the turbo nailhead is down but not out. had a crack in the oil pickup and wasted the bearings in the motor. well why it is apart might as well make it stronger. What cam specs are you guys running for turbo motors. i am reading go with high lsa. i havent called comp yet but will. just wanted to hear your opinion and what works and doesnt work. One other question, how do you guys feel about studded mains? worth it? Thanks Paul turbo 401 nailhead
i Would get a custom grind done. i think but I'm not sure that you wanna stay away from over lap As much as possible with boost and i don't think you need much of a split between intake and exhaust.
We ran Top Sportsman and some 10.5 tire outlaw with twin 88s on a 430 cid sbf in a 3200 lb car. Best was 6.82@ 210 at Boise ID. Tried a variety of cam profiles plus got plenty of feedback from others. Just like selecting a cam for N/A combinations, it depends upon the engine combination and where you need the power band to be. We started with .050" durations around 240 and a LSA of 110 (the engine came with it) and ran a 7.03@198 at Seattle. We had a peak acceleration of 2.4 g during first gear and could get engine rpm up and 9 lbs of launch boost from an idle in 2 seconds with a very tight torque converter. Went to bigger heads and 260 duration cams so we could make more power by running the engine at 8500 rpm. With the longer duration the LSA needed to be at 116 to keep the overlap low and the cam was advanced to regain some low end. Now it took 6 to 8 seconds to get the engine rpm up so we could get launch boost. The launch boost also needed to be higher at 12 lbs and peak 1st gear acceleration was only 1.9 g. The car made more peak horsepower and went faster in the 1/4 but was a real pain to get launched using a converter. Example: If you want boost in early and want all the power in by 5500 rpm, then you are looking at .050 intake durations around 215 degrees. With the short duration the LSA can be between 112 and 114 and still have very little overlap. The 112 LSA will have a lower torque curve and get boost in sooner while the 114 LSA will allow a little more compression and a little higher power band. The nailhead exhaust port would benefit by 5 or 6 degrees more exhaust duration but this also increases overlap so the split between intake and exhaust durations needs to be kept small. In the above example in order to keep the Dynamic compression ratio under 8:1 the Static compression ratio needs to be limited to around 9:1 Lift numbers should be as high as port flow allows meaning if port flow doesn't increase past a certain valve lift then run the valve lift to that point but no further. If head porting is done for more flow at higher lifts, then a roller cam may be required for a short duration high lift cam profile. TA just ground a 218/218 .520 lift on a 114 LSA roller cam for a 462 BBB street turbo project. The cam is at the shop waiting for block to be girdled and assembled. Volumetric Efficiency is one of the main considerations for the amount of power an engine makes for a given manifold pressure The amount of intercooling is the other. I gave you the longer story to give you a better picture. Hope this helps Paul
Paul, i love when i get to read a post from a guy like you.. i appreciate you sharing your exsperiance and knowledge to help out.. I am running a 67mm turbo with a .81ar. the heads are pretty stock with just a cleanup/ gasket match. the pistons are going to be ross with a compression of 9.3:1. i filled out a comp cams chart yesterday on what kinda cam i want and all the specs on the motor. i want to see what they send me for specs and compare them to your recs. i do not know anything about picking a turbo cam due to this is my first turbo engine that i am building. i just finished ordering my arp mains studs. my arp rod bolts and head studs are already in. once my main studs are in i will install them and take some cylinder measurement to order some pistons. $800 for the set of pistons with a 3 week wait. i didnt think that was bad at all. thanks for all you help Paul
The issue with align boring or honing is that it may move the crank a bit closer to the cam, making for a loose timing chain. A couple of manufactures use the same chain on the Ford 429 as the Nailhead. It's possible there is a tighter Ford chain available.
