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Chevy 400 DD ??

F250GO43

Well-known member
New Member today! Been reading for about a year, though.
Looking at a used airboat. 2003 DiamondBack alum. 12 ft hull w/ 2 ft solid rake with 2 double seats, stainless rigging. The engine is a 400 chevy direct drive to a powershift prop- wide 2 blade. The engine is a remanufactured "crate" less than 1 year old. I am learning rapidly about airboats, know a little and learning more from the forums. I curious about the engine and prop setup. I believe the 400 is a small block, but I have normally been seeing 350's with a gear reduction setup. I was suprised to see this as a direct drive. I was told it turns the prop a 3K rpms. The block had the number 509 on the sides and a remanufacture metal label# 805043. I do not think it is anything but stock with a weber carb.. Is this setup going to let me run the hill or will I be watching?
:shock:
thanx for responding
ab

ps., One of the best forums I have ever encountered, whether its the moderators or just the members-first class operation.
 
a 400 is a small block. there are allot of direct drive 350's by adding the gear box you are just increasing the amount of pro you can swing
 
Your 400SB will run the boat DD. As for running the hill, that is as much in the operator as in the engine. The engine has the ability to run some dry ground but not long hard runs. If you are wanting a hill runner get a redrive for it. 2.68:1 seems to be the in ratios now days.

With the redrive you will be able to pitch your prop deeper hence delivering more push for your boat. You will be using the redrive as a torque multiplyer not an RPM enabeler but in doing that you will be enabeling the engine to run at an RPM where it makes more HP and Torque.

Go for the gold and dont be afraid to experiment. I recommend spending your time before your money when it comes to airboats and mods etc. Lots of folks willing to help and answer questions here. Be sure to read allkt he old back threads, there is a wealth of knowledge stored there.

Welcome aboard. Check out the site support opertunities by clicking the member words under your name. Of course there will always be free memberships but the clubhouse (forum) dont fun for free man :)

Scotty
 
Excellent feedback.
How about the history or dependability of this Chevy 400SB? I haven't seen it talked about much.
Any known faults that I could do some minor mods or increase preventive maintenance? Like, electric fans for the radiator (its alum.) or synthetic oil?

The seller is asking what I feel is top dollar for this boat, I want to make sure my investment of the equipment will have longevity.

thanx Whitebear for the insight to the sit e supporter level--I didn't even catch on.
:?
ab
 
I'm running a 400, The only thing I can realy say is KEEP IT COOL. You wont need fan's if the radiator is near the prop. you also don't want to run a set up where you have to run high rpm's. does it have aluminum heads? you should find out what length rods were put in it etc. good luck.
 
Actually there were two 400s. The 400 small block, which is what I'm sure you're looking at, and a 402 big-block. The big-block came in pickups in the late 60s and early 70s.

One problem with the 400 small block was to get the bores big enough they had to eliminate the cooling passages between the cylinders and thus they are prone to running hot. Not something that can't be worked around, just something to think about.

When it comes to dd vs gearbox, the gearbox is an rpm enabler. If you look at a dyno sheet for a stock 400 chevy, it probably makes in the ballpark of (these really are just ballpark guesstimates) 250 hp at around 5K rpm. At 3K rpm it probably makes around 160-170 hp. The reduction lets you get up where your engine can make power but keeps the ends of your prop from going supersonic.

I know of stock 350 and 400 dds that will run dry but if it were me, I'd save up and do it right the first time. Get a box.
 
A couple of things I have seen with the 400 in car/truck applications that I don't particularly like. One is that the old block has siamese cylinders, that is the middle two cylinders have a common water jacket, no water flowing around the inside web of them. The other is that it is an externally balanced engine unlike the 350.

Neither is a deal breaker but in play trucks I had a temperature problem again and again and years ago I did a swap and used the harmonic balancer off of a 350 and that was a no no. Didnt take long to figure out that doesn't work on a 400.

There have been a lot of 400s campeigned very sucessfully at race tracks and I have seen a few real runners in airboats so the caviets about it are my personal opinion others have had good sucess with it.

Scotty
 
I agree with airduds, I almost forgot, make sure you find out the bore size. anything over .030 or max .040 run and run fast. I build my 400 but it was totaly experimental because of the good torque a 400 can put out. If I wanted a guaranteed reliability I would go with a beefy 350 and a 2.68 gear box. beleive me I almost settled for a dd with my 400. if all is possible get a gearbox.
 
Appreciate the responses--
I see if I can answer in order--

The radiator is in front of the prop, below and behind the engine. I believe the rigging is standard DiamondBack -- owner only has owned it a year and doesn't know. Selling it to provide startup cash for his new business.

I agree with you its a small block 400.

I capture the best setup is with a gearbox, will have to look at the rigging to see if can support the box and room required.

Not sure how to determine siamese cylinders-- the headers are pretty close in the center exhaust ports-- the block has the number 509 on it.

Not sure how to determine bore size -- I believe it to be a stock remanufacture "crate" engine less than 1 yr old with approx. 10 hrs. use. It has a metal label stating "Remanufacture 805043".

As far as the purchase its everything I have been looking for used--except for the power plant setup. Looking at alot of 500's and 350's, but hey I'm flexible with only so much cash. And its in town.

Whitebear- I took you advice and have been searching the forums for "400", I may have PM's some of you guys already- thx for your time.

ab
 
If you beleive this is the boat for you. go for it, all the 400 sbc's are a siamese bore. That is the downfall,another thing to find out is if it is a 2 or 4bold main. It is hard for some to understand but the 2 bolt "on a 400" is better. You can always go back and change anything. Gearbox,prop, engine etc. That is just the long way and more exp.
Reddwarf on here is running a 383 that will run dry fine from what I hear. But, he plans on going to a gear reduction. Good luck on your choice, let us know what you decide.

John
 
Well I guess its time for a test drive and to look at some paperwork backing up the rebuild etc..

thanx for your time and input. I feel more informed going into this decision.

btw, good finish to the Las Vegas Busch race today. Jeff Burton wrecked out Kyle Busch for 1st. Kyle cross the finish line backwards for second. yeehaww!

ab
 
I used to live not far from Jeff and Ward Burton, They are from South Boston Virginia, I lived in Martinsville Virginia, There some good ol country boys.
 
Check end play on the crank. That what caused my to . The 400 will run cool with a good radiator by the propeller about 6 inched off it. As far as i know they didn't make 2 bolt SB 400. It me about 1 year to wear out the crank thrust bearing. I will admit i pushed it hard but had to stay up with my friend in his cad motor boat. My self i may build another old LT1 motor but will be looking for a gear box when its completed. If i bought another air boat it will be Aircraft or gear box. You will want more power.
 
Crane cam, I just goat back from buying a 350 short block. I'm just gonna transfer parts from the 400. Can say this, That 400 had my attention, Plenty power,realy more than I needed so the 350 should do me fine, I know the longevity will be better.
 
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