Thread: Aftermarket heads need help

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Hello everyone. I have a big block chevrolet that I bought assembled used. It is supoosed to be a 505 ci motor. 4.250 stroke 4.350 bore. It is a markIV block I believe. (70 model 454) with cast iron heads that the guy did alittle work to. I dynoed the motor mainly for tunning purpose. It came out to 548hp and 589 tq. I am wanting to upgrade to try and get some more power. Everyone keeps telling me to get a good set of aluminum heads. The only problem is Im not a mechanic, as far as figuring out what head combination will work good on my motor. I can turn a wrench. As far as my vehicle, it is a 8000 lb tube frame mud truck. I run it in the woods trail riding, not street legal. 54" mud tires on 2.5 ton axles. I have read alot of good info on this site about motors so I figured I would ask here. Is this something that can be answered without alot of info on my motor or do I need an experinced mechanic to open up my motor to see what i have. I know I have a solid flat tappet cam with a 517 lift but not sure about anything else. Would i be better off getting a cam, intake and heads all together. Any help would be appreciated before I go to a performance shop and some one see's me coming and gouges me to death. Another question, Is the investment going to be worth it to make a diffrence in what I already have. I only have about 4500 dollars in the whole motor. I really dont want to spend 3000-4000 more and only see a minor change in hp and tq. Thanks

Welcome to CHR Gregory!

It would help us to know what RPM the HP and torque readings are from. I would assume (dangerous - I know) that you want a gob of torque to come on just off idle. Trail riding to me does not equate to high speeds.

Is this an automatic or stick shift vehicle?

Pat McCarthy is legendary with Chevy BB and he will be able to give you a ton of advice - listen to him as you'll get no better in terms of overall performance.

Regards,
Glenn

Thanks Glenn, the horse power peaked @ 6700 rpms. I got the rev limiter at 7000 rpm. No I dont have High speeds due to all the gear reduction. It is a standard transmission that I always run 2nd gear in. I calculated my wheel speed with my tire diameter and it came up 37mph. I run a profab transfer case that has quick change gears, right now im running a 1 to 1.5 gear. If i could get somewhere in the 650+ hp range i could go to a 1 to 1 ratio and get somewhere around 42 mph wheel speed. Yes I would like lots of torque to come off idle. Some of the mud we run in is really sticky. I have seen some 800 hp motors bog down in the mud and I'm thinking it might be due to low end torque. I have heard you can build horsepower with low tq or build it with torque and the horsepower will follow, like I said im really not a master engine builder by no means, I am a fabricator. I do however want to become a better mechanic in the future. Thanks again

a cam change only may help . the cam . intake .carb CFM . heads . and Piston compression. headders. all go long together there is many key parts that need to be right for all parts to be happy and play together so to speak. at the least i would need head casting numbers . piston numbers . nice to know some things about the cam i can fill in the rest. i have worked with the hill in hole guys hillclimbers .and mud pit guys .wheel speed is a key deal

Thanks pat The casting number on the heads that i have now is 352625. weiand dual plane intake and a 850 cfm holley double pumper. piston compression I dont know. I dont know about the cam except its an eljin with a .517 lift I think, just because he gave me a recipt with that and said thats what he put in it. I kinda want someone to tear into it and find out exactly what I got but it is running really good, just want some more power lol. Im sure that will be the problem from here on out.... The guy that dynoed it said he was kinda suprised at the numbers being what I have. At that time he told me he could put another cam & heads on that motor and get me another 60 to 80 hp at a cost of around 4500 bucks. To me that amount of increase wasnt worth the investment. We do this for fun not really racing or any kind of competion. I know in the drag world 60 or 80 hp would prolly be a big advantage, but I dont think i will really notice that out in the woods playing with a bunch of friends, but I could be wrong.

i do not under stand you say you want more power but then you say 60to 80 hp is not worth it to you .but you did dyno the engine you have why? it.s going to cost money to get power some do that better then others but it will still cost .i can do 60hp for abit less $$..? this has alot to do with your bottom end shape . cam s to small and so are heads are small O ports right ? small heads can work but in stock form but they have a limit .will the bottom end take more power ? if there is any bad machine work or some thing so/so it may not like the added power ? so your looking at a new long block or top end kit ?

Pat are you in Bay city texas. There is a big fast track in sweeny correct. As far as the bottom end I was told it has H beam rods but do not know the brand, also dont know the type of crank. I hate saying I dont know but its true. I bought the motor on a whim and for a decent price I belive. I might be better off having a motor built then I would know. I guess I could put the heads and such on there and see what happens if the bottom end cant handle it and it goes down atleast I would have the top end if it was not a catastrofic failure. Are you an engine builder. I can tell you know about the engine but I guess what Im trying to say is will you build an engine for someone. Maybe that will be a better option is to keep running what I got and build a new motor to have a spare in the shop. Being that I am really hard on a motor this is my 3rd one.

Originally Posted by gregory32

Pat are you in Bay city texas. There is a big fast track in sweeny correct. As far as the bottom end I was told it has H beam rods but do not know the brand, also dont know the type of crank. I hate saying I dont know but its true. I bought the motor on a whim and for a decent price I belive. I might be better off having a motor built then I would know. I guess I could put the heads and such on there and see what happens if the bottom end cant handle it and it goes down atleast I would have the top end if it was not a catastrofic failure. Are you an engine builder. I can tell you know about the engine but I guess what Im trying to say is will you build an engine for someone. Maybe that will be a better option is to keep running what I got and build a new motor to have a spare in the shop. Being that I am really hard on a motor this is my 3rd one.

nope bay city mich. McCarthy Performance 989-667-4071my web page is not up yet. but soon ...i hope ... i been building bbc for some time . look at my photos on here . i can build any thing you may need. i try not to sell on the forum but have built engines for guys on here . better to keep price and me selling any thing to the P.M if you have a need for that