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Old 06-11-2014, 07:53 AM   #1
Steffan
 
Join Date: May 2014
Vehicle: 70 Mach1
Location: DK
Posts: 25
Default What do i need to stroke my 351w? and what gear ratio is best?

Hello,

I am hoping some performance tuning experts in here will help me understand this.
Please note, that i am new to building engines, but i have a mechanic helping me put the parts in/on.. but still, please explain everything like i am a 5 year old.

I am trying to get my 1970 Mach1 351w to ~400-450HP and better low-end power.
The car is used for daily driving >65MPH and a little highway 65-75MPH, and i would like to still be able to drive like that, without the engine blowing up.

My engine has a Edelbrock "RPM Air-gap" (#7581) intake manifolt and the carburator is a Edelbrock 750CFM. Everything else looks stock.
I also have some new Headers laying around i plan on putting on too.

A top-end kit was my first thought, since it seems like the easiest way to get more HP.
But a lot of people suggested that i do the following instead of buying a top-end kit:

- Stroke it to 393 CUI or 408CUI
- higher gear ratio in the back, to give better low-rpm performance


I have the following questions:

1. What gear ratio would be the best for my driving, without hitting an insane RPM when driving 65-75MPH
2. Do i need different gear ratio's when stroking the engine that if it's not stroked? i can i change the gears first and then stroke it later without any problems?
3. Where can i buy a gear kit? i can't seem to find them. (if you know an European shop, that would be awesome)
4. 393 CUI or 408 CUI stroke? some say that 408 gives less high-rpm HP and only little extra low-end torque, so it's not worth the money
5. What do i need to stroke my engine besides a stroke kit?
6. Do i have to do anything to the top end when stroking the engine? (my specifications on current setup in top of post)
7. Do i have to overbore .030"? (i am guessing this is "drilling the cylinders wider", am i right?)
8. Would it be better/cheaper to buy a shiny new and already stroked short block instead, then put my top end from the current engine on it?
9. Any comments? suggestions? or anything before i throw my money at this?
10. If i stroke the engine, what kind of HP and torque boost should i expect to get from the engine?

If someone could explain to me how all this works, i would greatly appreciate it since i know nothing about it at all.
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Last edited by Steffan; 06-11-2014 at 11:59 AM.
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Old 06-11-2014, 08:43 AM   #2
racer_dave
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Engines are nothing more than a big air pump. More air in & more air out= more power. Given that, it comes down to budget and implementation. Budget is simple- more $$ =more power. Implementation is another story. If you want to drive the car 65-70mph do you really need 450hp? Would you be better off to spend a bit less, make a bit less power and still have a cool car with a nice rumble to it. Anyway...

1. What gear ratio would be the best for my driving, without hitting an insane RPM when driving 65-75MPG - Will depend on final engine combination, transmission choice and tire sizes
2. Do i need different gear ratio's when stroking the engine that if it's not stroked? i can i change the gears first and then stroke it later without any problems? - same answer as above
3. Where can i buy a gear kit? i can't seem to find them. (if you know an European shop, that would be awesome)- I don't know a European shop, maybe another user will. In the US I go to Motive Gear, Jegs, Summit
4. 393 CUI or 408 CUI stroke? some say that 408 gives less high-rpm HP and only little extra low-end torque, so it's not worth the money- Not a yes or no- depends on the piston/cam/heads/intake in combination. Cubic inches is not always needed. I get 540HP out of a 302 stroked to 347 in one of my racecars. Also, high HP at high RPM is better for long term high speed runs(not what you said you wanted), low RPM torque is what launches you away from a stoplight and lets you pull out and pass at will(which I think IS what you want given the whole 'daily driver' thing
5. What do i need to stroke my engine besides a stroke kit? - depending on the stroke change you will need the block machined for clearance
6. Do i have to do anything to the top end when stroking the engine? (my specifications on current setup in top of post) - Depends, but you will probably need new heads to increase the airflow.
7. Do i have to overbore .030"? (i am guessing this is "drilling the cylinders wider", am i right?) - depends on the condition of the block(if there is a big ridge/cylinder scarring you might need to go more- .040), but if you are gutting it then it is always better to get it bored. You'll also want to get it decked and align bored at a minimum, I also spend a lot of time working on/smoothing the oil drainback areas and lifter valley
8. Would it be better/cheaper to buy a shiny new and already stroked short block instead, then put my top end from the current engine on it? - Given the questions you're asking and since this is your first engine build(with help) I would seriously look at this, except I would look at a complete engine. Your stock heads won't be enough for a stroked small block. You'd end up choking the motor down. The big pluses are that you get a known good engine(or a warranty) and the parts selection is done for you. Really look into this, the better engine houses have good products and the prices, aren't much more than you buying the pieces. Plus you'll get it done faster.
9. Any comments? suggestions? or anything before i throw my money at this? I meant it- Look at getting the motor already done from a shop. There's nothing worse than trying to do it yourself and not getting the performance you want, or make an error in assembly that hurts the motor, or it takes a lot more time than expected and delays you getting to drive the car.
10. If i stroke the engine, what kind of HP and torque boost should i expect to get from the engine? Wholly dependent on what parts you buy, how they are installed and how they work together


