vf750f, 700cc piston swap?

I remember hearing someone mention that swapping pistons from a 700 into the 750 engine raises the compression to 11.2 making for an easy performance upgrade. Anyone here actually done this?

 

There have been a few guys who have done this before. My understanding is that you need not only the VF700 pistons but the rods also.

Back when you could get new pistons from Honda this was a pretty decent way to go. Using pistons that are used is probably not the best idea and getting custom pistons made is kind of expensive. If you went the custom route you might as well go higher than 11.2:1. I'd suggestion something more like 12.5:1.

 

It will require rods and crank.The stroke was 48.6 in 750 and 45.4 in 700. The the rods were longer in the 700's to make up the distance. Way to much effort for too little.

 

Thanks for the info guys.

Jamie: I checked the Honda parts fiche, and it looks like pistons are still available from the factory, std, 0.25 over, 0.75 over, or 1.00 over. They are only about $50 apiece. It's too bad though, conrods would be a bit too much listed at over $200 apiece.

Unfortunately, I need to do some engine work; after purchasing a number of sweet items for the old 750 the cams are fried. I thought since I'd be investing money in the engine it wouldn't hurt to freshen up with new pistons.

Anyone have a good source for a cheap set of hardened cams?

 

Give over, man, just get a newer VFR, like a gen 2; don't waste your time and money resurrecting that dinosaur.

You're not married for life to that old bag of bolts, don't need an annulment from Rome, and no one will gossip that you heartlessly traded her for a newer model !!

 

You need to have your dealer check warehouse stock. My guess is NLA.

You can get custom pistons from Weisco and others (don't use JE though) for around $400 a set. You can also find rods on eBay from time to time pretty cheap.

Take the cams you have and send them to Shadbolt. They do great work. Don't expect much help in the way of profile suggestions though. I've got a lot of notes on that, so I should be able to help you out with a good grind.

 

Jamie, why not JE? Aren't they the same company as Carillo?

 

Actually I think the crank is the same just different length rods, at least on the gen 2. but you are correct, a ton of work for not much gain.

 

I don't know about them being the same, but for Carillo's sake I hope not. JE parts are ok but their customer service sucks royally. They have totally screwed me over in the past and I refuse to use them ever again. You can get the same quality (or better) for the same cost through other places and not have to deal with that BS. Weisco, Arias, Ross are my choices in that order. My 145hp at the wheel VF1000R engine had Arias pistons in it, FWIW.

The cranks are different - the 750 has a longer stroke. Bore is the same between the two, that's why you can run VF700 pistons in a VF750 block. The deck height dimension is not the same, thus the need for VF700 rods.

The best choice is to stick with the VF750 rods and get custom pistons made. That would be the least amount of headache and result in the best overall performance.

 

The last time I talked to Dave Dodge, he told me all I needed to do was swap the pistons. Stroke was shorter in 700 because that's how Honda chose to turn the 750 into a 700. Check your bore numbers, they're the same. The rest of the difference is in the pistons, the 700's have a higher dome, which makes them a "drop-in" upgrade in the 750. Take caution when combining with high-performance cams.

Dave Dodge has been building fast V4 motors for a very long time!

 

Squirrelman, I did just buy a new bike, Buell 1125cr. This old vf is my baby though, my first street bike. Something inside me won't let it die. Plus, mods on this old bike are cheap compared to the thousands I watch my old man put in his harley.

 

Jamie, can you send me some of your cam profile suggestions?

 

Shoot me an e-mail with the rest of your engine configuration. It's all about the stuff matching. You can't throw a huge lift/duration cam into an otherwise stock engine and expect anything except trouble. The combo is key - the parts all need to work together. Oh yeah, and how much you have to spend plays a role too.

 

... ..........maybe he wants to....

 

I've found the "ignore user" feature to be really helpful in these situations. It keeps the clearly dilusional members from taking away from what this forum is meant to do - help people with questions about their particular bike. I support the freedom of everyone to post on all threads. I also support the abiliy to ignore them.

Since I've gotten a 2nd gen VFR I've noticed a striking similarily between it and the first gens. Interesting.