hoffman900

We’re not out there in that session. The GTV we run is a few seconds a lap faster, but that car is tough on a tighter circuit. It’s driven how these cars should, it is a race after all. The Elan should be MUCH faster.

Here is one of our competitors on one of our usual tracks. Note after his spin how much track he is using to catch back up. The car is a 1622cc (MGA) Elva Courier, also set up like I mentioned. Lap time wise it is a good 2-4” / lap faster than the fastest Triumphs at this year’s Kastner Cup (including the TR250k) A great TR4 can run this fast, but the fastest one in the US retired from racing and the car is in the garage. We run an Alfa GTV that is another 3” a lap faster than the video car. A little different than what you guys run, for sure.

I still disagree with this approach. We’re running on big fast, smooth tracks in the US (as well as some tighter club tracks) and the soft spring / big bar approach is absolutely the way to go, especially as curbing has increased in width. You can get the entire car out on the rumbles and basically expand the track by 5-6ft in places. On corner entry and the apex you can buy yourself a foot or more as well to the inside. Almost every modern racing chassis is a soft spring / big bar approach for this reason. That said, this is all rules dependent. In US vintage racing, it’s based off the 1967 or 1972 SCCA GCR (depending on run group) with some slight allowances. However, the SCCA rules allow a few things; * tube shocks in the read * axle locating devices can pass into the cockpit. * shocks are free as long as they don’t have remote reservoirs This means in the rear, you run a 3 link set up with spring rates around 100-125lbs-in (on a car like a TR, MGB, and anything else with similar weight), with a rear anti-roll bar and a panhard bar. The fast MGB racers are using revalved lever shocks in the rear (for reference, our fastest MGB competitor has turned 2:17s at Watkins Glen vs the Triumph TR250k which has done 2:19s, we’ve gone 2:17 flat (with room to spare) in a TR4). Rear spring rates on both were in the 125lbs-in neighborhood. Working on another car that is faster than both of those, but similar wright, and we’re even lighter on the rear spring. On the front, you get the travel by modifying the spindle. What you can do, and is legal here, is to move the spindle up (effectively buying you an inch without losing travel) as well as extend the kingpin up, making for a slightly taller upright, and improving camber gain. This is a pretty common modification across several makes / models at the front of the pack here. Shocks are free here except no remote reservoirs. To run at the front, you see some very expensive Penske, Ohlins, or Koni’s, as they have non remote reservoir shocks that are still a very high level. Again, these help immensely with FIA type curbing / rumble strips.

I don’t agree with the stiffer spring / smaller bar approach at all, and absolutely believe in the opposite. Soft springs, big bars, and the best shocks you can afford.

Set them for whatever the cam manufacturer recommends, hot. Warming up at idle won't suffice - the engine needs to be run. Setting them at the recommended lash cold for the first fire will get you there however. As I posted on the other site: Lash: Tightening the lash has the effect of increasing seat to seat valve lift duration and increasing peak valve lift slightly. Increasing the lash has the effect of reducing seat to seat valve lift duration and decreasing peak valve lift slightly. By increasing seat to seat duration, you're increasing the overlap area some. This is useful when doing camshaft development and trying to determine where to go next. From a very noted camshaft designer/grinder: Quote:want to see the dyno sheets for every move, and I want as much info being recorded as possible, including CFM. After running the cam on the numbers on the cam card, I'd go .004\" tighter on Intake lash, then Exhaust lash. If the power picked up, I'd go another .002\" at a time, until it hurt the power. If going tighter hurt the power, I'd go looser by .002\". After you find best power, I would advance the cam 2 degrees at a time, until it hurts the power. When you get the ICL to the point it's making the best power, now re-set the lash to what's on the card, and run it again. If you sent me all those dyno sheets, I'd have a really good idea of what's going on. So say I design / build a header that scavenges much better. This is going to require a change on the exhaust side with respect to valve timing requirements. Likely, you will want to remove duration in this case, but how do you know? You do a lash loop test. IE: add lash and see what happens. Take away lash and see what happens. etc. Generally you have some wiggle room with lash. The designer may say it needs to be .018" hot, but for testing purposes, you can go as tight as .010" or as large as .030" safely. This is something you need to talk to the cam designer with however.