Something to remember- what type of gas are you going to run? Its easy to say I want XX horsepower, but if you need to run 100 octane fuel to get there then your daily driver doesn't become such a daily driver any more
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Last edited by racer_dave; 06-11-2014 at 09:04 AM.
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Old 06-11-2014, 10:31 AM   #3
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Look, 400-450 hp is a lot for a street car.

For the purpose you have described above, a stroked 351 is way more than you will ever need. It is also really expensive to build it correctly and to build it to last. i would think based on my knowlege, you will be in the area of 6-8k to do it right.

If you current engine is in good shape, a really good set of heads, and a cam to match, with headers, ignition and a properly set up carb with a set of 3.55 rear end gears will be plenty of juice. (make sure to have your distributor set up for the car as well)

this set up should get you around 350-375 hp which is a lot of juice. If you looking for a little more seat of your pants feel then step it up to 3.73 gears and you should be very happy.

this route should cost you about 2800 for the heads,cam,headers, and ignition.

the gears (also i recommend a trac-loc for the rear end) once you buy them and have it set up should be about 800. i would do the gears and trac-loc first.
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Old 06-11-2014, 10:50 AM   #4
Steffan
 
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Quote:
Originally Posted by racer_dave View Post
Engines are nothing more than a big air pump. More air in & more air out= more power. Given that, it comes down to budget and implementation. Budget is simple- more $$ =more power. Implementation is another story. If you want to drive the car 65-70mph do you really need 450hp? Would you be better off to spend a bit less, make a bit less power and still have a cool car with a nice rumble to it. Anyway...

1. What gear ratio would be the best for my driving, without hitting an insane RPM when driving 65-75MPG - Will depend on final engine combination, transmission choice and tire sizes
2. Do i need different gear ratio's when stroking the engine that if it's not stroked? i can i change the gears first and then stroke it later without any problems? - same answer as above
3. Where can i buy a gear kit? i can't seem to find them. (if you know an European shop, that would be awesome)- I don't know a European shop, maybe another user will. In the US I go to Motive Gear, Jegs, Summit
4. 393 CUI or 408 CUI stroke? some say that 408 gives less high-rpm HP and only little extra low-end torque, so it's not worth the money- Not a yes or no- depends on the piston/cam/heads/intake in combination. Cubic inches is not always needed. I get 540HP out of a 302 stroked to 347 in one of my racecars. Also, high HP at high RPM is better for long term high speed runs(not what you said you wanted), low RPM torque is what launches you away from a stoplight and lets you pull out and pass at will(which I think IS what you want given the whole 'daily driver' thing
5. What do i need to stroke my engine besides a stroke kit? - depending on the stroke change you will need the block machined for clearance
6. Do i have to do anything to the top end when stroking the engine? (my specifications on current setup in top of post) - Depends, but you will probably need new heads to increase the airflow.
7. Do i have to overbore .030"? (i am guessing this is "drilling the cylinders wider", am i right?) - depends on the condition of the block(if there is a big ridge/cylinder scarring you might need to go more- .040), but if you are gutting it then it is always better to get it bored. You'll also want to get it decked and align bored at a minimum, I also spend a lot of time working on/smoothing the oil drainback areas and lifter valley
8. Would it be better/cheaper to buy a shiny new and already stroked short block instead, then put my top end from the current engine on it? - Given the questions you're asking and since this is your first engine build(with help) I would seriously look at this, except I would look at a complete engine. Your stock heads won't be enough for a stroked small block. You'd end up choking the motor down. The big pluses are that you get a known good engine(or a warranty) and the parts selection is done for you. Really look into this, the better engine houses have good products and the prices, aren't much more than you buying the pieces. Plus you'll get it done faster.
9. Any comments? suggestions? or anything before i throw my money at this? I meant it- Look at getting the motor already done from a shop. There's nothing worse than trying to do it yourself and not getting the performance you want, or make an error in assembly that hurts the motor, or it takes a lot more time than expected and delays you getting to drive the car.
10. If i stroke the engine, what kind of HP and torque boost should i expect to get from the engine? Wholly dependent on what parts you buy, how they are installed and how they work together


Something to remember- what type of gas are you going to run? Its easy to say I want XX horsepower, but if you need to run 100 octane fuel to get there then your daily driver doesn't become such a daily driver any more

This is some really great answer, thanks a lot for taking your time to answer this post!

