Re: engine won't rev out  
Re: Re: engine won't rev out -- Ken Merring Post Reply Top of thread Maverick Message Board
Posted by: Fred H
02/12/2002, 13:49:00
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:=What do you do to those things to keep them in one piece? I hear you can easily spend as much $ on one of those as a good old fashioned v-8.
........ANS. Forged piston/rod, hardened crank, very thin min. tension rings. Head has valve pockets machined in to handle hi cam lifts, Tillitson carb on alky, ported block ports and tuned exhaust. They end up with about 18 hp. and just hang on. On full modifieds, the power get in the 25 hp range.
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:=You say that those sprint car cams have 294 degrees of duration. Is that at .050 or advertised. I assume by the RPM range and the cam lift it is advertised. If advertised what is duration a .050?
.......ans. adv duration
:=Couple of other sprint car questions for you. I know that there is a class for motors around 410 ci. Do they run ~3.75" stroke with a large bore or ~4" stroke with a smaller bore? How hard do they turn them? Reason why I am asking is that I am going to be starting on a 408W (4" stroke) after the summer and have everything figured out except exact cam specs. I've got TFS High Ports, ~13.5 compression, Super Victor Manifold, 950HP carb and 4.30 rear end. Figured on a solid flat tappet .650-.675 lift, ~265 @ .050 intake dur/~270 at .050 on the exhaust (want to have a few more degrees of exhaust duration since I'm trying to shove all of it through a dinky 1.75" header tube). I am a little fuzzy on the lobe separation. I am thinking of 110 but am concerned that may be a little too tight. Do you think 112 would be more appropriate? Thinking this motor will be done between 7200 - 7500rpm.

:=..ans... Blocks are SVO SPECIAL out of the catalog, built to 410 dual fuel injection, turned to a max of about 8000 and make in excess of 800 HP. Bore stroke combos tend to be short stroke.
..On lobe seperation, the general rule is the wider seperation widens the power band but kills peak hp as the price paid. So select the seperation to cover the power band desired in order to keep as much peak as possible. On circle track, seperation in the 108 to 110 range is common because low end power is not used and depends on the class, weight, rules, track surface, tires allowed etc.

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Thanks for the advice. It seems like we tend to think simlarly. Hope that does not scare you. I think I'll keep l/s at 110. I want to pull a little bottom end out of the motor which should work fine with such a light car. Where do you suggest the cam be timed in? I am interested in about a 4500-7500 rpm range. I have been corking my 302 & 351 cams with a 4 degree lead. Is this appropriate for a 408 or is it too aggressive? Maybe +2 or straight up? The car is an automatic and converter size (stall) is not an issue.

Also, I have a solid roller in the car now and the heads have been machined for a 1.625 spring. Is there an 1.625 spring availble with light enough spring pressure (~160 on the seat,~450 on the nose w/ .650 net lift) to run on a flat stick? I have all of my flat tappet profiles ground on a NASCAR blank so I can run a little extra spring pressure and avoid float issues. In case you are wondering why I am finished with the solid roller it is because I am too lazy to keep on top of the maintenance and I feel that you can get 90-95% of a roller performance with a snappy flat cam.

This should be it for the questions. Thanks again for your help.


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