500cid caddy

I have a 15 1/2 foot Hoffman airboat. Four passenger with a 500 CID caddy motor direct drive, and a water walker 2 blade prop. I am looking to do a build on this motor for maximum torque and power on dry land. Does someone have some insight on a motor build to make this a so the speak “stump puller” from Idle up to 3000 RPMs . Would like to stay with the prop that I have, since it is new.
I do have a Edelbrock aluminum intake on it with a 800 CMF Edelbrock on it at this moment.
Thank in advance! Chris
 
I have a 15 1/2 foot Hoffman airboat. Four passenger with a 500 CID caddy motor direct drive, and a water walker 2 blade prop. I am looking to do a build on this motor for maximum torque and power on dry land. Does someone have some insight on a motor build to make this a so the speak “stump puller” from Idle up to 3000 RPMs . Would like to stay with the prop that I have, since it is new.
I do have a Edelbrock aluminum intake on it with a 800 CMF Edelbrock on it at this moment.
Thank in advance! Chris
Get rid of the 800 CFM Edelbrock and 2 passengers for starters. You describe a big sled that really needs more power than a direct drive can do. It might work on slippery ice but ain't gonna haul the mail.

500 CID @ 3000 RPM calls for a 500-600 CFM intake, carb setup. You want small runner intake, small and long exhaust headers. All that will net you minor improvements vs. the 2 seat delete.

Look for more input from Swamphunter45.
 
As Slidin stated, ditch the Edelbrock carb, way too much CFM a properly tuned 450 Holley will be beneficial, #68 primary jets, #73 secondary plate.
Now, you mentioned "build" ok, pull that stock 500 camshaft out, send it or a stock replacement to Oregon cam service, have them grind the profile to match a Sealed power CS-711,, 178 intake, 194 exhaust durations .233" intake lift, .256" exhaust, have them add 10° advance to it, you will have to add quite a bit of pitch to that prop and not have to shed any passengers.
 
As Slidin stated, ditch the Edelbrock carb, way too much CFM a properly tuned 450 Holley will be beneficial, #68 primary jets, #73 secondary plate.
Now, you mentioned "build" ok, pull that stock 500 camshaft out, send it or a stock replacement to Oregon cam service, have them grind the profile to match a Sealed power CS-711,, 178 intake, 194 exhaust durations .233" intake lift, .256" exhaust, have them add 10° advance to it, you will have to add quite a bit of pitch to that prop and not have to shed any passengers.
What would be your take on doing some head work? Porting? Valves? girdles?
 
What would be your take on doing some head work? Porting? Valves? girdles?
Well a proper valve job and new springs of course, if there was a way to tighten up the intake runners and ports for more velocity plus smaller valves, that would be quite the task.
Now, you mentioned aluminum intake, if it is based off the stock cast dual plane, great, if it is single plane, no good.
With the small lift of the cam profile, the stock Tbar rocker assemblies will be fine.
Gotta keep in mind, building a tow truck engine, not a hot rod.
 
Well a proper valve job and new springs of course, if there was a way to tighten up the intake runners and ports for more velocity plus smaller valves, that would be quite the task.
Now, you mentioned aluminum intake, if it is based off the stock cast dual plane, great, if it is single plane, no good.
With the small lift of the cam profile, the stock Tbar rocker assemblies will be fine.
Gotta keep in mind, building a tow truck engine, not a hot rod.
I agree, looking to build a stump puller torque from idle on up to 3000. The intake I have is a Edelbrock performer dual plan much like the stock. I was planning on boring the engine oversize lightweight forged pistons with more compression. I’ve built a lot of hot rod motors for racing, just never a motor for an airboat. Was kind of hoping somebody would have a formula to really boost the horsepower and torque.. I get grounded with it on dry land at the moment with one person.
 
I’ve built a lot of hot rod motors for racing, just never a motor for an airboat.

That's the interesting thing about a direct drive (DD) airboat engine, do the opposite of everything you would do for a hot rod racing engine. Take for instance this:
if there was a way to tighten up the intake runners and ports for more velocity plus smaller valves, that would be quite the task.

You asked about porting. A set of rodded DD heads would be full of JB weld to make the intake runners smaller to increase velocity and turbulence. As John stated, not sure how to make the valves smaller. It is the opposite of porting a set of heads for 6K RPM plus. You are looking to build a gas fired diesel here.

I was planning on boring the engine oversize lightweight forged pistons with more compression.
Bore and stroke are certainly your friends on this path, stroke more than bore. It is all about torque. Forged pistons are always a good move once you are into the bottom of the engine, but for a DD engine I would not pull apart just for that.

Was kind of hoping somebody would have a formula to really boost the horsepower and torque.. I get grounded with it on dry land at the moment with one person.
The simple formula is a gear box. No way that 711 cam grind adds 3 seats, but it is certainly cheaper.

Take a read of Radtech's posts, he is dealing with a similar situation. Here is a lead.

Gettin back in tha game
 
That's the interesting thing about a direct drive (DD) airboat engine, do the opposite of everything you would do for a hot rod racing engine. Take for instance this:


You asked about porting. A set of rodded DD heads would be full of JB weld to make the intake runners smaller to increase velocity and turbulence. As John stated, not sure how to make the valves smaller. It is the opposite of porting a set of heads for 6K RPM plus. You are looking to build a gas fired diesel here.


Bore and stroke are certainly your friends on this path, stroke more than bore. It is all about torque. Forged pistons are always a good move once you are into the bottom of the engine, but for a DD engine I would not pull apart just for that.


The simple formula is a gear box. No way that 711 cam grind adds 3 seats, but it is certainly cheaper.

Take a read of Radtech's posts, he is dealing with a similar situation. Here is a lead.

Gettin back in tha game
Thank you!
 
I ran a dd caddy for years with high compression 472. I dumped a bunch of money into it. tested 5 different carbs, did some of the intake mods, and every small detail I could.. Motor was on a 15' Hoffman rivemaster I could pull up and of the grass and with a light load run some dry.

Got a 2:1 box to put on it but a friend gave me a 5.3. The 5.3 with a 2:1 did a good bit better then my DD472. I had about the money in the 5.3 and as I did in rebuilding the caddy.

Don't get me wrong I loved my dd caddy but after running a ls gearbox boat I would have been money a head to make to change before I rebuilt my caddy.

Just my 2 cent
 
I ran a dd caddy for years with high compression 472. I dumped a bunch of money into it. tested 5 different carbs, did some of the intake mods, and every small detail I could.. Motor was on a 15' Hoffman rivemaster I could pull up and of the grass and with a light load run some dry.

Got a 2:1 box to put on it but a friend gave me a 5.3. The 5.3 with a 2:1 did a good bit better then my DD472. I had about the money in the 5.3 and as I did in rebuilding the caddy.

Don't get me wrong I loved my dd caddy but after running a ls gearbox boat I would have been money a head to make to change before I rebuilt my caddy.

Just my 2 cent
Good advice, resurrection of a roughly 50 year old powerplant seems like reverse engineering.
If I were to build a direct drive small block, Dart aluminum tall deck, big bore, 4.3 V8 heads intake and cam, modern injection, I'll stick with my old 220, lol.
 
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