I can get 95 and 92 octane where i live out of the pump.. I was under the impression that i could get 400HP easily with one of those. I don't really want to start using race-fuel or something like that, since the car is a sunny day, daily driver.

Can you recommend a crate engine with ~400HP where i can just use the intake manifolt and carburator i have (they are almost new)?


My budget is ~$4500-5000

Would you be able to build a ~400-450HP engine for 92 or 95 octane with that budget ? or will that cost more?

The problem regarding the low budget is where i live.. Denmark.. i have to pay 28-30% taxes on everything i order from the US that has to do with engines.. so if i buy a $4500 engine, it will cost me ~$5850 + shipping (~$500)!

I would really would just like the car to be a daily driver, that is able to burn some rubber easily when i need some fun. No racing.

What would you recommend me to do ? stroke it, top end kit it or just lower the gears in the back? It feels like the car has ~200HP now but i don't know for sure..
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Old 06-11-2014, 11:54 AM   #5
guitarman376
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I say get aluminum heads and roller conversion valvetrain( cam, lifters, rockers) . Even with that, a 750cfm is too much carb for a street driven car. My bet is these changes would net 75hp+ and probably 100ft/lbs torque. See if you want new gears later.
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Old 06-11-2014, 06:27 PM   #6
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I have a 351w with a top end kit and a c4 with 3.55 gears. its sucks on the highway so if im gonna do a lot of that driving I put in a 2.78 gear I have two centers so its fast to do. any way im running maybe 350 hp and its more then enough for a driver I think more would be a pain even with the 2.78 gears if I get on it leaving my house it spins the tires for ever
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Old 06-11-2014, 10:31 PM   #7
barnett468
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i worked up the following for a 410 yesterday fir someoine. the 392 will be similat



cam - comp xe284h hyd flat tappet 69 ivc, 64 when adv 4 degrees.

advance it 4 degrees with an adjustable timing chain set. good mid and top.

http://www.compcams.com/Company/CC/c...?csid=802&sb=0


slower option with good lower mid and mid power

Xe274h 63 ivc

http://www.compcams.com/Company/CC/c...?csid=801&sb=0



Carb – if you don’t need a choke maybe a 750 mechanical secondary 4500.

http://www.holley.com/types/4500%20Dominator%20HP.asp





Heads -Afr 195 or 205 72 cc chamber. Mill them 70 cc which will require around .012”


Block - 0 deck, it might be around .015” to get it there.

Lifters - Crane high rev or crower premium high rev etc.. NOT COMP CAMS.

Rockers - Scorpion “race” type

Rear gear -3.43

Stall converter - 2400

Static comp 9.94

Dyn comp 8.0

Cyl crank pressure 160

If you get your compression up to 10.5 static it will be better but as I mentioned, if you mill enough, you need to machine the intake or head intake surface.

Last edited by barnett468; 06-11-2014 at 10:35 PM.
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Old 06-12-2014, 12:13 AM   #8
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Quote:
Originally Posted by MonsterBilly View Post
Look, 400-450 hp is a lot for a street car.
not for me lol i have a 392stroker built by ford performance solutions.


but I will tell you its not a prius.. this girl chugs gas like nothing, lol.
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Old 06-12-2014, 01:31 AM   #9
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Quote:
Originally Posted by 1970 View Post
I have a 351w with a top end kit and a c4 with 3.55 gears. its sucks on the highway so if im gonna do a lot of that driving I put in a 2.78 gear I have two centers so its fast to do. any way im running maybe 350 hp and its more then enough for a driver I think more would be a pain even with the 2.78 gears if I get on it leaving my house it spins the tires for ever
Which top end kit do you have? and have you made any other modifications to the engine?

Last edited by Steffan; 06-12-2014 at 01:54 AM.
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Old 06-12-2014, 01:31 AM
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