I have a brand new (2months use) holley 750DP but people have been saying that its robbing me of HP. The car is not tuned and runs a 13.0 ET. Does anyone reccomend buying a different carb. I have jets to rejet too. Specs in sig...thanks in advance.

 

Your 750 cfm carb is not causing you to not see the ET /MPH
you expect. You can run well into the 10 sec range with it.
Not near enough difference in a bigger carb for the money.
It may not be calibrated right to get maximum horsepower out of it though.
Could be a fuel flow (volume) or ignition timing issure.
11.5:1 compression ratio is pretty high for street pump gas.
What octane gas are you using and what ignition timing.?
(total mechanical timing @ high rpm)

Need more specific info on your combination and performance
so far ( ET, MPH, 60ft , traction etc)
Thats enough motor to run well into the 11 sec range.
Something else is wrong.

 

I will try to get a time slip...I am at school right now. Off the top of my head I think I'm at about 10 degrees advance base timing, 36 total at 2500 RPM. I put a new holley high flow pump, fuel filter and all new fuel hoses to the carb. I tapped this pump into the gas tank via an aluiminum gas line. I do not think fuel is the issue unless I have to rejet. I adjusted the air/fuel to the best of my ability with the help of a vacuum gauge and my air/fuel meter (not the best gauge I've seen). I am running 93 octane gas but at the track I put octane booster in. Note that the duration @.50 is pretty high allowing me to get away with the 11.5:1 ratio. This motor and all the electronics are pretty much brand new (3months old)and I bought all the parts in it. The only part that isnt new is the bare block. My option now is to hit up a dyno. What jets do you recommend for the primaries and secondaries. I bought the holley jet kit but have yet to jet it.

 

Don't be sucked in to this I got a big cam so I can get away with running street gas with 11.5:1. compression.
Bull Hoooy. Its a myth.
Unless your actual measured cr is lower than what you think.
The EGR effect of the cam will help at part throttle cruise around town but you'll be detonating the motor at WOT. Octane booster
is only good for a few .1 .2 of an octane.
Your motor probabily needs a true 100 octane.
This may be your whole problem. A motor that is running in detonation will not make power. You won't likely hear it either.
The exhaust is too loud. Retest the car with the right octane gas.
(racing gas) and save the little can of octane booster for your
mini bike. You should be able to mix 110 race gas with 92 octane street gas to get a decent octane for street/ strip.
That being said, try 70/74 primary jetting and 80/84 secondary
jetting. A 4.5" powervalve and .035" shooters should be close.

Those 230cc heads are pretty big for a 383 and that cam and intake, but thats another issue.
Is the intake port matched to the heads?

 

Yes the intake is port matched. The entire engine was professionally built my a reputable machinist who works out of the Hanscom Air Force Base, MA. The measured compression was measured to be 11.5:1. What is the fuel mix...half and half? Damn this is gonna be pricey with that fuel. Do you think I will damage the engine running 93 on the streets?

 

You should have no problem running that on pump gas. 11.5 isn't that high at all considering the aluminum heads and largish cam. And no, it's not a myth, cam size has a huge effect on compression vs. gas requirment. I've run more compression on a smaller cam with full timing just fine on 92 octane. Altho it certainly couldn't hurt to try some hi-test at the track to eliminate one possibility. maybe you screwed up at some point, and your CR/timing is really much higher.

Bottom line, the car is not tuned, at all. Get a gauge and get to work on it before you complain too much.


FWIW, no it being 750 is not the root of your problem. I would get a little bigger, but thats costing you a tenth or two...not a couple seconds.

 

Jester
When you say get a gauge on it, what do you mean? I am used to working with FI and am brand new to carbs especially holley. Do you agree with the jets FBird recommends? Also thanks for the input.

 

Well I think thats gonna be a hair small on the jets...but that is just a guess. There are just too many variables on every motor for anyone to really be able to accurately say.

By a gauge I mean an A/F ratio gauge. They're $30-50, and while they do have limitations they're absolutly invaluable. It sure beats just wondering if it's close or not, and it's a whole lot cheaper than a couple hours on a dyno with a WBo2.

 

I have an A/F meter and tried to adjust to the best of my ability. I get it to stay green but then it will go rich by another notch (its digital). It's all over the place when I drive. The A/F should be close though. Let me try jetn and then its a trip to a dyno with a mechanic who is good with carbs.

 

You'll be fine for easy street cruising and could probabily get by if you knocked the timing back a few degrees.
(This will reduce power a little but save the motor.)

