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Author Topic:   420 dilemma
dchaught
Dirt Roller

Total posts: 12
posted February 22, 2002 12:49 PM
Ok, I am about to build a 420 for our Unlimited late model. I have discussed this topic with a number of people at work (Summit Racing), and am receiving a number of conflicting opinions, even from people who have built them.

We plan to use a stock 4-bolt block, .030" over, a good 3.875" stroke crank (Lunati, Crower, Scat or the like), and either Summit H-beam, Eagle H-beam, or Crower stroker rods (6" long). We will be using JE 18* pistons (About 14:1 compression), and Trick Flow 18*heads.


The questions are:
How much clearancing is involved on the pan rails. The big concern, however, is rod to cam clearance. Will I require a small base circle cam with this combination in order to achieve the .100" spec? I have been told that if I use the stroker rods, I might not have to. However, these are 1400 dollars, which is twice as much as the other rod choices. I would much rather spend that money elsewhere in the car. We have a solid roller cam from our last motor (a 377), that is ground on a 106* centerline, with about 260* of duration @ .050". Will this work with either of the h-beam rods? If you need further information before making a decision, please let me know. I do not mean to be rude, but please reply only if you have actually built this combination, or something similar before. I have already theorized with ten different people about this, and need someone with personal experience to help me out. Thanks.

Monster
Dirt Maniac

Total posts: 135
posted February 23, 2002 06:58 PM
It's been a couple of years since I built this combo, so memory is slightly hazy. Grinding is required on block. "How much" depends on what you mean. The problem is you want to remove only enough to clear, as there's water in them thar walls! Takes a full mock up to find out. Use a set of cheapo bearings so you don't booger up your good ones. We used a cam with as small a base circle as we could get. Used Eagle "3D" rods, which are cut back some in the shoulder area, everything was ok. If you mean the ".100 spec" as minimum cam/ rod clearance, I don't follow that. I put clay on the rod shoulders, crank it thru, measure whats left. Do it at full cam advance and retard as needed. I'll take .060.( I'll also take .030 intake valve to piston when needed, so you be the judge) Aluminum rods will not work(customer found out that the hard way). This is a very close fitting assembly, and requires a lot of time and effort, because of so many things that must be checked. The only way to do it is to do it step by step, checking every rod everywhere. As I recall, problems will show up back in the 5/7 rod area. I wouldn't suggest this as your first engine. FYI, you can make your own stroker rods if needed. Hendren can probably pin down the specifics better than me.

Monster
Dirt Maniac

Total posts: 135
posted February 23, 2002 07:04 PM
As I reread my post, I didn't mean a "full" mockup, cause you won't be able to turn it thru. I should have said "mockup every cylinder one by one".

awkwardjeff
Dirt Freak

Total posts: 458
posted February 24, 2002 01:17 AM
Personally I check the cam to rod clearance with a feeler guage....I won't put it together without .080 clearance. You can put a feeler guage in between the cam and the rod and turn the motor over as you clearance the block. As long as you put one side together at a time. Put one side in and check clearance, then remove those pistons/rods and install the other side.

I have a 406 with aluminum rods, and you will need a small base cam to get this to swing. You should call Dave Crower at Crower cams........he has built me a EXTREAMLY small base circle cam for the above motor......it needed to start with a billet core to keep deflextion within reason..........at first he refused to build me what I needed, but after talking about this completed motor minus a cam he did agree to build a special cam.....

we also had to grind the pan rail INTO the water for the rods to clear the block....this oil pan has 3 bolts per side

we core filled the block BEFORE we started.
A 420 will clear without hitting water. and will clear the cam with a standard small base circle cam.......these are shelf parts in todays world. The rods you decide to go with will dictate what base circle cam you can use.......this is where Dave would be able to tell you EXACTLY what crower rod with what base circle cam .........

Nobody here can help you without knowing exactly what parts you want to use. Dave can punch it in the computer and say these rods with this cam works or doesn't.

Crower cams, and Dave Crower in person has been the most helpful business person I have had the PLEASURE of doing business with.