Nice info Paul!:TU: For comparison, a stock cam has 209 degrees duration at 0.050". A typical mild performance cam like a Poston NH400 or TA25 has 218/228 duration. Paul, if flow peaked at 0.500, wouldn't it be beneficial to go to .530+ lift just so the valve is open longer at that .500 mark? While .600" lift might be useless on a Nailhead, the 'area under the curve' is greater with a hi-lift cam, a roller cam, or roller rockers. .....someday camshafts will be obsolete and we'll have programmable valve actuators!!:grin:
Walt Thanks for pointing out the typo. Fixed it. Yes that's is one method of getting additional flow, but for the street you are also looking at longevity so the increased ramp rate is harder on the valve train and you increase the chance of hydraulic lifter pump down at high rpm. When the cam only has a 215 duration, higher lifts create very steep lobe angles. As far as I know there are no oversized gear sets for the Nail Head engine. Line Honing is not an option since it removes as much material from the block as it does the cap. However if the goal is to correct the cap distortion due to the stud clamping force, a "Good" machinist can carefully line BORE and remove mainly cap material while barely touching the block side. Paul
So for a relatively mild cam for a turbo application, It sounds like higher ratio roller rockers would be the preferred way to achieve faster valve opening rates and higher lift...... it would be easier on the cam and lifters..... or is the added leverage from the valve spring and longer rocker just as bad? And I'd guess combining roller rockers and an aggressive cam would be overdoing it and lead to instability at the valve and valve spring end..... a cam should be chosen with stock or roller rockers in mind.
There is a balancing act between turbo size, torque converter stall RPM and desired RPM limit. It depends on your intended goals. Do you want a powerband like a stock grand national where the boost comes on just above idle? Or, are you going for max effort/horsepower and you are willing to run a high stall torque converted to get it moving? My immediate instinct is to leave the nailhead in its natural RPM range and use the turbo to maximize the volumetric efficiency. With that being said, I would pick a cam like 215/215 @ .050" with an LSA of 114-116. Pick a lift that is not too hard on the valve train. Consult with a reputable turbo expert like turbonetics to pick a turbo that will spool up quick but still make maximum horsepower. Choose a torque converter just slightly larger than stock, but make sure you get a really high quality piece because turbo nail head torque will kill a cheap converter. I cannot over emphasize how highly I recommend using the best air to air intercooler you can afford. A good intercooler will easily double the power improvement of your turbo.
Paul, have spoke to to comp and they are still putting a cam together. i got two replies from comp and both guys thought the other one was helping me out. spoke to them yesterday and they said they would get right on it. hope to hear from them shortly. Paul
Paul, I suggest a custom ground camshaft. This will not cost you anything extra over the price of a regular catalog cam except it takes a couple extra days to ship out. I can sell it to you for $306 shipped to the U.S. If you are interested in ordering it or anything directly from Comp Cams/www.CompCams.com please shoot me an email back or give me a ring at 1-800-365-9145 Extension 538. It benefits Tech Support personnel for orders to be placed directly with the person you are dealing with. The cam will spec as follows: Duration @ .050 224/224 Lift with 1.5 Rockers .509/.501 LSA 113 -Thanks what do you think about this cam ?? Paul 66larkgs turbo nailhead
I've been getting over a 1.6 ratio from the stock rocker arms at max lift.....0.270/0.261" on the car lobe = 0.448"/0.425" at the valve. This is on a stock '66 401 cam, using a solid lifter and zero lash, and a weak spring. In actual use, lift and ratio would be a little lower when things start to deflect from the higher spring pressures. I'm not an expert on cam design, but Nailheads generally like a longer exhaust duration, but I don't know if the turbo changes that....
Paul Even considering that the Nail Head reqiures a little extra duration because of the head flow, this cam will still make power to 6000 rpm with a turbocharger and will lack the bottom end for street use. I'm more concerned with the low end power and getting boost early. A 218/218 would be the most I would go but I still prefer the 215/215 on a 212 lobe center for street use. Paul
i havent heard back from comop yet. i emailed them with my concerns and i am to the point where i might throw the stock cam back in it. i got kinda aggrivated with comp. Paul 66lark gs
