One more chance for the big block

I had a smaller block open clone I tried for RR some years ago. It threw the billet rod at Summit Point in the main straight in front of the pits. Messed the whole engine. Not blaming just the rod itself, it was a billet ARC. I messed them up before at sprint tracks too. There is point everything just get hot and I don't think they hold even with the best oils. Much less in Road Racing. Maybe better with bigger blocks, but I wasn't lucky with the smaller ones and gave up. I do not race 4 cycles anymore but have RR some borrowed "stock' Animals and 206s without major issues. Stock 390s should hold together good. Many outdoor rental tracks in Europe use them and some in the US too and they are run non stop all day during summer months with no issues. Of course, stock.
 
Thanks Rainman. We have had great luck with clones and Animal engines. We've also been racing LO206's for 7 years without a rod or any kind of mechanical failure. I'm going to back down the compression ratio on these big blocks and make a few other modifications and see what happens. I will order a Bullfrog rod and compare it visually with the ARC.
 
Compu-kart said:
Smooth One:
You are lucky with that ARC con rod. The one in my gas VC460 lasted less than 10 minutes. BTW: I was having the same rpm issues as you are. I switched the 1.3 rocker ratio to 1.2 and switched the Mikuni 38 to a 34 and it worked great right up until it blew up. The GX390 runs, I mean RAN, on alcohol and it was great out the gate. No chassis issues, its mounted on a Tonykart, no bottoming out.
Click to expand...
Yes! I feel very lucky with that rod. I run gas because I can't carry enough alky to run a 30 minute road race. I run a 1.25 tubing Shadow. It is fantastic with Stock and Open Animals. I ran it with no stiffing bars. I have them now and I am curious and hopeful that the bars will cure the flexing of the big block. Dog gone it Compu-kart. You are getting me excited again to try my big block. Just as a side note, I am changing the head to stock size valves and a 33mm Flatslide. If there truly is a better rod for the GX390, please let me know. ARC has the capability to make a billet World Formula style rod for this application. I sure hope they will soon......
 
Smooth 1, the GX390 runs on alcohol. We have the 9.5 liter tank and can make the distance with about a liter to spare.

Make no mistake about it, the big blocks are an absolute blast on the long tracks. All the torque you want whether you need it or not. Pulls like a freight train thru the turns and the low down sound gets people talking. They are heavy compared to 2-cycle engines so engine placement is critical. Hopefully we can solve the rod issue and have a successful second half of the season.
 
No sign of detonation on the gas engine. Ran 93 octane gas. Top of the piston looked good. Driver said it made no unusual sounds before it let go. As for the alcohol gx390, this is my first venture into alky big blocks, I have no experience detecting denotation in these types of engines. Driver stated it was running strong at 6700rpm, he heard a "mechanical noise" about a nanosecond before it quit.
 
Compu-kart said:
Smooth 1, the GX390 runs on alcohol. We have the 9.5 liter tank and can make the distance with about a liter to spare.

Make no mistake about it, the big blocks are an absolute blast on the long tracks. All the torque you want whether you need it or not. Pulls like a freight train thru the turns and the low down sound gets people talking. They are heavy compared to 2-cycle engines so engine placement is critical. Hopefully we can solve the rod issue and have a successful second half of the seasonS
Click to expand...
Compu-kart, Thanks for the alky consumption info. I run a 7 quart aluminum tank(can't fit the 8.5 or 9.5 liter on the Shadow. I will add an additional tank and run alky. Bullfrog rod also has inserts. The Briggs Billet World Formula rod has no inserts and the rod has proven bullet proof. ARC needs to develop that type of rod for these big blocks.
 
I have no interest in 420's. I don't know anyone who is running them in the WKA. If someone wants to go with a big block clone there is no replacement for displacement, a VC460 is your friend (provided the rod holds up).
 
Compu-kart said:
I have no interest in 420's. I don't know anyone who is running them in the WKA. If someone wants to go with a big block clone there is no replacement for displacement, a VC460 is your friend (provided the rod holds up).
Click to expand...
O promise I know the 460s are the best bang for the buck in our area for open but a basically got a 420 for free
 
NR Racing (nrracing.com) has "Hop Up" kits for the 420 Predator. Looks like there are three options of kits you can put together.
 
I plan on doing some head mods billet rod billet fly wheel probably a milkuni carb on methanol I want to make a lil tourque! I've raced a big block before just dont know what was done internal.
 
I just measured a rod out of a kawasaki twin
4.476 c/c rod bearing 1.41 .585 wrist pin .
All caliper measurmets .
 
Just for my own knowledge, I assume you guys run these things in Open Sprint?
Interesting stuff....
Clark Gaynor Sr.
 
Thanks Flat Top. I will definitely check out the Kaw rod.

Yes, we run them in Open Sprint. We are working our way to the Unlimited class. I'd like to stay with 4 cycle engines but it's looking like the leap to 2-cycles will have to be made at some point.
 
You must log in or register to reply here.
Back
Top