Jeff

sdhnc29
Dirt Freak

Total posts: 467
posted February 24, 2002 10:52 PM
Not to be rude , but why would you use a stock 4 bolt block for an unlimited super late model engine with 14:1 compression ?? By the time you put 5 billet main caps on the block , and completely race prep it , you will have too much money tied up in a block that will still break the main web's !! If your looking to use a cast iron block , then I'd invest in a Dart Little M block . The block it's self is much stronger , and it already comes with the right main cap's . All you must do to this block when you get it , is deck it , finish bore and hone , and size the lifter bore's . I assume that when you say you work for Summit Racing , this would be the mail order catalog ? If so , then you know how inexpensive these block's are ! I would at least start with a good foundation !

As for rod's , use the Crower Billet Stroker rod's you spoke of ! These will be the best rod's you can buy out of the three mentioned !

If you use the Dart Little M block , there would be a minimal amount of clearancing involved . I do not use stock block's , or stock deck height blocks on anything that I build over a 406ci ( we use raised cam block's , and tall deck block's , such as the Rocket block , or Dart aluminum block). But with the 406 engine , we do use a small base circle cam . So it will be necessary to use one in your 420 , even with the stroker rod's .

Your existing cam will not work with any of the H-Beam rod's you listed . The biggest problem will come from #2 and #6 rod's . As for camshaft choice , Jeff is 110% correct !! Dave Crower is the man you should talk to if you want to speak directly to a cam manufacturer's . Be ready to answer a lot of questions from him , and have some flow number's handy as well .

Just for curiosity sake , what size intake runner's are you trying to use ? And what does Trick Flow claim to be getting for airflow on the head's your planning to use ??

In summary , both monster and jeff are correct in there advise and knowledge . If your trying to build a larger engine on what appears to be a tight budget , then you might want to consider a 406 .

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Hendren Racing Engines
Rutherfordton , NC
(828)286-0780

dchaught
Dirt Roller

Total posts: 12
posted February 25, 2002 01:21 PM
Gentlemen, Thanks for the abundance of information. sdhnc, you have confirmed many of our suspicions. You are correct, I do work at Summit Racing mail order. We are somewhat on a budget, and are trying to come up with the best combination possible for the money. We have also considered the long rod 406 combination as well, but would like to get the inches if possible without spending 2 grand on a block, when we have three 400 blocks in the garage. Now, if we go with the long rod 406, is it safe to assume that using a small base circle cam will allow us to use the h-beam rods?

Also, would you mind if my father or I contact you directly at the phone number you have listed? We have built numerous engines, but have not delved into a stroker engine of this magnitude and power level before. You seem to be extremely knowledgeable, and we may be able to make use of your expertise .

As far as Trick Flow heads are concerned, the flow numbers look like 336 cfm @ .600. You can go to http://www.trickflow.com/media/pr/pdf/18degree_sbc.pdf, and get all of the details on these heads. I have looked at the castings, and they are very nice. They are also very economical.

One more thing. Most people think of Summit Racing as a strictly straight line, drag race oriented company. We carry just about everything you need to build your stock car as well. We carry the entire Howe racing line, as well as all circle track oriented parts from numerous other vendors. We are attempting to broaden our customer base, and let people know that we can think in circles too. I will only make this plug once, as I am certain people do not want to hear me advertise every time I post. However, if you need anything, please contact me over the phone at 1-800-230-3030 extension 6321, or via email at dhaught@summitracing.com. Please spread the word, and I will always be happy to help. Thanks again for the help, and if you have any other info, please let me know.

sdhnc29
Dirt Freak

Total posts: 467
posted February 25, 2002 08:01 PM
No problem dchaught ! You can get in contact with me at any time , between the hour's of 8:30am-5:30pm Mon-Fri Eastern time . Heck , this time of the year you can usually catch me at work until 9-11pm . If I don't happen to be there when you call , you can speak to my dad Bill . He can help you out just as much , and probably more than I can .

Steve

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Hendren Racing Engines
Rutherfordton , NC
(828)286-0780

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