I get it. It's a cool project! Some things to consider: Carburetors work off pressure differential. Everything that happens downstream of the carburetor will effect how it meters fuel. Going back further, how well the camshaft is timed, the velocity through the ports (both intake and exhaust), and how well the exhaust is designed will have a huge impact on engine performance, but WOT and part throttle. Really what we're talking about is 'transient response'. Road racers and circle track racers tend to use the term 'transient response' while drag racers tend to use 'shift recovery'. Either way, they're after the same thing. So what am I talking about? It's really the engine's ability to recover and start. From a post by Dr. Neels Vannik, agreeing with Calvin Elston (a pioneer and one of the top exhaust designers/fabricators in the US (NASCAR, NHRA, WoO, IMSA, etc.)): So where am I going with this? You need to get the rest of the package sorted out before you can really try to measure and make any meaningful changes at part throttle and the recovery portion of the shift. Also, look at the thread I linked to. Jet signal is huge as this is what the jet sees. Improve the jet signal, and the carburetor will respond a lot faster as well to changes in depression. I'll post more later.

You're really missing a circuit if that's what you're after. Better to just use a Weber. With a tuner who really knows what they're doing, they are very hard to beat, even against EFI.

Backs off after passing the silver TR6. Started and was running 2nd OA for the Kastner Cup race the next day, but rain a few laps in weren't good for the tires being used.. A little 2016 warmup:

You can do something like this: http://www.vintageracerules.com/forums/ubbthreads.php/topics/11462/Re:_SU_Carburators

The GT40 peaked in the 6400rpm range. They also used FE engines which have a monstrously huge and much too big exhaust port. A lot has changed with the exhaust port and exhausts and what was done 50+ years ago at this point isn't really relevant. In that Ford example as above: In-car: 1.65"od x 8" > 1.75" od x 10-12" > 2" secondaries for 12" > 2.25" choke merge > 3" collector > 3" single tailpipe with an A/R chamber just after the Y. 310ci , stock appearing Iron heads, dual plane intake. 595bhp. Also, in Gareth's test example, it has much larger bend radii than what you can fit when trying to go down and under the car. It makes a HUGE difference. and yep! It's a good video and Gan San is a legend. This is a good blog to read: www.exhausting101.com , the site owner is this fellow www.elstonheaders.com . He has NASCAR, NHRA, World of Outlaws, and FIA championships to his credit.

These style headers have gone out of style. The primary lengths used to get that pairing only really works for an engine that peaks at 6500rpm and lower. A modern SBF road race engine with iron heads and a low rise dual plane intake will spin to 8000rpm. Here are some examples of I-6 headers done correctly: \\ video of the Comp/Eliminator car: they're making over 2hp/ci in that trim.

See my post above: "You can't use a 1.25" tube and use bend radii large enough to meet the flow requirements of the engine on a 6-3-1 header. Sorry for the triple post - I can't seem to edit them. Really what you're after is "How small can I keep things without giving anything up at the top of the curve". The large bend radii, packaging, and focus on the port / header transition is what will allow things to remain small without giving up the flow losses to hurt the the top of the curve. I personally saw an example where there was ~58hp per cylinder feeding into 1 3/8" primaries off the head. It made big gains everywhere. You can and should give up some equal length if it means smoother transitions and not a sharp turn off the head. 6-3-1 is too much not being able to see the forest bust for the trees.

On a 595bhp Ford V8 with 4-2-1 headers, the primaries are 18-20". This for an engine redlining at 8200rpm. First step occurs 8" from the head, then it is 10-12" wrong before merging into the secondaries. One thing of caution about using inlet duct calculators is the speed of sound is different due to the temperature differences.

Sorry for the triple post - I can't seem to edit them. Really what you're after is "How small can I keep things without giving anything up at the top of the curve". The large bend radii, packaging, and focus on the port / header transition is what will allow things to remain small without giving up the flow losses to hurt the the top of the curve.

This is a perfect example of what I'm talking about: No way you could get a 1.25" od pipe to flow what you need and get that pairing.