Bullfrog Hemi Predator High Compression Piston

#1
Has anyone ever used one of these high compression pistons from bullfrog motorsports in a Hemi predator? According to their website with no other mods it gets you to 11:1 compression. I was thinking it'd be a lot wiser to do this than mill my head to get 11:1. Ole4 reccomended this to me but I haven't seen any reviews so I thought I'd ask if any of you have seen, used or heard of this.
 

trinik7597

Active Member
#3
You planning on running alky ?? I personally don't like the domed pistons ..But you won't find a nicer guy to deal with than Jeremy ...I have a lot of his products
 

trinik7597

Active Member
#5
I am just not a fan ... People have been running them in animal motors for years with good results .. why are you shooting for such high comp. Ratio on a gasser ?
 
#6
I just don't want to run ally. I don't like the corrosive properties. Gas is more reliable. If I have to I'll run Sunnoco GTX 104 before I run alky. The reason I want to run a dome piston is to get to 11:1 without milling. Because I know nothing about valve train clearances and geometry when it comes to milling a Hemi head
 

trinik7597

Active Member
#7
I have a couple gas motors with high comp ratios and they run fine ... I was just curious .. I have never done it with a domed piston though .. my hemi is a 2.835 bore with a wiseco piston arc 3.707 rod with the piston milled to zero deck height and a Honda 14cc head ... Your way is a lot cheaper ..lol
 

fhpe77

Active Member
#8
Holy coincidences Batman, I just emailed Bullfrog yesterday with a list of questions about their hemi piston. Here's what I asked:

1. How much does it weigh?

2. Does your company manufacture it in-house or do you just machine a
blank forging?

3. If you are starting with a blank forging then which company produces
the blank?

4. Your website states that this piston works with the Arc billet rods
that are longer than stock (+0.020", etc.) Is a longer than stock rod
even necessary with this piston?

5. Some dimensions would be nice, can I get a CAD drawing of this part?

6. Are there cam lift and duration limits when considering piston to
valve clearance?

7. Is there enough meat in the crown to allow for further clearancing
the valve reliefs?

8. Will the existing valve reliefs accept larger than stock valves?

9. What is the volume of the pop-up in cc's?


Hopefully they get back to me with some answers. Prior to discovering that this piston is available I was considering going with the Arc +0.020" rod, a 0.040" head gasket, and having the head milled 0.030" to achieve an ~10.5:1 static compression ratio. The Bullfrog piston would eliminate the need for milling the head and probably end up costing more. So why would someone want to do this? Here's why:

Mopar - Chrysler 426 Hemi engine

It's simple. A real hemi needs a pop-up piston. :smile:

-Ray
 
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trinik7597

Active Member
#9
There are limitations on the hemi head in general ... If you are going to run a big lift cam that requires heavy springs .. the valves are short .. the spring pockets are narrow etc .. these things can all be over come but will need to be addressed .
 

fhpe77

Active Member
#11
scotty,

It's been over a week and I have not heard back from Bullfrog. If they do get back to me I will let you know what they have to say. The reality is that it would be cheaper just to use the stock piston and have the head shaved.
 

BWL

Active Member
#13
Yeah, maybe dial it back one for two questions just to get a conversation going. All those questions might sound like industrial espionage or something.
 
#15
I have not used one, I may but right now I am putting together a non hemi and trying multiple clone heads, Next hemi will either use that piston or If I can do it, weld up a hemi head and make it a bathtub hemi and use a stock flat top piston.
 

fhpe77

Active Member
#16
Or maybe I am building an engine and would like to know the specifications that most piston manufacturer's commonly publish. At first glance a cad drawing might seem to be a strange request but I would like to see if additional machine work will be necessary before I purchase their part. I like to plan things and not guess. Known dimensions will not eliminate the need to check PTV clearance with modeling clay but they would allow one to perform a positional analysis to see if a cam of known lift and duration will place the valves at the same point in space and time as the piston. Math really is the most powerful tool in your tool box.
 
#18
All I am saying is Jeremy is a very cool person to deal with and if you opened a line of communication a little bit differently you probably would have had all your answers already ...
 
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