To use or not to use...(flat top pistons) - Turbo Dodge Forums : Turbo Dodge Forum for Turbo Mopars, Shelbys, Dodge Daytona, Dodge SRT-4, Chrysler PT Cruiser, Omni and more!
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post #1 of 13 Old 09-22-2016, 12:57 PM Thread Starter
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To use or not to use...(flat top pistons)

OK guys, quick question that a search did not give me a clear answer. My son and I are building his first car. It is an 93 Shadow. The block could use some work so while it is at the machine shop I am thinking of installing flat top pistons for him. I know TBI motors will never be drag racers but I wouldn't mind giving him just a little more pep in his 2.5. Would you guys recommend flat top pistons for him? Or would just shaving the head some do just as well? Really, I have no issue leaving it bone stock, I am really just curious if the extra hundred bucks would be worth it or not.
Thanks
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post #2 of 13 Old 09-22-2016, 02:40 PM
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Re: To use or not to use...(flat top pistons)

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Originally Posted by Canty13 View Post
OK guys, quick question that a search did not give me a clear answer. My son and I are building his first car. It is an 93 Shadow. The block could use some work so while it is at the machine shop I am thinking of installing flat top pistons for him. I know TBI motors will never be drag racers but I wouldn't mind giving him just a little more pep in his 2.5. Would you guys recommend flat top pistons for him? Or would just shaving the head some do just as well? Really, I have no issue leaving it bone stock, I am really just curious if the extra hundred bucks would be worth it or not.
Thanks
I don't think you will notice the difference. Plus, with the swirl head, you may need to put valve notches in the flat tops, plus possibly run premium fuel due to the increase compression...

I'd save my money and look for a turbo parts car, and just do a turbo swap...
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post #3 of 13 Old 09-22-2016, 06:36 PM Thread Starter
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Re: To use or not to use...(flat top pistons)

Nope. Turbo is not an option. He is only 16 and I do not want him learning to drive with a turbo car. However, thanks for the advice on the pistons.
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post #4 of 13 Old 09-22-2016, 10:10 PM
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Re: To use or not to use...(flat top pistons)

the h.o. n/a carby motors had the block milled a smidge for a CR bump..

but yeah mill the head or block,,

increase CR = increase efficiency = increase HP & mpg

if yu go more than 0.3 -0.5 pts you should really get into 'tuning' to play with the spark & fuel curves,
then yu could 'free up' a few more Hp maybe
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post #5 of 13 Old 09-23-2016, 06:51 AM
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Re: To use or not to use...(flat top pistons)

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Originally Posted by Canty13 View Post
Nope. Turbo is not an option. He is only 16 and I do not want him learning to drive with a turbo car. However, thanks for the advice on the pistons.
No problem. I understand that, my son wanted my Daytona last year(until I swpped it from an auto to 5-speed ). And there was no way that was happening. Don't need that temptation for a 16 year old...

Quote:
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the h.o. n/a carby motors had the block milled a smidge for a CR bump..

but yeah mill the head or block,,

increase CR = increase efficiency = increase HP & mpg

if yu go more than 0.3 -0.5 pts you should really get into 'tuning' to play with the spark & fuel curves,
then yu could 'free up' a few more Hp maybe
Absolutely correct. The engine in the Scamp is an N/A motor and I decked the block .030" & the head .015". Got me to 10:1 compression. But I had to back off timing, and re-jet the carb. It still has the original flat tops in it, and I didn't need to notch them, BUT, it had a 445 G head on it, and the valves sit deeper in the chamber than a later swirl head. OP may be fine, but he needs to check clearance while re-assembling the engine. I was offering up more of a warning than anything. Guess I should have worded my response a little better...

