What specific parts to buy to run 6000-6500 RPM with a SC motor?

quick35th

Registered User
Guys I want to know what parts I need to buy to run higher RPM with my SC motor in my 35th. I know a cam, heads, blower, and bottom end all need to be be looked at to make it all work together. But I would like to know what specific cam I would need, and what rods/pistons to go with. I already know that a desent port job and valve train upgrade would be all the heads need along with a good blower.

I am asking this because I am trying to build a good autocross motor for my 35th. With the tire size that I used to run (225/50/16) I would run out of my power band in second gear pretty easily. I need to turn around 6000 RPM or at the highest 6500 RPM. Yeah the tire size is way small but Hoosier has a very limited tire size selection in for 16" wheels.

Any advice is alway appreciated guys.

Shane
 
It isn't very easy to make peak power in the 6000 rpm range, although you can make it pretty close. If you want to make a decent amount of power to be able to take it that far then I would say ported valves with oversized valves would be the best way to go. The 210/220, .493/.493 lift, 114lsa cam is the comp cam I believe then the Dr. Fred cam is a .520 lift cam. The cam I am running is the 212/220, .531/.539 114lsa cam. All of which are good for making good power up to the 6k rpm range. You can get the 1.73 RR's, but I don't believe there is any power gain in that. The 1.8 rockers will give you higher lift, but you have to run chromoly pushrods with those. Change of valve springs would be a need with the cam you choose, also.

I don't know how deep you are willing to reach into your pockets, but the best you can do with pistons and rods would be Wiseco pistons and Eagle or SCAT H-beams. However, they aren't very necessary as there are people making over 400rwhp on a stock shortblock. If I were you I would save your money and go with stock rods either the 89-93 rods or the 94/95 rods. The 94/95 rods are a good upgrade if you can get some, but if you can't find any you'll be fine. I would also bore the motor .040 and get the Sealed Power coated hypereutectic pistons that are about $27.99 for the coated ones.

A main stud girdle from Paul at BTM would be a good and smart modification to go with also.:)
 
That sounds like a somewhat cheap buildup that I would be very interested in considering. Yeah, I'll stick with the stock rods. Would the stock pistons take it? My motor in my 35th doesn't have many miles on it since the last rebuild so if I can get away with the stock rotating assembly I will be more than happy to do so.

What valve springs should I go with? How big of an oversized valve should I go with? I may have to upgrade to an AR :eek: for the supercharger upgrade hehe.

Shane
 
The stock pistons would be fine, just as long as you keep it tuned. Good valves to go with are the 1.84 intake and the 1.54 exhaust. The reason being that they work on stock seats, therefore, it saves you money.

Any comp spring is better than stock, it just depends how far you want to take the motor to. Here's the specs on them:

942 Single
Seat Load- 117@ 1.700
Open Load- 284@ 1.200
Rate (lb/in)- 339

985 Double
Seat Load- 164@ 1.750
Open Load- 331@ 1.250
Rate (lb/in)- 333

986 Double
Seat Load- 132@ 1.750
Open Load- 280@ 1.250
Rate (lb/in) 296

987 Double
Seat Load- 121@ 1.800
Open Load- 388@ 1.200
Rate (lb/in)- 344

The stock heights are 1.15" exhaust and 1.65" intake so the rates would be higher than the specs listed. The popular spring that most people have are the 942's I think. I run the 986's, in which has a higher seat load than the 942's, but the open seat pressure are about the same.
 
I would say the bigest problem will be valvetrain stability. Go with a beehive spring, Since they deal with harmonics better then a standered spring you can run less pressure. Also i would not use a 89-93 style rod, i think a 94-95 rod shotpeened and ARP bolts as a MIN. Use a main and head stud kit, 94-95 oil pump, 94-95 windage try, if you think you will be running over 6k for a long time i would make sure your oil pan holds more oil, and grind the drain back holes in the heads so they drain better. Get it tuned and keep it cool maybe a larger Rad.
 
Valve train stability is certainly going to be a limiting factor. Weight of the valvetrain playing a big role. If you want to really do this, I would consult with one of the guys that builds SC engines and see what they can do.

If you're not planning on bolting up a MPIII blower or AutoRotor plus running a big overdrive, gaining the stability at that RPM will be useless. An S model or stock blower isn't going to do anything but make heat and sap horsepower at that RPM. I've seen Dave Dalke's AutoRotor still making more horsepower on his stock bottom end at 6100rpm before shutting it down.

Good rod and main bearings, ARP fastners on the rods, high quality connecting rods. All play a role as well. But even with a bottom end that can take the RPM, you'll have to do something with the valve train to keep the valves from floating and the entire thing from coming apart.
 
Mike,
I think I read somewhere that either 351W or 351C rods fit our engines, is this true? If so I have a set of magnafluxed, polished and shot peened (sp?) DOVE 351C rods from like 1970 lol. I am serious about doing this. Oh and an AR maybe on the future mod list, well just have to see how much sponsorship money I get :D.

