Major 350 TBI upgrade!

I am in the final stages of what I hope will not have been a huge waste of good money. I have an "89" Silverado 3/4 Ton HD with 350 TBI and 400 Turbo automatic. I put 225K miles on the truck, and needless
to say she was beginning to get a bit tired. Instead of dropping 35K on a new truck, I decided to give my truck a complete transplant. Starting with a Stroker 383 w/ 4 bolt mains and rebuilt original style TBI heads. Throttle body and intake are bored out to 50mm, and with an adjustable pressure regulator installed in the TB, and a new high volume fuel pump in the fuel tank, it's supposed to be capable of flowing 750 CFM. A complete Roller Camshaft, Lifters, and Rocker Arms assembly. Heddman long tube headers with 3" dual exhaust. A custom ECM Chip burned by Harris Performance TBI Chips. The software claims this setup will produce 373HP / 483 LB Torque.
The Turbo 400 (3 speed / no overdrive) was completely rebuilt and modified by Mad Dog Transmissions to handle the extra horse power. The current rear gears are 3.73's and I am considering changing them out for 4.10's. And I am also installing an electronic Detroit Locker in the rear.
I have about $8,500 invested in this build. I know, I know... that's a lot of money to sinck into an "89". But for me, if all goes well, it will have been worth it. That is a big IF though :(
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wrote:

A few tips, first I do not see a new intake on that list. The stock intake is very restrictive. Elderbrock makes a TBI replaclement that I would use in place of stock intale if you want to seriously increase top end power. Next on the tranny, I would have gotten a mad dog 700R4 as they are very stout and it would have given you 4 gears and a deeper first gear and allowed you to run say a 4.56 for a serious performance increase and still cruise a a lower RPM that you have now. The THM400 was a good tranny in its day but that day has passed. The 700R4 needs no computer to work while the 4L80E (which is a THM400 with OD) has some electronic controls but could be made to work too because i9t was offered in trucks starting in 92. BTW, a 350/383 is no match for even a stock THM400 and it provides no real challange for it. One more thing, gear ratio selection would depend on tires size selection and cam duration. ----------------- TheSnoMan.com
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SnowMan, you are right about the intake. The new intake is an Edlebrock bored out to 50mm. I believe the original bore size was 38mm, but don't quote me on that. And, I nearly did go with the 700R4 from Mad Dog, but there was an issue with the drive shaft. I would have had to shorten it by 3 inches, which I was not comfortable with attempting to do myself. And I could not find any shops in my area that were willing to do it either. I don't know if it's a liability issue or what. So I just got frustrated and decided to stick with the Turbo 400. The truck has more top end now than I need, so I figured I could drop the rear a step or possibly two. Is there a ratio between the 4.10's and the 4.56's? I am running the stock tires (235 / 85R16)
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wrote:

No there is not. Unless you plan to run bigger tires I would go with a 4.10 since you have no OD. If bigger tires are in your future, go for a 4.56. Shortening your drive shaft is not a big problem and surely there is a shop somewhere around you that could have done it or maybe even a bone yard solution. That truck would have really rocked with a 4.56 and a 700R4 with a electric locker and that engine!!! ----------------- TheSnoMan.com
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SnowMan, I stand corrected on the tire sizes. They are actually 245 / 75R16. I don't imagine the 245 would make much of a difference. Your enthusiasm is really encouraging me to reconsider the 700R4. Because as it turns out, I need to ship the Turbo 400 back to them. Somehow Mad Dog Lou installed the wrong output shaft in my tranny, so it must go back to get swapped out. I don't imagine they would object to an upgrade! But, I was actually under the impression that the Turbo 400 is a more stout tranny, better suited for heavy towing, which is exactly what this truck will be doing. On average twice a month, about 400 (hilly) miles round trip pulling an 8,000 lb. boat.
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wrote:

The 700R4 is kinda based off the old THM 350 and the basic design is sound. Early 700R4 had design flaw (especailly 81 thur 83) but it was refined by 87 and a mature product. The 700R4 can easily be beefed up to handle 600 or 700 HP and I have seen them live well behind a big block when properly beefed up. The 700R4 bggest enemy is heat and tall gears when it comes to towing. Typically people that complain about 700R4 failures have trucks with lift and big tires and stock gears and when it drive or OD the tranny rides the stall a lot and it makes extra heat. The 700R4 with its 3.06 first gear can "launch" from a stand still a load with a 3.42 axle about as well a a THM 400 can with a 4.10 because of the much deeper first gear but their in lies the trap because drive is still drive (1 to 1) in either tranny and the false confidance that the 700R4 provides on lauch leads many to beleive that tall gears are okay because it takes off fine. The beauty of a 700R4 is you could have a 4.56 rear axle with your stock tires and be turning about 2200 RPM at 65 MPH in OD vs a THM 400 with a 3.73 turning about 2700 RPM or with a 4.10 turning about 2900 to 3000 RPM. A 700R4 let you have your cake and eat it too with correct axle ratios. Bulldog make a few nice sturdy 700R4 offerings too. One more thing since you tow a lot, the 700 R4 has a 10% deeper reverse gear than THM 400 and that tegeher with the abilty to use a deeper rear axle ratio will grealt improve backing performance with heavy loads. Below are few links, the first one is for a free no nag online axle ratio and tires size calculator and the other is a list of gear ratios used in most GM trannies.
http://www.snoman.com/HTML/axlecalc_5a.html
http://forum.snoman.com/viewtopic.php?t 3 ----------------- TheSnoMan.com
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] I would think you can get 4:33's in there as well.
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-----------
NO NO NO!! NOT a waste at all!
The 88 to 96 year chevy will go down as one of thier very finest trucks. I bought my 89 new, and did the very same thing you just did. NO WAY and i getting rid of that rig.
Enjoy...
HDS
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Would you mind sharing the details of your "89" build. Such as motor size, fuel delivery system, type of transmission, rear gears ratio. Is your truck a towing vehicle, or a daily driver?
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so the 700R is decent?.. I wanted to use one in my camaro but got bad reviews.. Hell heat won't be an issue as I will install a fan and extra cooling... Not hijackin a thread. just surprised to see the hype over the 700r I prefer the 400 over it but you learn something new every day. NICE
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