But full throttle full timing accelerations will require more octane.
More than 93. Exactly how much I can't tell you.
My educated guess would be 100/102 R/M octane.
You'll have to find that out for yourself. The place to start is with 110 octane race gas and work back.
But understand this, some proper mix of race gas and pump gas
is far cheaper then having to replace all the bearings or worse,
from detonation.
This is the place to start as any tuning gains will be compromised
by a need for sufficiant octane.
Try a 60/40 mix of 110 and 93.
Find what ignition timing gives the best mph in the quarter mile.
Only run as much timing as you need , no more.
If you get the same mph with 34 deg as 36 or 38, run 34.
The et will have more to do with traction and driving skill.
Then reduce the fuel mix to find out how much the motor wants for octane. You'll know cause the MPH will fall off. Make no other changes, just the fuel. You may want to use a knock listener to detect knock. (amplified headphone listener).
Then work on the jetting.
The jetting i recommended will be close. Do not try to squench out any detonation with WAY over rich mixtures as Jester is leading you, as you'll never get the full power that way.
( This is called "fuel dumping") Water/alcohol injection is much more effective. Fuel dumping is a crutch solution to insufficiant octane on a high compression motor.
What was the MPH in the quarter? Gives me an idea of where
you're at horsepowerwise.

 

Heres my timeslip:R/T .810
60' 1.882
330 5.425
1/8 8.398
MPH 82.67
1000 10.972
1/4 13.159
MPH 102.71

 

Gross horsepower is less than 400. About 50 to 70 less
than you would expect from your combination.

The 60' times are ok for HITHERE stock chassis car.
This car should be running mid to low 12's at 110+

What about the exhaust system. Can't get 470hp thru HITHERE
250hp system.

What jetting is in the carb now?

HITHERE'd try some high octane gas and take it from there.
Try uncaping the exhaust to see how efficient it is.
Then up the jetting 4 sizes pri/and sec and see how the
MPH reacts.
Be sure you''re not running too much advance @ high rpm.
should be 32 to 36.
What ever gives you more mph is HITHERE step in the right direction.

 

Should I just start with the pri/sec? How about the PV. I am not even sure how to change a powervalve. Im very new to carbs. I do have the holley jet kit though. What about initial timing- does 10 advanced sound ok and where should my idle be set when adjusting initial timing. I have had it set at 1000RPM. The motor was built with the help of desktop dyno 2000 and although not totally accurate the results were a wopping 600HP/530LBS TQ. Im sure the 4:11 gears and Moser rear should help alot. I have the NX nitrous system but am waiting until the car is better tuned before using it. I need to get that HP .

 

No start with High octane gas... read the post.
Stop thinking all over the place and start the tuning process.
If you operate a motor with insufficient octane gas you will not make any horsepower, any other tuning will be almost meaningless and you'll severly damage the motor in real short order. ( detonation).
The powervalve is irrelevant to this full throttle testing.
it opens as soon as you floor the gas reguardless of its rating.
(this motor will need a 3.5 or 4.5" power valve ( later)
The timing should be set for full timing at high rpm with either a timing tape or a advance timing light. 32 to 36 deg at high rpm.
like 4000+ rpm. be sure that the advance mechanism is fully advanced when checking it. Don't worry about the timing at idle.
It should be checked at as slow a speed as the motor will run at.
less than 1000 ( in gear.) You'll need more than 10 deg. more like 16/20 at idle. You can recurve the distributor later.
set for max high speed total advance for now. start at 32 with high octane gas. Go to 34 then 36 to see how the MPH reacts.
Do not go by the feel of the car.
Forget the Nitrous until the motor is tuned right. Unless you want to see what the inside looks like. This motor will definatly need 110+ octane gas to use nitrous.
As long as the jetting is 70/74 pri and 80/84 sec its ok for now.
Get a book on holley carbs if you're carb challanged.

The gears have nothing to do with the motors power output.
The exhaust system does. Discribe the exhaust system.

 

Im afraid to say the exhaust system is a complete hack job. I have hooker long tubes to a 2.5" pipe to a 2" pipe then back to 2.5" out to a flowmaster system. I am getting teh mufflex y-pipe soon, but have heard complications with them.
Also I put the bushings in the distributor so that I attain 36 total advance at 2500 RPM...should I take this out and do it all manually? I really appreciate your help and criticism. I plan to start the tuning this weekend.

 

Sounds like a 250 hp exhaust system. Uncap it at the track and unleash the hounds.

