees of timing depending on what we were doing. The start procedure becomes:
1: Turn on the lectric fuel pumps until you read pressure.
2: Pump the pedal twice (Holley 4500 x2)
3: ignition OFF
4: hit starter button
5: as the engine is cranking hit ignition ON

The starter won't like to spin 38 degrees of timing otherwise. We had the dizz in 2 different distributor machines, an Allen and a Sun, the diz (even with points) had no problems up to 12000 rpm. (in the machine) the car never went over 10500rpm. All of that being said, today's stuff is a lot better than what we had then, but it was simple, and it worked and there's a lot to be said for that.

 

Proper race motors use locked out timing. A timing curve is for part throttle operation and should be at full advance by 3000 rpm. Drag racers operate at WOT so no spark curve is needed. If the engine is hard to start at full advance, invest in an ignition with a start retard or a seperate start retard box to retard the timing for starting.

What timing works best will need to be learned. Timing that works well in one engine, normally isn't what your engine wants. Once the best timing is found, other changes such as jetting won't change where the engine likes it's timing. Start with 36*. Move it up or down 2* at a time until the best MPH/HP is reached then move on to the rest of the tuning.

 

We've driven the car on the street every once in a while, never on the highway though. Probably put less than 30 miles on it in a year around town. The compression isn't sky high, so hopefully the timing won't be too much on pump gas. My main concern was running the motor from idle-3000RPM with all that timing in the motor.

 

With the engine combination you are proposing you will never see idle to 3000 rpm anyways. That tunnel ram won't even start making power until 3000 rpm and with that high a lift you are building a high rpm engine. If your car is an auto you are going to need at a minimum of a 3200 stall or the car is going to be an absolute dog of the line. Also you're going to need some tall rear gears like 3.73 or higher to get you past the stall flash. If your car is manual you just will need a good clutch because you're going to be letting it out at 3000 rpm or so. I wouldn't worry about it being locked out, you'll never be at a low enough rpm to need a timing advance mechanism. Your only problem may be the starter, if the starter won't turn it over, just get an MSD start retard for it and you'll be fine.
Jeff

 

3000rpm? dude, run it up to 7 grand and sidestep the clutch, launch it like you mean it. That's why they make speedy-dry.

 

I was thinking more in the 4000-4500 range to use the tunnel ram and high lift cam to it's potential.

Nothing saying what you want to do won't work but your combination of parts are not being used to their full advantage.

High lift cam, good heads, tunnel ram. Then you choose 2 small carbs and low compreesion. If it's race motor only, then bump up the compression to at least 12:1 and use a couple of 650's or 750's on the tunnel ram.

 

Very true on the stall, I guess we have too little info on the intended use and actual combo to be making good calls on this. Whats the CID of the engine?
How about the duration of the solid roller?
Whats the rest of the combo? Tranny-rear gear- intended stall-weight of the car, this is all very important to making a good combo. Just opening a summit catalog and ordering big parts will end in disappointment, (not suggesting this is what you did).

Jeff

 

I'll try to clear some stuff up. The motor is 355 inches, 5.7" Eagle rods with L-19 bolts. The deck height is 9.025, so it'll be hard to squeeze enough compression out of it with the pistons I already have. If I use a 0.028" head gasket, compression will be 10.15, if I use a 0.015" head gasket, compression will be 10.47, all with the 66cc chamber that AFR comes with. 1.5 Roller rockers give 0.645/0.630" of lift, and 260/264* @ 0.050". The cam has an advertised RPM range of 3000-7000, which is exactly the RPM range I'm shooting for. The manifold is a Weiand Street Ram, which we got, with carbs, for a good price. The carbs might not be ideal, but for the price, we're going to use them, for now. We have 2-750 double pumpers, but I'm thinking they're too big for the CID and RPM range. This is not a race-only motor, but 90% race / 10% street motor, on pump gas. The trans is a 4-speed, 4.88 gear, and weight is ~3200lbs. Will probably be leaving at 5-6500, shifting at ~6800. I'm sure the car will never see <3000 RPM on the strip, but it will on the street. Likewise, I'm not concerned about the timing on the strip, but that much timing below 3000 on the street is what concerns me. Already looking into the start retard. Parts-wise, most everything that we plan to use has a good reason behind it. Any more suggestions?

 

Ditch the tunnel ram and go with a good single plane with tall plenium. Go faster with less headache. Tunnel rams on any type of bracket car are few and far between. Index racing or heads up it's a different story, but those motors are a whole lot bigger than what your proposing. Only been at this bracket racing gig for 4 yrs now and can honestly say in the 4 tracks I run, never ever seen a tunnel ram in the winners circle. Not only that but based off your heads/cam and rest of combo you'll be down on power since your static compression is already petty low, throw in the aluminum heads, you just stepped down roughly 1 point of compression due to excellent heat transfer and then add your big duration cam and cyclinder bleeding, your not gonna be going anywhere very fast. minimum 5K stall also!!

But to each his own. Good luck.

 

i ran a 9.8:1 comp motor on the street on 87 octane and timing locked at 32*. i got great mpg (18mpg) on the freeway and horrible(6mpg) on the street. i ran a 3200rpm stall and a 650cfm dp with a vortec head and 240/246* duration compcams xe284 . throttle responce was crisp, and it started instantly with a slight hit of the throttle. i consider myself lucky..........