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post #6 of 13 Old 09-23-2016, 09:04 AM
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Re: To use or not to use...(flat top pistons)

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Nope. Turbo is not an option. He is only 16 and I do not want him learning to drive with a turbo car. However, thanks for the advice on the pistons.
UM excuse me sir!!! im 17, and i drive a TURBO car! got when i was 16! its an 86' Turbo Z Auto. Theres nothing wrong with having a turbo! way better for the highway i find too!
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post #7 of 13 Old 09-23-2016, 10:54 AM
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All depends on the idgit behind the wheel. I can say that because I was a true idgit into my 20's.
A four banger Vega got me into plenty of stupidity opportunities.
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post #8 of 13 Old 09-23-2016, 05:46 PM
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Re: To use or not to use...(flat top pistons)

Man, if you wanted to be a COMPLETE IDJUT, like an old friend of mine back in the 70's, just drop a 350 in it...then add NO2!! That beater-looking Vega was a true sleeper back then. Guy was tall, skinny and had a blonde afro, we called him Q-Tip. 😀 Took me out in the country on a straightaway and opened it up. It shook so hard thought it was going to fall apart before he shut it down! 😲 He wound up gutting the interior and welding in some reinforcements to the frame and doors. Let's just say the tank wasn't always in the back....😨

I see so many young guys riding crotch rockets, with no helmet wearing a t-shirt and shorts, hauling azz weaving in and out of traffic popping wheelies. THAT'S REALLY SCARY!!
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post #9 of 13 Old 09-29-2016, 03:23 PM Thread Starter
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Re: To use or not to use...(flat top pistons)

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UM excuse me sir!!! im 17, and i drive a TURBO car! got when i was 16! its an 86' Turbo Z Auto. Theres nothing wrong with having a turbo! way better for the highway i find too!
There is NOTHING wrong with a turbo car. And one day you will understand why I, as a father, won't allow my son to start learning in a turbo car. Let him get use to driving THE RIGHT WAY, then we can drop in one of our turbo motors. Nothing against you Mr. 17, but I am just a protective father who has to pay the insurance on my sons car (turbo adds $$$).
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post #10 of 13 Old 09-29-2016, 06:09 PM
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Re: To use or not to use...(flat top pistons)

You can achieve about 170 to 180 psi on a 2.5 by just cutting the head level to the maximum cut square on the bottom of the head. If you cut head this much you will need a shorter timing belt. I have several of the short race belts made by Mopar performance. Another way to tighten the belt is to sleeve the timing belt idler to tighten the belt more. I have some of these special idlers too. Some people use a Volvo timing belt which is the right length but a little narrower.
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post #11 of 13 Old 09-29-2016, 07:25 PM Thread Starter
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If I go the Volvo TB route, could you tell me what year and motor to look for? I'd rather use a MP belt but the Volo info would be good to know. Also, would you part with one or two of those MP belts?
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post #12 of 13 Old 09-30-2016, 08:46 AM
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Re: To use or not to use...(flat top pistons)

Attributes
2.2

# of Teeth: 124
# of Teeth: 124
Belt Length: 46.5" (1181 mm)
Belt Tooth Pitch: .375" (9.5 mm)
Belt Top Width: .972" (25 mm)
Timing Belt Teeth Type: Trapezoidal (I)
Timing Marks: No
UNSPSC: 26111811

*Attributes
Volvo 2.3

# of Teeth: 123
# of Teeth: 123
Belt Length: 46.125" (1172 mm)
Belt Tooth Pitch: .375" (9.5 mm)
Belt Top Width: .75" (19 mm)
Timing Belt Teeth Type: Trapezoidal (I)
Timing Marks: Sí
UNSPSC: 26111811

*Both have trapezoid teeth. Your 2.5 will have round teeth. I think people used this Volvo belt on the early 2.2 with trapezoid teeth. I always used the Mopar belt and never tried the Volvo belt. You would have to change cam' intermediate' and crank gear to use the Volvo belt. The larger idler pulley will work with your factory belt.
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post #13 of 13 Old 10-03-2016, 05:39 AM
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Re: To use or not to use...(flat top pistons)

FYI
Cam timing is different between square and round tooth gears.
Going from a square to a round tooth cam gear retards the cam, and vise versa.
You would have to change the cam to a square tooth cam, which is not a big deal.
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