There is a good article on building hi performance no bull**** exhaust systems that make big power. Its by David Vizard.
Go figure. It was in one of the circle track mags.
Lots of good science and info. No bull. Essentually:

You need X amount of muffler flow to make Y amount of power.
The rest is details. I'd look to a custom mandrel bent/ welded
system with 3" pipes joining into a custom 3.5"/3.75" main pipe back over the axle into a pair of flowmaster race mufflers ( Delta Force) behind the axle. You cannot buy this you have to make it or get someone to make it for you. But should be actually cheaper than a popular off the shelf cat back system. You can buy the Y pipe and pipe pieces from Flowmaster and Dyno Max
(Walker)
If I find the article I'll send it to ya. May be on this computer somewhere. The distributor sounds fine as long as you're actually seeing full advance when you set the timing.
usually if you set it up for a real fast advance curve like that, it is very instable at idle. I prefer a little slower advance curve with lots of initial (16 to 20) at idle and 32 to 36 at high rpm. all in by 3000 or so. Much more stable.
You can buy a balancer timing tape cheap enough.

 

......... This should keep ya busy.... )

David Vizard Exhaust Article

 

damn man, i hope you get that figured out, you should be hitting 116 ish mph, with those parts in a relatively light car.

just because nobody else asked, what lobe separation angle is that cam on?

the compression ratio thing is all about OVERLAP

if you have a cam with 255 @ .050 on a 106degree LSA it will require less octane to run than the same 255 @ .050 on a 114 LSA



adam

 

The seperation is 110. Check this site it has my cam adn all the specs. It is part # 50169
http://www.holley.com/HiOctn/ProdLin...CC/Chevy4.html

 

Of course you're fully prepared to back that therory up with a full guarrantee against his engine damage, aren't you.

The cam timing will only have a minor effect on the engines octane requirement. Actually you have it backwards, unless
that motor actually needs a cam on something else than 106, like 110 then of course the motor would be down on power
as compared to the same motor with the right cam.
At best this will have a minor effect, much more minor then you think and only mostly at low rpm. Once the motor is in its power band and there is no more exessive egr or fuel passsing right through the motor, it will have high cylinder pressure @ WOT and need approxamatly the same octane to reach max power with out
some kind of power robbing tuning crutch.

Either way this motor will need more octane than 93.
Even if it say only really needs 95 octane to keep out of detonation, it will be damaged in short order with 93 octane, probabily without you hearing a thing. *It will need more then 95* Seen it first hand. A tough lesson of one of my friends.
Motor was a true 10.7:1 Destroyed the ring seal and pinched the piston pins from detonation in minutes of running at WOT.
There was no audible knocking noise coming from the motor.
A shame. One of the times ya really hate being right.

 

honestly, you shouldn't have to worry about that much compression with that much of a cam.......

hell in a factory engine that say has a 9.5:1 comp ratio with iron heads, just switching to aluminum will really need a full point of compression to maintain thermal efficency......

your bleeding alot of your compression off with that much duration..... i know of a guy running 11:1 on cast iron heads and he has one of the most *** awful camaros in my area.....

this is an area that has met alot of agrument from the racing community.... every combo is different on octane requirements and compression needed.....

i can only give you a few tips that might help but it's nothing that you haven't probably got.....

run a 160* thrmstat, and have the fans come on at 180*
run as cold as you can air intake to keep the intake charge temp low....

this will keep the chance of detonating to a minumum...

if you honestly feel uncomfortable, then go ahead like the guys said above and run ya some 100 octane and see if it helps.. if it dosen't then you know thats not the problem and can consentrate on other areas....

i'm sorry i cannot be more of help.. i hope you are able to find out what it is causing this...

good luck!! and i hope it works out for ya!

adam

 

Adam : ya don't get it do ya. This motor has nothing to do with
a 9.5:1 compression motor with or without alumium heads or
what ever.

"You know a guy who has 11:1 compression and the car is awesome."

How scientific. Give us a break.

Big cams bleed cylinder pressure at low rpm only.

The heat of compression is a constant (Gas Laws)
an 11:1 compression motor will heat the mixture aproxamitly the same temp rise reguardless of the cam timing. The pressure will vary a little but the temp will be near predictable. There are other factors that will affect it but only minorly.
Once the mixture exceeds the auto ignition point (temp)
detonation results.
Sure he'll be able to cruise around at part throttle on street gas but you can bet your friend runs better gas at the track when he gets in it heavy.
Won't be able to get near optimum ignition timing or jetting without better gas.
A true 10.5:1 I'd go along with. But not 11:1.
And not going up a hill on a scorching Texas afternoon.

