Tunnel Ram

[jim_ss409]

We finally got our homemade tunnel ram finished and installed in time to go racing this weekend. We made it out of steel because I didn't think I would be able to weld aluminum well enough. It's really not all that heavy, probably lighter than a cast iron manifold.:dunno It's a lot of work to build one of these things but I always thought the factory manifold was pretty bad and I also like the looks of a tunnel ram on a drag car.
I was pretty sure that I'd made the plenum too large and I was worried that it'd be prone to bogging off the line, but it ran okay on the first run. The ET was about the same as it would have been with the old manifold but it was up about 2 or 3 mph. It was running a bit lean and felt really lazy at lower rpms so we upped the jetting and shift points a bit and the ET came down a bit. Next we exchanged the 1/2" open spacers with 4 hole spacers and that helped a lot. Our ET's improved and the throttle responce was good. They say that 4 hole spacers will help to tame a manifold with too much plenum, in this case "they" were right. By the way we had to run a spacer in order to have clearance for the linkages.
When I compaired timeslips from other hot muggy days I figure we ran about 2 or 3 tenths quicker and gained about 2 or 3 mph so that's a good start. It's still a bit soft leaving the line and after shifts so I'm going to reduce the plenum volume and modify the spacers a bit. I think there's at least a couple of tenths to be gained yet. I wasn't really expecting huge gains with this setup because the engine is fairly tame... (476ci 9.75 to 1 with a 238 @.050 hydraulic roller cam) and I was already running a fairly well masaged factory dual quad intake. But I think it should work really well if we go to a bigger cam and more compression .I'll let you know how it goes next time out.:deal

[MRHP]

Looks nice. Must have taken quite a while to design. Even longer to make. Wish I had the time for such fabrication. You guys do top notch work!:clap

[Tom Kochtanek]

Jim, that big boy looks nasty! And you get performance as well as good looks. Way to go!

Best,
Tom

[Ronnie Russell]

Jim, I think you are being a little modest. 2 or 3 tenths is a huge gain. I think you are on the right track by reducing plenum volume. I also believe, as you do, that you still have 2 or 3 more tenths of improvement to see, with some tuning. So it is not out of the question that you will finally end up with a .5 sec. gain over a stock manifold. Quite a feat. Congratulations, and it looks good too.

[jim_ss409]

Ronnie, When I was figuring out how to make this thing I just made the runners the same size as they are at the intake gasket and added a little bit of taper so that they get slightly bigger at the top. I played with the idea of using smaller runners because the ports on the 690 heads looked kind of big to me.:scratch I wasn't sure if the smaller intake port leading into the larger head port would be a problem. But after seeing the way your manifold is done and doing some reading I think it would have been fine. I think smaller runners might make more low rpm power without giving anything away at the top end on my particular engine. I even played with the idea of running a filler strip of aluminum along the bottom of each port and even having it extend into the head an inch or two then tapering away to nothing. For now I think I'll just stick with plenum and spacer mods but after we get it out and establish that everything's working okay,,, who knows I might try experimenting.:cheers

[rstreet]

yeah... congradulatons from here. 2 to 3 tenths...unreal....what model carbs??

[region rat]

Jim, way to go. Sounds like you are real close. 2-3 tenths is HUGE. I think your on the right track with the bigger cam idea. A tunnel ram is for the big end and more cam might help all around. Talk to Allen about the plenum. I'm sure he has a handle on them. Bob

[jim_ss409]

rstreet, I'm running the same 500cfm Edelbrocks that I was running on the factory intake. Only difference is I had to put in bigger jets. In fact I had to put in the biggest jets I had to get the A/F ratio down into the 12.5 to 13 to 1 range.

Bob, I remember asking Allen about the intake he was running at the convention at KC. He said he thought the plenum might be too big. I've been reading a lot about manifold design lately and I get the idea that an overly large plenum is kind of like running too much cam. You make more total power but give up a lot of bottom end. I think I might be able to acheve a better ballance with a little less plenum volume. We're going racing again in a couple of weeks I'll let you know how it goes.:deal

[region rat]

Jims, I bought a t-ram that's aluminum, need to try it out . My plenum looked kinda big also. I bet if you try launching higher and shifting higher, you might negate some of the missing bottom end, unless that makes you run out of cam. Keep us posted. I'll try and find a way to measure my plenum. If it's smaller, you're welcome to try mine. Bob

[b-d409]

Very nice looking! You did a top notch job. The Phantom just keeps getting better and better. :clap

[jim_ss409]

I went ahead and pulled it off last night so that I could narrow down the plenum. I've never really been happy with the way it looked so I guess I was just looking for an excuse to change it. I got the best results shifting at about 6,100 rather than the usual 6,000 but when I tried more than that it went slower. (small cam)
Anyway, I'll be back at the track on July 15th. I'll let you guys know if the changes helped or not.:deal

[Skip FIx]

Not sure if you could weld it to use some of the commercial tunnel ram tops. Then you have some known engineering.

[bjburnout]

Hey Jim
Where will you be on the 15th?
Grand Bend, Cayuga or St. Thomas?

bj

[jim_ss409]

BJ, We're hoping to be at Cayuga on the 15th & 16th. :deal I've got lots to do around here but I'm pretty sure I'll have the car back together by then.

[jim_ss409]

We went racing this weekend with the "new improved" tunnel ram. Unfortunately the car ran about the same as last time.:dunno But that's okay, I still think it was worth the trouble of narrowing down the plenum because it looks better now. We also mounted an imitation Hilborn style scoop. It looks cool but the fuel/air mixture tends to go lean at high speed with the scoop in place so we may end up with a different style of air cleaner. We also milled the four hole spacers down to allow room for the air scoop but we'll probably experiment with other spacer combo's. And by the way, we took first place again this week.:beerbang I think it was more a case of good luck than good management though.:scratch


Here's some pictures of milling the spacers, completed manifold and buffing the scoop after welding a new back end on in order to shorten it.

[jim_ss409]

While I'm posting pictures, here's a few more of us lineing up at the awards cerimonies. (and one from the pits as we were packing up) Most of these cars were competing in the Canadian Fastest Street Car Shootout and had to run a lot of rounds against tough competitors to get there. We only had to race a few other cars from our club so I felt lucky just being in the photo.:D

[models916]

That is one good look'n Chevy, glad it runs well also.

[Ronnie Russell]

Jim, Any thing new to report on the change in plenum size? Any improvement?

[jim_ss409]

Ronnie, it ran about the same. It feels very responsive and there's no hint of bog but the 60' time and ET stayed about the same. (about 2 or 3 tenths quicker than the factory manifold) The MPH was actually up a bit so the HP's okay. My fuel/air meter shows that it's running rich at low speed and then leaning out at high speed so we might change the air cleaner setup. This would also allow us to experiment with different spacers. If we can get the fuel/air right I think it might just dip into the tens on a hot day. If not we'll just wait for cooler weather.:D We might install a larger cam over the winter or maybe even a new shortblock with more compression. I think the tunnel ram would work especially well on an engine with more cam.

[dq409]

Man,,, that looks BAD !!!!:clap