Shane
 
To run the 351 rods you need custom pistons with a relocated pin for the extra length. You will need to run a rocker stud kit with adj. roller rockers, CM push rods, and guide plates. The beehive springs will help greatly since you can usally run about 20psi less on your spring pressures. Also the retainers are so small (4.6 retainers) you are already saving a ton of weight of the top of the spring, Titanium retainers would be even better. Probably woulden't hurt to weld or epoxy up the rocker pedistals so they dont break around the larger studs.
 
David Neibert said:
Shane,

What power level are you after ?

David

David,

I dont want to go insane on the power level for the 35th. 300rwhp would probably be plenty for autocross. The way I see it is I could really sacrifice some low end torque for more mid range and lots more upper end power. Atleast thats what the car needs in its current state to be more competative. Not looking for a 1/4 mile missle here, just a competative autocrosser that has a bit more power to fend off all the subarus and modded fox mustangs.

Shane
 
quick35th said:
David,

I dont want to go insane on the power level for the 35th. 300rwhp would probably be plenty for autocross. The way I see it is I could really sacrifice some low end torque for more mid range and lots more upper end power. Atleast thats what the car needs in its current state to be more competative. Not looking for a 1/4 mile missle here, just a competative autocrosser that has a bit more power to fend off all the subarus and modded fox mustangs.

Shane

You don't need to turn high rpms to do that. Mostly you will want low end grunt since you plan to use tall gears. High rpm HP will be a waste of effort. 300rwhp doesn't even require an upgraded blower.
 
XR7 Dave said:
You don't need to turn high rpms to do that. Mostly you will want low end grunt since you plan to use tall gears. High rpm HP will be a waste of effort. 300rwhp doesn't even require an upgraded blower.

Dave,

I have a set of 3.27s that I plan to install when I get a new limited slip. My problem is I am running out of usable RPM in second gear and I dont want to have to shift to 3rd gear. So if I can extend my usable RPM range so that I can stay in second gear longer thats what I want to do.

I used to lift off the gas for a split second on some of the straights during an autocross event cause my RPM was traveling to 5500 and beyond. Power drops off at 4600 with my current combo so I am just wasting time reving it that high and hurting the motor.

Shane
 
XR7 Dave said:
You don't need to turn high rpms to do that. Mostly you will want low end grunt since you plan to use tall gears. High rpm HP will be a waste of effort. 300rwhp doesn't even require an upgraded blower.

Re-read the first post. He needs more RPM in second gear for autocrossing.
Maybe look into tranny options you have a 5-speed or auto? I know they have wide ratio gear sets for the AOD I dont know if the F-150 trannys have different gear ratios maybe you could swap in if you have a stick.
 
BKB said:
Re-read the first post. He needs more RPM in second gear for autocrossing.
Maybe look into tranny options you have a 5-speed or auto? I know they have wide ratio gear sets for the AOD I dont know if the F-150 trannys have different gear ratios maybe you could swap in if you have a stick.

My 35th has a M5R2 5spd in it. If there is an F150 M5R2 tranny with a different gear set in it I should be able to swap the parts over into my tranny.

Shane
 
6000 is a pretty reasonable rpm for a rebuild, so if you go with that you would gain 500 rpm over what you're running now. Thus saving the rebuild necessary to go for a 6700 rpm. Work out some numbers for your car with your tires and see what that 500 rpm might gain you.

As mentioned, 351 rods will work. They need a 2.311 end and then custom pistons to deal with the length. Stock length is 5.915. 351 stock length is 5.955. I'm going to be using rods that are 6.125 long with my pistons. I purchased my Weisco pistons through XR7 Dave.
 
Wider ratio's is going to make it worse. If you could find a 95 tranny it would help some but not much.

IMO gearing for high rpm is a mistake. You'll pull too many g's, starve the motor for oil, and kill it.

With 2.73's your second gear speed range is 35-70mph.

I'd put 4.56's in it and run 3-4 all the time. At least 3-4 is an easy shift that you won't have to worry about missing all the time. 3rd would give you 30-65mph and 4th would give you 60-95mph.

With a 6500rpm motor you'd have 35-80mph range in 2nd but you'd blow it up guaranteed.
 
Mike8675309 said:
I'm going to be using rods that are 6.125 long with my pistons. I purchased my Weisco pistons through XR7 Dave.

The sheet you sent me specified 6.2" rods. Did I screw up or is that your mistake? :confused:
 
XR7 Dave said:
The sheet you sent me specified 6.2" rods. Did I screw up or is that your mistake? :confused:

I'm retarded... I was flopping on rod size back and forth. checked my documents, yes 6.2 is what I'm going with. Sorry for the scare. I gotta get some sleep.

good thing I didn't order them yet. :eek:
 
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