 

but thats the whole point.....

aluminnium will carry heat away from around the combustion better, resulting in lower thermal effecincy..... thats why you would bump it up another point to compensate....

thats with a stock cam, which he dosen't have... he has a sizible cam thats bleeding off more cyl pressure resulting in him being able to run a higher compression ratio...... with timing being in check of course...

if he has a lower overall temp and if he keeps the intake charge as cool as possible then he will further add in keeping detonation away.....

detaonation is caused by hot spots in the combustion chamber, i think your confusing it with preignition........ preigniton is where the air fuel mix ignites before the sparkplug has a chance to do it because of the temp rise from compression.

and i argee with problems in a hot day say like around 100..... hell that could detonate a 10:1 comp motor very easily if the timing isn't in check......

now to say that compression temps will stay almost the same is true, but running the engine cooler and pulling the heat away from the combustion chamber will lower overall running temps, which in turn will lower combustion chamber temp.....

and the next time you feel like you have to address or try to correct me with a little attitude and remarks like you did, try to use a pm and have respect for others on here that dosen't want to read smart *** remarks...... i tried to give him a few tips if he hadn't already tried them, i even told him to go ahead and do like the feller said above and try some 100 octane, so theres no need to come in and throw remarks out like you did.....

 

with the cam on a 110 degree LSA, you WILL NEED MORE OCTANE.

11.5 to 1 could be done, however you better look at something on a 106 or a 107, it wont be as torquey, but it will run on pump gas.

call comp cams, they have always been very helpful to me.


adam

 

F-Bird88
I bought a new exhaust today from mufflex. Ya the combo that costs like a grand. I got the 4" catback with dual pipes and a spintech muffler. Maybe this will solve some problems for now. I am planning on jetting the carb in two weeks and taking it to the track. The people at mufflex said their whole system will bolt right in. Are you familiar with this or are they just taking me for a ride i.e gonna cost me for fabrication at the shop. Thanks

 

I doubt if its a true bolt on, but..... let me know how you make out. Getting a exhaust system that can breath will go much farther than a bigger carb. You're headed in the right direction
now. Take your time and make one change at a time.
You won't solve it all in one day but I believe it will come around for you with patience. Sometimes going fast if is all about patience and attention to details.
You have a good basic piece to work with anyways.

You have a good carb to work with that can be tweeked for more air flow in the future. The pro carb preparation shops
start with a carb like that and tweek 'em up to 950/1000 cfm with the response of a 750cfm sized carb so hang in there.
In the mean time you've got lots of more important tuning to do.

Good Luck

HardCore Hot Rods

 

Here's some numbers:
Int Dur = 281*
Exh Dur = 285*
Int Dur & .050" = 248*
Exh Dur & .050" = 252*
Cam Intensity = 33* (this is good)
L/S = 110*
Int C/L = 106*
Exh C/L =114*

I/O = 35*
I/C = 67* (This figure will build a lot of cyl pressure)
E/O = 77*
E/C = 29*

V/Overlap = 64*
Cam is Adv. 4*

Bore = 4.03"
Stroke = 3.75"
Cubic Inches = 383
Rod lenth = 5.7" (I think)
Total comb. chamber CC''s = 66

Comp. Ratio = 11.49 to 1

With an Int valve closing of 67* this will give you an Effective C/R of 9.043 to 1.
If your Efffective C/R is 8.5 to 1 or better you had better use Racing Gas and Dyno Tuning

Auggie

 

This is all well and good. But only to a minor degree. A lot more minor than many will admit. Till they've smoked a few motors
trying to run on the edge.

Only trouble is none of this Hot rod magazine bull***establishes the true octane requirement of His motor.
The fact remains this motor will need way more than 93 octane to run at full power and until the octane is sufficient to avoid detonation, all other tuning efforts will not
get you to full power. You're very likely to damage the motor trying too.
Are you going to drop a new shortblock off on his doorstep
when it eats the rings, pistons, bearings or more when your theory doesn't pan out. Not likely.
I still remember when you could buy real gas (Sunoco 260)
on any corner and cars came from the factory with 11.5:1.
Been hearing this bull*** ever since they took the lead out of the gas too.
The laws of physics hasn't changed.
Sorry, Been there done that, got the t-shirt.

A conventional SBC with 11.5:1 compression will need high octane gas. Reguardless,,, End of story.

