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Old 04-15-2002, 12:41 AM
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Lemieux Lemieux is offline
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Lightbulb Increasing my horsepower

Hello. I'm new to the Mopar family. I just bought a 1968 Plymouth Roadrunner with a 383.

Is it possible to pump it up to 400hp or more without having to beef up the transmission, rearend, etc, and without burning out the engine?

What's the best way without spending an arm and a leg? Will a tourque converter help improve hp?

I have a good cam. Would you recommend making the heads bigger? Buying a new head may be too expensive.

Anyhow, I'm open to suggestions.

Thanks!

Ron
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Old 04-15-2002, 12:54 AM
xroadrunnerx xroadrunnerx is offline
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Torque converters don't actually increase the horsepower, they increase the stall speed (higher rpm at idle). Engines perform the best around mid range (for the most part), the torque converter just moves the rpm to this mid range so when you take off it will seem like there is more horsepower, it's kind of like stepping on the accelerator and the brake at the same time and then releasing the brake and flooring it.

To get more power out of your 383 (rated at 335 horsepower i think) i would put an extreme energy COMP CAM in it. That oughta be good for 20-30 hp. Change the intake to an edelbrock performer RPM for about 10-15 hp. Maybe get the heads machined to raise compression for an extra 10-20 hp. Also changing the carb would probably be advisable. I'd recommend the street avenger holley 770cfm, it's a bit pricey though, should be good for 20+ hp. And if you don't have headers yet, get them, 15-30 hp. All this could be done for under $1000. Hope this helps.
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Old 04-15-2002, 01:07 AM
Fast One Fast One is offline
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Depends on the condition of your transmission, if there's no slipping etc & the fluid shows no signs of trouble, it might be ok but a shift kit would be a VERY good idea, TransGo seems quite popular, I'd be inclined to strip the trans down & inspect it's general condition / check clearances & freshen it up some, new bands / clutches/ thrust washers etc, but that's just me, FUSSY AS !

A good cam you say, need more info, cam swaps usually need the valve springs with the right lbs loading to suit the profile, or else valve float etc...

To get the most out of a combination depending on the cam specs it could involve a gear change in the diff.
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Old 04-15-2002, 01:32 AM
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cuda66273 cuda66273 is offline
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Welcome to the ultimate performance family, you have made a wise purchase, and I see many good times ahead of you.....


More power is not always the answer, sometimes more efficient use of what you have will give you the same satisfaction as doing a bunch of engine work. It really depends on what you want out of that beauty.

If your gonna race it seriously then you'll probaby want to pick up the HP and tork some, but these things come with a price.....Higher octane fuels, reliability, longevity and the perverbial weakest link.

If you primary purpose is to street drive it and run at the local track in a Sportsman class then maybe a gear set upgrade to a 4.10 or 4.30, Dynamic makes probably the best 3000 stall street/strip convertor in the business. Do some chassis tuning, the right split/valve shocks and you may be suprised to see how much crisper that RR feels.

As by my signature line .......just how fast can you afford to go?

Bring it over with a trunk full of $$$ and I'll get it into the 9's for you.....a.beer budget will get you just a touch more power and way more reliability.

The truth is, you can just as much fun bracket racing a really nice classic 14 second RR as you can racing a gutted out 10 second door slammer a win is a win is a win .. and they all feel good.

I went from 800+ HP 1300# Alky burning Outlaw Sprint cars burning up tracks all over the deep south and west coast to a simple 318- 66 Cuda drag car running in the low 12's and we're having way more fun and spending 1/100th the $$$$$$.

Try you question with more definitve goals.....

"I want to run mid 13's and drive the car to the track and hopefully home...this is what I've got ...........what do I need to do."

You'll get hundreds of good and bad suggestions look them all over and make your choices.

Then go win a race or two....

Don
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Old 04-15-2002, 09:47 PM
beepbeep2k1 beepbeep2k1 is offline
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Question power

i'm looking for 392 hemis on the road, in late 60's early 70's cars.
have some Q's about dist.
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  #6  
Old 04-16-2002, 11:34 AM
carolina440racer carolina440racer is offline
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the big question is how much do you want to spend?

The 68 motor should have a set of 906 heads, which are excellent. They can be pocket ported and will flow well. I like the .484 cam for the street, or the .509 for some strip action. If you redo the bottom end, make sure you don't drop compression too much or you may kill the motor. A good combination is:
1 7/8 headers
.484 Mopar cam
750 Holley carb
4.10-4.30 gear
Shoot for 10:1 compression or more.

The rear end should be a 8 3/4 and this will take all you give it. So will the 727 transmission. (Both up to 500 HP)

I think the key is the heads. The 906 casting can be ported and it would be good to put in big valves, 1.81 exh. 2.14 int. I have a set of these heads that were built by Bob Reed (SS-A drag racer) and they were good for .25 sec off my 1/8 mile times.

Bottom line is a 68 Road Runner has all the good stuff, and with a little work it can be made into a rocket.
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