A little more Horsepower
 

What are your best recommendations to squeeze out hp from your engine?

Interested in the cost/benefit analysis, for example: new AFR heads will get you 50 hp but it will cost you $1,800. Stuff like that..

Thanks.

Have you already decided that peak horsepower is your primary goal? I ask because producing big HP numbers often involves shifting the torque curve higher in the RPM range. Is that what you want? Or do you want more grunt at mid-RPMs to make driving around town more fun?

You're right; peak hp is not really the goal; as you put it, more grunt at mid-rpms would be better...

OK. Next question regards your current engine. I see it is a 351 W. Is it basically stock? What is the starting point for making it better?

You have an ERA FIA. Webers will give you a good kick in the butt difference. They aren't cheap but make a big difference. Cam change can make a big difference for a few bucks depending on what you are currently running.

Post the specs of your engine, ie your heads, compression ratio, displacement, cam specs, carb, etc. Without knowing anything about your engine at all, a kick-in-the-cam is usually the most noticable mod you can make.

Changing the carb. might do it. Way easier than changing a cam.

True, but chances are his engine builder properly sized the carb for his engine. If he posts his specs I'll plug them in to some of my software dyno simulators and then he can see what different changes will do to his torque curve. Those programs aren't perfect, but they tend to be more right than wrong. I think with a small block he can change the cam without having to pull the engine -- although I don't know that for sure. If so, a cam swap will surely cost less than a set of Webers.

fastd

I build my first motor a 302 in 2000. Each year I would upgrade and gain a little horsepower. I had it dyno'ed every year so I would knew what I gained or loss. Two years ago a bought a 354 stroker kit, new heads, cam and a lot of other parts. Last year I removed everything but the short block, called Keith Craft and told him what I wanted. "450 horsepower that was streetable". I drive my Cobra to the London Cobra Show every year and do a lot of cruising. No racing. But I don't want to embarrassed at the light.
I bought a custom cam ($300)and heads ($1700) from Keith. Bought the rest of parts from various places and put it together. Got it dyno'ed, 402 rear wheel hp and 416 tq. which was about a 80 hp gain. Very, very streetable. Best motor I ever had. Best money I've spend on my Cobra. Should have done it years ago. Would have been a lot cheaper.

I would call Keith or one of engine builders that hang out here on CC and tell them what you have and what you want.

Dwight

Guys,
Thanks for your responses.

I bought the car about 6 months ago, don't have a ton of info regarding the build but here is what I have:
351w
Holley 4160 750 cfm
Hydraulic cam; 224 intake, 234 exhaust, 500 lift
9.8 compression Wysco pistons
Dart cast iron heads
32 degrees of advance
found a receipt that said 365 hp @ 5800 rpms

I have started 2-3 gallons of 111 race fuel and the engine runs so much better; I have been looking at ways to increase air flow; starting with the basics:better/bigger air cleaner and exhaust, asked Patrickt about his turkey pan. Not that excited about changing the cam; I like the way it drives around town...

Planned on getting chassis dynoed today to see what a good tuning will do, but rain from Ida kept me indoors today; will try next week.

Sounds like a lotta Carburetor for that engine unless you are really winding it out a lot of the time. Something more in the 650 range might give you better response.

The first 400hp are pretty easy. Just about anybody can do that in their garage. It's the following smaller increments that are more difficult and more expensive.

Once you put the parts together, you have to spend time and money getting them all balanced and tuned properly. Don't be afraid to spend money at the dyno for a real tune, not just a power run.

I think you have too much timing; but it could just be semantics.

If your base timing is around 10-12*, and you add 32* of advance, you have 42-44* of total timing. Waaaay to much. And that is probably why it ran better on race fuel. Most SBF's tend to best around 34-36* total. Set base at 10, and 24* in the distributer and see what happens. You can experiment by moving the base up to 14* - for a total of 38*.

Carb is maybe too big, but maybe not. I'v seen lightly modded 351W's do very well with a 750 carb. Your dyno time will tell you what to do there.

The cheapest and easiest power usually comes from compression. Change the pistons and get compression up to around 10.5'ish. That much compression at low altitude needs carefull tuning, and conservative timing; especially with cast iron heads. But it does make good power.

You can shave the heads for more compression. But that changes valve train geometry, valve to piston clearance, and changes the swirl pattern.