Sorry, if ya took it as a bite in the a**....

 

You think that you have detenation problems? I am trying to convince my friend that has a 455 with around 10.5 or more on stock cast pistons(thats ungodly high for poncho's, they detonate on 8.5:1 sometimes)that he needs race gas, but he swears its ok on 93.......thing is, I will have to help rebuild the engine.

 

The 750 dp is a fine choice for a 383. As long as you have enough stall to keep bogs away, its perfect.

 

Tell you're friend if he wants to stretch the laws of physics, fine but he'll be paying ya to "help him", the second time.

I would not build it that high.

 

isnt that number, 11:1, a static compression ratio?

doesnt that mean that you only actually get an 11:1 with a 100% Volumetric efficiency?

if thats true, then when he makes his peak torque, that should be somwhere around 90% on a very well matched setup right?

so he never actually hits 11:1, right, just close to it...

but all the same, "effective compression" or "dynamic compression" Should still eventually be high enough to warrant detonation at that peak with 93, aluminum parts or no... right?

Ah, but there are other things that effect that right? dont air inlet temp, coolant temp, atomazation, exhaust flow, swirl, and a number of other things change the "efficiency" of an engine, make it react differently?

so in the end, if everything matches up, it comes down to those small variables to let us know if detonation is a real concern or not right? Not just a number, 11:1. Dont Lt-1's run 11:1 in stock trim? Sure they have a reverse cooling system, and probably never hit 90% VE in stock trim, but hey, they do it right? And on the other hand, my little 9.5:1 compression small block building 120% VE thanks to Mr. blower has had a blown headgasket running 100 octane fuel because of a cylinder pressure issue with the exhaust...

oh, HO! What were we talking about?

 

Well I bolted on the mufflex 4" exhaust this week. Took 4 weeks to get the system and about 7 calls--what a pain. After taking it out for a ride I was AMAZED at the power. I could hardly control the car when I launched it and the torque was incredible at every shift (automatic). I hope this is a big factor in the dissapointing times. Its really hard to tell since I havent driven my car since November. I head to the track on Wed and hopefully Ill dip down into the 12s. A friend of mine is coming to help me jet the carb.

What should I do for initial timing? I have it at 15degrees advanced but it is dieseling. If I start the car up and shut it down quick, the car wont diesel. I think maybe because the ide is high in park about 1200RPM. Do I lower the idle then check for dieseling or change the initial advance. Its at 36 deg advance at about 3000RPM.Any last minute track hints.

Also check out some pics of my mods being installed--- on my website. The tools for making the site are horrible so I need to find a new web maker (any suggestions). 88 Notchback

 

You know I had that same problem with my eng. (1984/355/10.3/steel heads). What I did was get one of those solanoids used to up the idle when the A/C is engauged and used it for my idle speed control. I made up a bracket and mounted it next to the A/C solanoide on the Q-Jet. I wired it so it would be on when the key is in the run pos. I then backed off my idle speed control screw on the carb all the way. When the eng. is cold and I turn the key to the on pos. the sol. dosen't have enough power to move the throttle against the spring tension, but that doesn't matter because I have to press the gas pedel to set the choke anyhow and the eng. idles on the fast idle cam (1800rpm). When the eng. warms up the sol. will hold the throttle at the adjusted idle speed of 1000 rpm (the sol. shaft is adjustable) in nutural. When I put the trans in park and shut the eng. off the power to the sol. is gone so it shuts off and the throttel plates close compleatly. This will not allow any air or fuel into the eng. so I don't have any run on. Anyhow it works great for me .

Auggie

 

I like that idea. Where did you get the selenoid and any wiring diagrams? My only concern is that there is another reason why I am getting the run-on and that by doing this I am just bandaiding it and could possibly be running the engine improperly.

 

I just went to a junk yard and got one off of an Olds but there everywere. As far as the wiring goes my car is still in storage but I probely just found a hot in run wire under the hood and taped into it.

Auggie

 

Well I ran last night and got some decent times considering I have not touched the carbs jets. Ran a 12.64 @108.66 and a 12.08 @ 114.7 with a 100 shot. I think I blew my tranny though. I have to rev up to about 5500rpm then let back to get into 2nd and then thats it, No third gear for me. You guys know where I can get a tranny to withstand this power. My nitrous will go up to 300HP. Also, Im jetting the carb tomorrow- should I go up 2 jet sizes primary and secondary for the first change?

 

not bad times. Certainly a step in the right direction.
Consider swaping in a th350. The overdrive in the th700r4 is near useless as far as mileage improvement with that big cam.
The extra cost of the th700r4 won't be returned by the gas savings of od. The th350 will be much cheaper, run better and more reliable.
As for the jetting, to soon to tell. You're supposed to get baseline runs then change jets the same day and retest to see a difference.
The weather changes performance day to day too much.
What gas did you try? what timing? what jets are in the carb now? I like to start slightly rich on jetting and then run down in jetting while watching the MPH and plugs. *On the same day.*
Rich jetting is safe and tuning towards "lean best power" shows
the performance better. As you aproach best jetting (power) the mph will increase. As you go further leaner (from best power) the performance will fall off quickly. All the time watching for preignition and plug overheating warning signs. Going richer from best power will only effect power slightly per jet change till it gets real fat. Can also mask a traction problem or octane problem.
Can confuse your tuning efforts. But running the jetting down from rich to lean always shows what the car wants quickly.

 

FBIRD-88, you've been a great help and my car seems to be getting faster every trip to the track. My main concern now is the tranny seeing as how I have to buy it next week and dont have a car. I do occasional 50 mile highway rides- maybe once a week at most and the track is 50 miles away. I have 4.11s in the rear. What problems will I run into with the TH-350? Whats the difference between the TH-350 and TH-400? Whats a good price to get it built to handle that much HP (600+nitrous of 300) and torque and I know its not a bolt-in which means more money (how much). Will this tranny increase 1/4 mile times? Im really leaning towards the TH-400 the more I think about it because people are saying the 700R4 even built wont handle the power. A guy quoted me 1700 for a 700R4 with all Art Carr products that handles 700+HP and 7-800LB/TQ-- is he full of it?

To answer your questions. I ran 93 octane because I was broke. On one run I got a fire out of the carb and the car stalled when I floored it. I increased the FP to 7#. When I floor it there is a hesitation and it seems to have a slight bog (I get nervous it will stall like the first run) so I have to ease into the gas. The timing is 15 degrees advanced and my plugs are light tan (not quite white). Plugs are gapped at .050. Jets in the carb are stock (whatever comes in a Holley 750DP). Ive yet to take the carb apart. Thanks again!!

 

Decrease the plug gap to .040" increase the accelerator pump shooters to .042" be sure you're getting a full shot of fuel. (linkage and pump cams) Get the hollow accel pump shooter screws too.
Recurve the distributor for more initial but the same total advance. ya need to time it for the total mechanical advance though. Setting and knowing the initial is not enough.
One indication of a lack of octane is a motor spitting back through
the carb. (over heated combustion chamber)you're really taking a chance running that motor on 93... What heat range plug are you using?
The th400 is stronger than the th350 but weights more.
both will cost less and perform better than the th700 over time.
The th350 is cheaper to build and freshen up.
The high gear clutches will be a maintanence item on all these trans over time @ that power level. Get used to it.
But hi perf clutches and a good valve body will help a lot.
Th350/400 torque converters are cheaper to buy and fix if nessessary.
I highly recommend a heavy duty 2nd gear sprag for the th350.
The th350 is easy to swap in with a B&M change over kit and a
FBody V6 5speed drive shaft. ( better get a heavy duty one built but that is the length). I'd really save the NOS till ya got it more dialed in.
You're making about 430/450 hp at the crank now. Based on 108mph trap speeds.
I've had the same TH350trans (one rebuild) for 25+yrs in 4 different cars behind 5different motors BB and SBC + NOS.
I never actually ever hurt this trans in all the yrs I've had it.
A friend borrowed it for his 9 sec race car and smoked high gear.
cost $400 bucks (Can) to rebuild.
Hard to complain about that. Don't think a TH700 is going to serve ya that well.

 

<b>I do occasional 50 mile highway rides- maybe once a week at most and the track is 50 miles away.</b>

just throwing in that fact that with a TH350/Th400 and 4.11:1 gears your RPMS on the highway during that 50 mile trip will be an extreme wear and tear factor on your motor.


that is, unless you like to drive 40 MPH the whole way.

you may be able to offset this a little tenny bit by driving there with 29-30" tall tires. that will drop your gear somwhere around 3.60:1, if you had a 26" tall tire on there before.

 

Don't be a whoose The rpm at 60mph would be 3350. (4.10's 26" tires) A good cruise rpm for this motor.
Not going to cause severe wear. I drive back and forth to the track all the time. There was only a small mileage penalty between the old th700r4 and the th350.