Changing the exhaust might be difficult to do. Depends on what you have, though.

Take a close look at your air cleaner. The thin Cobra oval air cleaners really cost you power. Use a round one, as tall as possible. And use a K&N filter top. That's usualy worth a few ponies right there.

Doing a little guess-work I can get those specs on the software dyno to put out maybe 350 at the flywheel, which will get you under 300 at the rear wheels. Do a dyno tune, see what your actual numbers and torque curve look like, and you can go from there. I believe the "sweet spot" in a Cobra is the 450 to 475 horsepower range (flywheel). That's easily done with your engine, but you're going to need new heads and a cam; it will still be very "street friendly" though. That's not terribly expensive either.

BTW, when I say "450 to 475 HP at the fly" that means that if you pulled your engine out of your Cobra, put it on the dyno with your sidepipes attached, and your water pump is pumping, and your belts are turning whatever accessories you have (at least an alternator), your numbers should be over 450HP. We all know the different tricks you can play with a dyno, but that's what I call "an honest 450 HP.";)

It sounds like you like the mild manors of the cam. If it is flat tappet, changing out to a roller cam will give you greater ramp rates, which gets the valves open sooner and keeps them open a little later, at the same durration, thus better breathing. More lift will help too. Depending on the lobe center line, you may be able to go with a little more durration without hurting the idle. Valve to piston clearance would have to be checked.

I would say a good set of aluminum heads will do a lot for your engine. From published data that I have seen about 1.25 lb-ft of torque per cubic inch of displacement is about a good as you will get normally asperated and still have reasonable monors at the low range. Which would say 440 torque is about as good as your going to get, and you are likely to be in the 380 range now. To get there you need real good heads with a cam matched up. For low rpm you do not want to go too large on the ports.

You didn't say if the intake is single or dual plane. I think a good dual plane would best suit what you want.

The quickest and cheapest kick in the pants would be to switch the rocker arms to a 1.7:1 ratio roller rocker set. Valve clearance would have to be checked. If you are not wanting to change the heads and cam, this would be my choice.

Just out of curiosity what is everyone's opinion on a rear end gear swap to a deeper gear.........hypothetically going from a 3:31 to something like a 3:55 or 3:73?

I know it does nothing for actual HP/TQ but shouldn't it help the seat-of-the-pants feel by moving his driving range into a higher RPM and consequently higher parts of the HP/TQ curve?

Slider701,

Good point; I am running 3.54 gears and I have .68 OD (Tremec TKO). In fifth gear I do feel like I lug a little everywhere but 65+ and at 70 mph I think rpms are about 2200; I ran on the track at VIR and in the straights, 5 gear really didn't really grab that much at all; went to about 115-120 mph in 4th but to take the next step in 5th seemed like too much work for the engine so waffled around between 4rth and 5th.

So if I couldn't find the top end on the track, and I am looking for a little pop on the street, seems like I could handle moving to 3.70s (or lower)?

I have the 3.54 and the .64OD gear ont the TKO600. The 5th gear is only used for pleasant cruising, not for racing. BUT, I spec'd my engine so that the first four gears allow me to hit 140 (solid cam, so I can rev a little higher). I think what you're looking for is more torque, not having to shift quicker. Assuming your dyno-tune doesn't get you a whole lot more power, the heads and cam from one of the guys on this forum is, roughly, a grand or so. Maybe upgrade the rockers as well. It's a one day job for your mechanic to bolt the heads on and stick a cam in ASSUMING you can do that without pulling the engine. We're not talking a huge money investment here. I wouldn't mess with your rear end ratio.

Patrickt,

What do you think about changing the heads without changing the cam? Any brand and spec recommendations for heads and cam?

Regards.

You could do it in steps. Changing the heads on SBF is something you can do yourself with medium mechanical skills (or the help of a friend). The brand of head is not nearly as important as the skill of the man that is doing the staging job. Nicely done aluminum heads will give you a good boost, but it will be important for you to chat over the fact that you are keeping the same 224/234 hydro cam, but that you might jump to something heavier if you're still not satisfied. Barry, Keith, Brent L. can all give you good deals on nicely staged SBF heads, maybe with an adjustable roller rocker set on there as well. That would give you plenty of options for the next step, should you choose to go there.